path: root/doc/microhttpd.texi

\input texinfo
@setfilename microhttpd.info
@include version.texi
@settitle The GNU libmicrohttpd Reference Manual
@copying
This manual documents GNU libmicrohttpd version @value{VERSION}, last
updated @value{UPDATED}. It is built upon the documentation in the
header file @file{microhttpd.h}.

@noindent

Copyright @copyright{} 2007, 2008, 2009, 2010, 2011 Christian Grothoff

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts.  A copy of the license is included in the section entitled "GNU
Free Documentation License".
@end quotation
GNU libmicrohttpd is a GNU package.
@end copying

@dircategory GNU Libraries
@direntry
* libmicrohttpd: (microhttpd).  Embedded HTTP server library.
@end direntry

@c
@c Titlepage
@c
@titlepage
@title The GNU libmicrohttpd Reference Manual
@subtitle Version @value{VERSION}
@subtitle @value{UPDATED}
@author Marco Maggi (@email{marco.maggi-ipsu@@poste.it})
@author Christian Grothoff (@email{christian@@grothoff.org})

@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@summarycontents
@contents


@macro gnu{}
@acronym{GNU}
@end macro

@macro gpl{}
@acronym{LGPL}
@end macro

@macro http{}
@acronym{HTTP}
@end macro

@macro tcp{}
@acronym{TCP}
@end macro

@macro api{}
@acronym{API}
@end macro

@macro urloc{}
@acronym{URL}
@end macro

@macro uri{}
@acronym{URI}
@end macro

@macro ascii{}
@acronym{ASCII}
@end macro

@c ............................................................

@macro cfunction{arg}
@code{\arg\()}
@end macro

@macro mynull{}
@code{NULL}
@end macro

@macro mhd{}
@acronym{MHD}
@end macro

@c ............................................................

@macro glibcref{NODE, NODE}
@pxref{\NODE\, \NODE\, \NODE\, libc}
@end macro

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


@c ------------------------------------------------------------
@ifnottex
@node Top
@top The GNU libmicrohttpd Library
@insertcopying
@end ifnottex

@menu
* microhttpd-intro::            Introduction.
* microhttpd-const::            Constants.
* microhttpd-struct::           Structures type definition.
* microhttpd-cb::               Callback functions definition.
* microhttpd-init::             Starting and stopping the server.
* microhttpd-inspect::          Implementing external @code{select}.
* microhttpd-requests::         Handling requests.
* microhttpd-responses::        Building responses to requests.
* microhttpd-dauth::            Utilizing Authentication.
* microhttpd-post::             Adding a @code{POST} processor.
* microhttpd-info::             Obtaining status information.

Appendices

* GNU-LGPL::                     The GNU Lesser General Public License says how you
                                 can copy and share almost all of `libmicrohttpd'.
* GNU GPL with eCos Extension::  The GNU General Public License with eCos extension says how you
                                 can copy and share some parts of `libmicrohttpd'.
* GNU-FDL::                     The GNU Free Documentation License says how you
                                can copy and share the documentation of `libmicrohttpd'.

Indices

* Concept Index::               Index of concepts and programs.
* Function and Data Index::     Index of functions, variables and data types.
* Type Index::                  Index of data types.
@end menu

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-intro
@chapter Introduction


@noindent
All symbols defined in the public @api{} start with @code{MHD_}.  @mhd{}
is a small @http{} daemon library.  As such, it does not have any @api{}
for logging errors (you can only enable or disable logging to stderr).
Also, it may not support all of the @http{} features directly, where
applicable, portions of @http{} may have to be handled by clients of the
library.

The library is supposed to handle everything that it must handle
(because the @api{} would not allow clients to do this), such as basic
connection management; however, detailed interpretations of headers ---
such as range requests --- and @http{} methods are left to clients.  The
library does understand @code{HEAD} and will only send the headers of
the response and not the body, even if the client supplied a body.  The
library also understands headers that control connection management
(specifically, @code{Connection: close} and @code{Expect: 100 continue}
are understood and handled automatically).

@mhd{} understands @code{POST} data and is able to decode certain
formats (at the moment only @code{application/x-www-form-urlencoded}
and @code{multipart/form-data}) using the post processor API.  The
data stream of a POST is also provided directly to the main
application, so unsupported encodings could still be processed, just
not conveniently by @mhd{}.

The header file defines various constants used by the @http{} protocol.
This does not mean that @mhd{} actually interprets all of these values.
The provided constants are exported as a convenience for users of the
library.  @mhd{} does not verify that transmitted @http{} headers are
part of the standard specification; users of the library are free to
define their own extensions of the @http{} standard and use those with
@mhd{}.

All functions are guaranteed to be completely reentrant and
thread-safe.  @mhd{} checks for allocation failures and tries to
recover gracefully (for example, by closing the connection).
Additionally, clients can specify resource limits on the overall
number of connections, number of connections per IP address and memory
used per connection to avoid resource exhaustion.

@section Including the microhttpd.h header
@cindex portability
@cindex microhttpd.h

Ideally, before including "microhttpd.h" you should add the necessary
includes to define the @code{uint64_t}, @code{size_t}, @code{fd_set},
@code{socklen_t} and @code{struct sockaddr} data types.  Which
specific headers are needed may depend on your platform and your build
system might include some tests to provide you with the necessary
conditional operations.  For possible suggestions consult
@code{platform.h} and @code{configure.ac} in the MHD distribution.

Once you have ensured that you manually (!) included the right headers
for your platform before "microhttpd.h", you should also add a line
with @code{#define MHD_PLATFORM_H} which will prevent the
"microhttpd.h" header from trying (and, depending on your platform, 
failing) to include the right headers.

If you do not define MHD_PLATFORM_H, the "microhttpd.h" header will
automatically include headers needed on GNU/Linux systems (possibly
causing problems when porting to other platforms).

@section SIGPIPE
@cindex signals
@mhd{} does not install a signal handler for SIGPIPE.  On platforms
where this is possible (such as GNU/Linux), it disables SIGPIPE for
its I/O operations (by passing MSG_NOSIGNAL).  On other platforms,
SIGPIPE signals may be generated from network operations by 
@mhd{} and will cause the process to die unless the developer
explicitly installs a signal handler for SIGPIPE.

Hence portable code using MHD must install a SIGPIPE handler or
explicitly block the SIGPIPE signal.  MHD does not do so in order 
to avoid messing with other parts of the application that may
need to handle SIGPIPE in a particular way.  You can make your application handle SIGPIPE by calling the following function in @code{main}:

@verbatim
static void
catcher (int sig)
{
}

static void
ignore_sigpipe ()
{
  struct sigaction oldsig;
  struct sigaction sig;

  sig.sa_handler = &catcher;
  sigemptyset (&sig.sa_mask);
#ifdef SA_INTERRUPT
  sig.sa_flags = SA_INTERRUPT;  /* SunOS */
#else
  sig.sa_flags = SA_RESTART;
#endif
  if (0 != sigaction (SIGPIPE, &sig, &oldsig))
    fprintf (stderr,
             "Failed to install SIGPIPE handler: %s\n", strerror (errno));
}
@end verbatim

@section MHD_LONG_LONG
@cindex long long
@cindex IAR
@cindex ARM
@cindex cortex m3

Some platforms do not support @code{long long}.  Hence MHD defines
a macro @code{MHD_LONG_LONG} which will default to @code{long long}.
If your platform does not support @code{long long}, you should
change "platform.h" to define @code{MHD_LONG_LONG} to an appropriate
alternative type and also define @code{MHD_LONG_LONG_PRINTF} to the
corresponding format string for printing such a data type (without
the percent sign).

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-const
@chapter Constants


@deftp {Enumeration} MHD_FLAG
Options for the @mhd{} daemon.

Note that if neither @code{MHD_USE_THREAD_PER_CONNECTION} nor
@code{MHD_USE_SELECT_INTERNALLY} is used, the client wants control over
the process and will call the appropriate microhttpd callbacks.

