MINOR: conn_stream: add an tx buffer to the conn_stream

To be symmetrical with the recv() part, we no handle retryable and partial
transmission using a intermediary buffer in the conn_stream. For now it's only
set to BUF_NULL and never allocated nor used.

It cannot yet be used as-is without risking to lose data on close since
conn_streams need to be orphaned for this.

include/proto/connection.h

@@ -616,6 +616,7 @@ static inline void cs_init(struct conn_stream *cs, struct connection *conn)
 	LIST_INIT(&cs->send_wait_list);
 	cs->conn = conn;
 	cs->rxbuf = BUF_NULL;
+	cs->txbuf = BUF_NULL;
 }
 
 /* Initializes all required fields for a new connection. Note that it does the
@@ -687,6 +688,17 @@ static inline void cs_drop_rxbuf(struct conn_stream *cs)
 	}
 }
 
+/* Releases the conn_stream's tx buf if it exists. The buffer is automatically
+ * replaced with a pointer to the empty buffer.
+ */
+static inline void cs_drop_txbuf(struct conn_stream *cs)
+{
+	if (b_size(&cs->txbuf)) {
+		b_free(&cs->txbuf);
+		offer_buffers(NULL, tasks_run_queue);
+	}
+}
+
 /* Releases a conn_stream previously allocated by cs_new(), as well as any
  * buffer it would still hold.
  */
@@ -696,6 +708,7 @@ static inline void cs_free(struct conn_stream *cs)
 		tasklet_free(cs->wait_list.task);
 
 	cs_drop_rxbuf(cs);
+	cs_drop_txbuf(cs);
 	pool_free(pool_head_connstream, cs);
 }
 

include/types/connection.h

@@ -373,6 +373,7 @@ struct conn_stream {
 	struct wait_list wait_list;          /* We're in a wait list for send */
 	struct list send_wait_list;          /* list of tasks to wake when we're ready to send */
 	struct buffer rxbuf;                 /* receive buffer, always valid (buf_empty or real buffer) */
+	struct buffer txbuf;                 /* transmission buffer, always valid (buf_empty or real buffer) */
 	void *data;                          /* pointer to upper layer's entity (eg: stream interface) */
 	const struct data_cb *data_cb;       /* data layer callbacks. Must be set before xprt->init() */
 	void *ctx;                           /* mux-specific context */