Adding upstream version 13.4.upstream/13.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 1109 insertions, 0 deletions

diff --git a/src/backend/replication/libpqwalreceiver/Makefile b/src/backend/replication/libpqwalreceiver/Makefile
new file mode 100644
index 0000000..f26daa1
--- /dev/null
+++ b/src/backend/replication/libpqwalreceiver/Makefile
@@ -0,0 +1,37 @@
+#-------------------------------------------------------------------------
+#
+# Makefile--
+#    Makefile for src/backend/replication/libpqwalreceiver
+#
+# IDENTIFICATION
+#    src/backend/replication/libpqwalreceiver/Makefile
+#
+#-------------------------------------------------------------------------
+
+subdir = src/backend/replication/libpqwalreceiver
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+override CPPFLAGS := -I$(srcdir) -I$(libpq_srcdir) $(CPPFLAGS)
+
+OBJS = \
+	$(WIN32RES) \
+	libpqwalreceiver.o
+SHLIB_LINK_INTERNAL = $(libpq)
+SHLIB_LINK = $(filter -lintl, $(LIBS))
+SHLIB_PREREQS = submake-libpq
+PGFILEDESC = "libpqwalreceiver - receive WAL during streaming replication"
+NAME = libpqwalreceiver
+
+all: all-shared-lib
+
+include $(top_srcdir)/src/Makefile.shlib
+
+install: all installdirs install-lib
+
+installdirs: installdirs-lib
+
+uninstall: uninstall-lib
+
+clean distclean maintainer-clean: clean-lib
+	rm -f $(OBJS)
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
new file mode 100644
index 0000000..98b0164
--- /dev/null
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -0,0 +1,1072 @@
+/*-------------------------------------------------------------------------
+ *
+ * libpqwalreceiver.c
+ *
+ * This file contains the libpq-specific parts of walreceiver. It's
+ * loaded as a dynamic module to avoid linking the main server binary with
+ * libpq.
+ *
+ * Portions Copyright (c) 2010-2020, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <unistd.h>
+#include <sys/time.h>
+
+#include "access/xlog.h"
+#include "catalog/pg_type.h"
+#include "common/connect.h"
+#include "funcapi.h"
+#include "libpq-fe.h"
+#include "mb/pg_wchar.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "pqexpbuffer.h"
+#include "replication/walreceiver.h"
+#include "utils/builtins.h"
+#include "utils/memutils.h"
+#include "utils/pg_lsn.h"
+#include "utils/tuplestore.h"
+
+PG_MODULE_MAGIC;
+
+void		_PG_init(void);
+
+struct WalReceiverConn
+{
+	/* Current connection to the primary, if any */
+	PGconn	   *streamConn;
+	/* Used to remember if the connection is logical or physical */
+	bool		logical;
+	/* Buffer for currently read records */
+	char	   *recvBuf;
+};
+
+/* Prototypes for interface functions */
+static WalReceiverConn *libpqrcv_connect(const char *conninfo,
+										 bool logical, const char *appname,
+										 char **err);
+static void libpqrcv_check_conninfo(const char *conninfo);
+static char *libpqrcv_get_conninfo(WalReceiverConn *conn);
+static void libpqrcv_get_senderinfo(WalReceiverConn *conn,
+									char **sender_host, int *sender_port);
+static char *libpqrcv_identify_system(WalReceiverConn *conn,
+									  TimeLineID *primary_tli);
+static int	libpqrcv_server_version(WalReceiverConn *conn);
+static void libpqrcv_readtimelinehistoryfile(WalReceiverConn *conn,
+											 TimeLineID tli, char **filename,
+											 char **content, int *len);
+static bool libpqrcv_startstreaming(WalReceiverConn *conn,
+									const WalRcvStreamOptions *options);
+static void libpqrcv_endstreaming(WalReceiverConn *conn,
+								  TimeLineID *next_tli);
+static int	libpqrcv_receive(WalReceiverConn *conn, char **buffer,
+							 pgsocket *wait_fd);
+static void libpqrcv_send(WalReceiverConn *conn, const char *buffer,
+						  int nbytes);
+static char *libpqrcv_create_slot(WalReceiverConn *conn,
+								  const char *slotname,
+								  bool temporary,
+								  CRSSnapshotAction snapshot_action,
+								  XLogRecPtr *lsn);
+static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
+static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
+									   const char *query,
+									   const int nRetTypes,
+									   const Oid *retTypes);
+static void libpqrcv_disconnect(WalReceiverConn *conn);
+
+static WalReceiverFunctionsType PQWalReceiverFunctions = {
+	libpqrcv_connect,
+	libpqrcv_check_conninfo,
+	libpqrcv_get_conninfo,