Starting the daemon may also fail if a particular option is not
implemented or not supported on the target platform (i.e. no support for
@acronym{SSL}, threads or IPv6).  SSL support generally depends on
options given during @mhd{} compilation.  Threaded operations
(including @code{MHD_USE_SELECT_INTERNALLY}) are not supported on
Symbian.

@table @code
@item MHD_NO_FLAG
No options selected.

@item MHD_USE_DEBUG
@cindex debugging
Run in debug mode.  If this flag is used, the library should print error
messages and warnings to stderr.  Note that for this
run-time option to have any effect, @mhd{} needs to be
compiled with messages enabled. This is done by default except you ran 
configure with the @code{--disable-messages} flag set. 

@item MHD_USE_SSL
Run in https mode (this option may not work with all threading modes yet).

@item MHD_USE_THREAD_PER_CONNECTION
Run using one thread per connection.

@item MHD_USE_SELECT_INTERNALLY
Run using an internal thread doing @code{SELECT}.

@item MHD_USE_IPv6
@cindex IPv6
Run using the IPv6 protocol (otherwise, @mhd{} will just support IPv4).


@item MHD_USE_PEDANTIC_CHECKS
Be pedantic about the protocol (as opposed to as tolerant as possible).
Specifically, at the moment, this flag causes @mhd{} to reject @http{}
1.1 connections without a @code{Host} header.  This is required by the
standard, but of course in violation of the ``be as liberal as possible
in what you accept'' norm.  It is recommended to turn this @strong{ON}
if you are testing clients against @mhd{}, and @strong{OFF} in
production.

@item MHD_USE_POLL
@cindex FD_SETSIZE
@cindex poll
@cindex select
Use poll instead of select. This allows sockets with descriptors
@code{>= FD_SETSIZE}.  This option only works in conjunction with
@code{MHD_USE_THREAD_PER_CONNECTION} (at this point).

@end table
@end deftp


@deftp {Enumeration} MHD_OPTION
@mhd{} options.  Passed in the varargs portion of
@cfunction{MHD_start_daemon}.

@table @code
@item MHD_OPTION_END
No more options / last option.  This is used to terminate the VARARGs
list.
  
@item MHD_OPTION_CONNECTION_MEMORY_LIMIT
@cindex memory, limiting memory utilization
Maximum memory size per connection (followed by a @code{size_t}).  The
default is 32 kB (32*1024 bytes) as defined by the internal constant
@code{MHD_POOL_SIZE_DEFAULT}.

@item MHD_OPTION_CONNECTION_LIMIT
@cindex connection, limiting number of connections
Maximum number of concurrent connections to accept (followed by an
@code{unsigned int}).  The default is @code{FD_SETSIZE - 4} (the
maximum number of file descriptors supported by @code{select} minus
four for @code{stdin}, @code{stdout}, @code{stderr} and the server
socket).  In other words, the default is as large as possible.  

Note that if you set a low connection limit, you can easily get into
trouble with browsers doing request pipelining.  For example, if your
connection limit is ``1'', a browser may open a first connection to
access your ``index.html'' file, keep it open but use a second 
connection to retrieve CSS files, images and the like.  In fact, modern
browsers are typically by default configured for up to 15 parallel
connections to a single server.  If this happens, MHD will refuse to
even accept the second connection until the first connection is
closed --- which does not happen until timeout.  As a result, the
browser will fail to render the page and seem to hang.  If you expect
your server to operate close to the connection limit, you should 
first consider using a lower timeout value and also possibly add
a ``Connection: close'' header to your response to ensure that
request pipelining is not used and connections are closed immediately
after the request has completed:
@example
MHD_add_response_header (response,
                         MHD_HTTP_HEADER_CONNECTION,
                         "close");
@end example

@item MHD_OPTION_CONNECTION_TIMEOUT
@cindex timeout
After how many seconds of inactivity should a connection automatically
be timed out? (followed by an @code{unsigned int}; use zero for no
timeout).  The default is zero (no timeout).

@item MHD_OPTION_NOTIFY_COMPLETED
Register a function that should be called whenever a request has been
completed (this can be used for application-specific clean up).
Requests that have never been presented to the application (via
@cfunction{MHD_AccessHandlerCallback}) will not result in
notifications.

This option should be followed by @strong{TWO} pointers.  First a
pointer to a function of type @cfunction{MHD_RequestCompletedCallback}
and second a pointer to a closure to pass to the request completed
callback.  The second pointer maybe @mynull{}.


@item MHD_OPTION_PER_IP_CONNECTION_LIMIT
Limit on the number of (concurrent) connections made to the
server from the same IP address.  Can be used to prevent one
IP from taking over all of the allowed connections.  If the
same IP tries to establish more than the specified number of
connections, they will be immediately rejected.  The option
should be followed by an @code{unsigned int}.  The default is
zero, which means no limit on the number of connections
from the same IP address.

@item MHD_OPTION_SOCK_ADDR
@cindex bind, restricting bind
Bind daemon to the supplied socket address. This option should be followed by a
@code{struct sockaddr *}.  If @code{MHD_USE_IPv6} is specified, 
the @code{struct sockaddr*} should point to a @code{struct sockaddr_in6}, 
otherwise to a @code{struct sockaddr_in}.  If this option is not specified,
the daemon will listen to incoming connections from anywhere.

@item MHD_OPTION_URI_LOG_CALLBACK
@cindex debugging
@cindex logging
@cindex query string
Specify a function that should be called before parsing the URI from
the client.  The specified callback function can be used for processing
the URI (including the options) before it is parsed.  The URI after
parsing will no longer contain the options, which maybe inconvenient for
logging.  This option should be followed by two arguments, the first
one must be of the form
@example
 void * my_logger(void * cls, const char * uri)
@end example
where the return value will be passed as
@code{*con_cls} in calls to the @code{MHD_AccessHandlerCallback}
when this request is processed later; returning a
value of NULL has no special significance; (however,
note that if you return non-NULL, you can no longer
rely on the first call to the access handler having
@code{NULL == *con_cls} on entry)
@code{cls} will be set to the second argument following
MHD_OPTION_URI_LOG_CALLBACK.  Finally, @code{uri} will
be the 0-terminated URI of the request.

@item MHD_OPTION_HTTPS_MEM_KEY
@cindex SSL
@cindex TLS
Memory pointer to the private key to be used by the
HTTPS daemon.  This option should be followed by an
"const char*" argument.
This should be used in conjunction with 'MHD_OPTION_HTTPS_MEM_CERT'.
   
@item MHD_OPTION_HTTPS_MEM_CERT
@cindex SSL
@cindex TLS
Memory pointer to the certificate to be used by the
HTTPS daemon.  This option should be followed by an
"const char*" argument.
This should be used in conjunction with 'MHD_OPTION_HTTPS_MEM_KEY'.
   
@item MHD_OPTION_HTTPS_MEM_TRUST
@cindex SSL
@cindex TLS
Memory pointer to the CA certificate to be used by the
HTTPS daemon to authenticate and trust clients certificates.
This option should be followed by an "const char*" argument.
The presence of this option activates the request of certificate
to the client. The request to the client is marked optional, and
it is the responsibility of the server to check the presence
of the certificate if needed.
Note that most browsers will only present a client certificate
only if they have one matching the specified CA, not sending
any certificate otherwise.
   
@item MHD_OPTION_HTTPS_CRED_TYPE
@cindex SSL
@cindex TLS
Daemon credentials type.  Either certificate or anonymous,
this option should be followed by one of the values listed in
"enum gnutls_credentials_type_t".
   
@item MHD_OPTION_HTTPS_PRIORITIES
@cindex SSL
@cindex TLS
@cindex cipher
SSL/TLS protocol version and ciphers.
This option must be followed by an "const char *" argument
specifying the SSL/TLS protocol versions and ciphers that
are acceptable for the application.  The string is passed
unchanged to gnutls_priority_init.  If this option is not
specified, ``NORMAL'' is used.

@item MHD_OPTION_DIGEST_AUTH_RANDOM
@cindex digest auth
@cindex random
Digest Authentication nonce's seed.

