From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 3 Jul 2026 11:57:35 +0000 (+0300)
Subject: Fix tracing of BackendKeyData and CancelRequest
X-Git-Tag: REL_19_BETA2~65
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0766bc57e9f94e5321e6ea4cb49db430224b2e60;p=thirdparty%2Fpostgresql.git

Fix tracing of BackendKeyData and CancelRequest

BackendKeyData length was increased from 4 bytes to a variable-length
length (up to 256 bytes) in a460251f0a. However, pqTrace still traces
it as a 4 bytes key, leading to a "mismatched message length" warning
message. The same issue impacts the tracing of CancelRequest.

This patch fixes the issue by using pqTraceOutputNchar instead of
pqTraceOutputInt32 in both cases.

Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Discussion: https://www.postgresql.org/message-id/CAO6_Xqo6gTv9=76H=k2qDRFU+KHuBiY2S=bQynEr6J8gS7L6xA@mail.gmail.com
Backpatch-through: 18
---

diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index c348b08c39b..2901fa5b451 100644
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -452,11 +452,12 @@ pqTraceOutput_CopyOutResponse(FILE *f, const char *message, int *cursor)
 }
 
 static void
-pqTraceOutput_BackendKeyData(FILE *f, const char *message, int *cursor, bool regress)
+pqTraceOutput_BackendKeyData(FILE *f, const char *message, int *cursor, int length,
+							 bool regress)
 {
 	fprintf(f, "BackendKeyData\t");
 	pqTraceOutputInt32(f, message, cursor, regress);
-	pqTraceOutputInt32(f, message, cursor, regress);
+	pqTraceOutputNchar(f, length - *cursor + 1, message, cursor, regress);
 }
 
 static void
@@ -762,7 +763,8 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
 			/* No message content */
 			break;
 		case PqMsg_BackendKeyData:
-			pqTraceOutput_BackendKeyData(conn->Pfdebug, message, &logCursor, regress);
+			pqTraceOutput_BackendKeyData(conn->Pfdebug, message, &logCursor,
+										 length, regress);
 			break;
 		case PqMsg_NoData:
 			fprintf(conn->Pfdebug, "NoData");
@@ -876,7 +878,8 @@ pqTraceOutputNoTypeByteMessage(PGconn *conn, const char *message)
 		pqTraceOutputInt16(conn->Pfdebug, message, &logCursor);
 		pqTraceOutputInt16(conn->Pfdebug, message, &logCursor);
 		pqTraceOutputInt32(conn->Pfdebug, message, &logCursor, regress);
-		pqTraceOutputInt32(conn->Pfdebug, message, &logCursor, regress);
+		pqTraceOutputNchar(conn->Pfdebug, length - logCursor, message,
+						   &logCursor, regress);
 	}
 	else if (version == NEGOTIATE_SSL_CODE)
 	{