[hackers] [sbase][PATCH] tar: meaningful error messages

[willy]

Hello everyone,

here is a patch to give more details about the "malformed tar archive"
message that pops up when chktar() fails.

diff --git a/tar.c b/tar.c
index 71719b0..4a81f8f 100644
--- a/tar.c
+++ b/tar.c
@@ -29,6 +29,12 @@ enum Type {
        RESERVED  = '7'
 };
 
+enum Error {
+       BADCHKSUM,
+       BADMAGIC,
+       BADPATH
+};
+
 struct header {
        char name[100];
        char mode[8];
@@ -71,6 +77,12 @@ static const char *filtertools[] = {
        ['z'] = "gzip",
 };
 
+static const char *errors[] = {
+       [BADCHKSUM] = "bad checksum",
+       [BADMAGIC]  = "bad magic",
+       [BADPATH]   = "empty filename"
+};
+
 static void
 pushdirtime(char *name, time_t mtime)
 {
@@ -407,27 +419,36 @@ chktar(struct header *h)
        char tmp[8], *err;
        char *p = (char *)h;
        long s1, s2, i;
+       int errnum;
 
-       if (h->prefix[0] == '\0' && h->name[0] == '\0')
+       if (h->prefix[0] == '\0' && h->name[0] == '\0') {
+               errnum = BADPATH;
                goto bad;
-       if (h->magic[0] && strncmp("ustar", h->magic, 5))
+       }
+       if (h->magic[0] && strncmp("ustar", h->magic, 5)) {
+               errnum = BADMAGIC;
                goto bad;
+       }
        memcpy(tmp, h->chksum, sizeof(tmp));
        for (i = 0; i < sizeof(tmp); i++)
                if (tmp[i] == ' ')
                        tmp[i] = '\0';
        s1 = strtol(tmp, &err, 8);
-       if (s1 < 0 || *err != '\0')
+       if (s1 < 0 || *err != '\0') {
+               errnum = BADCHKSUM;
                goto bad;
+       }
        memset(h->chksum, ' ', sizeof(h->chksum));
        for (i = 0, s2 = 0; i < sizeof(*h); i++)
                s2 += (unsigned char)p[i];
-       if (s1 != s2)
+       if (s1 != s2) {
+               errnum = BADCHKSUM;
                goto bad;
+       }
        memcpy(h->chksum, tmp, sizeof(h->chksum));
        return;
 bad:
-       eprintf("malformed tar archive\n");
+       eprintf("malformed tar archive: %s\n", errors[errnum]);
 }
 
 static void