This option should be followed by two arguments.  First an integer of
type "size_t" which specifies the size of the buffer pointed to by the
second argument in bytes.  Note that the application must ensure that
the buffer of the second argument remains allocated and unmodified
while the daemon is running.  For security, you SHOULD provide a fresh
random nonce when using MHD with Digest Authentication.  

@item MHD_OPTION_NONCE_NC_SIZE
@cindex digest auth
@cindex replay attack

Size of an array of nonce and nonce counter map.  This option must be
followed by an "unsigned int" argument that have the size (number of
elements) of a map of a nonce and a nonce-counter.  If this option
is not specified, a default value of 4 will be used (which might be
too small for servers handling many requests).  If you do not use
digest authentication at all, you can specify a value of zero to
save some memory.

You should calculate the value of NC_SIZE based on the number of
connections per second multiplied by your expected session duration
plus a factor of about two for hash table collisions.  For example, if
you expect 100 digest-authenticated connections per second and the
average user to stay on your site for 5 minutes, then you likely need
a value of about 60000.  On the other hand, if you can only expect
only 10 digest-authenticated connections per second, tolerate browsers
getting a fresh nonce for each request and expect a HTTP request
latency of 250 ms, then a value of about 5 should be fine.


@item MHD_OPTION_LISTEN_SOCKET
@cindex systemd
Listen socket to use.  Pass a listen socket for MHD to use
(systemd-style).  If this option is used, MHD will not open its own
listen socket(s). The argument passed must be of type "int" and refer
to an existing socket that has been bound to a port and is listening.
  
@item MHD_OPTION_EXTERNAL_LOGGER
@cindex logging
Use the given function for logging error messages.
This option must be followed by two arguments; the
first must be a pointer to a function
of type 'void fun(void * arg, const char * fmt, va_list ap)'
and the second a pointer of type 'void*' which will
be passed as the "arg" argument to "fun".
 
Note that MHD will not generate any log messages without  
the MHD_USE_DEBUG flag set and if MHD was compiled 
with the "--disable-messages" flag. 

@item MHD_OPTION_THREAD_POOL_SIZE
@cindex performance
Number (unsigned int) of threads in thread pool. Enable
thread pooling by setting this value to to something
greater than 1. Currently, thread model must be
MHD_USE_SELECT_INTERNALLY if thread pooling is enabled
(MHD_start_daemon returns NULL for an unsupported thread
model).

@item MHD_OPTION_ARRAY
@cindex options
@cindex foreign-function interface
This option can be used for initializing MHD using options from an
array.  A common use for this is writing an FFI for MHD.  The actual
options given are in an array of 'struct MHD_OptionItem', so this
option requires a single argument of type 'struct MHD_OptionItem'.
The array must be terminated with an entry @code{MHD_OPTION_END}.

An example for code using MHD_OPTION_ARRAY is:
@example
struct MHD_OptionItem ops[] = @{
 @{ MHD_OPTION_CONNECTION_LIMIT, 100, NULL @},
 @{ MHD_OPTION_CONNECTION_TIMEOUT, 10, NULL @},
 @{ MHD_OPTION_END, 0, NULL @}
@};
d = MHD_start_daemon(0, 8080, NULL, NULL, dh, NULL,
                     MHD_OPTION_ARRAY, ops,
                     MHD_OPTION_END);
@end example
For options that expect a single pointer argument, the
second member of the @code{struct MHD_OptionItem} is ignored.
For options that expect two pointer arguments, the first
argument must be cast to @code{intptr_t}.

@item MHD_OPTION_UNESCAPE_CALLBACK
@cindex internationalization
@cindex escaping

Specify a function that should be called for unescaping escape
sequences in URIs and URI arguments.  Note that this function will NOT
be used by the MHD_PostProcessor.  If this option is not specified,
the default method will be used which decodes escape sequences of the
form "%HH".  This option should be followed by two arguments, the
first one must be of the form

@example
  size_t my_unescaper(void * cls, struct MHD_Connection *c, char *s)
@end example

where the return value must be @code{strlen(s)} and @code{s} should be
updated.  Note that the unescape function must not lengthen @code{s}
(the result must be shorter than the input and still be 0-terminated).
@code{cls} will be set to the second argument following
MHD_OPTION_UNESCAPE_CALLBACK.

  
@item MHD_OPTION_THREAD_STACK_SIZE
@cindex stack, thread, pthread
Maximum stack size for threads created by MHD.  This option must be
followed by a @code{size_t}).  Not specifying this option or using
a value of zero means using the system default (which is likely to 
differ based on your platform).

@end table
@end deftp


@deftp {C Struct} MHD_OptionItem
Entry in an MHD_OPTION_ARRAY.  See the @code{MHD_OPTION_ARRAY} option
argument for its use. 

The @code{option} member is used to specify which option is specified
in the array.  The other members specify the respective argument.

Note that for options taking only a single pointer, the
@code{ptr_value} member should be set.  For options taking two pointer
arguments, the first pointer must be cast to @code{intptr_t} and both
the @code{value} and the @code{ptr_value} members should be used to
pass the two pointers.
@end deftp


@deftp {Enumeration} MHD_ValueKind
The @code{MHD_ValueKind} specifies the source of the key-value pairs in
the @http{} protocol.

@table @code
@item MHD_RESPONSE_HEADER_KIND
Response header.

@item MHD_HEADER_KIND
@http{} header.

@item MHD_COOKIE_KIND
@cindex cookie
Cookies.  Note that the original @http{} header containing the cookie(s)
will still be available and intact.

@item MHD_POSTDATA_KIND
@cindex POST method
@code{POST} data.  This is available only if a content encoding
supported by @mhd{} is used (currently only @acronym{URL} encoding), and
only if the posted content fits within the available memory pool.  Note
that in that case, the upload data given to the
@cfunction{MHD_AccessHandlerCallback} will be empty (since it has
already been processed).

@item MHD_GET_ARGUMENT_KIND
@code{GET} (@uri{}) arguments.

@item MHD_FOOTER_KIND
@http{} footer (only for http 1.1 chunked encodings).

@end table
@end deftp


@deftp {Enumeration} MHD_RequestTerminationCode
The @code{MHD_RequestTerminationCode} specifies reasons why a request
has been terminated (or completed).

@table @code
@item MHD_REQUEST_TERMINATED_COMPLETED_OK
We finished sending the response.

@item MHD_REQUEST_TERMINATED_WITH_ERROR
Error handling the connection (resources exhausted, other side closed
connection, application error accepting request, etc.)

@item MHD_REQUEST_TERMINATED_TIMEOUT_REACHED
No activity on the connection for the number of seconds specified using
@code{MHD_OPTION_CONNECTION_TIMEOUT}.

@item MHD_REQUEST_TERMINATED_DAEMON_SHUTDOWN
We had to close the session since @mhd{} was being shut down.
@end table
@end deftp


@deftp {Enumeration} MHD_ResponseMemoryMode
The @code{MHD_ResponeMemoryMode} specifies how MHD should treat
the memory buffer given for the response in 
@code{MHD_create_response_from_buffer}.

@table @code
@item MHD_RESPMEM_PERSISTENT
Buffer is a persistent (static/global) buffer that won't change
for at least the lifetime of the response, MHD should just use
it, not free it, not copy it, just keep an alias to it.
 
@item MHD_RESPMEM_MUST_FREE
Buffer is heap-allocated with @code{malloc} (or equivalent) and
should be freed by MHD after processing the response has
concluded (response reference counter reaches zero).
  
@item MHD_RESPMEM_MUST_COPY
Buffer is in transient memory, but not on the heap (for example,
on the stack or non-malloc allocated) and only valid during the
call to @code{MHD_create_response_from_buffer}.  MHD must make its
own private copy of the data for processing.

@end table
@end deftp


@deftp {Enumeration} MHD_ConnectionInfoType
Values of this enum are used to specify what information about a
connection is desired.

@table @code

@item MHD_CONNECTION_INFO_CIPHER_ALGO
What cipher algorithm is being used (HTTPS connections only).  
Takes no extra arguments.
NULL is returned for non-HTTPS connections.