+	libpqrcv_get_senderinfo,
+	libpqrcv_identify_system,
+	libpqrcv_server_version,
+	libpqrcv_readtimelinehistoryfile,
+	libpqrcv_startstreaming,
+	libpqrcv_endstreaming,
+	libpqrcv_receive,
+	libpqrcv_send,
+	libpqrcv_create_slot,
+	libpqrcv_get_backend_pid,
+	libpqrcv_exec,
+	libpqrcv_disconnect
+};
+
+/* Prototypes for private functions */
+static PGresult *libpqrcv_PQexec(PGconn *streamConn, const char *query);
+static PGresult *libpqrcv_PQgetResult(PGconn *streamConn);
+static char *stringlist_to_identifierstr(PGconn *conn, List *strings);
+
+/*
+ * Module initialization function
+ */
+void
+_PG_init(void)
+{
+	if (WalReceiverFunctions != NULL)
+		elog(ERROR, "libpqwalreceiver already loaded");
+	WalReceiverFunctions = &PQWalReceiverFunctions;
+}
+
+/*
+ * Establish the connection to the primary server for XLOG streaming
+ *
+ * Returns NULL on error and fills the err with palloc'ed error message.
+ */
+static WalReceiverConn *
+libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
+				 char **err)
+{
+	WalReceiverConn *conn;
+	PostgresPollingStatusType status;
+	const char *keys[5];
+	const char *vals[5];
+	int			i = 0;
+
+	/*
+	 * We use the expand_dbname parameter to process the connection string (or
+	 * URI), and pass some extra options.
+	 */
+	keys[i] = "dbname";
+	vals[i] = conninfo;
+	keys[++i] = "replication";
+	vals[i] = logical ? "database" : "true";
+	if (!logical)
+	{
+		/*
+		 * The database name is ignored by the server in replication mode, but
+		 * specify "replication" for .pgpass lookup.
+		 */
+		keys[++i] = "dbname";
+		vals[i] = "replication";
+	}
+	keys[++i] = "fallback_application_name";
+	vals[i] = appname;
+	if (logical)
+	{
+		keys[++i] = "client_encoding";
+		vals[i] = GetDatabaseEncodingName();
+	}
+	keys[++i] = NULL;
+	vals[i] = NULL;
+
+	Assert(i < sizeof(keys));
+
+	conn = palloc0(sizeof(WalReceiverConn));
+	conn->streamConn = PQconnectStartParams(keys, vals,
+											 /* expand_dbname = */ true);
+	if (PQstatus(conn->streamConn) == CONNECTION_BAD)
+	{
+		*err = pchomp(PQerrorMessage(conn->streamConn));
+		return NULL;
+	}
+
+	/*
+	 * Poll connection until we have OK or FAILED status.
+	 *
+	 * Per spec for PQconnectPoll, first wait till socket is write-ready.
+	 */
+	status = PGRES_POLLING_WRITING;
+	do
+	{
+		int			io_flag;
+		int			rc;
+
+		if (status == PGRES_POLLING_READING)
+			io_flag = WL_SOCKET_READABLE;
+#ifdef WIN32
+		/* Windows needs a different test while waiting for connection-made */
+		else if (PQstatus(conn->streamConn) == CONNECTION_STARTED)
+			io_flag = WL_SOCKET_CONNECTED;
+#endif
+		else
+			io_flag = WL_SOCKET_WRITEABLE;
+
+		rc = WaitLatchOrSocket(MyLatch,
+							   WL_EXIT_ON_PM_DEATH | WL_LATCH_SET | io_flag,
+							   PQsocket(conn->streamConn),
+							   0,
+							   WAIT_EVENT_LIBPQWALRECEIVER_CONNECT);
+
+		/* Interrupted? */
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			ProcessWalRcvInterrupts();
+		}
+
+		/* If socket is ready, advance the libpq state machine */
+		if (rc & io_flag)
+			status = PQconnectPoll(conn->streamConn);
+	} while (status != PGRES_POLLING_OK && status != PGRES_POLLING_FAILED);
+
+	if (PQstatus(conn->streamConn) != CONNECTION_OK)
+	{
+		*err = pchomp(PQerrorMessage(conn->streamConn));
+		return NULL;
+	}
+
+	if (logical)
+	{
+		PGresult   *res;
+
+		res = libpqrcv_PQexec(conn->streamConn,
+							  ALWAYS_SECURE_SEARCH_PATH_SQL);
+		if (PQresultStatus(res) != PGRES_TUPLES_OK)
+		{
+			PQclear(res);
+			ereport(ERROR,
+					(errmsg("could not clear search path: %s",
+							pchomp(PQerrorMessage(conn->streamConn)))));
+		}
+		PQclear(res);
+	}
+
+	conn->logical = logical;
+
+	return conn;
+}
+
+/*
+ * Validate connection info string (just try to parse it)
+ */
+static void
+libpqrcv_check_conninfo(const char *conninfo)
+{
+	PQconninfoOption *opts = NULL;
+	char	   *err = NULL;
+
+	opts = PQconninfoParse(conninfo, &err);
+	if (opts == NULL)
+	{
+		/* The error string is malloc'd, so we must free it explicitly */
+		char	   *errcopy = err ? pstrdup(err) : "out of memory";
+
+		PQfreemem(err);
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("invalid connection string syntax: %s", errcopy)));
+	}
+
+	PQconninfoFree(opts);
+}
+
+/*
+ * Return a user-displayable conninfo string.  Any security-sensitive fields
+ * are obfuscated.
