0001-Created-protocol.h.patch

From f12089999ee79ff0aed114b7790eb4df7bee9be9 Mon Sep 17 00:00:00 2001
From: Dave Cramer <davecramer@gmail.com>
Date: Thu, 20 Apr 2023 15:40:03 -0400
Subject: [PATCH] Created protocol.h Protocol.h has defines for every protocol
 message both backend and frontend Instead of using hardcoded values for each
 protocol message use defines to make code easier to read

---
 src/backend/access/common/printsimple.c |  5 +-
 src/backend/access/transam/parallel.c   | 15 ++---
 src/backend/backup/basebackup_copy.c    | 15 ++---
 src/backend/commands/async.c            |  3 +-
 src/backend/commands/copyfromparse.c    | 23 ++++----
 src/backend/commands/copyto.c           |  5 +-
 src/backend/libpq/auth-sasl.c           |  3 +-
 src/backend/libpq/auth.c                |  9 +--
 src/backend/postmaster/postmaster.c     |  3 +-
 src/backend/replication/walsender.c     | 19 +++---
 src/backend/tcop/dest.c                 |  5 +-
 src/backend/tcop/fastpath.c             |  3 +-
 src/backend/tcop/postgres.c             | 77 +++++++++++++------------
 src/backend/utils/error/elog.c          |  3 +-
 src/backend/utils/misc/guc.c            |  3 +-
 src/include/protocol.h                  | 59 +++++++++++++++++++
 src/interfaces/libpq/fe-auth.c          |  3 +-
 src/interfaces/libpq/fe-connect.c       | 15 ++---
 src/interfaces/libpq/fe-exec.c          | 41 ++++++-------
 src/interfaces/libpq/fe-protocol3.c     | 56 +++++++++---------
 src/interfaces/libpq/fe-trace.c         | 57 +++++++++---------
 21 files changed, 251 insertions(+), 171 deletions(-)
 create mode 100644 src/include/protocol.h

diff --git a/src/backend/access/common/printsimple.c b/src/backend/access/common/printsimple.c
index ef818228ac..70cb2e4c1d 100644
--- a/src/backend/access/common/printsimple.c
+++ b/src/backend/access/common/printsimple.c
@@ -21,6 +21,7 @@
 #include "access/printsimple.h"
 #include "catalog/pg_type.h"
 #include "libpq/pqformat.h"
+#include "protocol.h"
 #include "utils/builtins.h"
 
 /*
@@ -32,7 +33,7 @@ printsimple_startup(DestReceiver *self, int operation, TupleDesc tupdesc)
 	StringInfoData buf;
 	int			i;
 
-	pq_beginmessage(&buf, 'T'); /* RowDescription */
+	pq_beginmessage(&buf, ROW_DESCRIPTION_RESPONSE); /* RowDescription */
 	pq_sendint16(&buf, tupdesc->natts);
 
 	for (i = 0; i < tupdesc->natts; ++i)
@@ -65,7 +66,7 @@ printsimple(TupleTableSlot *slot, DestReceiver *self)
 	slot_getallattrs(slot);
 
 	/* Prepare and send message */
-	pq_beginmessage(&buf, 'D');
+	pq_beginmessage(&buf, DATA_ROW_RESPONSE);
 	pq_sendint16(&buf, tupdesc->natts);
 
 	for (i = 0; i < tupdesc->natts; ++i)
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 7133ec0b22..39a927bac3 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -32,6 +32,7 @@
 #include "miscadmin.h"
 #include "optimizer/optimizer.h"
 #include "pgstat.h"
+#include "protocol.h"
 #include "storage/ipc.h"
 #include "storage/predicate.h"
 #include "storage/sinval.h"
@@ -1126,7 +1127,7 @@ HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg)
 
 	switch (msgtype)
 	{
-		case 'K':				/* BackendKeyData */
+		case BACKEND_KEY_DATA:	/* BackendKeyData */
 			{
 				int32		pid = pq_getmsgint(msg, 4);
 
@@ -1136,8 +1137,8 @@ HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg)
 				break;
 			}
 
-		case 'E':				/* ErrorResponse */
-		case 'N':				/* NoticeResponse */
+		case ERROR_RESPONSE:	/* ErrorResponse */
+		case NOTICE_RESPONSE:	/* NoticeResponse */
 			{
 				ErrorData	edata;
 				ErrorContextCallback *save_error_context_stack;
@@ -1182,7 +1183,7 @@ HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg)
 				break;
 			}
 
-		case 'A':				/* NotifyResponse */
+		case NOTIFY_RESPONSE:	/* NotifyResponse */
 			{
 				/* Propagate NotifyResponse. */
 				int32		pid;
@@ -1199,7 +1200,7 @@ HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg)
 				break;
 			}
 
-		case 'X':				/* Terminate, indicating clean exit */
+		case TERMINATE_REQUEST:	/* Terminate, indicating clean exit */
 			{
 				shm_mq_detach(pcxt->worker[i].error_mqh);
 				pcxt->worker[i].error_mqh = NULL;
@@ -1354,7 +1355,7 @@ ParallelWorkerMain(Datum main_arg)
 	 * protocol message is defined, but it won't actually be used for anything
 	 * in this case.
 	 */
-	pq_beginmessage(&msgbuf, 'K');
+	pq_beginmessage(&msgbuf, BACKEND_KEY_DATA);
 	pq_sendint32(&msgbuf, (int32) MyProcPid);
 	pq_sendint32(&msgbuf, (int32) MyCancelKey);
 	pq_endmessage(&msgbuf);
@@ -1532,7 +1533,7 @@ ParallelWorkerMain(Datum main_arg)
 	DetachSession();
 
 	/* Report success. */
-	pq_putmessage('X', NULL, 0);
+	pq_putmessage(TERMINATE_REQUEST, NULL, 0);
 }
 
 /*
diff --git a/src/backend/backup/basebackup_copy.c b/src/backend/backup/basebackup_copy.c
index 73a3f4a970..885855c18c 100644
--- a/src/backend/backup/basebackup_copy.c
+++ b/src/backend/backup/basebackup_copy.c
@@ -32,6 +32,7 @@
 #include "executor/executor.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
+#include "protocol.h"
 #include "tcop/dest.h"
 #include "utils/builtins.h"
 #include "utils/timestamp.h"
@@ -169,7 +170,7 @@ bbsink_copystream_begin_archive(bbsink *sink, const char *archive_name)
 	StringInfoData buf;
 
 	ti = list_nth(state->tablespaces, state->tablespace_num);
-	pq_beginmessage(&buf, 'd'); /* CopyData */
+	pq_beginmessage(&buf, COPY_DATA); /* CopyData */
 	pq_sendbyte(&buf, 'n');		/* New archive */
 	pq_sendstring(&buf, archive_name);
 	pq_sendstring(&buf, ti->path == NULL ? "" : ti->path);
@@ -220,8 +221,8 @@ bbsink_copystream_archive_contents(bbsink *sink, size_t len)
 		{
 			mysink->last_progress_report_time = now;
 
-			pq_beginmessage(&buf, 'd'); /* CopyData */
-			pq_sendbyte(&buf, 'p'); /* Progress report */
+			pq_beginmessage(&buf, COPY_DATA); /* CopyData */
+			pq_sendbyte(&buf, COPY_PROGRESS); /* Progress report */
 			pq_sendint64(&buf, state->bytes_done);
 			pq_endmessage(&buf);
 			pq_flush_if_writable();
@@ -246,7 +247,7 @@ bbsink_copystream_end_archive(bbsink *sink)
 
 	mysink->bytes_done_at_last_time_check = state->bytes_done;
 	mysink->last_progress_report_time = GetCurrentTimestamp();
-	pq_beginmessage(&buf, 'd'); /* CopyData */
+	pq_beginmessage(&buf, COPY_DATA); /* CopyData */
 	pq_sendbyte(&buf, 'p');		/* Progress report */
 	pq_sendint64(&buf, state->bytes_done);
 	pq_endmessage(&buf);
@@ -261,7 +262,7 @@ bbsink_copystream_begin_manifest(bbsink *sink)
 {
 	StringInfoData buf;
 