@item MHD_CONNECTION_INFO_PROTOCOL,
Takes no extra arguments.   Allows finding out the TLS/SSL protocol used
(HTTPS connections only).
NULL is returned for non-HTTPS connections.

@item MHD_CONNECTION_INFO_CLIENT_ADDRESS
Returns information about the address of the client.  Returns 
essentially a @code{struct sockaddr **} (since the API returns
a @code{union MHD_ConnectionInfo *} and that union contains
a @code{struct sockaddr *}).

@item MHD_CONNECTION_INFO_GNUTLS_SESSION,
Takes no extra arguments.  Allows access to the underlying GNUtls session,
including access to the underlying GNUtls client certificate
(HTTPS connections only).  Takes no extra arguments.  
NULL is returned for non-HTTPS connections.

@item MHD_CONNECTION_INFO_GNUTLS_CLIENT_CERT,
Takes no extra arguments.  Allows access to the client certificate
including access to the underlying GNUtls client certificate
(HTTPS connections only).  Takes no extra arguments.

@item MHD_CONNECTION_INFO_DAEMON
Returns information about @code{struct MHD_Daemon} which manages
this connection.

@end table
@end deftp




@deftp {Enumeration} MHD_DaemonInfoType
Values of this enum are used to specify what
information about a daemon is desired.
@table @code
@item MHD_DAEMON_INFO_KEY_SIZE
Request information about the key size for a particular cipher
algorithm.  The cipher algorithm should be passed as an extra argument
(of type 'enum MHD_GNUTLS_CipherAlgorithm').

@item MHD_DAEMON_INFO_MAC_KEY_SIZE
Request information about the key size for a particular cipher
algorithm.  The cipher algorithm should be passed as an extra argument
(of type 'enum MHD_GNUTLS_HashAlgorithm').

@item MHD_DAEMON_INFO_LISTEN_FD
@cindex listen
Request the file-descriptor number that MHD is using to listen to the
server socket.  This can be useful if no port
was specified and a client needs to learn what port
is actually being used by MHD.
No extra arguments should be passed.

@end table
@end deftp


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-struct
@chapter Structures type definition


@deftp {C Struct} MHD_Daemon
Handle for the daemon (listening on a socket for @http{} traffic).
@end deftp


@deftp {C Struct} MHD_Connection
Handle for a connection / @http{} request.  With @http{}/1.1, multiple
requests can be run over the same connection.  However, @mhd{} will only
show one request per @tcp{} connection to the client at any given time.
@end deftp


@deftp {C Struct} MHD_Response
Handle for a response.
@end deftp


@deftp {C Struct} MHD_PostProcessor
@cindex POST method
Handle for @code{POST} processing.
@end deftp


@deftp {C Union} MHD_ConnectionInfo
Information about a connection.
@end deftp


@deftp {C Union} MHD_DaemonInfo
Information about an MHD daemon.
@end deftp


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-cb
@chapter Callback functions definition


@deftypefn {Function Pointer} int {*MHD_AcceptPolicyCallback} (void *cls, const struct sockaddr * addr, socklen_t addrlen)
Invoked in the context of a connection to allow or deny a client to
connect.  This callback return @code{MHD_YES} if connection is allowed,
@code{MHD_NO} if not.

@table @var
@item cls
custom value selected at callback registration time;
@item addr
address information from the client;
@item addrlen
length of the address information.
@end table
@end deftypefn


@deftypefn {Function Pointer} int {*MHD_AccessHandlerCallback} (void *cls, struct MHD_Connection * connection, const char *url, const char *method, const char *version, const char *upload_data, size_t *upload_data_size, void **con_cls)
Invoked in the context of a connection to answer a request from the
client.  This callback must call @mhd{} functions (example: the
@code{MHD_Response} ones) to provide content to give back to the client
and return an @http{} status code (i.e. @code{200} for OK, @code{404},
etc.).

@ref{microhttpd-post}, for details on how to code this callback.

Must return @code{MHD_YES} if the connection was handled successfully,
@code{MHD_NO} if the socket must be closed due to a serious error while
handling the request

@table @var
@item cls
custom value selected at callback registration time;

@item url
the @urloc{} requested by the client;

@item method
the @http{} method used by the client (@code{GET}, @code{PUT},
@code{DELETE}, @code{POST}, etc.);

@item version
the @http{} version string (i.e. @code{HTTP/1.1});

@item upload_data
the data being uploaded (excluding headers):
@cindex POST method
@cindex PUT method

@itemize
@item
for a @code{POST} that fits into memory and that is encoded with a
supported encoding, the @code{POST} data will @strong{NOT} be given in
@var{upload_data} and is instead available as part of
@cfunction{MHD_get_connection_values};

@item
very large @code{POST} data @strong{will} be made available
incrementally in @var{upload_data};
@end itemize

@item upload_data_size
set initially to the size of the @var{upload_data} provided; this
callback must update this value to the number of bytes @strong{NOT}
processed; unless external select is used, the callback maybe
required to process at least some data.  If the callback fails to
process data in multi-threaded or internal-select mode and if the
read-buffer is already at the maximum size that MHD is willing to
use for reading (about half of the maximum amount of memory allowed
for the connection), then MHD will abort handling the connection
and return an internal server error to the client.  In order to
avoid this, clients must be able to process upload data incrementally
and reduce the value of @code{upload_data_size}.

@item con_cls
reference to a pointer, initially set to @mynull{}, that this callback can
set to some address and that will be preserved by @mhd{} for future
calls for this request;

since the access handler may be called many times (i.e., for a
@code{PUT}/@code{POST} operation with plenty of upload data) this allows
the application to easily associate some request-specific state;

if necessary, this state can be cleaned up in the global
@code{MHD_RequestCompletedCallback} (which can be set with the
@code{MHD_OPTION_NOTIFY_COMPLETED}).
@end table
@end deftypefn


@deftypefn {Function Pointer} void {*MHD_RequestCompletedCallback} (void *cls, struct MHD_Connectionconnection, void **con_cls, enum MHD_RequestTerminationCode toe)
Signature of the callback used by @mhd{} to notify the application about
completed requests.

@table @var
@item cls
custom value selected at callback registration time;

@item connection
connection handle;

@item con_cls
value as set by the last call to the
@code{MHD_AccessHandlerCallback};

@item toe
reason for request termination see @code{MHD_OPTION_NOTIFY_COMPLETED}.
@end table
@end deftypefn


@deftypefn {Function Pointer} int {*MHD_KeyValueIterator} (void *cls, enum MHD_ValueKind kind, const char *key, const char *value)
Iterator over key-value pairs.  This iterator can be used to iterate
over all of the cookies, headers, or @code{POST}-data fields of a
request, and also to iterate over the headers that have been added to a
response.

Return @code{MHD_YES} to continue iterating, @code{MHD_NO} to abort the
iteration.
@end deftypefn


@deftypefn {Function Pointer} int {*MHD_ContentReaderCallback} (void *cls, uint64_t pos, char *buf, size_t max)
Callback used by @mhd{} in order to obtain content.  The callback has to
copy at most @var{max} bytes of content into @var{buf}.  The total
number of bytes that has been placed into @var{buf} should be returned.

Note that returning zero will cause @mhd{} to try again, either
``immediately'' if in multi-threaded mode (in which case the callback
may want to do blocking operations to avoid busy waiting) or in the
next round if @code{MHD_run} is used.  Returning zero for a daemon
that runs in internal @cfunction{select} mode is an error (since it
would result in busy waiting) and cause the program to be aborted
(@cfunction{abort}).

While usually the callback simply returns the number of bytes written
into @var{buf}, there are two special return value:

@code{MHD_CONTENT_READER_END_OF_STREAM} (-1) should be returned
for the regular end of transmission (with chunked encoding, MHD will then
terminate the chunk and send any HTTP footers that might be
present; without chunked encoding and given an unknown 
response size, @mhd{} will simply close the connection; note
that while returning @code{MHD_CONTENT_READER_END_OF_STREAM} is not technically
legal if a response size was specified, MHD accepts this
and treats it just as @code{MHD_CONTENT_READER_END_WITH_ERROR}.

