refine rtmp send protocol, use the same cache for header

@@ -31,7 +31,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 // current release version
 #define VERSION_MAJOR "0"
 #define VERSION_MINOR "9"
-#define VERSION_REVISION "39"
+#define VERSION_REVISION "40"
 #define RTMP_SIG_SRS_VERSION VERSION_MAJOR"."VERSION_MINOR"."VERSION_REVISION
 // server info.
 #define RTMP_SIG_SRS_KEY "srs"

@@ -424,12 +424,10 @@ int SrsProtocol::send_message(ISrsMessage* msg)
     // always write the header event payload is empty.
     do {
         // generate the header.
-        char* pheader = NULL;
-        int header_size = 0;
+        char* pheader = out_header_cache;
         
         if (p == (char*)msg->payload) {
             // write new chunk stream header, fmt is 0
-            pheader = out_header_fmt0;
             *pheader++ = 0x00 | (msg->get_perfer_cid() & 0x3F);
             
             // chunk message header, 11 bytes
@@ -470,12 +468,8 @@ int SrsProtocol::send_message(ISrsMessage* msg)
                 *pheader++ = pp[1];
                 *pheader++ = pp[0];
             }
-            
-            header_size = pheader - out_header_fmt0;
-            pheader = out_header_fmt0;
         } else {
             // write no message header chunk stream, fmt is 3
-            pheader = out_header_fmt3;
             *pheader++ = 0xC0 | (msg->get_perfer_cid() & 0x3F);
             
             // chunk extended timestamp header, 0 or 4 bytes, big-endian
@@ -499,9 +493,6 @@ int SrsProtocol::send_message(ISrsMessage* msg)
                 *pheader++ = pp[1];
                 *pheader++ = pp[0];
             }
-            
-            header_size = pheader - out_header_fmt3;
-            pheader = out_header_fmt3;
         }
         
         // sendout header and payload by writev.
@@ -509,9 +500,13 @@ int SrsProtocol::send_message(ISrsMessage* msg)
         int payload_size = msg->size - (p - (char*)msg->payload);
         payload_size = srs_min(payload_size, out_chunk_size);
         
+        // always has header
+        int header_size = pheader - out_header_cache;
+        srs_assert(header_size > 0);
+        
         // send by writev
         iovec iov[2];
-        iov[0].iov_base = pheader;
+        iov[0].iov_base = out_header_cache;
         iov[0].iov_len = header_size;
         iov[1].iov_base = p;
         iov[1].iov_len = payload_size;

@@ -106,7 +106,8 @@ class ISrsMessage;
 *     4bytes timestamp header,
 * that is, 1+4=5bytes.
 */
-#define RTMP_MAX_FMT3_HEADER_SIZE 5
+// always use fmt0 as cache.
+//#define RTMP_MAX_FMT3_HEADER_SIZE 5
 
 /**
 * the protocol provides the rtmp-message-protocol services,
@@ -141,8 +142,7 @@ private:
     AckWindowSize in_ack_size;
 // peer out
 private:
-    char out_header_fmt0[RTMP_MAX_FMT0_HEADER_SIZE];
-    char out_header_fmt3[RTMP_MAX_FMT3_HEADER_SIZE];
+    char out_header_cache[RTMP_MAX_FMT0_HEADER_SIZE];
     int32_t out_chunk_size;
 public:
     /**