-	pq_beginmessage(&buf, 'd'); /* CopyData */
+	pq_beginmessage(&buf, COPY_DATA); /* CopyData */
 	pq_sendbyte(&buf, 'm');		/* Manifest */
 	pq_endmessage(&buf);
 }
@@ -318,7 +319,7 @@ SendCopyOutResponse(void)
 {
 	StringInfoData buf;
 
-	pq_beginmessage(&buf, 'H');
+	pq_beginmessage(&buf, COPY_OUT_RESPONSE);
 	pq_sendbyte(&buf, 0);		/* overall format */
 	pq_sendint16(&buf, 0);		/* natts */
 	pq_endmessage(&buf);
@@ -330,7 +331,7 @@ SendCopyOutResponse(void)
 static void
 SendCopyDone(void)
 {
-	pq_putemptymessage('c');
+	pq_putemptymessage(COPY_DONE);
 }
 
 /*
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index ef909cf4e0..cd703bcf09 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -141,6 +141,7 @@
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
+#include "protocol.h"
 #include "storage/ipc.h"
 #include "storage/lmgr.h"
 #include "storage/proc.h"
@@ -2281,7 +2282,7 @@ NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid)
 	{
 		StringInfoData buf;
 
-		pq_beginmessage(&buf, 'A');
+		pq_beginmessage(&buf, NOTIFY_RESPONSE);
 		pq_sendint32(&buf, srcPid);
 		pq_sendstring(&buf, channel);
 		pq_sendstring(&buf, payload);
diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index 3853902a16..cd8924b37d 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -72,6 +72,7 @@
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "port/pg_bswap.h"
+#include "protocol.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -174,7 +175,7 @@ ReceiveCopyBegin(CopyFromState cstate)
 	int16		format = (cstate->opts.binary ? 1 : 0);
 	int			i;
 
-	pq_beginmessage(&buf, 'G');
+	pq_beginmessage(&buf, COPY_IN_RESPONSE);
 	pq_sendbyte(&buf, format);	/* overall format */
 	pq_sendint16(&buf, natts);
 	for (i = 0; i < natts; i++)
@@ -279,13 +280,13 @@ CopyGetData(CopyFromState cstate, void *databuf, int minread, int maxread)
 					/* Validate message type and set packet size limit */
 					switch (mtype)
 					{
-						case 'd':	/* CopyData */
+						case COPY_DATA:	/* CopyData */
 							maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 							break;
-						case 'c':	/* CopyDone */
-						case 'f':	/* CopyFail */
-						case 'H':	/* Flush */
-						case 'S':	/* Sync */
+						case COPY_DONE:	/* CopyDone */
+						case COPY_FAIL:	/* CopyFail */
+						case FLUSH_DATA_REQUEST: /* Flush */
+						case SYNC_DATA_REQUEST:	 /* Sync */
 							maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 							break;
 						default:
@@ -305,20 +306,20 @@ CopyGetData(CopyFromState cstate, void *databuf, int minread, int maxread)
 					/* ... and process it */
 					switch (mtype)
 					{
-						case 'd':	/* CopyData */
+						case COPY_DATA:	/* CopyData */
 							break;
-						case 'c':	/* CopyDone */
+						case COPY_DONE:	/* CopyDone */
 							/* COPY IN correctly terminated by frontend */
 							cstate->raw_reached_eof = true;
 							return bytesread;
-						case 'f':	/* CopyFail */
+						case COPY_FAIL:	/* CopyFail */
 							ereport(ERROR,
 									(errcode(ERRCODE_QUERY_CANCELED),
 									 errmsg("COPY from stdin failed: %s",
 											pq_getmsgstring(cstate->fe_msgbuf))));
 							break;
-						case 'H':	/* Flush */
-						case 'S':	/* Sync */
+						case FLUSH_DATA_REQUEST: /* Flush */
+						case SYNC_DATA_REQUEST:	 /* Sync */
 
 							/*
 							 * Ignore Flush/Sync for the convenience of client
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 9e4b2437a5..4eaa5b9ec3 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -34,6 +34,7 @@
 #include "miscadmin.h"
 #include "optimizer/optimizer.h"
 #include "pgstat.h"
+#include "protocol.h"
 #include "rewrite/rewriteHandler.h"
 #include "storage/fd.h"
 #include "tcop/tcopprot.h"
@@ -144,7 +145,7 @@ SendCopyBegin(CopyToState cstate)
 	int16		format = (cstate->opts.binary ? 1 : 0);
 	int			i;
 
-	pq_beginmessage(&buf, 'H');
+	pq_beginmessage(&buf, COPY_OUT_RESPONSE);
 	pq_sendbyte(&buf, format);	/* overall format */
 	pq_sendint16(&buf, natts);
 	for (i = 0; i < natts; i++)
@@ -159,7 +160,7 @@ SendCopyEnd(CopyToState cstate)
 	/* Shouldn't have any unsent data */
 	Assert(cstate->fe_msgbuf->len == 0);
 	/* Send Copy Done message */
-	pq_putemptymessage('c');
+	pq_putemptymessage(COPY_DONE);
 }
 
 /*----------
diff --git a/src/backend/libpq/auth-sasl.c b/src/backend/libpq/auth-sasl.c
index 684680897b..9477331e27 100644
--- a/src/backend/libpq/auth-sasl.c
+++ b/src/backend/libpq/auth-sasl.c
@@ -19,6 +19,7 @@
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
 #include "libpq/sasl.h"
+#include "protocol.h"
 
 /*
  * Maximum accepted size of SASL messages.
@@ -87,7 +88,7 @@ CheckSASLAuth(const pg_be_sasl_mech *mech, Port *port, char *shadow_pass,
 	{
 		pq_startmsgread();
 		mtype = pq_getbyte();
-		if (mtype != 'p')
+		if (mtype != GSS_RESPONSE)
 		{
 			/* Only log error if client didn't disconnect. */
 			if (mtype != EOF)
diff --git a/src/backend/libpq/auth.c b/src/backend/libpq/auth.c
index a1a826e37f..19f2ad3f47 100644
--- a/src/backend/libpq/auth.c
+++ b/src/backend/libpq/auth.c
@@ -34,6 +34,7 @@
 #include "libpq/scram.h"
 #include "miscadmin.h"
 #include "port/pg_bswap.h"
+#include "protocol.h"
 #include "postmaster/postmaster.h"
 #include "replication/walsender.h"
 #include "storage/ipc.h"
@@ -665,7 +666,7 @@ sendAuthRequest(Port *port, AuthRequest areq, const char *extradata, int extrale
 
 	CHECK_FOR_INTERRUPTS();
 
-	pq_beginmessage(&buf, 'R');
+	pq_beginmessage(&buf, AUTHENTICATION_REQUEST);
 	pq_sendint32(&buf, (int32) areq);
 	if (extralen > 0)
 		pq_sendbytes(&buf, extradata, extralen);
@@ -698,7 +699,7 @@ recv_password_packet(Port *port)
 
 	/* Expect 'p' message type */
 	mtype = pq_getbyte();
-	if (mtype != 'p')
+	if (mtype != PASSWORD_RESPONSE)
 	{
 		/*
 		 * If the client just disconnects without offering a password, don't
@@ -966,7 +967,7 @@ pg_GSS_recvauth(Port *port)
 		CHECK_FOR_INTERRUPTS();
 
 		mtype = pq_getbyte();
-		if (mtype != 'p')
+		if (mtype != GSS_RESPONSE)
 		{
 			/* Only log error if client didn't disconnect. */
 			if (mtype != EOF)
@@ -1237,7 +1238,7 @@ pg_SSPI_recvauth(Port *port)
 	{
 		pq_startmsgread();
 		mtype = pq_getbyte();
-		if (mtype != 'p')
+		if (mtype != GSS_RESPONSE)
 		{
 			if (sspictx != NULL)
 			{
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 4c49393fc5..75becab234 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -114,6 +114,7 @@
 #include "postmaster/pgarch.h"
 #include "postmaster/postmaster.h"
 #include "postmaster/syslogger.h"
+#include "protocol.h"
 #include "replication/logicallauncher.h"
 #include "replication/walsender.h"
 #include "storage/fd.h"
@@ -2385,7 +2386,7 @@ SendNegotiateProtocolVersion(List *unrecognized_protocol_options)
 	StringInfoData buf;
 	ListCell   *lc;
 
