xreadlink: Rewrite as a simple mreadlink wrapper.

[Jim Meyering]

I did most of this weeks ago and just noticed I never checked it in.
Ok with you, Bruno?

        Rewrite xreadlink as a trivial mreadlink wrapper.
        * lib/xreadlink.c (xreadlink): Rewrite as a simple mreadlink wrapper.
        * modules/xreadlink: Adjust dependencies.

Index: lib/xreadlink.c
===================================================================
RCS file: /cvsroot/gnulib/gnulib/lib/xreadlink.c,v
retrieving revision 1.26
diff -u -p -r1.26 xreadlink.c
--- lib/xreadlink.c     3 Mar 2007 19:20:41 -0000       1.26
+++ lib/xreadlink.c     23 Aug 2007 11:35:05 -0000
@@ -25,7 +25,6 @@
 /* Specification.  */
 #include "xreadlink.h"

-#include <stdio.h>
 #include <string.h>
 #include <errno.h>
 #include <limits.h>
@@ -40,92 +39,18 @@
 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
 #endif

-#ifdef NO_XMALLOC
-# define xmalloc malloc
-#else
-# include "xalloc.h"
-#endif
+#include "mreadlink.h"
+#include "xalloc.h"

-/* Call readlink to get the symbolic link value of FILENAME.
-   Return a pointer to that NUL-terminated string in malloc'd storage.
-   If readlink fails, return NULL (caller may use errno to diagnose).
-   If realloc fails, or if the link value is longer than SIZE_MAX :-),
-   give a diagnostic and exit.  */
+/* Call mreadlink to get the symbolic link value of FILENAME in malloc'd
+   storage.  If mreadlink fails, call xalloc_die.  Otherwise, return
+   the malloc'd string.  */

 char *
 xreadlink (char const *filename)
 {
-  /* The initial buffer size for the link value.  A power of 2
-     detects arithmetic overflow earlier, but is not required.  */
-#define INITIAL_BUF_SIZE 1024
-
-  /* Allocate the initial buffer on the stack.  This way, in the common
-     case of a symlink of small size, we get away with a single small malloc()
-     instead of a big malloc() followed by a shrinking realloc().  */
-  char initial_buf[INITIAL_BUF_SIZE];
-
-  char *buffer = initial_buf;
-  size_t buf_size = sizeof (initial_buf);
-
-  while (1)
-    {
-      /* Attempt to read the link into the current buffer.  */
-      ssize_t link_length = readlink (filename, buffer, buf_size);
-
-      /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
-        with errno == ERANGE if the buffer is too small.  */
-      if (link_length < 0 && errno != ERANGE)
-       {
-         if (buffer != initial_buf)
-           {
-             int saved_errno = errno;
-             free (buffer);
-             errno = saved_errno;
-           }
-         return NULL;
-       }
-
-      if ((size_t) link_length < buf_size)
-       {
-         buffer[link_length++] = '\0';
-
-         /* Return it in a chunk of memory as small as possible.  */
-         if (buffer == initial_buf)
-           {
-             buffer = (char *) xmalloc (link_length);
-#ifdef NO_XMALLOC
-             if (buffer == NULL)
-               return NULL;
-#endif
-             memcpy (buffer, initial_buf, link_length);
-           }
-         else
-           {
-             /* Shrink buffer before returning it.  */
-             if ((size_t) link_length < buf_size)
-               {
-                 char *smaller_buffer = (char *) realloc (buffer, link_length);
-
-                 if (smaller_buffer != NULL)
-                   buffer = smaller_buffer;
-               }
-           }
-         return buffer;
-       }
-
-      if (buffer != initial_buf)
-       free (buffer);
-      buf_size *= 2;
-      if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
-#ifdef NO_XMALLOC
-       return NULL;
-#else
-       xalloc_die ();
-#endif
-      buffer = (char *) xmalloc (buf_size);
-#ifdef NO_XMALLOC
-      if (buffer == NULL)
-       return NULL;
-#endif
-    }
+  char *p = mreadlink (filename);
+  if (p == NULL)
+    xalloc_die ();
+  return p;
 }
Index: modules/xreadlink
===================================================================
RCS file: /cvsroot/gnulib/gnulib/modules/xreadlink,v
retrieving revision 1.15
diff -u -p -r1.15 xreadlink
--- modules/xreadlink   3 Mar 2007 19:20:41 -0000       1.15
+++ modules/xreadlink   23 Aug 2007 11:35:05 -0000
@@ -1,15 +1,13 @@
 Description:
-Reading symbolic links without size limitation.
+Read symbolic links without size limitation.

 Files:
 lib/xreadlink.h
 lib/xreadlink.c

 Depends-on:
-readlink
-ssize_t
-unistd
-xalloc
+mreadlink
+xalloc-die

 configure.ac: