areadlinkat: new module

* lib/at-func.c (FUNC_FAIL): New define.
(AT_FUNC_NAME, VALIDATE_FLAG): Use it rather than raw -1.
* modules/areadlinkat: New module.
* lib/linkat.c (areadlinkat): Move...
* lib/areadlinkat.c (areadlinkat): ...to new file.
* lib/areadlink.h (areadlinkat): Declare it.
* modules/linkat (Depends-on): Add areadlinkat.
* MODULES.html.sh (File system functions): Mention it.
* modules/areadlinkat-tests: New test.
* tests/test-areadlinkat.c: New file.

Signed-off-by: Eric Blake <ebb9@byu.net>

11 files changed, 313 insertions, 83 deletions

diff --git a/ChangeLog b/ChangeLog
index 9a3148e946..0ac3c88e0c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2009-10-07  Eric Blake  <ebb9@byu.net>
 
+	areadlinkat: new module
+	* lib/at-func.c (FUNC_FAIL): New define.
+	(AT_FUNC_NAME, VALIDATE_FLAG): Use it rather than raw -1.
+	* modules/areadlinkat: New module.
+	* lib/linkat.c (areadlinkat): Move...
+	* lib/areadlinkat.c (areadlinkat): ...to new file.
+	* lib/areadlink.h (areadlinkat): Declare it.
+	* modules/linkat (Depends-on): Add areadlinkat.
+	* MODULES.html.sh (File system functions): Mention it.
+	* modules/areadlinkat-tests: New test.
+	* tests/test-areadlinkat.c: New file.
+
 	areadlink, areadlink-with-size: add tests
 	* modules/areadlink-tests: New test.
 	* modules/areadlink-with-size-tests: Likewise.
diff --git a/MODULES.html.sh b/MODULES.html.sh
index ee13eec585..b418ab621f 100755
--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -2448,6 +2448,7 @@ func_all_modules ()
   func_module acl
   func_module areadlink
   func_module areadlink-with-size
+  func_module areadlinkat
   func_module backupfile
   func_module canonicalize
   func_module canonicalize-lgpl
diff --git a/lib/areadlink.h b/lib/areadlink.h
index 8720ed9a61..580276188b 100644
--- a/lib/areadlink.h
+++ b/lib/areadlink.h
@@ -1,6 +1,7 @@
 /* Read symbolic links without size limitation.
 
-   Copyright (C) 2001, 2003, 2004, 2007 Free Software Foundation, Inc.
+   Copyright (C) 2001, 2003, 2004, 2007, 2009 Free Software
+   Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -21,3 +22,7 @@
 
 extern char *areadlink (char const *filename);
 extern char *areadlink_with_size (char const *filename, size_t size_hint);
+
+#if GNULIB_AREADLINKAT
+extern char *areadlinkat (int fd, char const *filename);
+#endif
diff --git a/lib/areadlinkat.c b/lib/areadlinkat.c
new file mode 100644
index 0000000000..5e8bf9d2ab
--- /dev/null
+++ b/lib/areadlinkat.c
@@ -0,0 +1,143 @@
+/* areadlink.c -- readlink wrapper to return the link name in malloc'd storage
+   Unlike xreadlinkat, only call exit on failure to change directory.
+
+   Copyright (C) 2001, 2003-2007, 2009 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Jim Meyering <jim@meyering.net>,
+   and Bruno Haible <bruno@clisp.org>,
+   and Eric Blake <ebb9@byu.net>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "areadlink.h"
+
+#include <string.h>
+#include <errno.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#ifndef SSIZE_MAX
+# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
+#endif
+
+#if HAVE_READLINKAT
+
+/* Call readlinkat to get the symbolic link value of FILENAME relative to FD.
+   Return a pointer to that NUL-terminated string in malloc'd storage.
+   If readlinkat fails, return NULL and set errno (although failure to
+   change directory will issue a diagnostic and exit).
+   If realloc fails, or if the link value is longer than SIZE_MAX :-),
+   return NULL and set errno to ENOMEM.  */
+
+char *
+areadlinkat (int fd, 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 = readlinkat (fd, 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 *) malloc (link_length);
+              if (buffer == NULL)
+                /* errno is ENOMEM.  */
+                return NULL;
+              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))
+        {
+          errno = ENOMEM;
+          return NULL;
+        }
+      buffer = (char *) malloc (buf_size);
+      if (buffer == NULL)
+        /* errno is ENOMEM.  */
+        return NULL;
+    }
+}
+
+#else /* !HAVE_READLINKAT */
+
+/* It is more efficient to change directories only once and call
+   areadlink, rather than repeatedly call the replacement
+   readlinkat.  */
+
+# define AT_FUNC_NAME areadlinkat
+# define AT_FUNC_F1 areadlink
+# define AT_FUNC_POST_FILE_PARAM_DECLS /* empty */
+# define AT_FUNC_POST_FILE_ARGS        /* empty */
+# define AT_FUNC_RESULT char *
+# define AT_FUNC_FAIL NULL
+# include "at-func.c"
+# undef AT_FUNC_NAME
+# undef AT_FUNC_F1
+# undef AT_FUNC_POST_FILE_PARAM_DECLS
+# undef AT_FUNC_POST_FILE_ARGS
+# undef AT_FUNC_RESULT
+# undef AT_FUNC_FAIL
+
+#endif /* !HAVE_READLINKAT */
diff --git a/lib/at-func.c b/lib/at-func.c
index 373b5f6bcb..b6aa0fd550 100644
--- a/lib/at-func.c
+++ b/lib/at-func.c
@@ -30,7 +30,7 @@
   if (flag & ~AT_FUNC_USE_F1_COND)		\
     {						\
       errno = EINVAL;				\
-      return -1;				\
+      return FUNC_FAIL;				\
     }
 #else
 # define CALL_FUNC(F) (AT_FUNC_F1 (F AT_FUNC_POST_FILE_ARGS))
@@ -43,11 +43,18 @@
 # define FUNC_RESULT int
 #endif
 
