From 513842e402841251c3a1d2dc0fac5fc51a0f2a9b Mon Sep 17 00:00:00 2001
From: Nathan Bossart <bossartn@amazon.com>
Date: Wed, 20 Oct 2021 21:42:54 +0000
Subject: [PATCH v4 1/2] Move logic for archiving via shell to its own file.

---
 src/backend/access/transam/xlog.c      |   2 +-
 src/backend/postmaster/Makefile        |   1 +
 src/backend/postmaster/pgarch.c        | 138 ++++----------------------------
 src/backend/postmaster/shell_archive.c | 139 +++++++++++++++++++++++++++++++++
 src/include/access/xlog.h              |  11 ++-
 src/include/postmaster/pgarch.h        |   6 ++
 6 files changed, 174 insertions(+), 123 deletions(-)
 create mode 100644 src/backend/postmaster/shell_archive.c

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 62862255fc..b0bb3d633e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8777,7 +8777,7 @@ ShutdownXLOG(int code, Datum arg)
 		 * process one more time at the end of shutdown). The checkpoint
 		 * record will go to the next XLOG file and won't be archived (yet).
 		 */
-		if (XLogArchivingActive() && XLogArchiveCommandSet())
+		if (XLogArchivingActive() && XLogArchivingConfigured())
 			RequestXLogSwitch(false);
 
 		CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
diff --git a/src/backend/postmaster/Makefile b/src/backend/postmaster/Makefile
index 787c6a2c3b..dbbeac5a82 100644
--- a/src/backend/postmaster/Makefile
+++ b/src/backend/postmaster/Makefile
@@ -23,6 +23,7 @@ OBJS = \
 	pgarch.o \
 	pgstat.o \
 	postmaster.o \
+	shell_archive.o \
 	startup.o \
 	syslogger.o \
 	walwriter.o
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 74a7d7c4d0..69e23e286f 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -25,18 +25,12 @@
  */
 #include "postgres.h"
 
-#include <fcntl.h>
-#include <signal.h>
-#include <time.h>
 #include <sys/stat.h>
-#include <sys/time.h>
-#include <sys/wait.h>
 #include <unistd.h>
 
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
 #include "libpq/pqsignal.h"
-#include "miscadmin.h"
 #include "pgstat.h"
 #include "postmaster/interrupt.h"
 #include "postmaster/pgarch.h"
@@ -78,6 +72,12 @@ typedef struct PgArchData
 	int			pgprocno;		/* pgprocno of archiver process */
 } PgArchData;
 
+/*
+ * PG_archive can be overwritten by modules to define custom archiving logic.
+ * By default, we use archive_command.
+ */
+PG_archive_t PG_archive = shell_archive;
+
 
 /* ----------
  * Local data
@@ -358,11 +358,11 @@ pgarch_ArchiverCopyLoop(void)
 			 */
 			HandlePgArchInterrupts();
 
-			/* can't do anything if no command ... */
-			if (!XLogArchiveCommandSet())
+			/* can't do anything if not configured ... */
+			if (!XLogArchivingConfigured())
 			{
 				ereport(WARNING,
-						(errmsg("archive_mode enabled, yet archive_command is not set")));
+						(errmsg("archive_mode enabled, yet archiving is not configured")));
 				return;
 			}
 
@@ -443,136 +443,32 @@ pgarch_ArchiverCopyLoop(void)
 /*
  * pgarch_archiveXlog
  *
- * Invokes system(3) to copy one archive file to wherever it should go
+ * Invokes PG_archive() to copy one archive file to wherever it should go
  *
  * Returns true if successful
  */
 static bool
 pgarch_archiveXlog(char *xlog)
 {
-	char		xlogarchcmd[MAXPGPATH];
 	char		pathname[MAXPGPATH];
 	char		activitymsg[MAXFNAMELEN + 16];
-	char	   *dp;
-	char	   *endp;
-	const char *sp;
-	int			rc;
-
-	snprintf(pathname, MAXPGPATH, XLOGDIR "/%s", xlog);
+	bool		ret;
 
-	/*
-	 * construct the command to be executed
-	 */
-	dp = xlogarchcmd;
-	endp = xlogarchcmd + MAXPGPATH - 1;
-	*endp = '\0';
+	Assert(PG_archive != NULL);
 
