Re: gzip --force bug

[Jim Meyering]

Mark Adler wrote:
>> 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 may have encountered this already
when I was trying to create a compressed file
of size one smaller than gzip's internal buffer size.
It appeared to be impossible.

Here's the output of "git format-patch --stdout -1"
for that patch.  I'll push it today.

>From 1204630c96e0c368b4325f95cbaef95c3f9c482a Mon Sep 17 00:00:00 2001
From: Mark Adler <address@hidden>
Date: Wed, 3 Feb 2010 10:11:33 +0100
Subject: [PATCH] gzip -cdf now handles concatenation of gzip'd and uncompressed 
data

* util.c (copy): Change semantics so as to honor a decremented inptr.
* gzip.c (get_method): When needed (-cdf), decrement inptr rather
than clearing it -- and output the first magic byte.
---
 gnulib |    2 +-
 gzip.c |   12 ++++++++++--
 util.c |   22 +++++++++++++---------
 3 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/gnulib b/gnulib
index a5b5500..9d0ad65 160000
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit a5b5500500ba4d6aaa9a1b3bb214f6917dc1ac3c
+Subproject commit 9d0ad652de159d08e5f679842f8a2a5658196361
diff --git a/gzip.c b/gzip.c
index f523be7..141397e 100644
--- a/gzip.c
+++ b/gzip.c
@@ -1239,6 +1239,7 @@ local int get_method(in)
 {
     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 @@ local int get_method(in)
      * 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 @@ local int get_method(in)
     } 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;

diff --git a/util.c b/util.c
index 1de2701..80b1075 100644
--- a/util.c
+++ b/util.c
@@ -44,21 +44,25 @@ extern ulg crc_32_tab[];   /* crc table, defined below */

 /* ===========================================================================
  * 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;
 }

--
1.7.0.rc1.193.ge8618