@code{MHD_CONTENT_READER_END_WITH_ERROR} (-2) is used to indicate a server
error generating the response; this will cause @mhd{} to simply
close the connection immediately.  If a response size was
given or if chunked encoding is in use, this will indicate
an error to the client.  Note, however, that if the client
does not know a response size and chunked encoding is not in
use, then clients will not be able to tell the difference between
@code{MHD_CONTENT_READER_END_WITH_ERROR} and 
@code{MHD_CONTENT_READER_END_OF_STREAM}.
This is not a limitation of @mhd{} but rather of the HTTP protocol.

@table @var
@item cls
custom value selected at callback registration time;

@item pos
position in the datastream to access; note that if an
@code{MHD_Response} object is re-used, it is possible for the same
content reader to be queried multiple times for the same data; however,
if an @code{MHD_Response} is not re-used, @mhd{} guarantees that
@var{pos} will be the sum of all non-negative return values obtained
from the content reader so far.
@end table

Return @code{-1} on error (@mhd{} will no longer try to read content and
instead close the connection with the client).
@end deftypefn


@deftypefn {Function Pointer} void {*MHD_ContentReaderFreeCallback} (void *cls)
This method is called by @mhd{} if we are done with a content reader.
It should be used to free resources associated with the content reader.
@end deftypefn


@deftypefn {Function Pointer} int {*MHD_PostDataIterator} (void *cls, enum MHD_ValueKind kind, const char *key, const char *filename, const char *content_type, const char *transfer_encoding, const char *data, uint64_t off, size_t size)
Iterator over key-value pairs where the value maybe made available in
increments and/or may not be zero-terminated.  Used for processing
@code{POST} data.

@table @var
@item cls
custom value selected at callback registration time;

@item kind
type of the value;

@item key
zero-terminated key for the value;

@item filename
name of the uploaded file, @mynull{} if not known;

@item content_type
mime-type of the data, @mynull{} if not known;

@item transfer_encoding
encoding of the data, @mynull{} if not known;

@item data
pointer to size bytes of data at the specified offset;

@item off
offset of data in the overall value;

@item size
number of bytes in data available.
@end table

Return @code{MHD_YES} to continue iterating, @code{MHD_NO} to abort the
iteration.
@end deftypefn


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-init
@chapter Starting and stopping the server

@deftypefun {void} MHD_set_panic_func (MHD_PanicCallback cb, void *cls)
Set a handler for fatal errors.

@table @var
@item cb 
function to call if MHD encounters a fatal internal error.  If no handler was set explicitly, MHD will call @code{abort}.

@item cls
closure argument for cb; the other arguments are the name of the source file, line number and a string describing the nature of the fatal error (which can be NULL)
@end table
@end deftypefun

@deftypefun {struct MHD_Daemon *} MHD_start_daemon (unsigned int flags, unsigned short port, MHD_AcceptPolicyCallback apc, void *apc_cls, MHD_AccessHandlerCallback dh, void *dh_cls, ...)
Start a webserver on the given port.

@table @var
@item flags
OR-ed combination of @code{MHD_FLAG} values;

@item port
port to bind to;

@item apc
callback to call to check which clients will be allowed to connect; you
can pass @mynull{} in which case connections from any @acronym{IP} will be
accepted;

@item apc_cls
extra argument to @var{apc};

@item dh
default handler for all @uri{}s;

@item dh_cls
extra argument to @var{dh}.
@end table

Additional arguments are a list of options (type-value pairs,
terminated with @code{MHD_OPTION_END}). It is mandatory to use
@code{MHD_OPTION_END} as last argument, even when there are no
additional arguments.

Return @mynull{} on error, handle to daemon on success.
@end deftypefun


@deftypefun void MHD_stop_daemon (struct MHD_Daemon *daemon)
Shutdown an @http{} daemon.
@end deftypefun


@deftypefun int MHD_run (struct MHD_Daemon *daemon)
Run webserver operations (without blocking unless in client callbacks).
This method should be called by clients in combination with
@cfunction{MHD_get_fdset} if the client-controlled @cfunction{select}
method is used.

Return @code{MHD_YES} on success, @code{MHD_NO} if this daemon was not
started with the right options for this call.
@end deftypefun


@deftypefun void MHD_add_connection (struct MHD_Daemon *daemon, int client_socket, const struct sockaddr *addr, socklen_t addrlen)
Add another client connection to the set of connections 
managed by MHD.  This API is usually not needed (since
MHD will accept inbound connections on the server socket).
Use this API in special cases, for example if your HTTP
server is behind NAT and needs to connect out to the 
HTTP client.

The given client socket will be managed (and closed!) by MHD after
this call and must no longer be used directly by the application
afterwards.

@table @var
@item daemon 
daemon that manages the connection
@item client_socket 
socket to manage (MHD will expect to receive an HTTP request from this socket next).
@item addr 
IP address of the client
@item addrlen 
number of bytes in addr
@end table

This function will return @code{MHD_YES} on success, 
@code{MHD_NO} if this daemon could
not handle the connection (i.e. malloc failed, etc).
The socket will be closed in any case.
@end deftypefun


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c -----------------------------------------------------------
@node microhttpd-inspect
@chapter Implementing external @code{select}


@deftypefun int MHD_get_fdset (struct MHD_Daemon *daemon, fd_set * read_fd_set, fd_set * write_fd_set, fd_set * except_fd_set, int *max_fd)
Obtain the @cfunction{select} sets for this daemon. The daemon's socket
is added to @var{read_fd_set}. The list of currently existent
connections is scanned and their file descriptors added to the correct
set.

@glibcref{Waiting for I/O}, for details on file descriptor sets.

After the call completed successfully: the variable referenced by
@var{max_fd} references the file descriptor with highest integer
identifier. The variable must be set to zero before invoking this
function.

Return @code{MHD_YES} on success, @code{MHD_NO} if: the arguments are
invalid (example: @mynull{} pointers); this daemon was not started with
the right options for this call.
@end deftypefun


@deftypefun int MHD_get_timeout (struct MHD_Daemon *daemon, unsigned long long *timeout)
@cindex timeout
Obtain timeout value for select for this daemon (only needed if
connection timeout is used).  The returned value is how long
@cfunction{select} should at most block, not the timeout value set for
connections.  This function must not be called if the
@code{MHD_USE_THREAD_PER_CONNECTION} mode is in use (since then it
is not meaningful to ask for a timeout, after all, there is 
concurrenct activity).  The function must also not be called by
user-code if @code{MHD_USE_INTERNAL_SELECT} is in use.  In the latter
case, the behavior is undefined.

@table @var
@cindex timeout
set to the timeout (in milliseconds).
@end table

Return @code{MHD_YES} on success, @code{MHD_NO} if timeouts are not used
(or no connections exist that would necessiate the use of a timeout
right now).
@end deftypefun


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c -----------------------------------------------------------
@node microhttpd-requests
@chapter Handling requests


@deftypefun int MHD_get_connection_values (struct MHD_Connection *connection, enum MHD_ValueKind kind, MHD_KeyValueIterator iterator, void *iterator_cls)
Get all the headers matching @var{kind} from the request.

The @var{iterator} callback is invoked once for each header, with
@var{iterator_cls} as first argument. Return the number of entries
iterated over; this can be less than the number of headers if, while
iterating, @var{iterator} returns @code{MHD_NO}.

@var{iterator} can be @mynull{}: in this case this function just counts
and returns the number of headers.
@end deftypefun


@deftypefun int MHD_set_connection_value (struct MHD_Connection *connection, enum MHD_ValueKind kind, const char * key, const char * value)
This function can be used to add an entry to
the HTTP headers of a connection (so that the 
MHD_get_connection_values function will return
them -- and the MHD PostProcessor will also 
see them).  This maybe required in certain
situations (see Mantis #1399) where (broken)
HTTP implementations fail to supply values needed
by the post processor (or other parts of the
application).

