(IS_EINTR): Define.

[gnulib.git] / lib / safe-read.c

diff --git a/lib/safe-read.c b/lib/safe-read.c
index aea32be..5d2cd9d 100644 (file)
--- a/lib/safe-read.c
+++ b/lib/safe-read.c
@@ -1,5 +1,5 @@
-/* safe-read.c -- an interface to read that retries after interrupts
-   Copyright (C) 1993, 1994 Free Software Foundation, Inc.
+/* An interface to read that retries after interrupts.
+   Copyright (C) 1993, 1994, 1998, 2002 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
@@ -12,17 +12,19 @@
    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, write to the Free Software
-   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
-   */
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
 
-#ifdef HAVE_CONFIG_H
+#if HAVE_CONFIG_H
 # include <config.h>
 #endif
 
-#include <sys/types.h>
+/* Specification.  */
+#include "safe-read.h"
 
-#ifdef HAVE_UNISTD_H
+/* Get ssize_t.  */
+#include <sys/types.h>
+#if HAVE_UNISTD_H
 # include <unistd.h>
 #endif
 
@@ -31,30 +33,57 @@
 extern int errno;
 #endif
 
-/* Read LEN bytes at PTR from descriptor DESC, retrying if interrupted.
-   Return the actual number of bytes read, zero for EOF, or negative
-   for an error.  */
+#ifdef EINTR
+# define IS_EINTR(x) ((x) == EINTR)
+#else
+# define IS_EINTR(x) 0
+#endif
+
+#include <limits.h>
+
+#ifndef CHAR_BIT
+# define CHAR_BIT 8
+#endif
 
-int
-safe_read (desc, ptr, len)
-     int desc;
-     char *ptr;
-     int len;
+/* The extra casts work around common compiler bugs.  */
+#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
+/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
+   It is necessary at least when t == time_t.  */
+#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
+                             ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
+#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
+
+#ifndef INT_MAX
+# define INT_MAX TYPE_MAXIMUM (int)
+#endif
+
+/* We don't pass an nbytes count > SSIZE_MAX to read() - POSIX says the
+   effect would be implementation-defined.  Also we don't pass an nbytes
+   count > INT_MAX but <= SSIZE_MAX to read() - this triggers a bug in
+   Tru64 5.1.  */
+#define MAX_BYTES_TO_READ INT_MAX
+
+/* Read up to COUNT bytes at BUF from descriptor FD, retrying if interrupted.
+   Return the actual number of bytes read, zero for EOF, or SAFE_READ_ERROR
+   upon error.  */
+size_t
+safe_read (int fd, void *buf, size_t count)
 {
-  int n_chars;
+  size_t nbytes_to_read = count;
+  ssize_t result;
 
-  if (len <= 0)
-    return len;
+  /* Limit the number of bytes to read, to avoid running into unspecified
+     behaviour.  But keep the file pointer block aligned when doing so.
+     Note that in this case we don't need to call read() multiple times here,
+     because the caller is prepared to partial results.  */
+  if (nbytes_to_read > MAX_BYTES_TO_READ)
+    nbytes_to_read = MAX_BYTES_TO_READ & ~8191;
 
-#ifdef EINTR
   do
     {
-      n_chars = read (desc, ptr, len);
+      result = read (fd, buf, nbytes_to_read);
     }
-  while (n_chars < 0 && errno == EINTR);
-#else
-  n_chars = read (desc, ptr, len);
-#endif
+  while (result < 0 && IS_EINTR (errno));
 
-  return n_chars;
+  return (size_t) result;
 }