Added workaround for external APIs

Some APIs require non-const pointer even when data is supposed to be
unmodifiable. Added workaround to deal with such APIs without compiler
warnings.

4 files changed, 17 insertions, 10 deletions

diff --git a/src/microhttpd/daemon.c b/src/microhttpd/daemon.c
index c2f4b2c7..81b3afa9 100644
--- a/src/microhttpd/daemon.c
+++ b/src/microhttpd/daemon.c
@@ -534,7 +534,7 @@ MHD_init_daemon_certificate (struct MHD_Daemon *daemon)
 #endif
       return -1;
     }
-    cert.data = (unsigned char *) daemon->https_mem_trust;
+    cert.data = (unsigned char *) _MHD_DROP_CONST (daemon->https_mem_trust);
     cert.size = (unsigned int) paramlen;
     if (gnutls_certificate_set_x509_trust_mem (daemon->x509_cred,
                                                &cert,
@@ -571,9 +571,9 @@ MHD_init_daemon_certificate (struct MHD_Daemon *daemon)
 #endif
       return -1;
     }
-    key.data = (unsigned char *) daemon->https_mem_key;
+    key.data = (unsigned char *) _MHD_DROP_CONST (daemon->https_mem_key);
     key.size = (unsigned int) param1len;
-    cert.data = (unsigned char *) daemon->https_mem_cert;
+    cert.data = (unsigned char *) _MHD_DROP_CONST (daemon->https_mem_cert);
     cert.size = (unsigned int) param2len;
 
     if (NULL != daemon->https_key_password)
@@ -4948,7 +4948,7 @@ MHD_epoll (struct MHD_Daemon *daemon,
          (-1 != daemon->epoll_upgrade_fd) ) )
   {
     event.events = EPOLLIN | EPOLLOUT;
-    event.data.ptr = (void *) upgrade_marker;
+    event.data.ptr = _MHD_DROP_CONST (upgrade_marker);
     if (0 != epoll_ctl (daemon->epoll_fd,
                         EPOLL_CTL_ADD,
                         daemon->epoll_upgrade_fd,
@@ -5850,7 +5850,7 @@ parse_options_va (struct MHD_Daemon *daemon,
 #endif
           return MHD_NO;
         }
-        dhpar.data = (unsigned char *) pstr;
+        dhpar.data = (unsigned char *) _MHD_DROP_CONST (pstr);
         pstr_len = strlen (pstr);
         if (UINT_MAX < pstr_len)
         {
@@ -6340,7 +6340,7 @@ setup_epoll_to_listen (struct MHD_Daemon *daemon)
   if (MHD_ITC_IS_VALID_ (daemon->itc))
   {
     event.events = EPOLLIN;
-    event.data.ptr = (void *) epoll_itc_marker;
+    event.data.ptr = _MHD_DROP_CONST (epoll_itc_marker);
     if (0 != epoll_ctl (daemon->epoll_fd,
                         EPOLL_CTL_ADD,
                         MHD_itc_r_fd_ (daemon->itc),
diff --git a/src/microhttpd/internal.h b/src/microhttpd/internal.h
index 95d301f9..3bedf8ed 100644
--- a/src/microhttpd/internal.h
+++ b/src/microhttpd/internal.h
@@ -63,6 +63,13 @@
 #include "mhd_sockets.h"
 #include "mhd_itc_types.h"
 
+/**
+ * Macro to drop 'const' qualifier from pointer without compiler warning.
+ * To be used *only* to deal with broken external APIs, which require non-const
+ * pointer to unmodifiable data.
+ * Must not be used to transform pointers for MHD needs.
+ */
+#define _MHD_DROP_CONST(ptr)    ((void *)((uintptr_t)((const void *)(ptr))))
 
 /**
  * @def _MHD_MACRO_NO
diff --git a/src/microhttpd/mhd_send.c b/src/microhttpd/mhd_send.c
index f0ebd38d..009283d6 100644
--- a/src/microhttpd/mhd_send.c
+++ b/src/microhttpd/mhd_send.c
@@ -1054,9 +1054,9 @@ MHD_send_hdr_and_body_ (struct MHD_Connection *connection,
 #endif /* ! HAVE_SENDMSG */
                    push_hdr || push_body);
 #if defined(HAVE_SENDMSG) || defined(HAVE_WRITEV)
-  vector[0].iov_base = (void *) header;
+  vector[0].iov_base = _MHD_DROP_CONST (header);
   vector[0].iov_len = header_size;
-  vector[1].iov_base = (void *) body;
+  vector[1].iov_base = _MHD_DROP_CONST (body);
   vector[1].iov_len = body_size;
 
 #if defined(HAVE_SENDMSG)
diff --git a/src/microhttpd/response.c b/src/microhttpd/response.c
index bf1d9c31..8ddde763 100644
--- a/src/microhttpd/response.c
+++ b/src/microhttpd/response.c
@@ -1623,14 +1623,14 @@ MHD_create_response_from_iovec (const struct MHD_IoVec *iov,
 #if defined(MHD_WINSOCK_SOCKETS) && defined(_WIN64)
       while (MHD_IOV_ELMN_MAX_SIZE < element_size)
       {
-        iov_copy[i_cp].iov_base = (char *) buf;
+        iov_copy[i_cp].iov_base = (char *) _MHD_DROP_CONST (buf);
         iov_copy[i_cp].iov_len = ULONG_MAX;
         buf += ULONG_MAX;
         element_size -= ULONG_MAX;
         i_cp++;
       }
 #endif /* MHD_WINSOCK_SOCKETS && _WIN64 */
-      iov_copy[i_cp].iov_base = (void *) buf;
+      iov_copy[i_cp].iov_base = _MHD_DROP_CONST (buf);
       iov_copy[i_cp].iov_len = (MHD_iov_size_) element_size;
       i_cp++;
     }