Re: gzip --force bug

[Mark Adler]

On Feb 3, 2010, at 8:19 AM, Mark Adler wrote:
> Below is a patch to the patch.
> 
> A test case will be forthcoming (I need to create a case that delicately 
> crosses a buffer boundary).  Once I get a test case working, you can push it.

Jim,

It turns out that is no condition in which the lack of the patch to the patch 
causes a problem.  So I have no test case for it.  I will leave the patch to 
the patch in nevertheless, since otherwise it still looks like a bug.

I fixed some other problems with how bytes_in is handled.  An updated total 
patch relative to 1.4 is below.  This patch is final.

Mark


--- gzip-1.4.c  2010-01-03 09:26:02.000000000 -0800
+++ gzip.c      2010-02-03 18:41:08.000000000 -0800
@@ -1239,6 +1239,7 @@
 {
     uch flags;     /* compression flags */
     char magic[2]; /* magic header */
+    int imagic0;   /* first magic byte or EOF */
     int imagic1;   /* like magic[1], but can represent EOF */
     ulg stamp;     /* time stamp */
 
@@ -1246,12 +1247,14 @@
      * premature end of file: use try_byte instead of get_byte.
      */
     if (force && to_stdout) {
-        magic[0] = (char)try_byte();
+        imagic0 = try_byte();
+        magic[0] = (char) imagic0;
         imagic1 = try_byte ();
         magic[1] = (char) imagic1;
         /* If try_byte returned EOF, magic[1] == (char) EOF.  */
     } else {
         magic[0] = (char)get_byte();
+        imagic0 = 0;
         if (magic[0]) {
             magic[1] = (char)get_byte();
             imagic1 = 0; /* avoid lint warning */
@@ -1395,8 +1398,13 @@
     } else if (force && to_stdout && !list) { /* pass input unchanged */
         method = STORED;
         work = copy;
-        inptr = 0;
+        if (imagic1 != EOF)
+            inptr--;
         last_member = 1;
+        if (imagic0 != EOF) {
+            write_buf(fileno(stdout), magic, 1);
+            bytes_out++;
+        }
     }
     if (method >= 0) return method;
 
--- util-1.4.c  2010-01-03 09:26:02.000000000 -0800
+++ util.c      2010-02-03 18:29:59.000000000 -0800
@@ -44,21 +44,25 @@
 
 /* ===========================================================================
  * Copy input to output unchanged: zcat == cat with --force.
- * IN assertion: insize bytes have already been read in inbuf.
+ * IN assertion: insize bytes have already been read in inbuf and inptr bytes
+ * already processed or copied.
  */
 int copy(in, out)
     int in, out;   /* input and output file descriptors */
 {
+    int got;
+
     errno = 0;
-    while (insize != 0 && (int)insize != -1) {
-        write_buf(out, (char*)inbuf, insize);
-        bytes_out += insize;
-        insize = read_buffer (in, (char *) inbuf, INBUFSIZ);
-    }
-    if ((int)insize == -1) {
-        read_error();
+    while (insize > inptr) {
+        write_buf(out, (char*)inbuf + inptr, insize - inptr);
+        bytes_out += insize - inptr;
+        got = read_buffer (in, (char *) inbuf, INBUFSIZ);
+        if (got == -1)
+            read_error();
+        bytes_in += got;
+        insize = (unsigned)got;
+        inptr = 0;
     }
-    bytes_in = bytes_out;
     return OK;
 }