Measure string lengths only once

Bernd Helmle complained that CreateReplicationSlot() was assigning the
same value to the same variable twice, so we could remove one of them.
Code inspection reveals that we can actually remove both assignments:
according to the author the assignment was there for beauty of the
strlen line only, and another possible fix to that is to put the strlen
in its own line, so do that.

To be consistent within the file, refactor all duplicated strlen()
calls, which is what we do elsewhere in the backend anyway.  In
basebackup.c, snprintf already returns the right length; no need for
strlen afterwards.

Backpatch to 9.4, where replication slots were introduced, to keep code
identical.  Some of this is older, but the patch doesn't apply cleanly
and it's only of cosmetic value anyway.

Discussion: http://www.postgresql.org/message-id/BE2FD71DEA35A2287EA5F018@eje.credativ.lan

src/backend/replication/basebackup.c

@@ -698,10 +698,15 @@ SendBackupHeader(List *tablespaces)
 		}
 		else
 		{
-			pq_sendint(&buf, strlen(ti->oid), 4);		/* length */
+			Size	len;
-			pq_sendbytes(&buf, ti->oid, strlen(ti->oid));
+
-			pq_sendint(&buf, strlen(ti->path), 4);		/* length */
+			len = strlen(ti->oid);
-			pq_sendbytes(&buf, ti->path, strlen(ti->path));
+			pq_sendint(&buf, len, 4);
+			pq_sendbytes(&buf, ti->oid, len);
+
+			len = strlen(ti->path);
+			pq_sendint(&buf, len, 4);
+			pq_sendbytes(&buf, ti->path, len);
 		}
 		if (ti->size >= 0)
 			send_int8_string(&buf, ti->size / 1024);
@@ -724,6 +729,7 @@ SendXlogRecPtrResult(XLogRecPtr ptr, TimeLineID tli)
 {
 	StringInfoData buf;
 	char		str[MAXFNAMELEN];
+	Size		len;
 
 	pq_beginmessage(&buf, 'T'); /* RowDescription */
 	pq_sendint(&buf, 2, 2);		/* 2 fields */
@@ -742,7 +748,7 @@ SendXlogRecPtrResult(XLogRecPtr ptr, TimeLineID tli)
 	pq_sendint(&buf, 0, 2);		/* attnum */
 
 	/*
-	 * int8 may seem like a surprising data type for this, but in thory int4
+	 * int8 may seem like a surprising data type for this, but in theory int4
 	 * would not be wide enough for this, as TimeLineID is unsigned.
 	 */
 	pq_sendint(&buf, INT8OID, 4);		/* type oid */
@@ -755,13 +761,15 @@ SendXlogRecPtrResult(XLogRecPtr ptr, TimeLineID tli)
 	pq_beginmessage(&buf, 'D');
 	pq_sendint(&buf, 2, 2);		/* number of columns */
 
-	snprintf(str, sizeof(str), "%X/%X", (uint32) (ptr >> 32), (uint32) ptr);
+	len = snprintf(str, sizeof(str),
-	pq_sendint(&buf, strlen(str), 4);	/* length */
+				   "%X/%X", (uint32) (ptr >> 32), (uint32) ptr);
-	pq_sendbytes(&buf, str, strlen(str));
+	pq_sendint(&buf, len, 4);
+	pq_sendbytes(&buf, str, len);
+
+	len = snprintf(str, sizeof(str), "%u", tli);
+	pq_sendint(&buf, len, 4);
+	pq_sendbytes(&buf, str, len);
 
-	snprintf(str, sizeof(str), "%u", tli);
-	pq_sendint(&buf, strlen(str), 4);	/* length */
-	pq_sendbytes(&buf, str, strlen(str));
 	pq_endmessage(&buf);
 
 	/* Send a CommandComplete message */

src/backend/replication/walsender.c

@@ -299,6 +299,7 @@ IdentifySystem(void)
 	char		xpos[MAXFNAMELEN];
 	XLogRecPtr	logptr;
 	char	   *dbname = NULL;
+	Size		len;
 
 	/*
 	 * Reply with a result set with one row, four columns. First col is system
@@ -380,21 +381,32 @@ IdentifySystem(void)
 	/* Send a DataRow message */
 	pq_beginmessage(&buf, 'D');
 	pq_sendint(&buf, 4, 2);		/* # of columns */
-	pq_sendint(&buf, strlen(sysid), 4); /* col1 len */
+
-	pq_sendbytes(&buf, (char *) &sysid, strlen(sysid));
+	/* column 1: system identifier */
-	pq_sendint(&buf, strlen(tli), 4);	/* col2 len */
+	len = strlen(sysid);
-	pq_sendbytes(&buf, (char *) tli, strlen(tli));
+	pq_sendint(&buf, len, 4);
-	pq_sendint(&buf, strlen(xpos), 4);	/* col3 len */
+	pq_sendbytes(&buf, (char *) &sysid, len);
-	pq_sendbytes(&buf, (char *) xpos, strlen(xpos));
+
-	/* send NULL if not connected to a database */
+	/* column 2: timeline */
+	len = strlen(tli);
+	pq_sendint(&buf, len, 4);
+	pq_sendbytes(&buf, (char *) tli, len);
+
+	/* column 3: xlog position */
+	len = strlen(xpos);
+	pq_sendint(&buf, len, 4);
+	pq_sendbytes(&buf, (char *) xpos, len);
+
+	/* column 4: database name, or NULL if none */
 	if (dbname)
 	{
-		pq_sendint(&buf, strlen(dbname), 4);	/* col4 len */
+		len = strlen(dbname);
-		pq_sendbytes(&buf, (char *) dbname, strlen(dbname));
+		pq_sendint(&buf, len, 4);
+		pq_sendbytes(&buf, (char *) dbname, len);
 	}
 	else
 	{
-		pq_sendint(&buf, -1, 4);	/* col4 len, NULL */
+		pq_sendint(&buf, -1, 4);
 	}
 
 	pq_endmessage(&buf);
@@ -413,6 +425,7 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 	int			fd;
 	off_t		histfilelen;
 	off_t		bytesleft;
+	Size		len;
 