-	for (sp = XLogArchiveCommand; *sp; sp++)
-	{
-		if (*sp == '%')
-		{
-			switch (sp[1])
-			{
-				case 'p':
-					/* %p: relative path of source file */
-					sp++;
-					strlcpy(dp, pathname, endp - dp);
-					make_native_path(dp);
-					dp += strlen(dp);
-					break;
-				case 'f':
-					/* %f: filename of source file */
-					sp++;
-					strlcpy(dp, xlog, endp - dp);
-					dp += strlen(dp);
-					break;
-				case '%':
-					/* convert %% to a single % */
-					sp++;
-					if (dp < endp)
-						*dp++ = *sp;
-					break;
-				default:
-					/* otherwise treat the % as not special */
-					if (dp < endp)
-						*dp++ = *sp;
-					break;
-			}
-		}
-		else
-		{
-			if (dp < endp)
-				*dp++ = *sp;
-		}
-	}
-	*dp = '\0';
-
-	ereport(DEBUG3,
-			(errmsg_internal("executing archive command \"%s\"",
-							 xlogarchcmd)));
+	snprintf(pathname, MAXPGPATH, XLOGDIR "/%s", xlog);
 
 	/* Report archive activity in PS display */
 	snprintf(activitymsg, sizeof(activitymsg), "archiving %s", xlog);
 	set_ps_display(activitymsg);
 
-	rc = system(xlogarchcmd);
-	if (rc != 0)
-	{
-		/*
-		 * If either the shell itself, or a called command, died on a signal,
-		 * abort the archiver.  We do this because system() ignores SIGINT and
-		 * SIGQUIT while waiting; so a signal is very likely something that
-		 * should have interrupted us too.  Also die if the shell got a hard
-		 * "command not found" type of error.  If we overreact it's no big
-		 * deal, the postmaster will just start the archiver again.
-		 */
-		int			lev = wait_result_is_any_signal(rc, true) ? FATAL : LOG;
-
-		if (WIFEXITED(rc))
-		{
-			ereport(lev,
-					(errmsg("archive command failed with exit code %d",
-							WEXITSTATUS(rc)),
-					 errdetail("The failed archive command was: %s",
-							   xlogarchcmd)));
-		}
-		else if (WIFSIGNALED(rc))
-		{
-#if defined(WIN32)
-			ereport(lev,
-					(errmsg("archive command was terminated by exception 0x%X",
-							WTERMSIG(rc)),
-					 errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
-					 errdetail("The failed archive command was: %s",
-							   xlogarchcmd)));
-#else
-			ereport(lev,
-					(errmsg("archive command was terminated by signal %d: %s",
-							WTERMSIG(rc), pg_strsignal(WTERMSIG(rc))),
-					 errdetail("The failed archive command was: %s",
-							   xlogarchcmd)));
-#endif
-		}
-		else
-		{
-			ereport(lev,
-					(errmsg("archive command exited with unrecognized status %d",
-							rc),
-					 errdetail("The failed archive command was: %s",
-							   xlogarchcmd)));
-		}
-
+	if ((ret = (*PG_archive) (xlog, pathname)))
+		snprintf(activitymsg, sizeof(activitymsg), "last was %s", xlog);
+	else
 		snprintf(activitymsg, sizeof(activitymsg), "failed on %s", xlog);
-		set_ps_display(activitymsg);
-
-		return false;
-	}
-	elog(DEBUG1, "archived write-ahead log file \"%s\"", xlog);
-
-	snprintf(activitymsg, sizeof(activitymsg), "last was %s", xlog);
 	set_ps_display(activitymsg);
 
