Skip .DS_Store files in server side utils

The macOS Finder application creates .DS_Store files in directories
when opened,  which creates problems for serverside utilities which
expect all files to be PostgreSQL specific files.  Skip these files
when encountered in pg_checksums, pg_rewind and pg_basebackup.

This was extracted from a larger patchset for skipping hidden files
and system files, where the concencus was to just skip these. Since
this is equally likely to happen in every version, backpatch to all
supported versions.

Reported-by: Mark Guertin <markguertin@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Tobias Bussmann <t.bussmann@gmx.net>
Discussion: https://postgr.es/m/E258CE50-AB0E-455D-8AAD-BB4FE8F882FB@gmail.com
Backpatch-through: v12

doc/src/sgml/protocol.sgml

@@ -3127,7 +3127,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
          <para>
           Files other than regular files and directories, such as symbolic
           links (other than for the directories listed above) and special
-          device files, are skipped.  (Symbolic links
+          device and operating system files, are skipped.  (Symbolic links
           in <filename>pg_tblspc</filename> are maintained.)
          </para>
         </listitem>

doc/src/sgml/ref/pg_basebackup.sgml

@@ -965,7 +965,8 @@ PostgreSQL documentation
    The backup will include all files in the data directory and tablespaces,
    including the configuration files and any additional files placed in the
    directory by third parties, except certain temporary files managed by
-   PostgreSQL.  But only regular files and directories are copied, except that
+   PostgreSQL and operating system files.  But only regular files and
+   directories are copied, except that
    symbolic links used for tablespaces are preserved.  Symbolic links pointing
    to certain directories known to PostgreSQL are copied as empty directories.
    Other symbolic links and special device files are skipped.

doc/src/sgml/ref/pg_rewind.sgml

@@ -403,8 +403,9 @@ GRANT EXECUTE ON function pg_catalog.pg_read_binary_file(text, bigint, bigint, b
       <filename>backup_label</filename>,
       <filename>tablespace_map</filename>,
       <filename>pg_internal.init</filename>,
-      <filename>postmaster.opts</filename>, and
-      <filename>postmaster.pid</filename>, as well as any file or directory
+      <filename>postmaster.opts</filename>,
+      <filename>postmaster.pid</filename> and
+      <filename>.DS_Store</filename> as well as any file or directory
       beginning with <filename>pgsql_tmp</filename>, are omitted.
      </para>
     </step>

src/backend/backup/basebackup.c

@@ -1265,6 +1265,10 @@ sendDir(bbsink *sink, const char *path, int basepathlen, bool sizeonly,
 					strlen(PG_TEMP_FILE_PREFIX)) == 0)
 			continue;
 
+		/* Skip macOS system files */
+		if (strcmp(de->d_name, ".DS_Store") == 0)
+			continue;
+
 		/*
 		 * Check if the postmaster has signaled us to exit, and abort with an
 		 * error in that case. The error handler further up will call

src/bin/pg_basebackup/t/010_pg_basebackup.pl

@@ -3,6 +3,7 @@
 
 use strict;
 use warnings FATAL => 'all';
+use Config;
 use File::Basename qw(basename dirname);
 use File::Path     qw(rmtree);
 use PostgreSQL::Test::Cluster;
@@ -179,6 +180,16 @@ foreach my $filename (
 	close $file;
 }
 
+# Test that macOS system files are skipped. Only test on non-macOS systems
+# however since creating incorrect .DS_Store files on a macOS system may have
+# unintended side effects.
+if ($Config{osname} ne 'darwin')
+{
+	open my $file, '>>', "$pgdata/.DS_Store";
+	print $file "DONOTCOPY";
+	close $file;
+}
+
 # Connect to a database to create global/pg_internal.init.  If this is removed
 # the test to ensure global/pg_internal.init is not copied will return a false
 # positive.
@@ -248,6 +259,12 @@ foreach my $filename (
 	ok(!-f "$tempdir/backup/$filename", "$filename not copied");
 }
 
+# We only test .DS_Store files being skipped on non-macOS systems
+if ($Config{osname} ne 'darwin')
+{
+	ok(!-f "$tempdir/backup/.DS_Store", ".DS_Store not copied");
+}
+
 # Unlogged relation forks other than init should not be copied
 ok(-f "$tempdir/backup/${baseUnloggedPath}_init",
 	'unlogged init fork in backup');

src/bin/pg_checksums/pg_checksums.c

@@ -329,6 +329,10 @@ scan_directory(const char *basedir, const char *subdir, bool sizeonly)
 					strlen(PG_TEMP_FILES_DIR)) == 0)
 			continue;
 
+		/* Skip macOS system files */
+		if (strcmp(de->d_name, ".DS_Store") == 0)
+			continue;
+
 		snprintf(fn, sizeof(fn), "%s/%s", path, de->d_name);
 		if (lstat(fn, &st) < 0)
 			pg_fatal("could not stat file \"%s\": %m", fn);

src/bin/pg_checksums/t/002_actions.pl

@@ -6,6 +6,7 @@
 
 use strict;
 use warnings FATAL => 'all';
+use Config;
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 
@@ -114,6 +115,12 @@ append_to_file "$pgdata/global/pgsql_tmp/1.1", "foo";
 append_to_file "$pgdata/global/pg_internal.init", "foo";
 append_to_file "$pgdata/global/pg_internal.init.123", "foo";
 
+# These are non-postgres macOS files, which should be ignored by the scan.
+# Only perform this test on non-macOS systems though as creating incorrect
+# system files may have side effects on macOS.
+append_to_file "$pgdata/global/.DS_Store", "foo"
+	unless ($Config{osname} eq 'darwin');
+
 # Enable checksums.
 command_ok([ 'pg_checksums', '--enable', '--no-sync', '-D', $pgdata ],
 	"checksums successfully enabled in cluster");

src/bin/pg_rewind/filemap.c

@@ -647,6 +647,10 @@ decide_file_action(file_entry_t *entry)
 	if (strcmp(path, "global/pg_control") == 0)
 		return FILE_ACTION_NONE;
 
+	/* Skip macOS system files */
+	if (strstr(path, ".DS_Store") != NULL)
+		return FILE_ACTION_NONE;
+
 	/*
 	 * Remove all files matching the exclusion filters in the target.
 	 */

src/bin/pg_rewind/t/003_extrafiles.pl

@@ -5,6 +5,7 @@
 
 use strict;
 use warnings FATAL => 'all';
+use Config;
 use PostgreSQL::Test::Utils;
 use Test::More;
 
@@ -53,6 +54,10 @@ sub run_test
 	append_to_file
 	  "$test_standby_datadir/tst_standby_dir/standby_subdir/standby_file4",
 	  "in standby4";
+	# Skip testing .DS_Store files on macOS to avoid risk of side effects
+	append_to_file
+	  "$test_standby_datadir/tst_standby_dir/.DS_Store",
+	  "macOS system file" unless ($Config{osname} eq 'darwin');
 
 	mkdir "$test_primary_datadir/tst_primary_dir";
 	append_to_file "$test_primary_datadir/tst_primary_dir/primary_file1",