listamsb: more warnings for bad files.

1 files changed, 24 insertions, 5 deletions

diff --git a/listamsb.c b/listamsb.c
index 11c7efa..efa0621 100644
--- a/listamsb.c
+++ b/listamsb.c
@@ -23,6 +23,13 @@
    even with cart-based AMSB2 and no DOS loaded. */
 #define MAX_PROGLEN 30000
 
+/* a program whose header has a length less than this can't be
+   a real AMSB program. The minimum size is what you get if you
+   SAVE when there's no program in memory (right after boot or
+   a NEW). The minimum size for a program that actually contains
+   code seems to be 5 (for 10 PRINT) */
+#define MIN_PROGLEN 2
+
 const char *self;
 
 char pipe_command[BUFSIZ + 1] = { "a8cat" };
@@ -77,13 +84,23 @@ int read_header(void) {
 	int proglen;
 
 	b = read_byte();
-	if(b) die("first byte not $00, not an AMSB file");
+	if(b) die("not an AMSB file: first byte not $00");
 
 	proglen = read_word();
 
+	if(verbose)
+		fprintf(stderr, "proglen == %d (%04x)\n", proglen, proglen);
+
 	if(proglen > MAX_PROGLEN) {
-		fprintf(stderr, "%s: program too big (%d bytes), won't fit in Atari memory\n",
+		fprintf(stderr, "%s: not an AMSB file: too big (%d bytes), won't fit in Atari memory\n",
 				self, proglen);
+		exit(1);
+	}
+
+	if(proglen < MIN_PROGLEN) {
+		fprintf(stderr, "%s: not an AMSB file: program size in header too small (%d)\n",
+				self, proglen);
+		exit(1);
 	}
 
 	return proglen;
@@ -266,8 +283,6 @@ int main(int argc, char **argv) {
 	open_output();
 
 	proglen = read_header();
-	if(verbose)
-		fprintf(stderr, "proglen == %d (%04x)\n", proglen, proglen);
 
 	while( (lineno = next_line()) != -1 )
 		if(verbose)
@@ -280,7 +295,11 @@ int main(int argc, char **argv) {
 		if(verbose)
 			fprintf(stderr, "file size matches proglen\n");
 	} else {
-		fprintf(stderr, "%s: trailing garbage at EOF\n", self);
+		fprintf(stderr, "%s: file size doesn't match length in header\n", self);
+	}
+
+	if(fgetc(infile) != EOF) {
+		fprintf(stderr, "%s: trailing garbage at end of file\n", self);
 	}
 
 	if(unknowns) {