Undo inadvertent loosening of archive filename checking.

Commit c8a350a439 attempted to consolidate
code for identify possibly-compressed tar archives by suffix into a new
function parse_tar_compress_algorithm(). Unfortunately, the refactoring
wasn't perfect, and slightly changed the behavior at both existing call
sites.

In CreateBackupStreamer(), the previous code required the filename to
consist of more than just a suffix, so the aforementioned commit had the
effect of allowing pg_basebackup to accept a file from the server whose
entire name was something like .tar.gz -- which should never happen, but
let's reject it as previous releases did.

In precheck_tar_backup_file(), the previous code required the suffix to
be immediately adjacent to the prefix already checked, so the commit
in question allowed pg_verifybackup to accept not only filenames like
base.tar.gz but also filenames like baseFOOBARBAZ.tar.gz. While such
filenames are perhaps unlikely, rejecting them is correct, so let's go
back to that behavior.

Discussion: http://postgr.es/m/CA+TgmoYJY8FkoeYKGF_YF1S6uOK7fd0Bd3zrw0XY_oZXbmVFpQ@mail.gmail.com
Reported-by: Sarath Kumar <Sarath@iitmpravartak.net>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Backpatch-through: 19

src/bin/pg_basebackup/pg_basebackup.c

@@ -1082,8 +1082,8 @@ CreateBackupStreamer(char *archive_name, char *spclocation,
 	inject_manifest = (format == 't' && strcmp(basedir, "-") == 0 && manifest);
 
 	/* Check whether it is a tar archive and its compression type */
-	is_tar = parse_tar_compress_algorithm(archive_name,
-										  &compressed_tar_algorithm);
+	is_tar = (parse_tar_compress_algorithm(archive_name,
+										   &compressed_tar_algorithm) > 0);
 
 	/* Is this any kind of compressed tar? */
 	is_compressed_tar = (is_tar &&

src/bin/pg_verifybackup/pg_verifybackup.c

@@ -967,8 +967,12 @@ precheck_tar_backup_file(verifier_context *context, char *relpath,
 		tblspc_oid = (Oid) num;
 	}
 
-	/* Now, check the compression type of the tar */
-	if (!parse_tar_compress_algorithm(suffix, &compress_algorithm))
+	/*
+	 * If parse_tar_compress_algorithm returns exactly 0, there are no
+	 * characters between the prefix we already checked and the detected
+	 * suffix. Any other case is unexpected.
+	 */
+	if (parse_tar_compress_algorithm(suffix, &compress_algorithm) != 0)
 	{
 		report_backup_error(context,
 							"file \"%s\" is not expected in a tar format backup",

src/bin/pg_waldump/pg_waldump.c

@@ -1242,7 +1242,7 @@ main(int argc, char **argv)
 	if (waldir != NULL)
 	{
 		/* Check whether the path looks like a tar archive by its extension */
-		if (parse_tar_compress_algorithm(waldir, &compression))
+		if (parse_tar_compress_algorithm(waldir, &compression) >= 0)
 		{
 			split_path(waldir, &private.archive_dir, &private.archive_name);
 		}
@@ -1286,7 +1286,8 @@ main(int argc, char **argv)
 				pg_fatal("could not open directory \"%s\": %m", waldir);
 		}
 
-		if (fname != NULL && parse_tar_compress_algorithm(fname, &compression))
+		if (fname != NULL &&
+			parse_tar_compress_algorithm(fname, &compression) >= 0)
 		{
 			private.archive_dir = waldir;
 			private.archive_name = fname;

src/common/compression.c

@@ -42,33 +42,47 @@ static bool expect_boolean_value(char *keyword, char *value,
 								 pg_compress_specification *result);
 
 /*
- * Look up a compression algorithm by archive file extension. Returns true and
- * sets *algorithm if the extension is recognized. Otherwise returns false.
+ * Look up a compression algorithm by archive file extension. Sets *algorithm
+ * and returns the length of the non-extension portion of the filename, or -1
+ * if the filename does not end with a recognized tar extension.
  */
-bool
+int
 parse_tar_compress_algorithm(const char *fname, pg_compress_algorithm *algorithm)
 {
-	size_t		fname_len = strlen(fname);
+	int			fname_len = strlen(fname);
 
 	if (fname_len >= 4 &&
 		strcmp(fname + fname_len - 4, ".tar") == 0)
+	{
 		*algorithm = PG_COMPRESSION_NONE;
+		return fname_len - 4;
+	}
 	else if (fname_len >= 4 &&
 			 strcmp(fname + fname_len - 4, ".tgz") == 0)
+	{
 		*algorithm = PG_COMPRESSION_GZIP;
+		return fname_len - 4;
+	}
 	else if (fname_len >= 7 &&
 			 strcmp(fname + fname_len - 7, ".tar.gz") == 0)
+	{
 		*algorithm = PG_COMPRESSION_GZIP;
+		return fname_len - 7;
+	}
 	else if (fname_len >= 8 &&
 			 strcmp(fname + fname_len - 8, ".tar.lz4") == 0)
+	{
 		*algorithm = PG_COMPRESSION_LZ4;
+		return fname_len - 8;
+	}
 	else if (fname_len >= 8 &&
 			 strcmp(fname + fname_len - 8, ".tar.zst") == 0)
+	{
 		*algorithm = PG_COMPRESSION_ZSTD;
-	else
-		return false;
+		return fname_len - 8;
+	}
 
-	return true;
+	return -1;
 }
 
 /*

src/include/common/compression.h

@@ -41,7 +41,7 @@ typedef struct pg_compress_specification
 
 extern void parse_compress_options(const char *option, char **algorithm,
 								   char **detail);
-extern bool parse_tar_compress_algorithm(const char *fname,
+extern int	parse_tar_compress_algorithm(const char *fname,
 										 pg_compress_algorithm *algorithm);
 extern bool parse_compress_algorithm(char *name, pg_compress_algorithm *algorithm);
 extern const char *get_compress_algorithm_name(pg_compress_algorithm algorithm);