alf: Don't create output file until the first input file is successfully crunched (avoids 0-byte turds in case of error).

1 files changed, 19 insertions, 16 deletions

diff --git a/src/alf.c b/src/alf.c
index 4fca2f3..e47320a 100644
--- a/src/alf.c
+++ b/src/alf.c
@@ -256,6 +256,13 @@ void crunch(void) {
 	update_header();
 }
 
+void make_backup(void) {
+	char bak[PATH_MAX + 2];
+	strncpy(bak, out_filename, PATH_MAX);
+	strcat(bak, "~");
+	rename(out_filename, bak);
+}
+
 void crunch_file(const char *filename) {
 	init_table();
 
@@ -284,14 +291,19 @@ void crunch_file(const char *filename) {
 	/* crunches the entire input to memory! */
 	crunch();
 
-	fwrite(output_buf, 1, output_len, out_file);
-}
+	/* don't open the output file until crunch() has succeeded once.
+	   this avoids leaving 0-byte turds */
+	if(!out_file) {
+		if(!opt_overwrite) make_backup();
+		out_file = fopen(out_filename, opt_append ? "ab" : "wb");
+		if(!out_file) {
+			fprintf(stderr, "%s: fatal: ", self);
+			perror(out_filename);
+			exit(1);
+		}
+	}
 
-void make_backup(void) {
-	char bak[PATH_MAX + 2];
-	strncpy(bak, out_filename, PATH_MAX);
-	strcat(bak, "~");
-	rename(out_filename, bak);
+	fwrite(output_buf, 1, output_len, out_file);
 }
 
 void usage(void) {
@@ -339,15 +351,6 @@ int main(int argc, char **argv) {
 		exit(1);
 	}
 
-	if(!opt_overwrite) make_backup();
-
-	out_file = fopen(out_filename, opt_append ? "ab" : "wb");
-	if(!out_file) {
-		fprintf(stderr, "%s: fatal: ", self);
-		perror(out_filename);
-		exit(1);
-	}
-
 	while(optind < argc) {
 		crunch_file(argv[optind++]);
 	}