fix: add input validation and error logging to tcp_mux_encode function

Signed-off-by: Dengfeng Liu <liudf0716@gmail.com>

tcpmux.c

@@ -185,12 +185,40 @@ int validate_tcp_mux_protocol(struct tcp_mux_header *tmux_hdr) {
  * @param length The length of the TCP MUX message payload.
  * @param tmux_hdr Pointer to the tcp_mux_header structure to be filled.
  */
+/**
+ * @brief Encodes a TCP multiplexer header with the specified parameters
+ *
+ * This function fills a TCP multiplexer header structure with the provided values,
+ * performing necessary network byte order conversions for cross-platform compatibility.
+ *
+ * @param type The type of TCP multiplexer message (e.g., DATA, WINDOW_UPDATE)
+ * @param flags Control flags for the message
+ * @param stream_id Identifier for the stream this message belongs to
+ * @param length Length of the message payload
+ * @param tmux_hdr Pointer to header structure to be filled
+ *
+ * @pre tmux_hdr must not be NULL
+ * @pre type must be a valid tcp_mux_type enum value
+ */
 void tcp_mux_encode(enum tcp_mux_type type, enum tcp_mux_flag flags,
                     uint32_t stream_id, uint32_t length,
                     struct tcp_mux_header *tmux_hdr) {
-    assert(tmux_hdr);
+    // Validate input parameters
+    if (!tmux_hdr) {
+        debug(LOG_ERR, "NULL header pointer provided");
+        return;
+    }
+
+    if (type > GO_AWAY) {
+        debug(LOG_ERR, "Invalid TCP MUX type: %d", type);
+        return;
+    }
+
+    // Fill header fields with provided values
     tmux_hdr->version = proto_version;
     tmux_hdr->type = type;
+
+    // Convert multi-byte fields to network byte order
     tmux_hdr->flags = htons(flags);
     tmux_hdr->stream_id = htonl(stream_id);
     tmux_hdr->length = length ? htonl(length) : 0;