refine the srs-librtmp, add hijack get the object.

@@ -290,6 +290,11 @@ SimpleSocketStream::~SimpleSocketStream()
     }
 }
 
+srs_hijack_io_t SimpleSocketStream::hijack_io()
+{
+    return io;
+}
+
 int SimpleSocketStream::create_socket()
 {
     srs_assert(io);

@@ -50,6 +50,7 @@ public:
     SimpleSocketStream();
     virtual ~SimpleSocketStream();
 public:
+    virtual srs_hijack_io_t hijack_io();
     virtual int create_socket();
     virtual int connect(const char* server, int port);
 // ISrsBufferReader

@@ -534,7 +534,10 @@ srs_rtmp_t srs_rtmp_create2(const char* url)
 
 void srs_rtmp_destroy(srs_rtmp_t rtmp)
 {
-    srs_assert(rtmp != NULL);
+    if (!rtmp) {
+        return;
+    }
+    
     Context* context = (Context*)rtmp;
     
     srs_freep(context);
@@ -2424,6 +2427,23 @@ const char* srs_human_format_time()
     return buf;
 }
 
+
+#ifdef SRS_HIJACK_IO
+srs_hijack_io_t srs_hijack_io_get(srs_rtmp_t rtmp)
+{
+    if (!rtmp) {
+        return NULL;
+    }
+    
+    Context* context = (Context*)rtmp;
+    if (!context->skt) {
+        return NULL;
+    }
+    
+    return context->skt->hijack_io();
+}
+#endif
+
 #ifdef __cplusplus
 }
 #endif

@@ -107,7 +107,7 @@ extern srs_rtmp_t srs_rtmp_create(const char* url);
 extern srs_rtmp_t srs_rtmp_create2(const char* url);
 /**
 * close and destroy the rtmp stack.
-* @remark, user should use the rtmp again.
+* @remark, user should never use the rtmp again.
 */
 extern void srs_rtmp_destroy(srs_rtmp_t rtmp);
 
@@ -895,15 +895,22 @@ extern const char* srs_human_format_time();
 *************************************************************/
 // the void* will convert to your handler for io hijack.
 typedef void* srs_hijack_io_t;
-// define the following macro and functions in your module to hijack the io.
-// the example @see https://github.com/winlinvip/st-load
-// which use librtmp but use its own io(use st also).
 #ifdef SRS_HIJACK_IO
     #ifndef _WIN32
         // for iovec.
         #include <sys/uio.h>
     #endif
     /**
+    * get the hijack io object in rtmp protocol sdk.
+    * @remark, user should never provides this method, srs-librtmp provides it.
+    */
+    extern srs_hijack_io_t srs_hijack_io_get(srs_rtmp_t rtmp);
+#endif
+// define the following macro and functions in your module to hijack the io.
+// the example @see https://github.com/winlinvip/st-load
+// which use librtmp but use its own io(use st also).
+#ifdef SRS_HIJACK_IO
+    /**
     * create hijack.
     * @return NULL for error; otherwise, ok.
     */