-	pq_beginmessage(&buf, 'v'); /* NegotiateProtocolVersion */
+	pq_beginmessage(&buf, NEGOTIATE_PROTOCOL); /* NegotiateProtocolVersion */
 	pq_sendint32(&buf, PG_PROTOCOL_LATEST);
 	pq_sendint32(&buf, list_length(unrecognized_protocol_options));
 	foreach(lc, unrecognized_protocol_options)
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 45b8b3684f..4e43ec3458 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -69,6 +69,7 @@
 #include "nodes/replnodes.h"
 #include "pgstat.h"
 #include "postmaster/interrupt.h"
+#include "protocol.h"
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/slot.h"
@@ -603,7 +604,7 @@ SendTimeLineHistory(TimeLineHistoryCmd *cmd)
 	dest->rStartup(dest, CMD_SELECT, tupdesc);
 
 	/* Send a DataRow message */
-	pq_beginmessage(&buf, 'D');
+	pq_beginmessage(&buf, DATA_ROW_RESPONSE);
 	pq_sendint16(&buf, 2);		/* # of columns */
 	len = strlen(histfname);
 	pq_sendint32(&buf, len);	/* col1 len */
@@ -801,7 +802,7 @@ StartReplication(StartReplicationCmd *cmd)
 		WalSndSetState(WALSNDSTATE_CATCHUP);
 
 		/* Send a CopyBothResponse message, and start streaming */
-		pq_beginmessage(&buf, 'W');
+		pq_beginmessage(&buf, COPY_BOTH_RESPONSE);
 		pq_sendbyte(&buf, 0);
 		pq_sendint16(&buf, 0);
 		pq_endmessage(&buf);
@@ -1295,7 +1296,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	WalSndSetState(WALSNDSTATE_CATCHUP);
 
 	/* Send a CopyBothResponse message, and start streaming */
-	pq_beginmessage(&buf, 'W');
+	pq_beginmessage(&buf, COPY_BOTH_RESPONSE);
 	pq_sendbyte(&buf, 0);
 	pq_sendint16(&buf, 0);
 	pq_endmessage(&buf);
@@ -1924,11 +1925,11 @@ ProcessRepliesIfAny(void)
 		/* Validate message type and set packet size limit */
 		switch (firstchar)
 		{
-			case 'd':
+			case COPY_DATA:
 				maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 				break;
-			case 'c':
-			case 'X':
+			case COPY_DONE:
+			case TERMINATE_REQUEST:
 				maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 				break;
 			default:
@@ -1956,7 +1957,7 @@ ProcessRepliesIfAny(void)
 				/*
 				 * 'd' means a standby reply wrapped in a CopyData packet.
 				 */
-			case 'd':
+			case COPY_DATA:
 				ProcessStandbyMessage();
 				received = true;
 				break;
@@ -1965,7 +1966,7 @@ ProcessRepliesIfAny(void)
 				 * CopyDone means the standby requested to finish streaming.
 				 * Reply with CopyDone, if we had not sent that already.
 				 */
-			case 'c':
+			case COPY_DONE:
 				if (!streamingDoneSending)
 				{
 					pq_putmessage_noblock('c', NULL, 0);
@@ -1979,7 +1980,7 @@ ProcessRepliesIfAny(void)
 				/*
 				 * 'X' means that the standby is closing down the socket.
 				 */
-			case 'X':
+			case TERMINATE_REQUEST:
 				proc_exit(0);
 
 			default:
diff --git a/src/backend/tcop/dest.c b/src/backend/tcop/dest.c
index c0406e2ee5..4b5e2e12e5 100644
--- a/src/backend/tcop/dest.c
+++ b/src/backend/tcop/dest.c
@@ -39,6 +39,7 @@
 #include "executor/tstoreReceiver.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
+#include "protocol.h"
 #include "utils/portal.h"
 
 
@@ -220,7 +221,7 @@ NullCommand(CommandDest dest)
 		case DestRemoteSimple:
 
 			/* Tell the FE that we saw an empty query string */
-			pq_putemptymessage('I');
+			pq_putemptymessage(EMPTY_QUERY_RESPONSE);
 			break;
 
 		case DestNone:
@@ -258,7 +259,7 @@ ReadyForQuery(CommandDest dest)
 			{
 				StringInfoData buf;
 
-				pq_beginmessage(&buf, 'Z');
+				pq_beginmessage(&buf, READY_FOR_QUERY);
 				pq_sendbyte(&buf, TransactionBlockStatusCode());
 				pq_endmessage(&buf);
 			}
diff --git a/src/backend/tcop/fastpath.c b/src/backend/tcop/fastpath.c
index 2f70ebd5fa..83320cd3f7 100644
--- a/src/backend/tcop/fastpath.c
+++ b/src/backend/tcop/fastpath.c
@@ -27,6 +27,7 @@
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "port/pg_bswap.h"
+#include "protocol.h"
 #include "tcop/fastpath.h"
 #include "tcop/tcopprot.h"
 #include "utils/acl.h"
@@ -69,7 +70,7 @@ SendFunctionResult(Datum retval, bool isnull, Oid rettype, int16 format)
 {
 	StringInfoData buf;
 
-	pq_beginmessage(&buf, 'V');
+	pq_beginmessage(&buf, FUNCTION_CALL_RESPONSE);
 
 	if (isnull)
 	{
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 01b6cc1f7d..0b084a4292 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -55,6 +55,7 @@
 #include "postmaster/autovacuum.h"
 #include "postmaster/interrupt.h"
 #include "postmaster/postmaster.h"
+#include "protocol.h"
 #include "replication/logicallauncher.h"
 #include "replication/logicalworker.h"
 #include "replication/slot.h"
@@ -402,37 +403,37 @@ SocketBackend(StringInfo inBuf)
 	 */
 	switch (qtype)
 	{
-		case 'Q':				/* simple query */
+		case SIMPLE_QUERY:			/* simple query */
 			maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 			doing_extended_query_message = false;
 			break;
 
-		case 'F':				/* fastpath function call */
+		case FUNCTION_CALL_REQUEST:	/* fastpath function call */
 			maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 			doing_extended_query_message = false;
 			break;
 
-		case 'X':				/* terminate */
+		case TERMINATE_REQUEST:		/* terminate */
 			maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 			doing_extended_query_message = false;
 			ignore_till_sync = false;
 			break;
 
-		case 'B':				/* bind */
-		case 'P':				/* parse */
+		case BIND_REQUEST :			/* bind */
+		case PARSE_REQUEST:			/* parse */
 			maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 			doing_extended_query_message = true;
 			break;
 
-		case 'C':				/* close */
-		case 'D':				/* describe */
-		case 'E':				/* execute */
-		case 'H':				/* flush */
+		case CLOSE_REQUEST:			/* close */
+		case DESCRIBE_REQUEST:		/* describe */
+		case EXECUTE_REQUEST:		/* execute */
+		case FLUSH_DATA_REQUEST:	/* flush */
 			maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 			doing_extended_query_message = true;
 			break;
 
-		case 'S':				/* sync */
+		case SYNC_DATA_REQUEST:		/* sync */
 			maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 			/* stop any active skip-till-Sync */
 			ignore_till_sync = false;
@@ -440,13 +441,13 @@ SocketBackend(StringInfo inBuf)
 			doing_extended_query_message = false;
 			break;
 