+#ifdef AT_FUNC_FAIL
+# define FUNC_FAIL AT_FUNC_FAIL
+#else
+# define FUNC_FAIL -1
+#endif
+
 /* Call AT_FUNC_F1 to operate on FILE, which is in the directory
    open on descriptor FD.  If AT_FUNC_USE_F1_COND is defined to a value,
    AT_FUNC_POST_FILE_PARAM_DECLS must inlude a parameter named flag;
    call AT_FUNC_F2 if FLAG is 0 or fail if FLAG contains more bits than
-   AT_FUNC_USE_F1_COND.  If possible, do it without changing the
+   AT_FUNC_USE_F1_COND.  Return int and fail with -1 unless AT_FUNC_RESULT
+   or AT_FUNC_FAIL are defined.  If possible, do it without changing the
    working directory.  Otherwise, resort to using save_cwd/fchdir,
    then AT_FUNC_F?/restore_cwd.  If either the save_cwd or the restore_cwd
    fails, then give a diagnostic and exit nonzero.  */
@@ -96,7 +103,7 @@ AT_FUNC_NAME (int fd, char const *file AT_FUNC_POST_FILE_PARAM_DECLS)
          begin with.  */
       free_cwd (&saved_cwd);
       errno = EBADF;
-      return -1;
+      return FUNC_FAIL;
     }
 
   if (fchdir (fd) != 0)
@@ -104,7 +111,7 @@ AT_FUNC_NAME (int fd, char const *file AT_FUNC_POST_FILE_PARAM_DECLS)
       saved_errno = errno;
       free_cwd (&saved_cwd);
       errno = saved_errno;
-      return -1;
+      return FUNC_FAIL;
     }
 
   err = CALL_FUNC (file);
@@ -121,3 +128,4 @@ AT_FUNC_NAME (int fd, char const *file AT_FUNC_POST_FILE_PARAM_DECLS)
 }
 #undef CALL_FUNC
 #undef FUNC_RESULT
+#undef FUNC_FAIL
diff --git a/lib/linkat.c b/lib/linkat.c
index e0dd8f2867..524ddde6a0 100644
--- a/lib/linkat.c
+++ b/lib/linkat.c
@@ -189,83 +189,6 @@ linkat (int fd1, char const *file1, int fd2, char const *file2, int flag)
 
 # undef linkat
 
-/* Read a symlink, like areadlink, but relative to FD.  */
-
-static char *
-areadlinkat (int fd, 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 = readlinkat (fd, 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 *) malloc (link_length);
-              if (buffer == NULL)
-                /* errno is ENOMEM.  */
-                return NULL;
-              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))
-        {
-          errno = ENOMEM;
-          return NULL;
-        }
-      buffer = (char *) malloc (buf_size);
-      if (buffer == NULL)
-        /* errno is ENOMEM.  */
-        return NULL;
-    }
-}
-
 /* Create a link.  If FILE1 is a symlink, create a hardlink to the
    canonicalized file.  */
 
