REGTEST: Add an HTX reg-test to check an edge case

This test checks that an HTTP message is properly processed when we failed to
add the HTX EOM block in an HTX message during the parsing because the buffer is
full. Some space must be released in the buffer to make it possible. This
requires an extra pass in the H1 multiplexer. Here, we must be sure the mux is
called while there is no more incoming data.

It is a "devel" test because conditions to run the test successfully is highly
dependent on the implementation. So if it fail, it is not necessarily a bug. It
may be due of an internal change. It relies on internal HTX sample fetches.
diff --git a/reg-tests/http-messaging/http_msg_full_on_eom.vtc b/reg-tests/http-messaging/http_msg_full_on_eom.vtc
new file mode 100644
index 0000000..8052b7b
--- /dev/null
+++ b/reg-tests/http-messaging/http_msg_full_on_eom.vtc
@@ -0,0 +1,61 @@
+varnishtest "cannot add the HTX EOM block because the buffer is full"
+feature ignore_unknown_macro
+
+#REQUIRE_VERSION=2.2
+#REGTEST_TYPE=devel
+
+# This test checks that an HTTP message is properly processed when we failed to
+# add the HTX EOM block in an HTX message during the parsing because the buffer
+# is full. Some space must be released in the buffer to make it possible. This
+# requires an extra pass in the H1 multiplexer. Here, we must be sure the mux is
+# called while there is no more incoming data.
+
+server s1 {
+    rxreq
+    expect req.bodylen == 15200
+    txresp -bodylen 15220
+} -start
+
+syslog S -level info {
+    recv
+    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: .* .* fe1 be1/srv1 [0-9]*/[0-9]*/[0-9]*/[0-9]*/[0-9]* 200 .* - - ---- .* .* \"GET / HTTP/1\\.1\""
+} -start
+
+haproxy h1 -conf {
+    global
+        tune.bufsize    16384
+        tune.maxrewrite 1024
+
+    defaults
+        mode http
+        timeout client  100ms
+        timeout server  1s
+        timeout connect 1s
+
+    backend be1
+        tcp-response inspect-delay 100ms
+	tcp-response content accept if { res.len gt 15272 }
+	tcp-response content reject
+
+        http-response deny if { htx.has_eom -m bool } or { htx.free_data gt 1024 }
+        server srv1 ${s1_addr}:${s1_port}
+
+    frontend fe1
+        option httplog
+        option http-buffer-request
+        log ${S_addr}:${S_port} local0 debug err
+        bind "fd@${fe1}"
+        http-request deny if ! { req.body_len eq 15200 } or { htx.has_eom -m bool } or { htx.free_data gt 1024 }
+        use_backend be1
+} -start
+
+haproxy h1 -cli {
+    send "trace h1 sink stderr; trace h1 level developer; trace h1 verbosity complete; trace h1 start now"
+}
+
+client c1 -connect ${h1_fe1_sock} {
+  txreq -bodylen 15200
+  rxresp
+  expect resp.status == 200
+  expect resp.bodylen == 15220
+} -run