Remove server and libpq support for old FE/BE protocol version 2.

Protocol version 3 was introduced in PostgreSQL 7.4. There shouldn't be
many clients or servers left out there without version 3 support. But as
a courtesy, I kept just enough of the old protocol support that we can
still send the "unsupported protocol version" error in v2 format, so that
old clients can display the message properly. Likewise, libpq still
understands v2 ErrorResponse messages when establishing a connection.

The impetus to do this now is that I'm working on a patch to COPY
FROM, to always prefetch some data. We cannot do that safely with the
old protocol, because it requires parsing the input one byte at a time
to detect the end-of-copy marker.

Reviewed-by: Tom Lane, Alvaro Herrera, John Naylor
Discussion: https://www.postgresql.org/message-id/9ec25819-0a8a-d51a-17dc-4150bb3cca3b%40iki.fi

1 files changed, 18 insertions, 142 deletions

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 9812a14662..c16a7bd9f2 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2289,10 +2289,6 @@ PQconnectPoll(PGconn *conn)
 		case CONNECTION_MADE:
 			break;
 
-			/* We allow pqSetenvPoll to decide whether to proceed. */
-		case CONNECTION_SETENV:
-			break;
-
 			/* Special cases: proceed without waiting. */
 		case CONNECTION_SSL_STARTUP:
 		case CONNECTION_NEEDED:
@@ -2956,12 +2952,8 @@ keep_going:						/* We will come back to here until there is
 				/*
 				 * Build the startup packet.
 				 */
-				if (PG_PROTOCOL_MAJOR(conn->pversion) >= 3)
-					startpacket = pqBuildStartupPacket3(conn, &packetlen,
-														EnvironmentOptions);
-				else
-					startpacket = pqBuildStartupPacket2(conn, &packetlen,
-														EnvironmentOptions);
+				startpacket = pqBuildStartupPacket3(conn, &packetlen,
+													EnvironmentOptions);
 				if (!startpacket)
 				{
 					appendPQExpBufferStr(&conn->errorMessage,
@@ -3247,19 +3239,11 @@ keep_going:						/* We will come back to here until there is
 					goto error_return;
 				}
 
-				if (PG_PROTOCOL_MAJOR(conn->pversion) >= 3)
-				{
-					/* Read message length word */
-					if (pqGetInt(&msgLength, 4, conn))
-					{
-						/* We'll come back when there is more data */
-						return PGRES_POLLING_READING;
-					}
-				}
-				else
+				/* Read message length word */
+				if (pqGetInt(&msgLength, 4, conn))
 				{
-					/* Set phony message length to disable checks below */
-					msgLength = 8;
+					/* We'll come back when there is more data */
+					return PGRES_POLLING_READING;
 				}
 
 				/*
@@ -3268,7 +3252,9 @@ keep_going:						/* We will come back to here until there is
 				 * auth requests may not be that small.  Errors can be a
 				 * little larger, but not huge.  If we see a large apparent
 				 * length in an error, it means we're really talking to a
-				 * pre-3.0-protocol server; cope.
+				 * pre-3.0-protocol server; cope.  (Before version 14, the
+				 * server also used the old protocol for errors that happened
+				 * before processing the startup packet.)
 				 */
 				if (beresp == 'R' && (msgLength < 8 || msgLength > 2000))
 				{
@@ -3296,25 +3282,11 @@ keep_going:						/* We will come back to here until there is
 					 */
 					appendPQExpBufferChar(&conn->errorMessage, '\n');
 
-					/*
-					 * If we tried to open the connection in 3.0 protocol,
-					 * fall back to 2.0 protocol.
-					 */
-					if (PG_PROTOCOL_MAJOR(conn->pversion) >= 3)
-					{
-						conn->pversion = PG_PROTOCOL(2, 0);
-						need_new_connection = true;
-						goto keep_going;
-					}
-
 					goto error_return;
 				}
 
 				/*
 				 * Can't process if message body isn't all here yet.
-				 *
-				 * (In protocol 2.0 case, we are assuming messages carry at
-				 * least 4 bytes of data.)
 				 */
 				msgLength -= 4;
 				avail = conn->inEnd - conn->inCursor;
@@ -3335,21 +3307,10 @@ keep_going:						/* We will come back to here until there is
 				/* Handle errors. */
 				if (beresp == 'E')
 				{
-					if (PG_PROTOCOL_MAJOR(conn->pversion) >= 3)
+					if (pqGetErrorNotice3(conn, true))
 					{
-						if (pqGetErrorNotice3(conn, true))
-						{
-							/* We'll come back when there is more data */
-							return PGRES_POLLING_READING;
-						}
-					}
-					else
-					{
-						if (pqGets_append(&conn->errorMessage, conn))
-						{
-							/* We'll come back when there is more data */
-							return PGRES_POLLING_READING;
-						}
+						/* We'll come back when there is more data */
+						return PGRES_POLLING_READING;
 					}
 					/* OK, we read the message; mark data consumed */
 					conn->inStart = conn->inCursor;
@@ -3434,33 +3395,6 @@ keep_going:						/* We will come back to here until there is
 				msgLength -= 4;
 
