[master] 115da2ee8 http2: Log H2_Send_Frame() write error details

[Nils Goroll]

commit 115da2ee807dba868268309b090ac9eaf02ba8cd
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Mon Mar 3 20:27:34 2025 +0100

    http2: Log H2_Send_Frame() write error details
    
    Trying to understand if this is the place where #4293 happens

diff --git a/bin/varnishd/http2/cache_http2_send.c b/bin/varnishd/http2/cache_http2_send.c
index 880fb9876..d4e66aab8 100644
--- a/bin/varnishd/http2/cache_http2_send.c
+++ b/bin/varnishd/http2/cache_http2_send.c
@@ -212,6 +212,11 @@ H2_Send_Frame(struct worker *wrk, struct h2_sess *h2,
 			H2S_Lock_VSLb(h2, SLT_SessError,
 			     "H2: stream %u: Hit idle_send_timeout", stream);
 		}
+		else {
+			H2S_Lock_VSLb(h2, SLT_Debug,
+			    "H2: stream %u: write error s=%zd/%zu errno=%d",
+			    stream, s, sizeof hdr + len, errno);
+		}
 		/*
 		 * There is no point in being nice here, we will be unable
 		 * to send a GOAWAY once the code unrolls, so go directly