 	/*
 	 * Reply with a result set with one row, and two columns. The first col is
@@ -448,8 +461,9 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 	/* Send a DataRow message */
 	pq_beginmessage(&buf, 'D');
 	pq_sendint(&buf, 2, 2);		/* # of columns */
-	pq_sendint(&buf, strlen(histfname), 4);		/* col1 len */
+	len = strlen(histfname);
-	pq_sendbytes(&buf, histfname, strlen(histfname));
+	pq_sendint(&buf, len, 4);		/* col1 len */
+	pq_sendbytes(&buf, histfname, len);
 
 	fd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0666);
 	if (fd < 0)
@@ -674,6 +688,7 @@ StartReplication(StartReplicationCmd *cmd)
 	{
 		char		tli_str[11];
 		char		startpos_str[8 + 1 + 8 + 1];
+		Size		len;
 
 		snprintf(tli_str, sizeof(tli_str), "%u", sendTimeLineNextTLI);
 		snprintf(startpos_str, sizeof(startpos_str), "%X/%X",
@@ -710,11 +725,13 @@ StartReplication(StartReplicationCmd *cmd)
 		pq_beginmessage(&buf, 'D');
 		pq_sendint(&buf, 2, 2); /* number of columns */
 
-		pq_sendint(&buf, strlen(tli_str), 4);	/* length */
+		len = strlen(tli_str);
-		pq_sendbytes(&buf, tli_str, strlen(tli_str));
+		pq_sendint(&buf, len, 4);	/* length */
+		pq_sendbytes(&buf, tli_str, len);
 
-		pq_sendint(&buf, strlen(startpos_str), 4);		/* length */
+		len = strlen(startpos_str);
-		pq_sendbytes(&buf, startpos_str, strlen(startpos_str));
+		pq_sendint(&buf, len, 4);		/* length */
+		pq_sendbytes(&buf, startpos_str, len);
 
 		pq_endmessage(&buf);
 	}
@@ -762,10 +779,10 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 static void
 CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 {
-	const char *slot_name;
 	const char *snapshot_name = NULL;
 	char		xpos[MAXFNAMELEN];
 	StringInfoData buf;
+	Size		len;
 
 	Assert(!MyReplicationSlot);
 
@@ -791,14 +808,11 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 	initStringInfo(&output_message);
 
-	slot_name = NameStr(MyReplicationSlot->data.name);
-
 	if (cmd->kind == REPLICATION_KIND_LOGICAL)
 	{
 		LogicalDecodingContext *ctx;
 
-		ctx = CreateInitDecodingContext(
+		ctx = CreateInitDecodingContext(cmd->plugin, NIL,
-										cmd->plugin, NIL,
 										logical_read_xlog_page,
 										WalSndPrepareWrite, WalSndWriteData);
 
@@ -834,7 +848,6 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		ReplicationSlotSave();
 	}
 
-	slot_name = NameStr(MyReplicationSlot->data.name);
 	snprintf(xpos, sizeof(xpos), "%X/%X",
 			 (uint32) (MyReplicationSlot->data.confirmed_flush >> 32),
 			 (uint32) MyReplicationSlot->data.confirmed_flush);
@@ -885,30 +898,34 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	pq_sendint(&buf, 4, 2);		/* # of columns */
 
 	/* slot_name */
-	pq_sendint(&buf, strlen(slot_name), 4);		/* col1 len */
+	len = strlen(NameStr(MyReplicationSlot->data.name));
-	pq_sendbytes(&buf, slot_name, strlen(slot_name));
+	pq_sendint(&buf, len, 4);		/* col1 len */
+	pq_sendbytes(&buf, NameStr(MyReplicationSlot->data.name), len);
 
 	/* consistent wal location */
-	pq_sendint(&buf, strlen(xpos), 4);	/* col2 len */
+	len = strlen(xpos);
-	pq_sendbytes(&buf, xpos, strlen(xpos));
+	pq_sendint(&buf, len, 4);
+	pq_sendbytes(&buf, xpos, len);
 
-	/* snapshot name */
+	/* snapshot name, or NULL if none */
 	if (snapshot_name != NULL)
 	{
-		pq_sendint(&buf, strlen(snapshot_name), 4);		/* col3 len */
+		len = strlen(snapshot_name);
-		pq_sendbytes(&buf, snapshot_name, strlen(snapshot_name));
+		pq_sendint(&buf, len, 4);
+		pq_sendbytes(&buf, snapshot_name, len);
 	}
 	else
-		pq_sendint(&buf, -1, 4);	/* col3 len, NULL */
+		pq_sendint(&buf, -1, 4);
 
-	/* plugin */
+	/* plugin, or NULL if none */
 	if (cmd->plugin != NULL)
 	{
-		pq_sendint(&buf, strlen(cmd->plugin), 4);		/* col4 len */
+		len = strlen(cmd->plugin);
-		pq_sendbytes(&buf, cmd->plugin, strlen(cmd->plugin));
+		pq_sendint(&buf, len, 4);
+		pq_sendbytes(&buf, cmd->plugin, len);
 	}
 	else
-		pq_sendint(&buf, -1, 4);	/* col4 len, NULL */
+		pq_sendint(&buf, -1, 4);
 
 	pq_endmessage(&buf);