+ */
+static char *
+libpqrcv_get_conninfo(WalReceiverConn *conn)
+{
+	PQconninfoOption *conn_opts;
+	PQconninfoOption *conn_opt;
+	PQExpBufferData buf;
+	char	   *retval;
+
+	Assert(conn->streamConn != NULL);
+
+	initPQExpBuffer(&buf);
+	conn_opts = PQconninfo(conn->streamConn);
+
+	if (conn_opts == NULL)
+		ereport(ERROR,
+				(errmsg("could not parse connection string: %s",
+						_("out of memory"))));
+
+	/* build a clean connection string from pieces */
+	for (conn_opt = conn_opts; conn_opt->keyword != NULL; conn_opt++)
+	{
+		bool		obfuscate;
+
+		/* Skip debug and empty options */
+		if (strchr(conn_opt->dispchar, 'D') ||
+			conn_opt->val == NULL ||
+			conn_opt->val[0] == '\0')
+			continue;
+
+		/* Obfuscate security-sensitive options */
+		obfuscate = strchr(conn_opt->dispchar, '*') != NULL;
+
+		appendPQExpBuffer(&buf, "%s%s=%s",
+						  buf.len == 0 ? "" : " ",
+						  conn_opt->keyword,
+						  obfuscate ? "********" : conn_opt->val);
+	}
+
+	PQconninfoFree(conn_opts);
+
+	retval = PQExpBufferDataBroken(buf) ? NULL : pstrdup(buf.data);
+	termPQExpBuffer(&buf);
+	return retval;
+}
+
+/*
+ * Provides information of sender this WAL receiver is connected to.
+ */
+static void
+libpqrcv_get_senderinfo(WalReceiverConn *conn, char **sender_host,
+						int *sender_port)
+{
+	char	   *ret = NULL;
+
+	*sender_host = NULL;
+	*sender_port = 0;
+
+	Assert(conn->streamConn != NULL);
+
+	ret = PQhost(conn->streamConn);
+	if (ret && strlen(ret) != 0)
+		*sender_host = pstrdup(ret);
+
+	ret = PQport(conn->streamConn);
+	if (ret && strlen(ret) != 0)
+		*sender_port = atoi(ret);
+}
+
+/*
+ * Check that primary's system identifier matches ours, and fetch the current
+ * timeline ID of the primary.
+ */
+static char *
+libpqrcv_identify_system(WalReceiverConn *conn, TimeLineID *primary_tli)
+{
+	PGresult   *res;
+	char	   *primary_sysid;
+
+	/*
+	 * Get the system identifier and timeline ID as a DataRow message from the
+	 * primary server.
+	 */
+	res = libpqrcv_PQexec(conn->streamConn, "IDENTIFY_SYSTEM");
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("could not receive database system identifier and timeline ID from "
+						"the primary server: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+	}
+	if (PQnfields(res) < 3 || PQntuples(res) != 1)
+	{
+		int			ntuples = PQntuples(res);
+		int			nfields = PQnfields(res);
+
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("invalid response from primary server"),
+				 errdetail("Could not identify system: got %d rows and %d fields, expected %d rows and %d or more fields.",
+						   ntuples, nfields, 3, 1)));
+	}
+	primary_sysid = pstrdup(PQgetvalue(res, 0, 0));
+	*primary_tli = pg_strtoint32(PQgetvalue(res, 0, 1));
+	PQclear(res);
+
+	return primary_sysid;
+}
+
+/*
+ * Thin wrapper around libpq to obtain server version.