This function MUST only be called from within
the MHD_AccessHandlerCallback (otherwise, access
maybe improperly synchronized).  Furthermore,
the client must guarantee that the key and
value arguments are 0-terminated strings that
are NOT freed until the connection is closed.
(The easiest way to do this is by passing only
arguments to permanently allocated strings.).

@var{connection} is the connection for which 
the entry for @var{key} of the given @var{kind}
should be set to the given @var{value}.

The function returns @code{MHD_NO} if the operation 
could not be performed due to insufficient memory
and @code{MHD_YES} on success.
@end deftypefun


@deftypefun {const char *} MHD_lookup_connection_value (struct MHD_Connection *connection, enum MHD_ValueKind kind, const char *key)
Get a particular header value.  If multiple values match the @var{kind},
return one of them (the ``first'', whatever that means).  @var{key} must
reference a zero-terminated @ascii{}-coded string representing the
header to look for: it is compared against the headers using
@cfunction{strcasecmp}, so case is ignored.  Return @mynull{} if no such
item was found.
@end deftypefun


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-responses
@chapter Building answers to responses


@noindent
Response objects handling by @mhd{} is asynchronous with respect to the
application execution flow. Instances of the @code{MHD_Response}
structure are not associated to a daemon and neither to a client
connection: they are managed with reference counting.

In the simplest case: we allocate a new @code{MHD_Response} structure
for each response, we use it once and finally we destroy it.

@mhd{} allows more efficient resources usages.

Example: we allocate a new @code{MHD_Response} structure for each
response @strong{kind}, we use it every time we have to give that
response and we finally destroy it only when the daemon shuts down.

@menu
* microhttpd-response enqueue:: Enqueuing a response.
* microhttpd-response create::  Creating a response object.
* microhttpd-response headers:: Adding headers to a response.
* microhttpd-response inspect:: Inspecting a response object.
@end menu

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-response enqueue
@section Enqueuing a response


@deftypefun int MHD_queue_response (struct MHD_Connection *connection, unsigned int status_code, struct MHD_Response *response)
Queue a response to be transmitted to the client as soon as possible
but only after MHD_AccessHandlerCallback returns.  This function
checks that it is legal to queue a response at this time for the
given connection.  It also increments the internal reference
counter for the response object (the counter will be decremented
automatically once the response has been transmitted).

@table @var
@item connection
the connection identifying the client;

@item status_code
@http{} status code (i.e. @code{200} for OK);

@item response
response to transmit.
@end table

Return @code{MHD_YES} on success or if message has been queued.  Return
@code{MHD_NO}: if arguments are invalid (example: @mynull{} pointer); on
error (i.e. reply already sent).
@end deftypefun


@deftypefun void MHD_destroy_response (struct MHD_Response *response)
Destroy a response object and associated resources (decrement the
reference counter).  Note that @mhd{} may keep some of the resources
around if the response is still in the queue for some clients, so the
memory may not necessarily be freed immediately.
@end deftypefun


An explanation of reference counting@footnote{Note to readers acquainted
to the Tcl @api{}: reference counting on @code{MHD_Connection}
structures is handled in the same way as Tcl handles @code{Tcl_Obj}
structures through @cfunction{Tcl_IncrRefCount} and
@cfunction{Tcl_DecrRefCount}.}:

@enumerate
@item
a @code{MHD_Response} object is allocated:

@example
struct MHD_Response * response = MHD_create_response_from_buffer(...);
/* here: reference counter = 1 */
@end example

@item
the @code{MHD_Response} object is enqueued in a @code{MHD_Connection}:

@example
MHD_queue_response(connection, , response);
/* here: reference counter = 2 */
@end example

@item
the creator of the response object discharges responsibility for it:

@example
MHD_destroy_response(response);
/* here: reference counter = 1 */
@end example

@item
the daemon handles the connection sending the response's data to the
client then decrements the reference counter by calling
@cfunction{MHD_destroy_response}: the counter's value drops to zero and
the @code{MHD_Response} object is released.
@end enumerate


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-response create
@section Creating a response object


@deftypefun {struct MHD_Response *} MHD_create_response_from_callback (uint64_t size, size_t block_size, MHD_ContentReaderCallback crc, void *crc_cls, MHD_ContentReaderFreeCallback crfc)
Create a response object.  The response object can be extended with
header information and then it can be used any number of times.

@table @var
@item size
size of the data portion of the response, @code{-1} for unknown;

@item block_size
preferred block size for querying @var{crc} (advisory only, @mhd{} may
still call @var{crc} using smaller chunks); this is essentially the
buffer size used for @acronym{IO}, clients should pick a value that is
appropriate for @acronym{IO} and memory performance requirements;

@item crc
callback to use to obtain response data;

@item crc_cls
extra argument to @var{crc};

@item crfc
callback to call to free @var{crc_cls} resources.
@end table

Return @mynull{} on error (i.e. invalid arguments, out of memory).
@end deftypefun



@deftypefun {struct MHD_Response *} MHD_create_response_from_fd (uint64_t size, int fd)
Create a response object.  The response object can be extended with
header information and then it can be used any number of times.
Function is deprecated, use @code{MHD_create_response_from_fd_at_offset}
instead (with an offset of zero).

@table @var
@item size
size of the data portion of the response (should be smaller or equal to the
size of the file)

@item fd
file descriptor referring to a file on disk with the data; will be
closed when response is destroyed; note that 'fd' must be an actual 
file descriptor (not a pipe or socket) since MHD might use 'sendfile' 
or 'seek' on it.  The descriptor should be in blocking-IO mode.
@end table

Return @mynull{} on error (i.e. invalid arguments, out of memory).
@end deftypefun


@deftypefun {struct MHD_Response *} MHD_create_response_from_fd_at_offset (uint64_t size, int fd, off_t offset)
Create a response object.  The response object can be extended with
header information and then it can be used any number of times.
Note that you need to be a bit careful about @code{off_t} when
writing this code.  Depending on your platform, @mhd{} is likely
to have been compiled with support for 64-bit files.  When you
compile your own application, you must make sure that @code{off_t}
is also a 64-bit value.  If not, your compiler may pass a 32-bit
value as @code{off_t}, which will result in 32-bits of garbage.

If you use the autotools, use the @code{AC_SYS_LARGEFILE} autoconf
macro and make sure to include the generated @file{config.h} file
before @file{microhttpd.h} to avoid problems.  If you do not have a
build system and only want to run on a GNU/Linux system, you could
also use
@verbatim
#define _FILE_OFFSET_BITS 64
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <microhttpd.h>
@end verbatim
to ensure 64-bit @code{off_t}.  Note that if your operating system
does not support 64-bit files, @mhd{} will be compiled with a 32-bit
@code{off_t} (in which case the above would be wrong...).

@table @var
@item size
size of the data portion of the response (number of bytes to transmit from the
file starting at offset).

@item fd
file descriptor referring to a file on disk with the data; will be
closed when response is destroyed; note that 'fd' must be an actual 
file descriptor (not a pipe or socket) since MHD might use 'sendfile' 
or 'seek' on it.    The descriptor should be in blocking-IO mode.

@item offset
offset to start reading from in the file
@end table

Return @mynull{} on error (i.e. invalid arguments, out of memory).
@end deftypefun


@deftypefun {struct MHD_Response *} MHD_create_response_from_buffer (size_t size, void *data, enum MHD_ResponseMemoryMode mode)
Create a response object.  The response object can be extended with
header information and then it can be used any number of times.

@table @var
@item size
size of the data portion of the response;

@item buffer
the data itself;

@item mode 
memory management options for buffer; use 
MHD_RESPMEM_PERSISTENT if the buffer is static/global memory,
use MHD_RESPMEM_MUST_FREE if the buffer is heap-allocated and
should be freed by @mhd{} and MHD_RESPMEM_MUST_COPY if the
buffer is in transient memory (i.e. on the stack) and must
be copied by @mhd{};
@end table

Return @mynull{} on error (i.e. invalid arguments, out of memory).
@end deftypefun


@deftypefun {struct MHD_Response *} MHD_create_response_from_data (size_t size, void *data, int must_free, int must_copy)
Create a response object.  The response object can be extended with
header information and then it can be used any number of times.
This function is deprecated, use @code{MHD_create_response_from_buffer} instead.

