MINOR: mux-quic: support app graceful shutdown

Adjust qcc_emit_cc_app() to allow the delay of emission of a
CONNECTION_CLOSE. This will only set the error code but the quic-conn
layer is not flagged for immediate close. The quic-conn will be
responsible to shut the connection when deemed suitable.

This change will allow to implement application graceful shutdown, such
as HTTP/3 with GOAWAY emission. This will allow to emit closing frames
on MUX release. Once all work is done at the lower layer, the quic-conn
should emit a CONNECTION_CLOSE with the registered error code.
diff --git a/include/haproxy/mux_quic.h b/include/haproxy/mux_quic.h
index dbb6fe6..0ad94cf 100644
--- a/include/haproxy/mux_quic.h
+++ b/include/haproxy/mux_quic.h
@@ -21,7 +21,7 @@
 void qcs_notify_recv(struct qcs *qcs);
 void qcs_notify_send(struct qcs *qcs);
 
-void qcc_emit_cc_app(struct qcc *qcc, int err);
+void qcc_emit_cc_app(struct qcc *qcc, int err, int immediate);
 void qcc_reset_stream(struct qcs *qcs, int err);
 int qcc_recv(struct qcc *qcc, uint64_t id, uint64_t len, uint64_t offset,
              char fin, char *data);
diff --git a/src/h3.c b/src/h3.c
index 0740166..7fb5f94 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -168,7 +168,7 @@
 	switch (type) {
 	case H3_UNI_S_T_CTRL:
 		if (h3c->flags & H3_CF_UNI_CTRL_SET) {
-			qcc_emit_cc_app(qcs->qcc, H3_STREAM_CREATION_ERROR);
+			qcc_emit_cc_app(qcs->qcc, H3_STREAM_CREATION_ERROR, 1);
 			return -1;
 		}
 		h3c->flags |= H3_CF_UNI_CTRL_SET;
@@ -182,7 +182,7 @@
 
 	case H3_UNI_S_T_QPACK_DEC:
 		if (h3c->flags & H3_CF_UNI_QPACK_DEC_SET) {
-			qcc_emit_cc_app(qcs->qcc, H3_STREAM_CREATION_ERROR);
+			qcc_emit_cc_app(qcs->qcc, H3_STREAM_CREATION_ERROR, 1);
 			return -1;
 		}
 		h3c->flags |= H3_CF_UNI_QPACK_DEC_SET;
@@ -192,7 +192,7 @@
 
 	case H3_UNI_S_T_QPACK_ENC:
 		if (h3c->flags & H3_CF_UNI_QPACK_ENC_SET) {
-			qcc_emit_cc_app(qcs->qcc, H3_STREAM_CREATION_ERROR);
+			qcc_emit_cc_app(qcs->qcc, H3_STREAM_CREATION_ERROR, 1);
 			return -1;
 		}
 		h3c->flags |= H3_CF_UNI_QPACK_ENC_SET;
@@ -621,7 +621,7 @@
 			total += hlen;
 
 			if (!h3_is_frame_valid(h3c, qcs, ftype)) {
-				qcc_emit_cc_app(qcs->qcc, H3_FRAME_UNEXPECTED);
+				qcc_emit_cc_app(qcs->qcc, H3_FRAME_UNEXPECTED, 1);
 				return -1;
 			}
 
@@ -643,7 +643,7 @@
 			 * excessive decompressed size.
 			 */
 			if (flen > QC_S_RX_BUF_SZ) {
-				qcc_emit_cc_app(qcs->qcc, H3_EXCESSIVE_LOAD);
+				qcc_emit_cc_app(qcs->qcc, H3_EXCESSIVE_LOAD, 1);
 				return -1;
 			}
 			break;
@@ -665,7 +665,7 @@
 				 * only close the stream once RESET_STREAM is
 				 * supported.
 				 */
-				qcc_emit_cc_app(qcs->qcc, h3c->err);
+				qcc_emit_cc_app(qcs->qcc, h3c->err, 1);
 				return -1;
 			}
 			break;
@@ -679,7 +679,7 @@
 		case H3_FT_SETTINGS:
 			ret = h3_parse_settings_frm(qcs->qcc->ctx, b, flen);
 			if (ret < 0) {
-				qcc_emit_cc_app(qcs->qcc, h3c->err);
+				qcc_emit_cc_app(qcs->qcc, h3c->err, 1);
 				return -1;
 			}
 			h3c->flags |= H3_CF_SETTINGS_RECV;
diff --git a/src/mux_quic.c b/src/mux_quic.c
index 065ffa5..658a974 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -667,13 +667,24 @@
 }
 
 /* Emit a CONNECTION_CLOSE_APP with error <err>. Reserved for application error
- * code. This will interrupt all future send/receive operations.
+ * code. To close the connection right away, set <immediate> : this is useful
+ * when dealing with a connection fatal error. Else a graceful shutdown will be
+ * conducted : the error-code is only registered. The lower layer is
+ * responsible to close the connection when deemed suitable. Note that in this
+ * case the error code might be overwritten if an immediate close is requested
+ * in the interval.
  */
-void qcc_emit_cc_app(struct qcc *qcc, int err)
+void qcc_emit_cc_app(struct qcc *qcc, int err, int immediate)
 {
-	quic_set_connection_close(qcc->conn->handle.qc, quic_err_app(err));
-	qcc->flags |= QC_CF_CC_EMIT;
-	tasklet_wakeup(qcc->wait_event.tasklet);
+	if (immediate) {
+		quic_set_connection_close(qcc->conn->handle.qc, quic_err_app(err));
+		qcc->flags |= QC_CF_CC_EMIT;
+		tasklet_wakeup(qcc->wait_event.tasklet);
+	}
+	else {
+		/* Only register the error code for graceful shutdown. */
+		qcc->conn->handle.qc->err = quic_err_app(err);
+	}
 }
 
 /* Prepare for the emission of RESET_STREAM on <qcs> with error code <err>. */