+ */
+static int
+libpqrcv_server_version(WalReceiverConn *conn)
+{
+	return PQserverVersion(conn->streamConn);
+}
+
+/*
+ * Start streaming WAL data from given streaming options.
+ *
+ * Returns true if we switched successfully to copy-both mode. False
+ * means the server received the command and executed it successfully, but
+ * didn't switch to copy-mode.  That means that there was no WAL on the
+ * requested timeline and starting point, because the server switched to
+ * another timeline at or before the requested starting point. On failure,
+ * throws an ERROR.
+ */
+static bool
+libpqrcv_startstreaming(WalReceiverConn *conn,
+						const WalRcvStreamOptions *options)
+{
+	StringInfoData cmd;
+	PGresult   *res;
+
+	Assert(options->logical == conn->logical);
+	Assert(options->slotname || !options->logical);
+
+	initStringInfo(&cmd);
+
+	/* Build the command. */
+	appendStringInfoString(&cmd, "START_REPLICATION");
+	if (options->slotname != NULL)
+		appendStringInfo(&cmd, " SLOT \"%s\"",
+						 options->slotname);
+
+	if (options->logical)
+		appendStringInfoString(&cmd, " LOGICAL");
+
+	appendStringInfo(&cmd, " %X/%X",
+					 (uint32) (options->startpoint >> 32),
+					 (uint32) options->startpoint);
+
+	/*
+	 * Additional options are different depending on if we are doing logical
+	 * or physical replication.
+	 */
+	if (options->logical)
+	{
+		char	   *pubnames_str;
+		List	   *pubnames;
+		char	   *pubnames_literal;
+
+		appendStringInfoString(&cmd, " (");
+
+		appendStringInfo(&cmd, "proto_version '%u'",
+						 options->proto.logical.proto_version);
+
+		pubnames = options->proto.logical.publication_names;
+		pubnames_str = stringlist_to_identifierstr(conn->streamConn, pubnames);
+		if (!pubnames_str)
+			ereport(ERROR,
+					(errmsg("could not start WAL streaming: %s",
+							pchomp(PQerrorMessage(conn->streamConn)))));
+		pubnames_literal = PQescapeLiteral(conn->streamConn, pubnames_str,
+										   strlen(pubnames_str));
+		if (!pubnames_literal)
+			ereport(ERROR,
+					(errmsg("could not start WAL streaming: %s",
+							pchomp(PQerrorMessage(conn->streamConn)))));
+		appendStringInfo(&cmd, ", publication_names %s", pubnames_literal);
+		PQfreemem(pubnames_literal);
+		pfree(pubnames_str);
+
+		appendStringInfoChar(&cmd, ')');
+	}
+	else
+		appendStringInfo(&cmd, " TIMELINE %u",
+						 options->proto.physical.startpointTLI);
+
+	/* Start streaming. */
+	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
+	pfree(cmd.data);
+
+	if (PQresultStatus(res) == PGRES_COMMAND_OK)
+	{
+		PQclear(res);
+		return false;
+	}
+	else if (PQresultStatus(res) != PGRES_COPY_BOTH)
+	{
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("could not start WAL streaming: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+	}
+	PQclear(res);
+	return true;
+}
+
+/*
+ * Stop streaming WAL data. Returns the next timeline's ID in *next_tli, as
+ * reported by the server, or 0 if it did not report it.
+ */
+static void
+libpqrcv_endstreaming(WalReceiverConn *conn, TimeLineID *next_tli)
+{
+	PGresult   *res;
+
+	/*
+	 * Send copy-end message.  As in libpqrcv_PQexec, this could theoretically
+	 * block, but the risk seems small.
+	 */
+	if (PQputCopyEnd(conn->streamConn, NULL) <= 0 ||
+		PQflush(conn->streamConn))
+		ereport(ERROR,
+				(errmsg("could not send end-of-streaming message to primary: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+
+	*next_tli = 0;
+
+	/*
+	 * After COPY is finished, we should receive a result set indicating the
+	 * next timeline's ID, or just CommandComplete if the server was shut
+	 * down.
+	 *
+	 * If we had not yet received CopyDone from the backend, PGRES_COPY_OUT is
+	 * also possible in case we aborted the copy in mid-stream.