@table @var
@item size
size of the data portion of the response;

@item data
the data itself;

@item must_free
if true: @mhd{} should free data when done;

@item must_copy
if true: @mhd{} allocates a block of memory and use it to make a copy of
@var{data} embedded in the returned @code{MHD_Response} structure;
handling of the embedded memory is responsibility of @mhd{}; @var{data}
can be released anytime after this call returns.
@end table

Return @mynull{} on error (i.e. invalid arguments, out of memory).
@end deftypefun


Example: create a response from a statically allocated string:

@example
const char * data = "<html><body><p>Error!</p></body></html>";

struct MHD_Connection * connection = ...;
struct MHD_Response *   response;

response = MHD_create_response_from_buffer (strlen(data), data,
                                            MHD_RESPMEM_PERSISTENT);
MHD_queue_response(connection, 404, response);
MHD_destroy_response(response);
@end example



@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-response headers
@section Adding headers to a response


@deftypefun int MHD_add_response_header (struct MHD_Response *response, const char *header, const char *content)
Add a header line to the response. The strings referenced by
@var{header} and @var{content} must be zero-terminated and they are
duplicated into memory blocks embedded in @var{response}.

Notice that the strings must not hold newlines, carriage returns or tab
chars.

Return @code{MHD_NO} on error (i.e. invalid header or content format or
memory allocation error).
@end deftypefun


@deftypefun int MHD_add_response_footer (struct MHD_Response *response, const char *footer, const char *content)
Add a footer line to the response. The strings referenced by
@var{footer} and @var{content} must be zero-terminated and they are
duplicated into memory blocks embedded in @var{response}.  

Notice that the strings must not hold newlines, carriage returns or tab
chars.  You can add response footers at any time before signalling the
end of the response to MHD (not just before calling 'MHD_queue_response').
Footers are useful for adding cryptographic checksums to the reply or to
signal errors encountered during data generation.  This call was introduced
in MHD 0.9.3.

Return @code{MHD_NO} on error (i.e. invalid header or content format or
memory allocation error).
@end deftypefun



@deftypefun int MHD_del_response_header (struct MHD_Response *response, const char *header, const char *content)
Delete a header (or footer) line from the response.  Return @code{MHD_NO} on error
(arguments are invalid or no such header known).
@end deftypefun


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-response inspect
@section Inspecting a response object


@deftypefun int MHD_get_response_headers (struct MHD_Response *response, MHD_KeyValueIterator iterator, void *iterator_cls)
Get all of the headers added to a response.

Invoke the @var{iterator} callback for each header in the response,
using @var{iterator_cls} as first argument. Return number of entries
iterated over.  @var{iterator} can be @mynull{}: in this case the function
just counts headers.

@var{iterator} should not modify the its key and value arguments, unless
we know what we are doing.
@end deftypefun


@deftypefun {const char *} MHD_get_response_header (struct MHD_Response *response, const char *key)
Find and return a pointer to the value of a particular header from the
response.  @var{key} must reference a zero-terminated string
representing the header to look for. The search is case sensitive.
Return @mynull{} if header does not exist or @var{key} is @mynull{}.

We should not modify the value, unless we know what we are doing.
@end deftypefun


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-dauth
@chapter Utilizing Authentication

@noindent
@mhd{} support three types of client authentication.

Basic authentication uses a simple authentication method based
on BASE64 algorithm. Username and password are exchanged in clear
between the client and the server, so this method must only be used
for non-sensitive content or when the session is protected with https.
When using basic authentication @mhd{} will have access to the clear
password, possibly allowing to create a chained authentication
toward an external authentication server.

Digest authentication uses a one-way authentication method based
on MD5 hash algorithm. Only the hash will transit over the network,
hence protecting the user password. The nonce will prevent replay
attacks. This method is appropriate for general use, especially
when https is not used to encrypt the session.

Client certificate authentication uses a X.509 certificate from
the client. This is the strongest authentication mechanism but it
requires the use of HTTPS. Client certificate authentication can
be used simultaneously with Basic or Digest Authentication in order
to provide a two levels authentication (like for instance separate
machine and user authentication).  A code example for using
client certificates is presented in the @mhd{} tutorial.

@menu
* microhttpd-dauth basic:: Using Basic Authentication.
* microhttpd-dauth digest:: Using Digest Authentication.
@end menu

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-dauth basic
@section Using Basic Authentication

@deftypefun {char *} MHD_basic_auth_get_username_password (struct MHD_Connection *connection, char** password)
Get the username and password from the basic authorization header sent by the client.
Return @mynull{} if no username could be found, a pointer to the username if found.
If returned value is not @mynull{}, the value must be @code{free()}'ed.

@var{password} reference a buffer to store the password. It can be @mynull{}.
If returned value is not @mynull{}, the value must be @code{free()}'ed.
@end deftypefun

@deftypefun {int} MHD_queue_basic_auth_fail_response (struct MHD_Connection *connection, const char *realm, struct MHD_Response *response)
Queues a response to request basic authentication from the client.
Return @code{MHD_YES} if successful, otherwise @code{MHD_NO}.

@var{realm} must reference to a zero-terminated string representing the realm.

@var{response} a response structure to specify what shall be presented to the
client with a 401 HTTP status.
@end deftypefun

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-dauth digest
@section Using Digest Authentication

@deftypefun {char *} MHD_digest_auth_get_username (struct MHD_Connection *connection)
Find and return a pointer to the username value from the request header.
Return @mynull{} if the value is not found or header does not exist.
If returned value is not @mynull{}, the value must be @code{free()}'ed.
@end deftypefun

@deftypefun int MHD_digest_auth_check (struct MHD_Connection *connection, const char *realm, const char *username, const char *password, unsigned int nonce_timeout)
Checks if the provided values in the WWW-Authenticate header are valid
and sound according to RFC2716. If valid return @code{MHD_YES}, otherwise return @code{MHD_NO}.

@var{realm} must reference to a zero-terminated string representing the realm.

@var{username} must reference to a zero-terminated string representing the username,
it is usually the returned value from MHD_digest_auth_get_username.

@var{password} must reference to a zero-terminated string representing the password,
most probably it will be the result of a lookup of the username against a local database.

@var{nonce_timeout} is the amount of time in seconds for a nonce to be invalid.
Most of the time it is sound to specify 300 seconds as its values.
@end deftypefun

@deftypefun int MHD_queue_auth_fail_response (struct MHD_Connection *connection, const char *realm, const char *opaque, struct MHD_Response *response, int signal_stale)
Queues a response to request authentication from the client,
return @code{MHD_YES} if successful, otherwise @code{MHD_NO}.

@var{realm} must reference to a zero-terminated string representing the realm.

@var{opaque} must reference to a zero-terminated string representing a value
that gets passed to the client and expected to be passed again to the server
as-is. This value can be a hexadecimal or base64 string.

@var{response} a response structure to specify what shall be presented to the
client with a 401 HTTP status.

@var{signal_stale} a value that signals "stale=true" in the response header to
indicate the invalidity of the nonce and no need to ask for authentication
parameters and only a new nonce gets generated. @code{MHD_YES} to generate a new
nonce, @code{MHD_NO} to ask for authentication parameters.
@end deftypefun

Example: handling digest authentication requests and responses.

