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@setfilename microhttpd.info

@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{NAME}
@code{\NAME\()}
@end macro

@macro null{}
@code{NULL}
@end macro

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

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

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


@c ------------------------------------------------------------
@node microhttpd
@appendix Libmicrohttpd documentation


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


@noindent
This appendix documents Libmicrohttpd version 0.1.2. It is built upon
the documentation in the header file @file{microhttpd.h}.

@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::          Inspection.
* microhttpd requests::         Handling requests.
* microhttpd responses::        Building responses to requests.
* microhttpd post::             Adding a @code{POST} processor.
@end menu

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

@c ------------------------------------------------------------
@node microhttpd intro
@appendixsec 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}) if
the entire data fits into the allowed amount of memory for the
connection.  Unsupported encodings and large @code{POST} submissions are
provided as a stream to the main application (and thus can 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.



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

@c ------------------------------------------------------------
@node microhttpd const
@appendixsec Constants


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

Note that if neither @code{MHD_USER_THREAD_PER_CONNECTION} nor
@code{MHD_USE_SELECT_INTERNALLY} are 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).

@table @code
@item MHD_NO_FLAG
No options selected.

@item MHD_USE_DEBUG
Run in debug mode.  If this flag is used, the library should print error
messages and warnings to stderr.

@item MHD_USE_SSL
Run in https mode.

@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
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.
@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
Maximum memory size per connection (followed by an @code{unsigned int}).

@item MHD_OPTION_CONNECTION_LIMIT
Maximum number of concurrenct connections to accept (followed by an
@code{unsigned int}).

@item MHD_OPTION_CONNECTION_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).

@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 @null{}.
@end table
@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
Cookies.  Note that the original @http{} header containing the cookie(s)
will still be available and intact.

@item MHD_POSTDATA_KIND
@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.
@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


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

@c ------------------------------------------------------------
@node microhttpd struct
@appendixsec 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
Handle for @code{POST} processing.
@end deftp


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

@c ------------------------------------------------------------
@node microhttpd cb
@appendixsec 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, unsigned int *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):

@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;

@item con_cls
reference to a pointer, initially set to @null{}, 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, size_t pos, char *buf, int 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) or in the next round if 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 will cause the program to be aborted (@cfunction{abort}).

@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, size_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, @null{} if not known;

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

@item transfer_encoding
encoding of the data, @null{} 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
@appendixsec Starting and stopping the server


@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 @null{} 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 @null{} 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


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

@c -----------------------------------------------------------
@node microhttpd inspect
@appendixsec Inspection


@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: @null{} 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)
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.

@table @var
@item 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
@appendixsec Handling requests


@menu
* microhttpd handlers::         @uri{} specific handlers.
* microhttpd values::           Connection headers and small
                                @code{POST} data.
@end menu


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

@c ------------------------------------------------------------
@node microhttpd handlers
@appendixsubsec @uri{} specific handlers


@noindent
A set of callbacks can be registered in the state of a daemon
(@code{MHD_Daemon}) to handle request for specific sets of
resources.  The set is selected by specifying the prefix string of the
@uri{}, example:

@example
/bookcase
@end example

@noindent
matches all of the following:

@example
/bookcase/book.html
/bookcase/pencil.html
/bookcase/strawberry.html
@end example

Handlers are stored in a linked list (managed with @cfunction{malloc}
and @cfunction{free}). Prefixes are compared with @cfunction{strcmp}.


@deftypefun int MHD_register_handler (struct MHD_Daemon *daemon, const char *uri_prefix, MHD_AccessHandlerCallback dh, void *dh_cls)
Register an access handler for all @uri{}s beginning with
@var{uri_prefix}, a zero-terminated @ascii{}-coded string.

Return @code{MRI_NO} if: the arguments are invalid (example: @null{}
pointers); a handler for this exact prefix already exists; an error
allocating memory happens.
@end deftypefun


@deftypefun int MHD_unregister_handler (struct MHD_Daemon *daemon, const char *uri_prefix, MHD_AccessHandlerCallback dh, void *dh_cls)
Unregister an access handler for the @uri{}s beginning with
@var{uri_prefix}.

Return @code{MHD_NO} if: the arguments are invalid (example: @null{}
pointers); a handler for this exact prefix is not known for this daemon.
@end deftypefun


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

@c ------------------------------------------------------------
@node microhttpd values
@appendixsubsec Connection headers and small @code{POST} data


@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 @null{}: in this case this function just counts
and returns the number of headers.
@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 @null{} if no such
item was found.
@end deftypefun


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

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


@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


@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
responce and we finally destroy it only when the daemon shuts down.


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

@c ------------------------------------------------------------
@node microhttpd response enqueue
@appendixsubsec 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
(increment the reference counter).

@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: @null{} 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 immediatley.
@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_data(...);
/* 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
@appendixsubsec Creating response objects


@deftypefun {struct MHD_Response *} MHD_create_response_from_callback (size_t size, unsigned int 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 @null{} 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.

@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 @null{} 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_data(strlen(data), data,
                                         MHD_NO, MHD_NO);
MHD_queue_response(connection, 404, response);
MHD_destroy_response(response);
@end example



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

@c ------------------------------------------------------------
@node microhttpd response headers
@appendixsubsec 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_del_response_header (struct MHD_Response *response, const char *header, const char *content)
Delete a header 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
@appendixsubsec 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 @null{}: 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 @null{} if header does not exist or @var{key} is @null{}.

