Move routine definitions of xlogarchive.c to a new header file

The definitions of the routines defined in xlogarchive.c have been part
of xlog_internal.h which is included by several frontend tools, but all
those routines are only called by the backend.  More cleanup could be
done within xlog_internal.h, but that's already a nice cut.

This will help a follow-up patch for pg_rewind where handling of
restore_command is added for frontends.

Author: Alexey Kondratov, Michael Paquier
Reviewed-by: Álvaro Herrera, Alexander Korotkov
Discussion: https://postgr.es/m/a3acff50-5a0d-9a2c-b3b2-ee36168955c1@postgrespro.ru

src/backend/access/transam/timeline.c

@@ -37,6 +37,7 @@
 #include "access/timeline.h"
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
+#include "access/xlogarchive.h"
 #include "access/xlogdefs.h"
 #include "pgstat.h"
 #include "storage/fd.h"

src/backend/access/transam/xlog.c

@@ -33,6 +33,7 @@
 #include "access/twophase.h"
 #include "access/xact.h"
 #include "access/xlog_internal.h"
+#include "access/xlogarchive.h"
 #include "access/xloginsert.h"
 #include "access/xlogreader.h"
 #include "access/xlogutils.h"

src/backend/access/transam/xlogarchive.c

@@ -21,6 +21,7 @@
 
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
+#include "access/xlogarchive.h"
 #include "common/archive.h"
 #include "miscadmin.h"
 #include "postmaster/startup.h"

src/backend/replication/walreceiver.c

@@ -55,6 +55,7 @@
 #include "access/timeline.h"
 #include "access/transam.h"
 #include "access/xlog_internal.h"
+#include "access/xlogarchive.h"
 #include "catalog/pg_authid.h"
 #include "catalog/pg_type.h"
 #include "common/ip.h"

src/include/access/xlog_internal.h

@@ -320,22 +320,4 @@ extern bool InArchiveRecovery;
 extern bool StandbyMode;
 extern char *recoveryRestoreCommand;
 
-/*
- * Prototypes for functions in xlogarchive.c
- */
-extern bool RestoreArchivedFile(char *path, const char *xlogfname,
-								const char *recovername, off_t expectedSize,
-								bool cleanupEnabled);
-extern void ExecuteRecoveryCommand(const char *command, const char *commandName,
-								   bool failOnSignal);
-extern void KeepFileRestoredFromArchive(const char *path, const char *xlogfname);
-extern void XLogArchiveNotify(const char *xlog);
-extern void XLogArchiveNotifySeg(XLogSegNo segno);
-extern void XLogArchiveForceDone(const char *xlog);
-extern bool XLogArchiveCheckDone(const char *xlog);
-extern bool XLogArchiveIsBusy(const char *xlog);
-extern bool XLogArchiveIsReady(const char *xlog);
-extern bool XLogArchiveIsReadyOrDone(const char *xlog);
-extern void XLogArchiveCleanup(const char *xlog);
-
 #endif							/* XLOG_INTERNAL_H */

src/include/access/xlogarchive.h

@@ -0,0 +1,35 @@
+/*------------------------------------------------------------------------
+ *
+ * xlogarchive.h
+ *		Prototypes for WAL archives in the backend
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/include/access/xlogarchive.h
+ *
+ *------------------------------------------------------------------------
+ */
+
+#ifndef XLOG_ARCHIVE_H
+#define XLOG_ARCHIVE_H
+
+#include "access/xlogdefs.h"
+
+extern bool RestoreArchivedFile(char *path, const char *xlogfname,
+								const char *recovername, off_t expectedSize,
+								bool cleanupEnabled);
+extern void ExecuteRecoveryCommand(const char *command, const char *commandName,
+								   bool failOnSignal);
+extern void KeepFileRestoredFromArchive(const char *path, const char *xlogfname);
+extern void XLogArchiveNotify(const char *xlog);
+extern void XLogArchiveNotifySeg(XLogSegNo segno);
+extern void XLogArchiveForceDone(const char *xlog);
+extern bool XLogArchiveCheckDone(const char *xlog);
+extern bool XLogArchiveIsBusy(const char *xlog);
+extern bool XLogArchiveIsReady(const char *xlog);
+extern bool XLogArchiveIsReadyOrDone(const char *xlog);
+extern void XLogArchiveCleanup(const char *xlog);
+
+#endif							/* XLOG_ARCHIVE_H */