-	return true;
+	return ret;
 }
 
 /*
diff --git a/src/backend/postmaster/shell_archive.c b/src/backend/postmaster/shell_archive.c
new file mode 100644
index 0000000000..9bbe1cbe0f
--- /dev/null
+++ b/src/backend/postmaster/shell_archive.c
@@ -0,0 +1,139 @@
+/*-------------------------------------------------------------------------
+ *
+ * shell_archive.c
+ *
+ * This archiving function uses a user-specified shell command (the
+ * archive_command GUC) to copy write-ahead log files.  It is used as the
+ * default for PG_archive, but other modules may define their own custom
+ * archiving logic.
+ *
+ * Copyright (c) 2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/postmaster/shell_archive.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <sys/wait.h>
+
+#include "access/xlog.h"
+#include "postmaster/pgarch.h"
+
+bool
+shell_archive(const char *file, const char *path)
+{
+	char		xlogarchcmd[MAXPGPATH];
+	char	   *dp;
+	char	   *endp;
+	const char *sp;
+	int			rc;
+
+	Assert(file != NULL);
+	Assert(path != NULL);
+
+	/*
+	 * construct the command to be executed
+	 */
+	dp = xlogarchcmd;
+	endp = xlogarchcmd + MAXPGPATH - 1;
+	*endp = '\0';
+
+	for (sp = XLogArchiveCommand; *sp; sp++)
+	{
+		if (*sp == '%')
+		{
+			switch (sp[1])
+			{
+				case 'p':
+					/* %p: relative path of source file */
+					sp++;
+					strlcpy(dp, path, endp - dp);
+					make_native_path(dp);
+					dp += strlen(dp);
+					break;
+				case 'f':
+					/* %f: filename of source file */
+					sp++;
+					strlcpy(dp, file, endp - dp);
+					dp += strlen(dp);
+					break;
+				case '%':
+					/* convert %% to a single % */
+					sp++;
+					if (dp < endp)
+						*dp++ = *sp;
+					break;
+				default:
+					/* otherwise treat the % as not special */
+					if (dp < endp)
+						*dp++ = *sp;
+					break;
+			}
+		}
+		else
+		{
+			if (dp < endp)
+				*dp++ = *sp;
+		}
+	}
+	*dp = '\0';
+
+	ereport(DEBUG3,
+			(errmsg_internal("executing archive command \"%s\"",
+							 xlogarchcmd)));
+
+	rc = system(xlogarchcmd);
+	if (rc != 0)
+	{
+		/*
+		 * If either the shell itself, or a called command, died on a signal,
+		 * abort the archiver.  We do this because system() ignores SIGINT and
+		 * SIGQUIT while waiting; so a signal is very likely something that
+		 * should have interrupted us too.  Also die if the shell got a hard
+		 * "command not found" type of error.  If we overreact it's no big
+		 * deal, the postmaster will just start the archiver again.
+		 */
+		int			lev = wait_result_is_any_signal(rc, true) ? FATAL : LOG;
+
+		if (WIFEXITED(rc))
+		{
+			ereport(lev,
+					(errmsg("archive command failed with exit code %d",
+							WEXITSTATUS(rc)),
+					 errdetail("The failed archive command was: %s",
+							   xlogarchcmd)));
+		}
+		else if (WIFSIGNALED(rc))
+		{
+#if defined(WIN32)
+			ereport(lev,
+					(errmsg("archive command was terminated by exception 0x%X",
+							WTERMSIG(rc)),
+					 errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
+					 errdetail("The failed archive command was: %s",
+							   xlogarchcmd)));
+#else
+			ereport(lev,
+					(errmsg("archive command was terminated by signal %d: %s",
+							WTERMSIG(rc), pg_strsignal(WTERMSIG(rc))),
+					 errdetail("The failed archive command was: %s",
+							   xlogarchcmd)));
+#endif
+		}
+		else
+		{
+			ereport(lev,
+					(errmsg("archive command exited with unrecognized status %d",
+							rc),
+					 errdetail("The failed archive command was: %s",
+							   xlogarchcmd)));
+		}
+
+		return false;
+	}
+
+	elog(DEBUG1, "archived write-ahead log file \"%s\"", file);
+	return true;
+}
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 5e2c94a05f..f38e383600 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -18,6 +18,7 @@
 #include "datatype/timestamp.h"
 #include "lib/stringinfo.h"
 #include "nodes/pg_list.h"
+#include "postmaster/pgarch.h"
 #include "storage/fd.h"
 
 
@@ -157,7 +158,15 @@ extern PGDLLIMPORT int wal_level;
 /* Is WAL archiving enabled always (even during recovery)? */
 #define XLogArchivingAlways() \
 	(AssertMacro(XLogArchiveMode == ARCHIVE_MODE_OFF || wal_level >= WAL_LEVEL_REPLICA), XLogArchiveMode == ARCHIVE_MODE_ALWAYS)
-#define XLogArchiveCommandSet() (XLogArchiveCommand[0] != '\0')
+
+/*
+ * Is WAL archiving configured?  For consistency with previous releases, this
+ * checks that archive_command is set when archiving via shell is enabled.
+ * Otherwise, we just check that an archive function is set, and it is the
+ * responsibility of that archive function to ensure it is properly configured.
+ */
+#define XLogArchivingConfigured() \
+	(PG_archive && (PG_archive != shell_archive || XLogArchiveCommand[0] != '\0'))
 
 /*
  * Is WAL-logging necessary for archival or log-shipping, or can we skip
diff --git a/src/include/postmaster/pgarch.h b/src/include/postmaster/pgarch.h
index 1e47a143e1..59fefb3458 100644
--- a/src/include/postmaster/pgarch.h
+++ b/src/include/postmaster/pgarch.h
@@ -32,4 +32,10 @@ extern bool PgArchCanRestart(void);
 extern void PgArchiverMain(void) pg_attribute_noreturn();
 extern void PgArchWakeup(void);
 
+typedef bool (*PG_archive_t) (const char *file, const char *path);
+extern PGDLLIMPORT PG_archive_t PG_archive;
+
+/* in shell_archive.c */
+extern bool shell_archive(const char *file, const char *path);
+
 #endif							/* _PGARCH_H */
-- 
2.16.6

