[7.4] 6ecc9eccb http2_session: Implement transport polling

[Dridi Boukelmoune]

commit 6ecc9eccb6c9b733684a6ad304ee6d9cd1e7fd2c
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Wed Oct 11 12:38:21 2023 +0200

    http2_session: Implement transport polling
    
    The error check is not performed in a critical section to avoid
    contention, at the risk of not seeing the error until the next
    transport poll.

diff --git a/bin/varnishd/http2/cache_http2_session.c b/bin/varnishd/http2/cache_http2_session.c
index 672b40d64..ef0d88ede 100644
--- a/bin/varnishd/http2/cache_http2_session.c
+++ b/bin/varnishd/http2/cache_http2_session.c
@@ -441,6 +441,16 @@ h2_new_session(struct worker *wrk, void *arg)
 	wrk->vsl = NULL;
 }
 
+static int v_matchproto_(vtr_poll_f)
+h2_poll(struct req *req)
+{
+	struct h2_req *r2;
+
+	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);
+	CAST_OBJ_NOTNULL(r2, req->transport_priv, H2_REQ_MAGIC);
+	return (r2->error ? -1 : 1);
+}
+
 struct transport HTTP2_transport = {
 	.name =			"HTTP/2",
 	.magic =		TRANSPORT_MAGIC,
@@ -450,4 +460,5 @@ struct transport HTTP2_transport = {
 	.req_body =		h2_req_body,
 	.req_fail =		h2_req_fail,
 	.sess_panic =		h2_sess_panic,
+	.poll =			h2_poll,
 };
diff --git a/bin/varnishtest/tests/t02014.vtc b/bin/varnishtest/tests/t02014.vtc
index 8add78a0d..f4083c890 100644
--- a/bin/varnishtest/tests/t02014.vtc
+++ b/bin/varnishtest/tests/t02014.vtc
@@ -5,6 +5,9 @@ barrier b2 sock 3
 barrier b3 sock 3
 barrier b4 sock 3
 
+barrier b2_err cond 2
+barrier b3_err cond 2
+
 server s1 {
 	rxreq
 	txresp -bodylen 66300
@@ -64,6 +67,13 @@ client c1 {
 	stream 0 -wait
 } -run
 
+varnish v1 -vsl_catchup
+
+logexpect l2 -v v1 -g raw {
+	expect * * ReqMethod GET
+	expect * = VCL_call DELIVER
+} -start
+
 client c2 {
 	stream 0 {
 		barrier b2 sync
@@ -71,6 +81,7 @@ client c2 {
 
 	stream 1 {
 		txreq -hdr barrier ${b2_sock}
+		barrier b2_err sync
 		txdata -data "fail"
 		rxrst
 		expect rst.err == STREAM_CLOSED
@@ -78,7 +89,17 @@ client c2 {
 	} -run
 
 	stream 0 -wait
-} -run
+} -start
+
+logexpect l2 -wait
+barrier b2_err sync
+
+client c2 -wait
+
+logexpect l3 -v v1 -g raw {
+	expect * * ReqMethod POST
+	expect * = VCL_call DELIVER
+} -start
 
 client c3 {
 	stream 0 {
@@ -96,6 +117,7 @@ client c3 {
 	stream 1 {
 		txreq -req "POST" -hdr barrier ${b3_sock} -nostrend
 		txdata -data "ok"
+		barrier b3_err sync
 		txdata -data "fail"
 		rxrst
 		expect rst.err == STREAM_CLOSED
@@ -117,4 +139,9 @@ client c3 {
 	} -run
 
 	stream 0 -wait
-} -run
+} -start
+
+logexpect l3 -wait
+barrier b3_err sync
+
+client c3 -wait
diff --git a/bin/varnishtest/tests/t02025.vtc b/bin/varnishtest/tests/t02025.vtc
new file mode 100644
index 000000000..3b7e90e8a
--- /dev/null
+++ b/bin/varnishtest/tests/t02025.vtc
@@ -0,0 +1,49 @@
+varnishtest "h2 reset interrupt"
+
+barrier b1 sock 2
+barrier b2 sock 2
+
+varnish v1 -cliok "param.set feature +http2"
+varnish v1 -cliok "param.set debug +syncvsl"
+varnish v1 -vcl {
+	import vtc;
+
+	backend be none;
+
+	sub vcl_recv {
+		vtc.barrier_sync("${b1_sock}");
+		vtc.barrier_sync("${b2_sock}");
+	}
+
+	sub vcl_miss {
+		vtc.panic("unreachable");
+	}
+} -start
+
+logexpect l1 -v v1 -g raw -i Debug {
+	expect * * Debug "^H2RXF RST_STREAM"
+} -start
+
+client c1 {
+	stream 1 {
+		txreq
+		barrier b1 sync
+		txrst
+	} -run
+} -start
+
+logexpect l1 -wait
+barrier b2 sync
+
+varnish v1 -vsl_catchup
+varnish v1 -expect req_reset == 1
+
+# NB: The varnishncsa command below shows a minimal pattern to collect
+# "rapid reset" suspects per session, with the IP address. Here rapid
+# is interpreted as before a second elapsed. Session VXIDs showing up
+# numerous times become increasingly more suspicious. The format can of
+# course be extended to add anything else useful for data mining.
+shell -expect "1000 ${localhost}" {
+	varnishncsa -n ${v1_name} -d \
+		-q 'Timestamp:Reset[2] < 1.0' -F '%{VSL:Begin[2]}x %h'
+}
diff --git a/doc/sphinx/reference/vsl.rst b/doc/sphinx/reference/vsl.rst
index d8b440a08..98c126d2d 100644
--- a/doc/sphinx/reference/vsl.rst
+++ b/doc/sphinx/reference/vsl.rst
@@ -77,7 +77,8 @@ Restart
 	Client request is being restarted.
 
 Reset
-        The client closed its connection or reset its stream. Request
+        The client closed its connection, reset its stream or caused
+        a stream error that forced Varnish to reset the stream. Request
         processing is interrupted and considered failed.
 
 Pipe handling timestamps
diff --git a/lib/libvsc/VSC_main.vsc b/lib/libvsc/VSC_main.vsc
index 13c35d9be..14f3e266f 100644
--- a/lib/libvsc/VSC_main.vsc
+++ b/lib/libvsc/VSC_main.vsc
@@ -350,7 +350,9 @@
 	:oneliner:	Requests reset
 
 	Number of times a client left before the VCL processing of its
-	requests completed.
+	requests completed. For HTTP/2 sessions, either the stream was
+	reset by an RST_STREAM frame from the client, or a stream or
+	connection error occurred.
 
 .. varnish_vsc:: n_object
 	:type:	gauge