-		case 'd':				/* copy data */
+		case COPY_DATA:				/* copy data */
 			maxmsglen = PQ_LARGE_MESSAGE_LIMIT;
 			doing_extended_query_message = false;
 			break;
 
-		case 'c':				/* copy done */
-		case 'f':				/* copy fail */
+		case COPY_DONE:				/* copy done */
+		case COPY_FAIL:				/* copy fail */
 			maxmsglen = PQ_SMALL_MESSAGE_LIMIT;
 			doing_extended_query_message = false;
 			break;
@@ -1589,7 +1590,7 @@ exec_parse_message(const char *query_string,	/* string to execute */
 	 * Send ParseComplete.
 	 */
 	if (whereToSendOutput == DestRemote)
-		pq_putemptymessage('1');
+		pq_putemptymessage(PARSE_COMPLETE_RESPONSE);
 
 	/*
 	 * Emit duration logging if appropriate.
@@ -2047,7 +2048,7 @@ exec_bind_message(StringInfo input_message)
 	 * Send BindComplete.
 	 */
 	if (whereToSendOutput == DestRemote)
-		pq_putemptymessage('2');
+		pq_putemptymessage(BIND_COMPLETE_RESPONSE);
 
 	/*
 	 * Emit duration logging if appropriate.
@@ -2290,7 +2291,7 @@ exec_execute_message(const char *portal_name, long max_rows)
 	{
 		/* Portal run not complete, so send PortalSuspended */
 		if (whereToSendOutput == DestRemote)
-			pq_putemptymessage('s');
+			pq_putemptymessage(PORTAL_SUSPENDED_RESPONSE);
 
 		/*
 		 * Set XACT_FLAGS_PIPELINING whenever we suspend an Execute message,
@@ -2683,7 +2684,7 @@ exec_describe_statement_message(const char *stmt_name)
 								  NULL);
 	}
 	else
-		pq_putemptymessage('n');	/* NoData */
+		pq_putemptymessage(NO_DATA_RESPONSE);	/* NoData */
 }
 
 /*
@@ -2736,7 +2737,7 @@ exec_describe_portal_message(const char *portal_name)
 								  FetchPortalTargetList(portal),
 								  portal->formats);
 	else
-		pq_putemptymessage('n');	/* NoData */
+		pq_putemptymessage(NO_DATA_RESPONSE);	/* NoData */
 }
 
 
@@ -4239,7 +4240,7 @@ PostgresMain(const char *dbname, const char *username)
 	{
 		StringInfoData buf;
 
-		pq_beginmessage(&buf, 'K');
+		pq_beginmessage(&buf, BACKEND_KEY_DATA);
 		pq_sendint32(&buf, (int32) MyProcPid);
 		pq_sendint32(&buf, (int32) MyCancelKey);
 		pq_endmessage(&buf);
@@ -4613,7 +4614,7 @@ PostgresMain(const char *dbname, const char *username)
 
 		switch (firstchar)
 		{
-			case 'Q':			/* simple query */
+			case SIMPLE_QUERY:			/* simple query */
 				{
 					const char *query_string;
 
@@ -4637,7 +4638,7 @@ PostgresMain(const char *dbname, const char *username)
 				}
 				break;
 
-			case 'P':			/* parse */
+			case PARSE_REQUEST:			/* parse */
 				{
 					const char *stmt_name;
 					const char *query_string;
@@ -4667,7 +4668,7 @@ PostgresMain(const char *dbname, const char *username)
 				}
 				break;
 
-			case 'B':			/* bind */
+			case BIND_REQUEST:			/* bind */
 				forbidden_in_wal_sender(firstchar);
 
 				/* Set statement_timestamp() */
@@ -4682,7 +4683,7 @@ PostgresMain(const char *dbname, const char *username)
 				/* exec_bind_message does valgrind_report_error_query */
 				break;
 
-			case 'E':			/* execute */
+			case EXECUTE_REQUEST:			/* execute */
 				{
 					const char *portal_name;
 					int			max_rows;
@@ -4702,7 +4703,7 @@ PostgresMain(const char *dbname, const char *username)
 				}
 				break;
 
-			case 'F':			/* fastpath function call */
+			case FUNCTION_CALL_REQUEST:			/* fastpath function call */
 				forbidden_in_wal_sender(firstchar);
 
 				/* Set statement_timestamp() */
@@ -4737,7 +4738,7 @@ PostgresMain(const char *dbname, const char *username)
 				send_ready_for_query = true;
 				break;
 
-			case 'C':			/* close */
+			case CLOSE_REQUEST:		/* close */
 				{
 					int			close_type;
 					const char *close_target;
@@ -4750,7 +4751,7 @@ PostgresMain(const char *dbname, const char *username)
 
 					switch (close_type)
 					{
-						case 'S':
+						case DESCRIBE_PREPARED:
 							if (close_target[0] != '\0')
 								DropPreparedStatement(close_target, false);
 							else
@@ -4759,7 +4760,7 @@ PostgresMain(const char *dbname, const char *username)
 								drop_unnamed_stmt();
 							}
 							break;
-						case 'P':
+						case DESCRIBE_PORTAL:
 							{
 								Portal		portal;
 
@@ -4777,13 +4778,13 @@ PostgresMain(const char *dbname, const char *username)
 					}
 
 					if (whereToSendOutput == DestRemote)
-						pq_putemptymessage('3');	/* CloseComplete */
+						pq_putemptymessage(CLOSE_COMPLETE_RESPONSE);	/* CloseComplete */
 
 					valgrind_report_error_query("CLOSE message");
 				}
 				break;
 
-			case 'D':			/* describe */
+			case DESCRIBE_REQUEST:		/* describe */
 				{
 					int			describe_type;
 					const char *describe_target;
@@ -4799,10 +4800,10 @@ PostgresMain(const char *dbname, const char *username)
 
 					switch (describe_type)
 					{
-						case 'S':
+						case DESCRIBE_PREPARED:
 							exec_describe_statement_message(describe_target);
 							break;
-						case 'P':
+						case DESCRIBE_PORTAL:
 							exec_describe_portal_message(describe_target);
 							break;
 						default:
@@ -4817,13 +4818,13 @@ PostgresMain(const char *dbname, const char *username)
 				}
 				break;
 
-			case 'H':			/* flush */
+			case FLUSH_DATA_REQUEST:	/* flush */
 				pq_getmsgend(&input_message);
 				if (whereToSendOutput == DestRemote)
 					pq_flush();
 				break;
 
-			case 'S':			/* sync */
+			case SYNC_DATA_REQUEST:		/* sync */
 				pq_getmsgend(&input_message);
 				finish_xact_command();
 				valgrind_report_error_query("SYNC message");
@@ -4842,7 +4843,7 @@ PostgresMain(const char *dbname, const char *username)
 
 				/* FALLTHROUGH */
 
-			case 'X':
+			case TERMINATE_REQUEST:
 
 				/*
 				 * Reset whereToSendOutput to prevent ereport from attempting
@@ -4860,9 +4861,9 @@ PostgresMain(const char *dbname, const char *username)
 				 */
 				proc_exit(0);
 
-			case 'd':			/* copy data */
-			case 'c':			/* copy done */
-			case 'f':			/* copy fail */
+			case COPY_DATA:			/* copy data */
+			case COPY_DONE:			/* copy done */
+			case COPY_FAIL:			/* copy fail */
 
 				/*
 				 * Accept but ignore these messages, per protocol spec; we
@@ -4892,7 +4893,7 @@ forbidden_in_wal_sender(char firstchar)
 {
 	if (am_walsender)
 	{
-		if (firstchar == 'F')
+		if (firstchar == FUNCTION_CALL_REQUEST)
 			ereport(ERROR,
 					(errcode(ERRCODE_PROTOCOL_VIOLATION),
 					 errmsg("fastpath function calls not supported in a replication connection")));
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 5898100acb..17c75479b6 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -77,6 +77,7 @@
 #include "postmaster/bgworker.h"
 #include "postmaster/postmaster.h"
 #include "postmaster/syslogger.h"
+#include "protocol.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
 #include "tcop/tcopprot.h"
@@ -3465,7 +3466,7 @@ send_message_to_frontend(ErrorData *edata)
 		char		tbuf[12];
 