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


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

@c ------------------------------------------------------------
@node microhttpd post
@appendixsec Adding a @code{POST} processor


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


@noindent
When a small amount of data comes from a client's @code{POST} request:
the data is available through the values interface. @ref{microhttpd
values}, for details. In this case @mhd{} invokes
@code{MHD_AccessHandlerCallback} only once and the callback must process
all the data during that invocation.

When a big amount of data comes from 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 @null{}. When @code{POST}
data comes in the upload buffer it is @strong{mandatory} to use the
@var{con_cls} to hold data or to mark an ongoing process.

To detect that a new connection has come with the @code{POST} method:

@example
int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, unsigned int *upload_data_size,
                void **con_cls)
@{
  static int old_connection_marker;
  int new_connection = (NULL == *con_cls);
  int method_is_post = strcmp("POST",method);

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

  ...
@}
@end example

@noindent
in this example the value of @code{*con_cls} is just an unused pointer
to an unused integer: its purpose is to make @code{*con_cls} different
from @null{}. When serious processing of @code{POST} data is needed: it
can be a pointer to a dynamically allocated data structure.

To detect that @code{POST} data is in the upload buffer:

@example
int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, unsigned int *upload_data_size,
                void **con_cls)
@{
  static int old_connection_marker;
  int new_connection = (NULL == *con_cls);
  int method_is_post = strcmp("POST",method);

  if (new_connection && method_is_post)
    @{
      int data_in_upload_buffer = (0 != *upload_data_size);

      if (data_in_upload_buffer)
        @{
          *con_cls = &old_connection_marker;
          /* POST data in the buffer */
        @}
      else
        /* POST data accessible with the values API */
    @}

  ...
@}
@end example


At each invocation there are two options:

@enumerate
@item
the callback can process the whole chunk by itself; every time @mhd{}
invokes it a new chunk is fully processed; with this mode the callback
has to @code{*upload_data_size = 0} before returning @code{MHD_YES};

@item
the callback can process a section of the chunk by itself; every time
@mhd{} invokes it the buffer holds the old data as well as new data
coming from the client; with this mode the callback has to set
@code{*upload_data_size} to the numbe of bytes still to process before
returning @code{MHD_YES};

example: @mhd{} invokes the callback with @code{100 ==
*upload_data_size}; the callback processes the first 80 bytes and before
returning the callback sets @code{*upload_data_size = 20}; the last
unprocessed 20 bytes will be the first 20 at the next invocation;

@item
when a new connection with @code{POST} data in the buffer comes: the
callback allocates a PostProcessor and hand to it the responsibility of
processing data; a pointer to the PostProcessor structure is saved in
@code{*con_cls}, so that it is available at each subsequent invocation;

the post processor data can be freed by a later invocation to an
appropriate callback.
@end enumerate


Let's see how to implement strategy 1:

@example
int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, unsigned int *upload_data_size,
                void **con_cls)
@{
  static int old_connection_marker;
  int new_connection = (NULL == *con_cls);
  int method_is_post = strcmp("POST",method);

  if (new_connection && method_is_post)
    @{
      int data_in_upload_buffer = (0 != *upload_data_size);

      if (data_in_upload_buffer)
        @{
          *con_cls = &old_connection_marker;
        @}
      else
        @{
          /* POST data accessible with the values API */
          return MHD_YES;
        @}
    @}

  if (&old_connection_marker == *con_cls)
    @{
      consume_data(upload_data, *upload_data_size);
      *upload_data_size = 0;
      return MHD_YES;
    @}

  /* process other methods */
  return MHD_YES;
@}
@end example

Let's see how to implement strategy 2:

@example
int
access_handler (void *cls,
                struct MHD_Connection * connection,
                const char *url,
                const char *method, const char *version,
                const char *upload_data, unsigned int *upload_data_size,
                void **con_cls)
@{
  static int old_connection_marker;
  int new_connection = (NULL == *con_cls);
  int method_is_post = strcmp("POST",method);

  if (new_connection && method_is_post)
    @{
      int data_in_upload_buffer = (0 != *upload_data_size);

      if (data_in_upload_buffer)
        @{
          *con_cls = &old_connection_marker;
        @}
      else
        @{
          /* POST data accessible with the values API */
          return MHD_YES;
        @}
    @}

  if (&old_connection_marker == *con_cls)
    @{
      int number_of_bytes_to_consume = 100;

      if (number_of_bytes_to_consume > *upload_data_size)
        number_of_bytes_to_consume = *upload_data_size;

      consume_some_data(upload_data, number_of_bytes_to_consume);
      *upload_data_size -= number_of_bytes_to_consume;
      return MHD_YES;
    @}

  /* process other methods */
  return MHD_YES;
@}

@end example



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

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



@deftypefun {struct MHD_PostProcessor *} MHD_create_post_processor (struct MHD_Connection *connection, unsigned int 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
@null{};

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

Return @null{} 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, unsigned int 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 void MHD_destroy_post_processor (struct MHD_PostProcessor *pp)
Release PostProcessor resources.
@end deftypefun


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