@example
#define PAGE "<html><head><title>libmicrohttpd demo</title></head><body>Access granted</body></html>"
#define DENIED "<html><head><title>libmicrohttpd demo</title></head><body>Access denied</body></html>"
#define OPAQUE "11733b200778ce33060f31c9af70a870ba96ddd4"

static int
ahc_echo (void *cls,
          struct MHD_Connection *connection,
          const char *url,
          const char *method,
          const char *version,
          const char *upload_data, size_t *upload_data_size, void **ptr)
@{
  struct MHD_Response *response;
  char *username;
  const char *password = "testpass";
  const char *realm = "test@@example.com";
  int ret;

  username = MHD_digest_auth_get_username(connection);
  if (username == NULL) 
    @{
      response = MHD_create_response_from_buffer(strlen (DENIED), 
					         DENIED,
					         MHD_RESPMEM_PERSISTENT);  
      ret = MHD_queue_auth_fail_response(connection, realm,
					 OPAQUE,
					 response,
					 MHD_NO);    
      MHD_destroy_response(response);  
      return ret;
    @}
  ret = MHD_digest_auth_check(connection, realm,
			      username, 
			      password, 
			      300);
  free(username);
  if ( (ret == MHD_INVALID_NONCE) ||
       (ret == MHD_NO) )
    @{
      response = MHD_create_response_from_buffer(strlen (DENIED), 
					         DENIED,
					         MHD_RESPMEM_PERSISTENT);  
      if (NULL == response) 
	return MHD_NO;
      ret = MHD_queue_auth_fail_response(connection, realm,
					 OPAQUE,
					 response,
					 (ret == MHD_INVALID_NONCE) ? MHD_YES : MHD_NO);  
      MHD_destroy_response(response);  
      return ret;
    @}
  response = MHD_create_response_from_buffer (strlen(PAGE), PAGE,
 					      MHD_RESPMEM_PERSISTENT);
  ret = MHD_queue_response(connection, MHD_HTTP_OK, response);  
  MHD_destroy_response(response);
  return ret;
@}
@end example

@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-post
@chapter Adding a @code{POST} processor
@cindex POST method

@menu
* microhttpd-post api::         Programming interface for the
                                @code{POST} processor.
@end menu


@noindent
@mhd{} provides the post processor API to make it easier for applications to
parse the data of a client's @code{POST} request: the
@code{MHD_AccessHandlerCallback} will be invoked multiple times to
process data as it arrives; at each invocation a new chunk of data must
be processed. The arguments @var{upload_data} and @var{upload_data_size}
are used to reference the chunk of data.

When @code{MHD_AccessHandlerCallback} is invoked for a new connection:
its @code{*@var{con_cls}} argument is set to @mynull{}. When @code{POST}
data comes in the upload buffer it is @strong{mandatory} to use the
@var{con_cls} to store a reference to per-connection data.  The fact
that the pointer was initially @mynull{} can be used to detect that
this is a new request.  

One method to detect that a new connection was established is
to set @code{*con_cls} to an unused integer:

@example
int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, size_t *upload_data_size,
                void **con_cls)
@{
  static int old_connection_marker;
  int new_connection = (MYNULL == *con_cls);

  if (new_connection) 
    @{
      /* new connection with POST */
      *con_cls = &old_connection_marker;
    @}

  ...
@}
@end example

@noindent
In contrast to the previous example, for @code{POST} requests in particular,
it is more common to use the value of @code{*con_cls} to keep track of
actual state used during processing, such as the post processor (or a
struct containing a post processor):

@example
int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, size_t *upload_data_size,
                void **con_cls)
@{
  struct MHD_PostProcessor * pp = *con_cls;

  if (pp == NULL) 
    @{
      pp = MHD_create_post_processor(connection, ...);
      *con_cls = pp;
      return MHD_YES;
    @}
  if (*upload_data_size) 
    @{
      MHD_post_process(pp, upload_data, *upload_data_size);
      *upload_data_size = 0;
      return MHD_YES;
    @}
  else
    @{
      MHD_destroy_post_processor(pp);
      return MHD_queue_response(...);
    @}
@}
@end example

Note that the callback from @code{MHD_OPTION_NOTIFY_COMPLETED}
should be used to destroy the post processor.  This cannot be
done inside of the access handler since the connection may not
always terminate normally.


@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-post api
@section Programming interface for the @code{POST} processor
@cindex POST method

@deftypefun {struct MHD_PostProcessor *} MHD_create_post_processor (struct MHD_Connection *connection, size_t buffer_size, MHD_PostDataIterator iterator, void *iterator_cls)
Create a PostProcessor.  A PostProcessor can be used to (incrementally)
parse the data portion of a @code{POST} request.

@table @var
@item connection
the connection on which the @code{POST} is happening (used to determine
the @code{POST} format);

@item buffer_size
maximum number of bytes to use for internal buffering (used only for the
parsing, specifically the parsing of the keys).  A tiny value (256-1024)
should be sufficient; do @strong{NOT} use a value smaller than 256;

@item iterator
iterator to be called with the parsed data; must @strong{NOT} be
@mynull{};

@item iterator_cls
custom value to be used as first argument to @var{iterator}.
@end table

Return @mynull{} on error (out of memory, unsupported encoding), otherwise
a PP handle.
@end deftypefun


@deftypefun int MHD_post_process (struct MHD_PostProcessor *pp, const char *post_data, size_t post_data_len)
Parse and process @code{POST} data.  Call this function when @code{POST}
data is available (usually during an @code{MHD_AccessHandlerCallback})
with the @var{upload_data} and @var{upload_data_size}.  Whenever
possible, this will then cause calls to the
@code{MHD_IncrementalKeyValueIterator}.

@table @var
@item pp
the post processor;

@item post_data
@var{post_data_len} bytes of @code{POST} data;

@item post_data_len
length of @var{post_data}.
@end table

Return @code{MHD_YES} on success, @code{MHD_NO} on error
(out-of-memory, iterator aborted, parse error).
@end deftypefun


@deftypefun int MHD_destroy_post_processor (struct MHD_PostProcessor *pp)
Release PostProcessor resources.  After this function is being called,
the PostProcessor is guaranteed to no longer call its iterator.  There
is no special call to the iterator to indicate the end of the post processing
stream.  After destroying the PostProcessor, the programmer should
perform any necessary work to complete the processing of the iterator.

Return @code{MHD_YES} if processing completed nicely, @code{MHD_NO} 
if there were spurious characters or formatting problems with
the post request.  It is common to ignore the return value
of this function.


@end deftypefun



@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

@c ------------------------------------------------------------
@node microhttpd-info
@chapter Obtaining status information.


@menu
* microhttpd-info daemon::        State information about an MHD daemon
* microhttpd-info conn::          State information about a connection
@end menu


@c ------------------------------------------------------------
@node microhttpd-info daemon
@section Obtaining state information about an MHD daemon

@deftypefun {const union MHD_DaemonInfo *} MHD_get_daemon_info (struct MHD_Daemon *daemon, enum MHD_DaemonInfoType infoType, ...)
Obtain information about the given daemon.  This function
is currently not fully implemented.

@table @var
@item daemon
the daemon about which information is desired;

@item infoType
type of information that is desired

@item ...
additional arguments about the desired information (depending on
infoType)
@end table

Returns a union with the respective member (depending on
infoType) set to the desired information), or NULL
in case the desired information is not available or
applicable.
@end deftypefun

@c ------------------------------------------------------------
@node microhttpd-info conn
@section Obtaining state information about a connection


@deftypefun {const union MHD_ConnectionInfo *} MHD_get_connection_info (struct MHD_Connection *daemon, enum MHD_ConnectionInfoType infoType, ...)
Obtain information about the given connection.

@table @var
@item connection
the connection about which information is desired;

@item infoType
type of information that is desired

@item ...
additional arguments about the desired information (depending on
infoType)
@end table

Returns a union with the respective member (depending on
infoType) set to the desired information), or NULL
in case the desired information is not available or
applicable.
@end deftypefun



@c ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


@c **********************************************************
@c *******************  Appendices  *************************
@c **********************************************************

@node GNU-LGPL
@unnumbered GNU-LGPL
@cindex license
@include lgpl.texi

@node GNU GPL with eCos Extension
@unnumbered GNU GPL with eCos Extension
@cindex license
@include ecos.texi

@node GNU-FDL
@unnumbered GNU-FDL
@cindex license
@include fdl-1.3.texi

@node Concept Index
@unnumbered Concept Index

@printindex cp

@node Function and Data Index
@unnumbered Function and Data Index

@printindex fn

@node Type Index
@unnumbered Type Index

@printindex tp

@bye