 		/* 'N' (Notice) is for nonfatal conditions, 'E' is for errors */
-		pq_beginmessage(&msgbuf, (edata->elevel < ERROR) ? 'N' : 'E');
+		pq_beginmessage(&msgbuf, (edata->elevel < ERROR) ? NOTICE_RESPONSE : ERROR_RESPONSE);
 
 		sev = error_severity(edata->elevel);
 		pq_sendbyte(&msgbuf, PG_DIAG_SEVERITY);
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 9dd624b3ae..724b422b44 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -37,6 +37,7 @@
 #include "libpq/pqformat.h"
 #include "parser/scansup.h"
 #include "port/pg_bitutils.h"
+#include "protocol.h"
 #include "storage/fd.h"
 #include "storage/lwlock.h"
 #include "storage/shmem.h"
@@ -2592,7 +2593,7 @@ ReportGUCOption(struct config_generic *record)
 	{
 		StringInfoData msgbuf;
 
-		pq_beginmessage(&msgbuf, 'S');
+		pq_beginmessage(&msgbuf, PARAMETER_STATUS_RESPONSE);
 		pq_sendstring(&msgbuf, record->name);
 		pq_sendstring(&msgbuf, val);
 		pq_endmessage(&msgbuf);
diff --git a/src/include/protocol.h b/src/include/protocol.h
new file mode 100644
index 0000000000..ffdaf91414
--- /dev/null
+++ b/src/include/protocol.h
@@ -0,0 +1,59 @@
+/*-------------------------------------------------------------------------
+ *
+ * protocol.h
+ *	  Exports from postmaster/postmaster.c.
+ *
+ * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
+ *
+ * src/include/protocol.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef _PROTOCOL_H
+#define _PROTOCOL_H
+
+#define BIND_REQUEST                'B'
+#define CLOSE_REQUEST               'C'
+#define DESCRIBE_REQUEST            'D'
+#define EXECUTE_REQUEST             'E'
+#define FUNCTION_CALL_REQUEST       'F'
+#define FLUSH_DATA_REQUEST          'H'
+#define BACKEND_KEY_DATA            'K'
+#define PARSE_REQUEST               'P'
+#define AUTHENTICATION_REQUEST      'R'
+#define SYNC_DATA_REQUEST           'S'
+#define SIMPLE_QUERY                'Q'
+#define TERMINATE_REQUEST           'X'
+#define COPY_FAIL                   'f'
+#define COPY_DONE                   'c'
+#define COPY_DATA                   'd'
+#define COPY_PROGRESS               'p'
+#define DESCRIBE_PREPARED           'S'
+#define DESCRIBE_PORTAL             'P'
+
+/*
+Responses
+*/
+#define PARSE_COMPLETE_RESPONSE '1'
+#define BIND_COMPLETE_RESPONSE  '2'
+#define CLOSE_COMPLETE_RESPONSE '3'
+#define NOTIFY_RESPONSE         'A'
+#define COMMAND_COMPLETE        'C'
+#define DATA_ROW_RESPONSE       'D'
+#define ERROR_RESPONSE          'E'
+#define COPY_IN_RESPONSE        'G'
+#define COPY_OUT_RESPONSE       'H'
+#define EMPTY_QUERY_RESPONSE    'I'
+#define NOTICE_RESPONSE         'N'
+#define FUNCTION_CALL_RESPONSE  'V'
+#define PARAMETER_STATUS_RESPONSE 'S'
+#define ROW_DESCRIPTION_RESPONSE 'T'
+#define COPY_BOTH_RESPONSE      'W'
+#define READY_FOR_QUERY         'Z'
+#define NO_DATA_RESPONSE        'n'
+#define PASSWORD_RESPONSE       'p'
+#define GSS_RESPONSE            'p'
+#define PORTAL_SUSPENDED_RESPONSE 's'
+#define PARAMETER_DESCRIPTION_RESPONSE 't'
+#define NEGOTIATE_PROTOCOL      'v'
+#endif
\ No newline at end of file
diff --git a/src/interfaces/libpq/fe-auth.c b/src/interfaces/libpq/fe-auth.c
index fe2634230a..b1158946df 100644
--- a/src/interfaces/libpq/fe-auth.c
+++ b/src/interfaces/libpq/fe-auth.c
@@ -42,6 +42,7 @@
 #include "fe-auth.h"
 #include "fe-auth-sasl.h"
 #include "libpq-fe.h"
+#include "protocol.h"
 
 #ifdef ENABLE_GSS
 /*
@@ -585,7 +586,7 @@ pg_SASL_init(PGconn *conn, int payloadlen)
 	/*
 	 * Build a SASLInitialResponse message, and send it.
 	 */
-	if (pqPutMsgStart('p', conn))
+	if (pqPutMsgStart(GSS_RESPONSE, conn))
 		goto error;
 	if (pqPuts(selected_mechanism, conn))
 		goto error;
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index fcd3d0d9a3..035a5aa407 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -32,6 +32,7 @@
 #include "mb/pg_wchar.h"
 #include "pg_config_paths.h"
 #include "port/pg_bswap.h"
+#include "protocol.h"
 
 #ifdef WIN32
 #include "win32.h"
@@ -3593,7 +3594,7 @@ keep_going:						/* We will come back to here until there is
 				 * Anything else probably means it's not Postgres on the other
 				 * end at all.
 				 */
-				if (!(beresp == 'R' || beresp == 'v' || beresp == 'E'))
+				if (!(beresp == AUTHENTICATION_REQUEST || beresp == NEGOTIATE_PROTOCOL || beresp == ERROR_RESPONSE))
 				{
 					libpq_append_conn_error(conn, "expected authentication request from server, but received %c",
 											beresp);
@@ -3620,19 +3621,19 @@ keep_going:						/* We will come back to here until there is
 				 * 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))
+				if (beresp == AUTHENTICATION_REQUEST && (msgLength < 8 || msgLength > 2000))
 				{
 					libpq_append_conn_error(conn, "received invalid authentication request");
 					goto error_return;
 				}
-				if (beresp == 'v' && (msgLength < 8 || msgLength > 2000))
+				if (beresp == NEGOTIATE_PROTOCOL && (msgLength < 8 || msgLength > 2000))
 				{
 					libpq_append_conn_error(conn, "received invalid protocol negotiation message");
 					goto error_return;
 				}
 
 #define MAX_ERRLEN 30000
-				if (beresp == 'E' && (msgLength < 8 || msgLength > MAX_ERRLEN))
+				if (beresp == ERROR_RESPONSE && (msgLength < 8 || msgLength > MAX_ERRLEN))
 				{
 					/* Handle error from a pre-3.0 server */
 					conn->inCursor = conn->inStart + 1; /* reread data */
@@ -3695,7 +3696,7 @@ keep_going:						/* We will come back to here until there is
 				}
 
 				/* Handle errors. */
-				if (beresp == 'E')
+				if (beresp == ERROR_RESPONSE)
 				{
 					if (pqGetErrorNotice3(conn, true))
 					{
@@ -3772,7 +3773,7 @@ keep_going:						/* We will come back to here until there is
 
 					goto error_return;
 				}
-				else if (beresp == 'v')
+				else if (beresp == NEGOTIATE_PROTOCOL)
 				{
 					if (pqGetNegotiateProtocolVersion3(conn))
 					{
@@ -4542,7 +4543,7 @@ sendTerminateConn(PGconn *conn)
 		 * Try to send "close connection" message to backend. Ignore any
 		 * error.
 		 */
-		pqPutMsgStart('X', conn);
+		pqPutMsgStart(TERMINATE_REQUEST, conn);
 		pqPutMsgEnd(conn);
 		(void) pqFlush(conn);
 	}
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index a16bbf32ef..850043dc91 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -27,6 +27,7 @@
 #include "libpq-fe.h"
 #include "libpq-int.h"
 #include "mb/pg_wchar.h"
+#include "protocol.h"
 
