Allow to avoid NUL-byte management for stringinfos and use in format.c.

In a lot of the places having appendBinaryStringInfo() maintain a
trailing NUL byte wasn't actually meaningful, e.g. when appending an
integer which can contain 0 in one of its bytes.

Removing this yields some small speedup, but more importantly will be
more consistent when providing faster variants of pq_sendint etc.

Author: Andres Freund
Discussion: https://postgr.es/m/20170914063418.sckdzgjfrsbekae4@alap3.anarazel.de

src/backend/lib/stringinfo.c

@@ -202,7 +202,7 @@ appendStringInfoSpaces(StringInfo str, int count)
  * appendBinaryStringInfo
  *
  * Append arbitrary binary data to a StringInfo, allocating more space
- * if necessary.
+ * if necessary. Ensures that a trailing null byte is present.
  */
 void
 appendBinaryStringInfo(StringInfo str, const char *data, int datalen)
@@ -224,6 +224,25 @@ appendBinaryStringInfo(StringInfo str, const char *data, int datalen)
 	str->data[str->len] = '\0';
 }
 
+/*
+ * appendBinaryStringInfoNT
+ *
+ * Append arbitrary binary data to a StringInfo, allocating more space
+ * if necessary. Does not ensure a trailing null-byte exists.
+ */
+void
+appendBinaryStringInfoNT(StringInfo str, const char *data, int datalen)
+{
+	Assert(str != NULL);
+
+	/* Make more room if needed */
+	enlargeStringInfo(str, datalen);
+
+	/* OK, append the data */
+	memcpy(str->data + str->len, data, datalen);
+	str->len += datalen;
+}
+
 /*
  * enlargeStringInfo
  *

src/backend/libpq/pqformat.c

@@ -138,13 +138,13 @@ pq_sendcountedtext(StringInfo buf, const char *str, int slen,
 	{
 		slen = strlen(p);
 		pq_sendint(buf, slen + extra, 4);
-		appendBinaryStringInfo(buf, p, slen);
+		appendBinaryStringInfoNT(buf, p, slen);
 		pfree(p);
 	}
 	else
 	{
 		pq_sendint(buf, slen + extra, 4);
-		appendBinaryStringInfo(buf, str, slen);
+		appendBinaryStringInfoNT(buf, str, slen);
 	}
 }
 
@@ -191,11 +191,11 @@ pq_sendstring(StringInfo buf, const char *str)
 	if (p != str)				/* actual conversion has been done? */
 	{
 		slen = strlen(p);
-		appendBinaryStringInfo(buf, p, slen + 1);
+		appendBinaryStringInfoNT(buf, p, slen + 1);
 		pfree(p);
 	}
 	else
-		appendBinaryStringInfo(buf, str, slen + 1);
+		appendBinaryStringInfoNT(buf, str, slen + 1);
 }
 
 /* --------------------------------
@@ -242,15 +242,15 @@ pq_sendint(StringInfo buf, int i, int b)
 	{
 		case 1:
 			n8 = (unsigned char) i;
-			appendBinaryStringInfo(buf, (char *) &n8, 1);
+			appendBinaryStringInfoNT(buf, (char *) &n8, 1);
 			break;
 		case 2:
 			n16 = pg_hton16((uint16) i);
-			appendBinaryStringInfo(buf, (char *) &n16, 2);
+			appendBinaryStringInfoNT(buf, (char *) &n16, 2);
 			break;
 		case 4:
 			n32 = pg_hton32((uint32) i);
-			appendBinaryStringInfo(buf, (char *) &n32, 4);
+			appendBinaryStringInfoNT(buf, (char *) &n32, 4);
 			break;
 		default:
 			elog(ERROR, "unsupported integer size %d", b);
@@ -271,7 +271,7 @@ pq_sendint64(StringInfo buf, int64 i)
 {
 	uint64		n64 = pg_hton64(i);
 
-	appendBinaryStringInfo(buf, (char *) &n64, sizeof(n64));
+	appendBinaryStringInfoNT(buf, (char *) &n64, sizeof(n64));
 }
 
 /* --------------------------------
@@ -297,7 +297,7 @@ pq_sendfloat4(StringInfo buf, float4 f)
 	swap.f = f;
 	swap.i = pg_hton32(swap.i);
 
-	appendBinaryStringInfo(buf, (char *) &swap.i, 4);
+	appendBinaryStringInfoNT(buf, (char *) &swap.i, 4);
 }
 
 /* --------------------------------

src/include/lib/stringinfo.h

@@ -143,6 +143,14 @@ extern void appendStringInfoSpaces(StringInfo str, int count);
 extern void appendBinaryStringInfo(StringInfo str,
 					   const char *data, int datalen);
 
+/*------------------------
+ * appendBinaryStringInfoNT
+ * Append arbitrary binary data to a StringInfo, allocating more space
+ * if necessary. Does not ensure a trailing null-byte exists.
+ */
+extern void appendBinaryStringInfoNT(StringInfo str,
+					   const char *data, int datalen);
+
 /*------------------------
  * enlargeStringInfo
  * Make sure a StringInfo's buffer can hold at least 'needed' more bytes.