 				/*
-				 * Ensure the password salt is in the input buffer, if it's an
-				 * MD5 request.  All the other authentication methods that
-				 * contain extra data in the authentication request are only
-				 * supported in protocol version 3, in which case we already
-				 * read the whole message above.
-				 */
-				if (areq == AUTH_REQ_MD5 && PG_PROTOCOL_MAJOR(conn->pversion) < 3)
-				{
-					msgLength += 4;
-
-					avail = conn->inEnd - conn->inCursor;
-					if (avail < 4)
-					{
-						/*
-						 * Before returning, try to enlarge the input buffer
-						 * if needed to hold the whole message; see notes in
-						 * pqParseInput3.
-						 */
-						if (pqCheckInBufferSpace(conn->inCursor + (size_t) 4,
-												 conn))
-							goto error_return;
-						/* We'll come back when there is more data */
-						return PGRES_POLLING_READING;
-					}
-				}
-
-				/*
 				 * Process the rest of the authentication request message, and
 				 * respond to it if necessary.
 				 *
@@ -3567,15 +3501,6 @@ keep_going:						/* We will come back to here until there is
 					goto error_return;
 				}
 
-				/* Fire up post-connection housekeeping if needed */
-				if (PG_PROTOCOL_MAJOR(conn->pversion) < 3)
-				{
-					conn->status = CONNECTION_SETENV;
-					conn->setenv_state = SETENV_STATE_CLIENT_ENCODING_SEND;
-					conn->next_eo = EnvironmentOptions;
-					return PGRES_POLLING_WRITING;
-				}
-
 				/* Almost there now ... */
 				conn->status = CONNECTION_CHECK_TARGET;
 				goto keep_going;
@@ -3596,17 +3521,9 @@ keep_going:						/* We will come back to here until there is
 					 * If the server didn't report
 					 * "default_transaction_read_only" or "in_hot_standby" at
 					 * startup, we must determine its state by sending the
-					 * query "SHOW transaction_read_only".  Servers before 7.4
-					 * lack the transaction_read_only GUC, but by the same
-					 * token they don't have any read-only mode, so we may
-					 * just assume the results.
+					 * query "SHOW transaction_read_only".  This GUC exists in
+					 * all server versions that support 3.0 protocol.
 					 */
-					if (conn->sversion < 70400)
-					{
-						conn->default_transaction_read_only = PG_BOOL_NO;
-						conn->in_hot_standby = PG_BOOL_NO;
-					}
-
 					if (conn->default_transaction_read_only == PG_BOOL_UNKNOWN ||
 						conn->in_hot_standby == PG_BOOL_UNKNOWN)
 					{
@@ -3719,39 +3636,6 @@ keep_going:						/* We will come back to here until there is
 				return PGRES_POLLING_OK;
 			}
 
-		case CONNECTION_SETENV:
-			{
-				/*
-				 * Do post-connection housekeeping (only needed in protocol
-				 * 2.0).
-				 *
-				 * We pretend that the connection is OK for the duration of
-				 * these queries.
-				 */
-				conn->status = CONNECTION_OK;
-
-				switch (pqSetenvPoll(conn))
-				{
-					case PGRES_POLLING_OK:	/* Success */
-						break;
-
-					case PGRES_POLLING_READING: /* Still going */
-						conn->status = CONNECTION_SETENV;
-						return PGRES_POLLING_READING;
-
-					case PGRES_POLLING_WRITING: /* Still going */
-						conn->status = CONNECTION_SETENV;
-						return PGRES_POLLING_WRITING;
-
-					default:
-						goto error_return;
-				}
-
-				/* Almost there now ... */
-				conn->status = CONNECTION_CHECK_TARGET;
-				goto keep_going;
-			}
-
 		case CONNECTION_CONSUME:
 			{
 				/*
@@ -4042,7 +3926,6 @@ makeEmptyPGconn(void)
 	conn->xactStatus = PQTRANS_IDLE;
 	conn->options_valid = false;
 	conn->nonblocking = false;
-	conn->setenv_state = SETENV_STATE_IDLE;
 	conn->client_encoding = PG_SQL_ASCII;
 	conn->std_strings = false;	/* unless server says differently */
 	conn->default_transaction_read_only = PG_BOOL_UNKNOWN;
@@ -4259,7 +4142,7 @@ sendTerminateConn(PGconn *conn)
 		 * Try to send "close connection" message to backend. Ignore any
 		 * error.
 		 */
-		pqPutMsgStart('X', false, conn);
+		pqPutMsgStart('X', conn);
 		pqPutMsgEnd(conn);
 		(void) pqFlush(conn);
 	}
@@ -4652,16 +4535,13 @@ PQrequestCancel(PGconn *conn)
  *
  * RETURNS: STATUS_ERROR if the write fails, STATUS_OK otherwise.
  * SIDE_EFFECTS: may block.
- *
- * Note: all messages sent with this routine have a length word, whether
- * it's protocol 2.0 or 3.0.
  */
 int
 pqPacketSend(PGconn *conn, char pack_type,
 			 const void *buf, size_t buf_len)
 {
 	/* Start the message. */
-	if (pqPutMsgStart(pack_type, true, conn))
+	if (pqPutMsgStart(pack_type, conn))
 		return STATUS_ERROR;
 
 	/* Send the message body. */
@@ -6917,13 +6797,9 @@ PQsetClientEncoding(PGconn *conn, const char *encoding)
 	else
 	{
 		/*
-		 * In protocol 2 we have to assume the setting will stick, and adjust
-		 * our state immediately.  In protocol 3 and up we can rely on the
-		 * backend to report the parameter value, and we'll change state at
-		 * that time.
+		 * We rely on the backend to report the parameter value, and we'll
+		 * change state at that time.
 		 */
-		if (PG_PROTOCOL_MAJOR(conn->pversion) < 3)
-			pqSaveParameterStatus(conn, "client_encoding", encoding);
 		status = 0;				/* everything is ok */
 	}
 	PQclear(res);