 /* keep this in same order as ExecStatusType in libpq-fe.h */
 char	   *const pgresStatus[] = {
@@ -1458,7 +1459,7 @@ PQsendQueryInternal(PGconn *conn, const char *query, bool newQuery)
 
 	/* Send the query message(s) */
 	/* construct the outgoing Query message */
-	if (pqPutMsgStart('Q', conn) < 0 ||
+	if (pqPutMsgStart(SIMPLE_QUERY, conn) < 0 ||
 		pqPuts(query, conn) < 0 ||
 		pqPutMsgEnd(conn) < 0)
 	{
@@ -1571,7 +1572,7 @@ PQsendPrepare(PGconn *conn,
 		return 0;				/* error msg already set */
 
 	/* construct the Parse message */
-	if (pqPutMsgStart('P', conn) < 0 ||
+	if (pqPutMsgStart(PARSE_REQUEST, conn) < 0 ||
 		pqPuts(stmtName, conn) < 0 ||
 		pqPuts(query, conn) < 0)
 		goto sendFailed;
@@ -1599,7 +1600,7 @@ PQsendPrepare(PGconn *conn,
 	/* Add a Sync, unless in pipeline mode. */
 	if (conn->pipelineStatus == PQ_PIPELINE_OFF)
 	{
-		if (pqPutMsgStart('S', conn) < 0 ||
+		if (pqPutMsgStart(SYNC_DATA_REQUEST, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			goto sendFailed;
 	}
@@ -1784,7 +1785,7 @@ PQsendQueryGuts(PGconn *conn,
 	if (command)
 	{
 		/* construct the Parse message */
-		if (pqPutMsgStart('P', conn) < 0 ||
+		if (pqPutMsgStart(PARSE_REQUEST, conn) < 0 ||
 			pqPuts(stmtName, conn) < 0 ||
 			pqPuts(command, conn) < 0)
 			goto sendFailed;
@@ -1808,7 +1809,7 @@ PQsendQueryGuts(PGconn *conn,
 	}
 
 	/* Construct the Bind message */
-	if (pqPutMsgStart('B', conn) < 0 ||
+	if (pqPutMsgStart(BIND_REQUEST, conn) < 0 ||
 		pqPuts("", conn) < 0 ||
 		pqPuts(stmtName, conn) < 0)
 		goto sendFailed;
@@ -1874,14 +1875,14 @@ PQsendQueryGuts(PGconn *conn,
 		goto sendFailed;
 
 	/* construct the Describe Portal message */
-	if (pqPutMsgStart('D', conn) < 0 ||
+	if (pqPutMsgStart(DESCRIBE_PORTAL, conn) < 0 ||
 		pqPutc('P', conn) < 0 ||
 		pqPuts("", conn) < 0 ||
 		pqPutMsgEnd(conn) < 0)
 		goto sendFailed;
 
 	/* construct the Execute message */
-	if (pqPutMsgStart('E', conn) < 0 ||
+	if (pqPutMsgStart(EXECUTE_REQUEST, conn) < 0 ||
 		pqPuts("", conn) < 0 ||
 		pqPutInt(0, 4, conn) < 0 ||
 		pqPutMsgEnd(conn) < 0)
@@ -1890,7 +1891,7 @@ PQsendQueryGuts(PGconn *conn,
 	/* construct the Sync message if not in pipeline mode */
 	if (conn->pipelineStatus == PQ_PIPELINE_OFF)
 	{
-		if (pqPutMsgStart('S', conn) < 0 ||
+		if (pqPutMsgStart(SYNC_DATA_REQUEST, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			goto sendFailed;
 	}
@@ -2423,7 +2424,7 @@ PQdescribePrepared(PGconn *conn, const char *stmt)
 {
 	if (!PQexecStart(conn))
 		return NULL;
-	if (!PQsendDescribe(conn, 'S', stmt))
+	if (!PQsendDescribe(conn, DESCRIBE_PREPARED, stmt))
 		return NULL;
 	return PQexecFinish(conn);
 }
@@ -2442,7 +2443,7 @@ PQdescribePortal(PGconn *conn, const char *portal)
 {
 	if (!PQexecStart(conn))
 		return NULL;
-	if (!PQsendDescribe(conn, 'P', portal))
+	if (!PQsendDescribe(conn, DESCRIBE_PORTAL, portal))
 		return NULL;
 	return PQexecFinish(conn);
 }
@@ -2457,7 +2458,7 @@ PQdescribePortal(PGconn *conn, const char *portal)
 int
 PQsendDescribePrepared(PGconn *conn, const char *stmt)
 {
-	return PQsendDescribe(conn, 'S', stmt);
+	return PQsendDescribe(conn, DESCRIBE_PREPARED, stmt);
 }
 
 /*
@@ -2470,7 +2471,7 @@ PQsendDescribePrepared(PGconn *conn, const char *stmt)
 int
 PQsendDescribePortal(PGconn *conn, const char *portal)
 {
-	return PQsendDescribe(conn, 'P', portal);
+	return PQsendDescribe(conn, DESCRIBE_PORTAL, portal);
 }
 
 /*
@@ -2499,7 +2500,7 @@ PQsendDescribe(PGconn *conn, char desc_type, const char *desc_target)
 		return 0;				/* error msg already set */
 
 	/* construct the Describe message */
-	if (pqPutMsgStart('D', conn) < 0 ||
+	if (pqPutMsgStart(DESCRIBE_REQUEST, conn) < 0 ||
 		pqPutc(desc_type, conn) < 0 ||
 		pqPuts(desc_target, conn) < 0 ||
 		pqPutMsgEnd(conn) < 0)
@@ -2508,7 +2509,7 @@ PQsendDescribe(PGconn *conn, char desc_type, const char *desc_target)
 	/* construct the Sync message */
 	if (conn->pipelineStatus == PQ_PIPELINE_OFF)
 	{
-		if (pqPutMsgStart('S', conn) < 0 ||
+		if (pqPutMsgStart(SYNC_DATA_REQUEST, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			goto sendFailed;
 	}
@@ -2615,7 +2616,7 @@ PQputCopyData(PGconn *conn, const char *buffer, int nbytes)
 				return pqIsnonblocking(conn) ? 0 : -1;
 		}
 		/* Send the data (too simple to delegate to fe-protocol files) */
-		if (pqPutMsgStart('d', conn) < 0 ||
+		if (pqPutMsgStart(COPY_DATA, conn) < 0 ||
 			pqPutnchar(buffer, nbytes, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			return -1;
@@ -2650,7 +2651,7 @@ PQputCopyEnd(PGconn *conn, const char *errormsg)
 	if (errormsg)
 	{
 		/* Send COPY FAIL */
-		if (pqPutMsgStart('f', conn) < 0 ||
+		if (pqPutMsgStart(COPY_FAIL, conn) < 0 ||
 			pqPuts(errormsg, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			return -1;
@@ -2658,7 +2659,7 @@ PQputCopyEnd(PGconn *conn, const char *errormsg)
 	else
 	{
 		/* Send COPY DONE */
-		if (pqPutMsgStart('c', conn) < 0 ||
+		if (pqPutMsgStart(COPY_DONE, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			return -1;
 	}
@@ -2670,7 +2671,7 @@ PQputCopyEnd(PGconn *conn, const char *errormsg)
 	if (conn->cmd_queue_head &&
 		conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE)
 	{
-		if (pqPutMsgStart('S', conn) < 0 ||
+		if (pqPutMsgStart(SYNC_DATA_REQUEST, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			return -1;
 	}
@@ -3181,7 +3182,7 @@ PQpipelineSync(PGconn *conn)
 	entry->query = NULL;
 
 	/* construct the Sync message */
-	if (pqPutMsgStart('S', conn) < 0 ||
+	if (pqPutMsgStart(SYNC_DATA_REQUEST, conn) < 0 ||
 		pqPutMsgEnd(conn) < 0)
 		goto sendFailed;
 