diff --git a/modules/areadlinkat b/modules/areadlinkat
new file mode 100644
index 0000000000..d5712d9cf9
--- /dev/null
+++ b/modules/areadlinkat
@@ -0,0 +1,26 @@
+Description:
+Reading symbolic links without size limitation, relative to fd.
+
+Files:
+lib/areadlink.h
+lib/areadlinkat.c
+
+Depends-on:
+areadlink
+stdint
+symlinkat
+
+configure.ac:
+gl_MODULE_INDICATOR([areadlinkat])
+
+Makefile.am:
+lib_SOURCES += areadlinkat.c
+
+Include:
+"areadlink.h"
+
+License:
+GPL
+
+Maintainer:
+Jim Meyering, Eric Blake
diff --git a/modules/areadlinkat-tests b/modules/areadlinkat-tests
new file mode 100644
index 0000000000..ca0adc42ea
--- /dev/null
+++ b/modules/areadlinkat-tests
@@ -0,0 +1,14 @@
+Files:
+tests/test-areadlink.h
+tests/test-areadlinkat.c
+
+Depends-on:
+stdbool
+symlink
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-areadlinkat
+check_PROGRAMS += test-areadlinkat
+test_areadlinkat_LDADD = $(LDADD) @LIBINTL@
diff --git a/modules/linkat b/modules/linkat
index 6b56144dcf..0c94227dcd 100644
--- a/modules/linkat
+++ b/modules/linkat
@@ -8,6 +8,7 @@ m4/linkat.m4
 
 Depends-on:
 areadlink
+areadlinkat
 dirname
 errno
 extensions
diff --git a/tests/test-areadlink.h b/tests/test-areadlink.h
index 1da2e1b7df..07ccf232dc 100644
--- a/tests/test-areadlink.h
+++ b/tests/test-areadlink.h
@@ -66,7 +66,6 @@ test_areadlink (char * (*func) (char const *, size_t), bool print)
   ASSERT (errno == EINVAL);
   {
     /* Too small a guess is okay.  */
-    size_t len = strlen (BASE "dir");
     char *buf = func (BASE "link", 1);
     ASSERT (buf);
     ASSERT (strcmp (buf, BASE "dir") == 0);
diff --git a/tests/test-areadlinkat.c b/tests/test-areadlinkat.c
new file mode 100644
index 0000000000..6b0c96c77f
--- /dev/null
+++ b/tests/test-areadlinkat.c
@@ -0,0 +1,98 @@
+/* Tests of areadlinkat.
+   Copyright (C) 2009 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Eric Blake <ebb9@byu.net>, 2009.  */
+
+#include <config.h>
+
+#include "areadlink.h"
+
+#include <fcntl.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define ASSERT(expr) \
+  do                                                                         \
+    {                                                                        \
+      if (!(expr))                                                           \
+        {                                                                    \
+          fprintf (stderr, "%s:%d: assertion failed\n", __FILE__, __LINE__);  \
+          fflush (stderr);                                                   \
+          abort ();                                                          \
+        }                                                                    \
+    }                                                                        \
+  while (0)
+
+#define BASE "test-areadlinkat.t"
+
+#include "test-areadlink.h"
+
+static int dfd = AT_FDCWD;
+
+/* Wrapper for testing areadlinkat.  */
+static char *
+do_areadlinkat (char const *name, size_t ignored _UNUSED_PARAMETER_)
+{
+  return areadlinkat (dfd, name);
+}
+
+int
+main ()
+{
+  int result;
+
+  /* Remove any leftovers from a previous partial run.  */
+  ASSERT (system ("rm -rf " BASE "*") == 0);
+
+  /* Basic tests.  */
+  result = test_areadlink (do_areadlinkat, false);
+  dfd = open (".", O_RDONLY);
+  ASSERT (0 <= dfd);
+  ASSERT (test_areadlink (do_areadlinkat, false) == result);
+
+  /* Relative tests.  */
+  if (result == 77)
+    fputs ("skipping test: symlinks not supported on this filesystem\n",
+           stderr);
+  else
+    {
+      char *buf;
+      ASSERT (symlink ("nowhere", BASE "link") == 0);
+      ASSERT (mkdir (BASE "dir", 0700) == 0);
+      ASSERT (chdir (BASE "dir") == 0);
+      buf = areadlinkat (dfd, BASE "link");
+      ASSERT (buf);
+      ASSERT (strcmp (buf, "nowhere") == 0);
+      free (buf);
+      errno = 0;
+      ASSERT (areadlinkat (-1, BASE "link") == NULL);
+      ASSERT (errno == EBADF);
+      errno = 0;
+      ASSERT (areadlinkat (AT_FDCWD, BASE "link") == NULL);
+      ASSERT (errno == ENOENT);
+      ASSERT (chdir ("..") == 0);
+      ASSERT (rmdir (BASE "dir") == 0);
+      ASSERT (unlink (BASE "link") == 0);
+    }
+
+  ASSERT (close (dfd) == 0);
+  return result;
+}