+	 */
+	res = libpqrcv_PQgetResult(conn->streamConn);
+	if (PQresultStatus(res) == PGRES_TUPLES_OK)
+	{
+		/*
+		 * Read the next timeline's ID. The server also sends the timeline's
+		 * starting point, but it is ignored.
+		 */
+		if (PQnfields(res) < 2 || PQntuples(res) != 1)
+			ereport(ERROR,
+					(errmsg("unexpected result set after end-of-streaming")));
+		*next_tli = pg_strtoint32(PQgetvalue(res, 0, 0));
+		PQclear(res);
+
+		/* the result set should be followed by CommandComplete */
+		res = libpqrcv_PQgetResult(conn->streamConn);
+	}
+	else if (PQresultStatus(res) == PGRES_COPY_OUT)
+	{
+		PQclear(res);
+
+		/* End the copy */
+		if (PQendcopy(conn->streamConn))
+			ereport(ERROR,
+					(errmsg("error while shutting down streaming COPY: %s",
+							pchomp(PQerrorMessage(conn->streamConn)))));
+
+		/* CommandComplete should follow */
+		res = libpqrcv_PQgetResult(conn->streamConn);
+	}
+
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		ereport(ERROR,
+				(errmsg("error reading result of streaming command: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+	PQclear(res);
+
+	/* Verify that there are no more results */
+	res = libpqrcv_PQgetResult(conn->streamConn);
+	if (res != NULL)
+		ereport(ERROR,
+				(errmsg("unexpected result after CommandComplete: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+}
+
+/*
+ * Fetch the timeline history file for 'tli' from primary.
+ */
+static void
+libpqrcv_readtimelinehistoryfile(WalReceiverConn *conn,
+								 TimeLineID tli, char **filename,
+								 char **content, int *len)
+{
+	PGresult   *res;
+	char		cmd[64];
+
+	Assert(!conn->logical);
+
+	/*
+	 * Request the primary to send over the history file for given timeline.
+	 */
+	snprintf(cmd, sizeof(cmd), "TIMELINE_HISTORY %u", tli);
+	res = libpqrcv_PQexec(conn->streamConn, cmd);
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("could not receive timeline history file from "
+						"the primary server: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+	}
+	if (PQnfields(res) != 2 || PQntuples(res) != 1)
+	{
+		int			ntuples = PQntuples(res);
+		int			nfields = PQnfields(res);
+
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("invalid response from primary server"),
+				 errdetail("Expected 1 tuple with 2 fields, got %d tuples with %d fields.",
+						   ntuples, nfields)));
+	}
+	*filename = pstrdup(PQgetvalue(res, 0, 0));
+
+	*len = PQgetlength(res, 0, 1);
+	*content = palloc(*len);
+	memcpy(*content, PQgetvalue(res, 0, 1), *len);
+	PQclear(res);
+}
+
+/*
+ * Send a query and wait for the results by using the asynchronous libpq
+ * functions and socket readiness events.
+ *
+ * We must not use the regular blocking libpq functions like PQexec()
+ * since they are uninterruptible by signals on some platforms, such as
+ * Windows.
+ *
+ * The function is modeled on PQexec() in libpq, but only implements
+ * those parts that are in use in the walreceiver api.
+ *
+ * May return NULL, rather than an error result, on failure.
+ */
+static PGresult *
+libpqrcv_PQexec(PGconn *streamConn, const char *query)
+{
+	PGresult   *lastResult = NULL;
+
+	/*
+	 * PQexec() silently discards any prior query results on the connection.
+	 * This is not required for this function as it's expected that the caller
+	 * (which is this library in all cases) will behave correctly and we don't
+	 * have to be backwards compatible with old libpq.
+	 */
+
+	/*
+	 * Submit the query.  Since we don't use non-blocking mode, this could
+	 * theoretically block.  In practice, since we don't send very long query
+	 * strings, the risk seems negligible.
+	 */
+	if (!PQsendQuery(streamConn, query))
+		return NULL;
+
+	for (;;)
+	{
+		/* Wait for, and collect, the next PGresult. */
+		PGresult   *result;
+
+		result = libpqrcv_PQgetResult(streamConn);
+		if (result == NULL)
+			break;				/* query is complete, or failure */
+
+		/*
+		 * Emulate PQexec()'s behavior of returning the last result when there
+		 * are many.  We are fine with returning just last error message.
+		 */
+		PQclear(lastResult);
+		lastResult = result;
+
+		if (PQresultStatus(lastResult) == PGRES_COPY_IN ||
+			PQresultStatus(lastResult) == PGRES_COPY_OUT ||
+			PQresultStatus(lastResult) == PGRES_COPY_BOTH ||
+			PQstatus(streamConn) == CONNECTION_BAD)
+			break;
+	}
+
+	return lastResult;
+}
+
+/*
+ * Perform the equivalent of PQgetResult(), but watch for interrupts.