@@ -3229,7 +3230,7 @@ PQsendFlushRequest(PGconn *conn)
 		return 0;
 	}
 
-	if (pqPutMsgStart('H', conn) < 0 ||
+	if (pqPutMsgStart(FLUSH_DATA_REQUEST, conn) < 0 ||
 		pqPutMsgEnd(conn) < 0)
 	{
 		return 0;
diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 8ab6a88416..2e6c6c9132 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -28,14 +28,16 @@
 #include "libpq-int.h"
 #include "mb/pg_wchar.h"
 #include "port/pg_bswap.h"
+#include "protocol.h"
 
 /*
  * This macro lists the backend message types that could be "long" (more
  * than a couple of kilobytes).
  */
 #define VALID_LONG_MESSAGE_TYPE(id) \
-	((id) == 'T' || (id) == 'D' || (id) == 'd' || (id) == 'V' || \
-	 (id) == 'E' || (id) == 'N' || (id) == 'A')
+	((id) == ROW_DESCRIPTION_RESPONSE || (id) == DATA_ROW_RESPONSE || (id) == COPY_DATA || \
+	 (id) == FUNCTION_CALL_RESPONSE ||  (id) == ERROR_RESPONSE || (id) == NOTICE_RESPONSE || \
+	 (id) == NOTIFY_RESPONSE)
 
 
 static void handleSyncLoss(PGconn *conn, char id, int msgLength);
@@ -140,12 +142,12 @@ pqParseInput3(PGconn *conn)
 		 * from config file due to SIGHUP), but otherwise we hold off until
 		 * BUSY state.
 		 */
-		if (id == 'A')
+		if (id == NOTIFY_RESPONSE)
 		{
 			if (getNotify(conn))
 				return;
 		}
-		else if (id == 'N')
+		else if (id == NOTICE_RESPONSE)
 		{
 			if (pqGetErrorNotice3(conn, false))
 				return;
@@ -165,12 +167,12 @@ pqParseInput3(PGconn *conn)
 			 * it is about to close the connection, so we don't want to just
 			 * discard it...)
 			 */
-			if (id == 'E')
+			if (id == ERROR_RESPONSE)
 			{
 				if (pqGetErrorNotice3(conn, false /* treat as notice */ ))
 					return;
 			}
-			else if (id == 'S')
+			else if (id == PARAMETER_STATUS_RESPONSE)
 			{
 				if (getParameterStatus(conn))
 					return;
@@ -192,7 +194,7 @@ pqParseInput3(PGconn *conn)
 			 */
 			switch (id)
 			{
-				case 'C':		/* command complete */
+				case COMMAND_COMPLETE:		/* command complete */
 					if (pqGets(&conn->workBuffer, conn))
 						return;
 					if (!pgHavePendingResult(conn))
@@ -210,12 +212,12 @@ pqParseInput3(PGconn *conn)
 								CMDSTATUS_LEN);
 					conn->asyncStatus = PGASYNC_READY;
 					break;
-				case 'E':		/* error return */
+				case ERROR_RESPONSE:		/* error return */
 					if (pqGetErrorNotice3(conn, true))
 						return;
 					conn->asyncStatus = PGASYNC_READY;
 					break;
-				case 'Z':		/* sync response, backend is ready for new
+				case READY_FOR_QUERY:		/* sync response, backend is ready for new
 								 * query */
 					if (getReadyForQuery(conn))
 						return;
@@ -246,7 +248,7 @@ pqParseInput3(PGconn *conn)
 						conn->asyncStatus = PGASYNC_IDLE;
 					}
 					break;
-				case 'I':		/* empty query */
+				case EMPTY_QUERY_RESPONSE:		/* empty query */
 					if (!pgHavePendingResult(conn))
 					{
 						conn->result = PQmakeEmptyPGresult(conn,
@@ -259,7 +261,7 @@ pqParseInput3(PGconn *conn)
 					}
 					conn->asyncStatus = PGASYNC_READY;
 					break;
-				case '1':		/* Parse Complete */
+				case PARSE_COMPLETE_RESPONSE:		/* Parse Complete */
 					/* If we're doing PQprepare, we're done; else ignore */
 					if (conn->cmd_queue_head &&
 						conn->cmd_queue_head->queryclass == PGQUERY_PREPARE)
@@ -277,15 +279,15 @@ pqParseInput3(PGconn *conn)
 						conn->asyncStatus = PGASYNC_READY;
 					}
 					break;
-				case '2':		/* Bind Complete */
-				case '3':		/* Close Complete */
+				case BIND_COMPLETE_RESPONSE:		/* Bind Complete */
+				case CLOSE_COMPLETE_RESPONSE:		/* Close Complete */
 					/* Nothing to do for these message types */
 					break;
-				case 'S':		/* parameter status */
+				case PARAMETER_STATUS_RESPONSE:		/* parameter status */
 					if (getParameterStatus(conn))
 						return;
 					break;
-				case 'K':		/* secret key data from the backend */
+				case BACKEND_KEY_DATA:		/* secret key data from the backend */
 
 					/*
 					 * This is expected only during backend startup, but it's
@@ -297,7 +299,7 @@ pqParseInput3(PGconn *conn)
 					if (pqGetInt(&(conn->be_key), 4, conn))
 						return;
 					break;
-				case 'T':		/* Row Description */
+				case ROW_DESCRIPTION_RESPONSE:		/* Row Description */
 					if (conn->error_result ||
 						(conn->result != NULL &&
 						 conn->result->resultStatus == PGRES_FATAL_ERROR))
@@ -329,7 +331,7 @@ pqParseInput3(PGconn *conn)
 						return;
 					}
 					break;
-				case 'n':		/* No Data */
+				case NO_DATA_RESPONSE:		/* No Data */
 
 					/*
 					 * NoData indicates that we will not be seeing a
@@ -357,11 +359,11 @@ pqParseInput3(PGconn *conn)
 						conn->asyncStatus = PGASYNC_READY;
 					}
 					break;
-				case 't':		/* Parameter Description */
+				case PARAMETER_DESCRIPTION_RESPONSE:		/* Parameter Description */
 					if (getParamDescriptions(conn, msgLength))
 						return;
 					break;
-				case 'D':		/* Data Row */
+				case DATA_ROW_RESPONSE:		/* Data Row */
 					if (conn->result != NULL &&
 						conn->result->resultStatus == PGRES_TUPLES_OK)
 					{
@@ -388,24 +390,24 @@ pqParseInput3(PGconn *conn)
 						conn->inCursor += msgLength;
 					}
 					break;
-				case 'G':		/* Start Copy In */
+				case COPY_IN_RESPONSE:		/* Start Copy In */
 					if (getCopyStart(conn, PGRES_COPY_IN))
 						return;
 					conn->asyncStatus = PGASYNC_COPY_IN;
 					break;
-				case 'H':		/* Start Copy Out */
+				case COPY_OUT_RESPONSE:		/* Start Copy Out */
 					if (getCopyStart(conn, PGRES_COPY_OUT))
 						return;
 					conn->asyncStatus = PGASYNC_COPY_OUT;
 					conn->copy_already_done = 0;
 					break;
-				case 'W':		/* Start Copy Both */
+				case COPY_BOTH_RESPONSE:		/* Start Copy Both */
 					if (getCopyStart(conn, PGRES_COPY_BOTH))
 						return;
 					conn->asyncStatus = PGASYNC_COPY_BOTH;
 					conn->copy_already_done = 0;
 					break;
-				case 'd':		/* Copy Data */
+				case COPY_DATA:		/* Copy Data */
 
 					/*
 					 * If we see Copy Data, just silently drop it.  This would
@@ -414,7 +416,7 @@ pqParseInput3(PGconn *conn)
 					 */
 					conn->inCursor += msgLength;
 					break;
-				case 'c':		/* Copy Done */
+				case COPY_DONE:		/* Copy Done */
 
