MINOR: quic: Do not consume the RX buffer on QUIC sock i/o handler side

Rename quic_lstnr_dgram_read() to quic_lstnr_dgram_dispatch() to reflect its new role.
After calling this latter, the sock i/o handler must consume the buffer only if
the datagram it received is detected as wrong by quic_lstnr_dgram_dispatch().
The datagram handler task mark the datagram as consumed atomically setting ->buf
to NULL value. The sock i/o handler is responsible of flushing its RX buffer
before using it. It also keeps a datagram among the consumed ones so that
to pass it to quic_lstnr_dgram_dispatch() and prevent it from allocating a new one.

include/haproxy/xprt_quic-t.h

@@ -250,6 +250,7 @@ extern struct pool_head *pool_head_quic_rxbuf;
 extern struct pool_head *pool_head_quic_rx_packet;
 extern struct pool_head *pool_head_quic_tx_packet;
 extern struct pool_head *pool_head_quic_frame;
+extern struct pool_head *pool_head_quic_dgram;
 
 /* QUIC connection id data.
  *

include/haproxy/xprt_quic.h

@@ -1185,8 +1185,9 @@ void chunk_frm_appendf(struct buffer *buf, const struct quic_frame *frm);
 void quic_set_tls_alert(struct quic_conn *qc, int alert);
 int quic_set_app_ops(struct quic_conn *qc, const unsigned char *alpn, size_t alpn_len);
 struct task *quic_lstnr_dghdlr(struct task *t, void *ctx, unsigned int state);
-int quic_lstnr_dgram_read(unsigned char *buf, size_t len, void *owner,
+int quic_lstnr_dgram_dispatch(unsigned char *buf, size_t len, void *owner,
-                          struct sockaddr_storage *saddr, struct list *dgrams);
+                              struct sockaddr_storage *saddr,
+                              struct quic_dgram *new_dgram, struct list *dgrams);
 
 #endif /* USE_QUIC */
 #endif /* _HAPROXY_XPRT_QUIC_H */

src/quic_sock.c

@@ -175,6 +175,7 @@ void quic_sock_fd_iocb(int fd)
 	struct sockaddr_storage saddr = {0};
 	size_t max_sz;
 	socklen_t saddrlen;
+	struct quic_dgram *dgram, *dgramp, *new_dgram;
 
 	BUG_ON(!l);
 
@@ -187,8 +188,23 @@ void quic_sock_fd_iocb(int fd)
 	rxbuf = MT_LIST_POP(&l->rx.rxbuf_list, typeof(rxbuf), mt_list);
 	if (!rxbuf)
 		goto out;
+
 	buf = &rxbuf->buf;
 
+	new_dgram = NULL;
+	/* Remove all consumed datagrams of this buffer */
+	list_for_each_entry_safe(dgram, dgramp, &rxbuf->dgrams, list) {
+		if (HA_ATOMIC_LOAD(&dgram->buf))
+			break;
+
+		LIST_DELETE(&dgram->list);
+		b_del(buf, dgram->len);
+		if (!new_dgram)
+			new_dgram = dgram;
+		else
+			pool_free(pool_head_quic_dgram, dgram);
+	}
+
 	params = &l->bind_conf->quic_params;
 	max_sz = params->max_udp_payload_size;
 	if (b_contig_space(buf) < max_sz) {
@@ -212,9 +228,11 @@ void quic_sock_fd_iocb(int fd)
 	} while (0);
 
 	b_add(buf, ret);
-	quic_lstnr_dgram_read((unsigned char *)b_head(buf), ret,
+	if (!quic_lstnr_dgram_dispatch((unsigned char *)b_head(buf), ret,
-	                      l, &saddr, &rxbuf->dgrams);
+	                               l, &saddr, new_dgram, &rxbuf->dgrams)) {
-	b_del(buf, ret);
+		/* If wrong, consume this datagram */
+		b_del(buf, ret);
+	}
  out:
 	MT_LIST_APPEND(&l->rx.rxbuf_list, &rxbuf->mt_list);
 }

src/xprt_quic.c

@@ -5403,6 +5403,8 @@ struct task *quic_lstnr_dghdlr(struct task *t, void *ctx, unsigned int state)
 			/* If the packet length could not be found, we cannot continue. */
 			break;
 	} while (pos < end);
+	/* Mark this datagram as consumed */
+	HA_ATOMIC_STORE(&dgram->buf, NULL);
 
 	/* Increasing the received bytes counter by the UDP datagram length
 	 * if this datagram could be associated to a connection.
@@ -5449,8 +5451,13 @@ static int quic_get_dgram_dcid(unsigned char *buf, const unsigned char *end,
 	return 0;
 }
 
-int quic_lstnr_dgram_read(unsigned char *buf, size_t len, void *owner,
+/* Retrieve the DCID from the datagram found in <buf> and deliver it to the
-                          struct sockaddr_storage *saddr, struct list *dgrams)
+ * correct datagram handler.
+ * Return 1 if a correct datagram could be found, 0 if not.
+ */
+int quic_lstnr_dgram_dispatch(unsigned char *buf, size_t len, void *owner,
+                              struct sockaddr_storage *saddr,
+                              struct quic_dgram *new_dgram, struct list *dgrams)
 {
 	struct quic_dgram *dgram;
 	unsigned char *dcid;
@@ -5461,7 +5468,7 @@ int quic_lstnr_dgram_read(unsigned char *buf, size_t len, void *owner,
 	if (!len || !quic_get_dgram_dcid(buf, buf + len, &dcid, &dcid_len))
 		goto err;
 
-	dgram = pool_alloc(pool_head_quic_dgram);
+	dgram = new_dgram ? new_dgram : pool_alloc(pool_head_quic_dgram);
 	if (!dgram)
 		goto err;