+ */
+static PGresult *
+libpqrcv_PQgetResult(PGconn *streamConn)
+{
+	/*
+	 * Collect data until PQgetResult is ready to get the result without
+	 * blocking.
+	 */
+	while (PQisBusy(streamConn))
+	{
+		int			rc;
+
+		/*
+		 * We don't need to break down the sleep into smaller increments,
+		 * since we'll get interrupted by signals and can handle any
+		 * interrupts here.
+		 */
+		rc = WaitLatchOrSocket(MyLatch,
+							   WL_EXIT_ON_PM_DEATH | WL_SOCKET_READABLE |
+							   WL_LATCH_SET,
+							   PQsocket(streamConn),
+							   0,
+							   WAIT_EVENT_LIBPQWALRECEIVER_RECEIVE);
+
+		/* Interrupted? */
+		if (rc & WL_LATCH_SET)
+		{
+			ResetLatch(MyLatch);
+			ProcessWalRcvInterrupts();
+		}
+
+		/* Consume whatever data is available from the socket */
+		if (PQconsumeInput(streamConn) == 0)
+		{
+			/* trouble; return NULL */
+			return NULL;
+		}
+	}
+
+	/* Now we can collect and return the next PGresult */
+	return PQgetResult(streamConn);
+}
+
+/*
+ * Disconnect connection to primary, if any.
+ */
+static void
+libpqrcv_disconnect(WalReceiverConn *conn)
+{
+	PQfinish(conn->streamConn);
+	if (conn->recvBuf != NULL)
+		PQfreemem(conn->recvBuf);
+	pfree(conn);
+}
+
+/*
+ * Receive a message available from XLOG stream.
+ *
+ * Returns:
+ *
+ *	 If data was received, returns the length of the data. *buffer is set to
+ *	 point to a buffer holding the received message. The buffer is only valid
+ *	 until the next libpqrcv_* call.
+ *
+ *	 If no data was available immediately, returns 0, and *wait_fd is set to a
+ *	 socket descriptor which can be waited on before trying again.
+ *
+ *	 -1 if the server ended the COPY.
+ *
+ * ereports on error.
+ */
+static int
+libpqrcv_receive(WalReceiverConn *conn, char **buffer,
+				 pgsocket *wait_fd)
+{
+	int			rawlen;
+
+	if (conn->recvBuf != NULL)
+		PQfreemem(conn->recvBuf);
+	conn->recvBuf = NULL;
+
+	/* Try to receive a CopyData message */
+	rawlen = PQgetCopyData(conn->streamConn, &conn->recvBuf, 1);
+	if (rawlen == 0)
+	{
+		/* Try consuming some data. */
+		if (PQconsumeInput(conn->streamConn) == 0)
+			ereport(ERROR,
+					(errmsg("could not receive data from WAL stream: %s",
+							pchomp(PQerrorMessage(conn->streamConn)))));
+
+		/* Now that we've consumed some input, try again */
+		rawlen = PQgetCopyData(conn->streamConn, &conn->recvBuf, 1);
+		if (rawlen == 0)
+		{
+			/* Tell caller to try again when our socket is ready. */
+			*wait_fd = PQsocket(conn->streamConn);
+			return 0;
+		}
+	}
+	if (rawlen == -1)			/* end-of-streaming or error */
+	{
+		PGresult   *res;
+
+		res = libpqrcv_PQgetResult(conn->streamConn);
+		if (PQresultStatus(res) == PGRES_COMMAND_OK)
+		{
+			PQclear(res);
+
+			/* Verify that there are no more results. */
+			res = libpqrcv_PQgetResult(conn->streamConn);
+			if (res != NULL)
+			{
+				PQclear(res);
+
+				/*
+				 * If the other side closed the connection orderly (otherwise
+				 * we'd seen an error, or PGRES_COPY_IN) don't report an error
+				 * here, but let callers deal with it.