 					/*
 					 * If we see Copy Done, just silently drop it.  This is
@@ -1911,7 +1913,7 @@ pqEndcopy3(PGconn *conn)
 	if (conn->asyncStatus == PGASYNC_COPY_IN ||
 		conn->asyncStatus == PGASYNC_COPY_BOTH)
 	{
-		if (pqPutMsgStart('c', conn) < 0 ||
+		if (pqPutMsgStart(COPY_DONE, conn) < 0 ||
 			pqPutMsgEnd(conn) < 0)
 			return 1;
 
@@ -1922,7 +1924,7 @@ pqEndcopy3(PGconn *conn)
 		if (conn->cmd_queue_head &&
 			conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE)
 		{
-			if (pqPutMsgStart('S', conn) < 0 ||
+			if (pqPutMsgStart(SYNC_DATA_REQUEST, conn) < 0 ||
 				pqPutMsgEnd(conn) < 0)
 				return 1;
 		}
@@ -2005,7 +2007,7 @@ pqFunctionCall3(PGconn *conn, Oid fnid,
 
 	/* PQfn already validated connection state */
 
-	if (pqPutMsgStart('F', conn) < 0 || /* function call msg */
+	if (pqPutMsgStart(FUNCTION_CALL_REQUEST, conn) < 0 || /* function call msg */
 		pqPutInt(fnid, 4, conn) < 0 ||	/* function id */
 		pqPutInt(1, 2, conn) < 0 || /* # of format codes */
 		pqPutInt(1, 2, conn) < 0 || /* format code: BINARY */
diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index 402784f40e..a39228816d 100644
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -28,6 +28,7 @@
 #include "libpq-fe.h"
 #include "libpq-int.h"
 #include "port/pg_bswap.h"
+#include "protocol.h"
 
 
 /* Enable tracing */
@@ -562,72 +563,72 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
 
 	switch (id)
 	{
-		case '1':
+		case PARSE_COMPLETE_RESPONSE:
 			fprintf(conn->Pfdebug, "ParseComplete");
 			/* No message content */
 			break;
-		case '2':
+		case BIND_COMPLETE_RESPONSE:
 			fprintf(conn->Pfdebug, "BindComplete");
 			/* No message content */
 			break;
-		case '3':
+		case CLOSE_COMPLETE_RESPONSE:
 			fprintf(conn->Pfdebug, "CloseComplete");
 			/* No message content */
 			break;
-		case 'A':				/* Notification Response */
+		case NOTIFY_RESPONSE:				/* Notification Response */
 			pqTraceOutputA(conn->Pfdebug, message, &logCursor, regress);
 			break;
-		case 'B':				/* Bind */
+		case BIND_REQUEST:				/* Bind */
 			pqTraceOutputB(conn->Pfdebug, message, &logCursor);
 			break;
-		case 'c':
+		case COPY_DONE:
 			fprintf(conn->Pfdebug, "CopyDone");
 			/* No message content */
 			break;
-		case 'C':				/* Close(F) or Command Complete(B) */
+		case COMMAND_COMPLETE:				/* Close(F) or Command Complete(B) */
 			pqTraceOutputC(conn->Pfdebug, toServer, message, &logCursor);
 			break;
-		case 'd':				/* Copy Data */
+		case COPY_DATA:				/* Copy Data */
 			/* Drop COPY data to reduce the overhead of logging. */
 			break;
-		case 'D':				/* Describe(F) or Data Row(B) */
+		case DESCRIBE_REQUEST:		/* Describe(F) or Data Row(B) */
 			pqTraceOutputD(conn->Pfdebug, toServer, message, &logCursor);
 			break;
-		case 'E':				/* Execute(F) or Error Response(B) */
+		case EXECUTE_REQUEST:		/* Execute(F) or Error Response(B) */
 			pqTraceOutputE(conn->Pfdebug, toServer, message, &logCursor,
 						   regress);
 			break;
-		case 'f':				/* Copy Fail */
+		case COPY_FAIL:				/* Copy Fail */
 			pqTraceOutputf(conn->Pfdebug, message, &logCursor);
 			break;
-		case 'F':				/* Function Call */
+		case FUNCTION_CALL_REQUEST:	/* Function Call */
 			pqTraceOutputF(conn->Pfdebug, message, &logCursor, regress);
 			break;
-		case 'G':				/* Start Copy In */
+		case COPY_IN_RESPONSE:		/* Start Copy In */
 			pqTraceOutputG(conn->Pfdebug, message, &logCursor);
 			break;
-		case 'H':				/* Flush(F) or Start Copy Out(B) */
+		case FLUSH_DATA_REQUEST:	/* Flush(F) or Start Copy Out(B) */
 			if (!toServer)
 				pqTraceOutputH(conn->Pfdebug, message, &logCursor);
 			else
 				fprintf(conn->Pfdebug, "Flush");	/* no message content */
 			break;
-		case 'I':
+		case EMPTY_QUERY_RESPONSE:
 			fprintf(conn->Pfdebug, "EmptyQueryResponse");
 			/* No message content */
 			break;
-		case 'K':				/* secret key data from the backend */
+		case BACKEND_KEY_DATA:		/* secret key data from the backend */
 			pqTraceOutputK(conn->Pfdebug, message, &logCursor, regress);
 			break;
-		case 'n':
+		case NO_DATA_RESPONSE:
 			fprintf(conn->Pfdebug, "NoData");
 			/* No message content */
 			break;
-		case 'N':
+		case NOTICE_RESPONSE:
 			pqTraceOutputNR(conn->Pfdebug, "NoticeResponse", message,
 							&logCursor, regress);
 			break;
-		case 'P':				/* Parse */
+		case PARSE_REQUEST:		/* Parse */
 			pqTraceOutputP(conn->Pfdebug, message, &logCursor, regress);
 			break;
 		case 'Q':				/* Query */
@@ -636,36 +637,36 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
 		case 'R':				/* Authentication */
 			pqTraceOutputR(conn->Pfdebug, message, &logCursor);
 			break;
-		case 's':
+		case PORTAL_SUSPENDED_RESPONSE:
 			fprintf(conn->Pfdebug, "PortalSuspended");
 			/* No message content */
 			break;
-		case 'S':				/* Parameter Status(B) or Sync(F) */
+		case SYNC_DATA_REQUEST:	/* Parameter Status(B) or Sync(F) */
 			if (!toServer)
 				pqTraceOutputS(conn->Pfdebug, message, &logCursor);
 			else
 				fprintf(conn->Pfdebug, "Sync"); /* no message content */
 			break;
-		case 't':				/* Parameter Description */
+		case PARAMETER_DESCRIPTION_RESPONSE:	/* Parameter Description */
 			pqTraceOutputt(conn->Pfdebug, message, &logCursor, regress);
 			break;
-		case 'T':				/* Row Description */
+		case ROW_DESCRIPTION_RESPONSE:			/* Row Description */
 			pqTraceOutputT(conn->Pfdebug, message, &logCursor, regress);
 			break;
-		case 'v':				/* Negotiate Protocol Version */
+		case NEGOTIATE_PROTOCOL:				/* Negotiate Protocol Version */
 			pqTraceOutputv(conn->Pfdebug, message, &logCursor);
 			break;
-		case 'V':				/* Function Call response */
+		case FUNCTION_CALL_RESPONSE:			/* Function Call response */
 			pqTraceOutputV(conn->Pfdebug, message, &logCursor);
 			break;
-		case 'W':				/* Start Copy Both */
+		case COPY_BOTH_RESPONSE:				/* Start Copy Both */
 			pqTraceOutputW(conn->Pfdebug, message, &logCursor, length);
 			break;
-		case 'X':
+		case TERMINATE_REQUEST:
 			fprintf(conn->Pfdebug, "Terminate");
 			/* No message content */
 			break;
-		case 'Z':				/* Ready For Query */
+		case READY_FOR_QUERY:					/* Ready For Query */
 			pqTraceOutputZ(conn->Pfdebug, message, &logCursor);
 			break;
 		default:
-- 
2.37.1 (Apple Git-137.1)