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commit    0766bc57e9f94e5321e6ea4cb49db430224b2e60
Author:   Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:     Fri Jul 03 11:57:35 2026 +0000
First released in: 18.6

    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


 src/interfaces/libpq/fe-trace.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

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)
 	{


[parent: fb284f2f9bdb]