+				 */
+				if (PQstatus(conn->streamConn) == CONNECTION_BAD)
+					return -1;
+
+				ereport(ERROR,
+						(errmsg("unexpected result after CommandComplete: %s",
+								PQerrorMessage(conn->streamConn))));
+			}
+
+			return -1;
+		}
+		else if (PQresultStatus(res) == PGRES_COPY_IN)
+		{
+			PQclear(res);
+			return -1;
+		}
+		else
+		{
+			PQclear(res);
+			ereport(ERROR,
+					(errmsg("could not receive data from WAL stream: %s",
+							pchomp(PQerrorMessage(conn->streamConn)))));
+		}
+	}
+	if (rawlen < -1)
+		ereport(ERROR,
+				(errmsg("could not receive data from WAL stream: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+
+	/* Return received messages to caller */
+	*buffer = conn->recvBuf;
+	return rawlen;
+}
+
+/*
+ * Send a message to XLOG stream.
+ *
+ * ereports on error.
+ */
+static void
+libpqrcv_send(WalReceiverConn *conn, const char *buffer, int nbytes)
+{
+	if (PQputCopyData(conn->streamConn, buffer, nbytes) <= 0 ||
+		PQflush(conn->streamConn))
+		ereport(ERROR,
+				(errmsg("could not send data to WAL stream: %s",
+						pchomp(PQerrorMessage(conn->streamConn)))));
+}
+
+/*
+ * Create new replication slot.
+ * Returns the name of the exported snapshot for logical slot or NULL for
+ * physical slot.
+ */
+static char *
+libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
+					 bool temporary, CRSSnapshotAction snapshot_action,
+					 XLogRecPtr *lsn)
+{
+	PGresult   *res;
+	StringInfoData cmd;
+	char	   *snapshot;
+
+	initStringInfo(&cmd);
+
+	appendStringInfo(&cmd, "CREATE_REPLICATION_SLOT \"%s\"", slotname);
+
+	if (temporary)
+		appendStringInfoString(&cmd, " TEMPORARY");
+
+	if (conn->logical)
+	{
+		appendStringInfoString(&cmd, " LOGICAL pgoutput");
+		switch (snapshot_action)
+		{
+			case CRS_EXPORT_SNAPSHOT:
+				appendStringInfoString(&cmd, " EXPORT_SNAPSHOT");
+				break;
+			case CRS_NOEXPORT_SNAPSHOT:
+				appendStringInfoString(&cmd, " NOEXPORT_SNAPSHOT");
+				break;
+			case CRS_USE_SNAPSHOT:
+				appendStringInfoString(&cmd, " USE_SNAPSHOT");
+				break;
+		}
+	}
+	else
+	{
+		appendStringInfoString(&cmd, " PHYSICAL RESERVE_WAL");
+	}
+
+	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
+	pfree(cmd.data);
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		PQclear(res);
+		ereport(ERROR,
+				(errmsg("could not create replication slot \"%s\": %s",
+						slotname, pchomp(PQerrorMessage(conn->streamConn)))));
+	}
+
+	if (lsn)
+		*lsn = DatumGetLSN(DirectFunctionCall1Coll(pg_lsn_in, InvalidOid,
+												   CStringGetDatum(PQgetvalue(res, 0, 1))));
+
+	if (!PQgetisnull(res, 0, 2))
+		snapshot = pstrdup(PQgetvalue(res, 0, 2));
+	else
+		snapshot = NULL;
+
+	PQclear(res);
+
+	return snapshot;
+}
+
+/*
+ * Return PID of remote backend process.
+ */
+static pid_t
+libpqrcv_get_backend_pid(WalReceiverConn *conn)
+{
+	return PQbackendPID(conn->streamConn);
+}
+
+/*
+ * Convert tuple query result to tuplestore.
+ */
+static void
+libpqrcv_processTuples(PGresult *pgres, WalRcvExecResult *walres,
+					   const int nRetTypes, const Oid *retTypes)
+{
+	int			tupn;
+	int			coln;
+	int			nfields = PQnfields(pgres);
+	HeapTuple	tuple;
+	AttInMetadata *attinmeta;
+	MemoryContext rowcontext;
+	MemoryContext oldcontext;
+
+	/* Make sure we got expected number of fields. */
+	if (nfields != nRetTypes)
+		ereport(ERROR,
+				(errmsg("invalid query response"),
+				 errdetail("Expected %d fields, got %d fields.",
+						   nRetTypes, nfields)));
+
+	walres->tuplestore = tuplestore_begin_heap(true, false, work_mem);
+
+	/* Create tuple descriptor corresponding to expected result. */
+	walres->tupledesc = CreateTemplateTupleDesc(nRetTypes);
+	for (coln = 0; coln < nRetTypes; coln++)
+		TupleDescInitEntry(walres->tupledesc, (AttrNumber) coln + 1,
+						   PQfname(pgres, coln), retTypes[coln], -1, 0);
+	attinmeta = TupleDescGetAttInMetadata(walres->tupledesc);
+
+	/* No point in doing more here if there were no tuples returned. */
+	if (PQntuples(pgres) == 0)
+		return;
+
+	/* Create temporary context for local allocations. */
+	rowcontext = AllocSetContextCreate(CurrentMemoryContext,
+									   "libpqrcv query result context",
+									   ALLOCSET_DEFAULT_SIZES);
+
+	/* Process returned rows. */
+	for (tupn = 0; tupn < PQntuples(pgres); tupn++)
+	{
+		char	   *cstrs[MaxTupleAttributeNumber];
+
+		ProcessWalRcvInterrupts();
+
+		/* Do the allocations in temporary context. */
+		oldcontext = MemoryContextSwitchTo(rowcontext);
+
+		/*
+		 * Fill cstrs with null-terminated strings of column values.
