(MAXSIZE): New macro.

(xreadlink): Use it instead of SSIZE_MAX.  Ensure initial buffer
size does not exceed MAXSIZE.  Avoid cast.
As suggested by Mark D. Baushke in
<http://lists.gnu.org/archive/html/bug-gnulib/2004-11/msg00009.html>,
if readlink fails with buffer size just under MAXSIZE, try again
with MAXSIZE.

diff --git a/lib/xreadlink.c b/lib/xreadlink.c
index 2e66c07f240791c8c1b05609da58ca58e6dd3b34..c38e2d3aad892630f37d84b906b272f93ad7f925 100644 (file)
--- a/lib/xreadlink.c
+++ b/lib/xreadlink.c
@@ -41,6 +41,8 @@
 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
 #endif
 
+#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
+
 #include "xalloc.h"
 
 /* Call readlink to get the symbolic link value of FILENAME.
@@ -56,14 +58,15 @@ xreadlink (char const *filename, size_t size)
 {
   /* The initial buffer size for the link value.  A power of 2
      detects arithmetic overflow earlier, but is not required.  */
-  size_t buf_size = size + 1;
+  size_t buf_size = size < MAXSIZE ? size + 1 : MAXSIZE;
 
   while (1)
     {
       char *buffer = xmalloc (buf_size);
-      ssize_t link_length = readlink (filename, buffer, buf_size);
+      ssize_t r = readlink (filename, buffer, buf_size);
+      size_t link_length = r;
 
-      if (link_length < 0)
+      if (r < 0)
        {
          int saved_errno = errno;
          free (buffer);
@@ -71,15 +74,18 @@ xreadlink (char const *filename, size_t size)
          return NULL;
        }
 
-      if ((size_t) link_length < buf_size)
+      if (link_length < buf_size)
        {
          buffer[link_length] = 0;
          return buffer;
        }
 
       free (buffer);
-      buf_size *= 2;
-      if (! (0 < buf_size && buf_size <= SSIZE_MAX))
+      if (buf_size <= MAXSIZE / 2)
+       buf_size *= 2;
+      else if (buf_size < MAXSIZE)
+       buf_size = MAXSIZE;
+      else
        xalloc_die ();
     }
 }