Move the server's backup manifest code to a separate file.

basebackup.c is already a pretty big and complicated file, so it
makes more sense to keep the backup manifest support routines
in a separate file, for clarity and ease of maintenance.

Discussion: http://postgr.es/m/CA+TgmoavRak5OdP76P8eJExDYhPEKWjMb0sxW7dF01dWFgE=uA@mail.gmail.com

src/backend/replication/Makefile

@@ -15,6 +15,7 @@ include $(top_builddir)/src/Makefile.global
 override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
 
 OBJS = \
+	backup_manifest.o \
 	basebackup.o \
 	repl_gram.o \
 	slot.o \

src/include/replication/backup_manifest.h

+/*-------------------------------------------------------------------------
+ *
+ * backup_manifest.h
+ *	  Routines for generating a backup manifest.
+ *
+ * Portions Copyright (c) 2010-2020, PostgreSQL Global Development Group
+ *
+ * src/include/replication/backup_manifest.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef BACKUP_MANIFEST_H
+#define BACKUP_MANIFEST_H
+
+#include "access/xlogdefs.h"
+#include "common/checksum_helper.h"
+#include "pgtime.h"
+#include "storage/buffile.h"
+
+typedef enum manifest_option
+{
+	MANIFEST_OPTION_YES,
+	MANIFEST_OPTION_NO,
+	MANIFEST_OPTION_FORCE_ENCODE
+} manifest_option;
+
+typedef struct manifest_info
+{
+	BufFile    *buffile;
+	pg_checksum_type checksum_type;
+	pg_sha256_ctx manifest_ctx;
+	uint64		manifest_size;
+	bool		force_encode;
+	bool		first_file;
+	bool		still_checksumming;
+} manifest_info;
+
+extern void InitializeManifest(manifest_info *manifest,
+							   manifest_option want_manifest,
+							   pg_checksum_type manifest_checksum_type);
+extern void AppendStringToManifest(manifest_info *manifest, char *s);
+extern void AddFileToManifest(manifest_info *manifest, const char *spcoid,
+							  const char *pathname, size_t size,
+							  pg_time_t mtime,
+							  pg_checksum_context *checksum_ctx);
+extern void AddWALInfoToManifest(manifest_info *manifest, XLogRecPtr startptr,
+								 TimeLineID starttli, XLogRecPtr endptr,
+								 TimeLineID endtli);
+extern void SendBackupManifest(manifest_info *manifest);
+
+#endif