+		 */
+		for (coln = 0; coln < nfields; coln++)
+		{
+			if (PQgetisnull(pgres, tupn, coln))
+				cstrs[coln] = NULL;
+			else
+				cstrs[coln] = PQgetvalue(pgres, tupn, coln);
+		}
+
+		/* Convert row to a tuple, and add it to the tuplestore */
+		tuple = BuildTupleFromCStrings(attinmeta, cstrs);
+		tuplestore_puttuple(walres->tuplestore, tuple);
+
+		/* Clean up */
+		MemoryContextSwitchTo(oldcontext);
+		MemoryContextReset(rowcontext);
+	}
+
+	MemoryContextDelete(rowcontext);
+}
+
+/*
+ * Public interface for sending generic queries (and commands).
+ *
+ * This can only be called from process connected to database.
+ */
+static WalRcvExecResult *
+libpqrcv_exec(WalReceiverConn *conn, const char *query,
+			  const int nRetTypes, const Oid *retTypes)
+{
+	PGresult   *pgres = NULL;
+	WalRcvExecResult *walres = palloc0(sizeof(WalRcvExecResult));
+
+	if (MyDatabaseId == InvalidOid)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("the query interface requires a database connection")));
+
+	pgres = libpqrcv_PQexec(conn->streamConn, query);
+
+	switch (PQresultStatus(pgres))
+	{
+		case PGRES_SINGLE_TUPLE:
+		case PGRES_TUPLES_OK:
+			walres->status = WALRCV_OK_TUPLES;
+			libpqrcv_processTuples(pgres, walres, nRetTypes, retTypes);
+			break;
+
+		case PGRES_COPY_IN:
+			walres->status = WALRCV_OK_COPY_IN;
+			break;
+
+		case PGRES_COPY_OUT:
+			walres->status = WALRCV_OK_COPY_OUT;
+			break;
+
+		case PGRES_COPY_BOTH:
+			walres->status = WALRCV_OK_COPY_BOTH;
+			break;
+
+		case PGRES_COMMAND_OK:
+			walres->status = WALRCV_OK_COMMAND;
+			break;
+
+			/* Empty query is considered error. */
+		case PGRES_EMPTY_QUERY:
+			walres->status = WALRCV_ERROR;
+			walres->err = _("empty query");
+			break;
+
+		case PGRES_NONFATAL_ERROR:
+		case PGRES_FATAL_ERROR:
+		case PGRES_BAD_RESPONSE:
+			walres->status = WALRCV_ERROR;
+			walres->err = pchomp(PQerrorMessage(conn->streamConn));
+			break;
+	}
+
+	PQclear(pgres);
+
+	return walres;
+}
+
+/*
+ * Given a List of strings, return it as single comma separated
+ * string, quoting identifiers as needed.
+ *
+ * This is essentially the reverse of SplitIdentifierString.
+ *
+ * The caller should free the result.
+ */
+static char *
+stringlist_to_identifierstr(PGconn *conn, List *strings)
+{
+	ListCell   *lc;
+	StringInfoData res;
+	bool		first = true;
+
+	initStringInfo(&res);
+
+	foreach(lc, strings)
+	{
+		char	   *val = strVal(lfirst(lc));
+		char	   *val_escaped;
+
+		if (first)
+			first = false;
+		else
+			appendStringInfoChar(&res, ',');
+
+		val_escaped = PQescapeIdentifier(conn, val, strlen(val));
+		if (!val_escaped)
+		{
+			free(res.data);
+			return NULL;
+		}
+		appendStringInfoString(&res, val_escaped);
+		PQfreemem(val_escaped);
+	}
+
+	return res.data;
+}