Orthogonal approach to read()/write() that handles EINTR and counts > 2^31

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

diff --git a/lib/safe-read.c b/lib/safe-read.c
index e404586..79d8541 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, 1998 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
@@ -13,15 +13,17 @@
 
    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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
-   */
+   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
 
 #if HAVE_CONFIG_H
 # include <config.h>
 #endif
 
-#include <sys/types.h>
+/* Specification.  */
+#include "safe-read.h"
 
+/* Get ssize_t.  */
+#include <sys/types.h>
 #if HAVE_UNISTD_H
 # include <unistd.h>
 #endif
@@ -31,29 +33,51 @@
 extern int errno;
 #endif
 
-#include "safe-read.h"
+#include <limits.h>
 
-/* 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.  */
+/* 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
 
-ssize_t
-safe_read (int desc, void *ptr, size_t len)
+/* Read up to COUNT bytes at BUF from descriptor FD, retrying if interrupted.
+   Return the actual number of bytes read, zero for EOF, or (size_t) -1
+   for an error.  */
+size_t
+safe_read (int fd, void *buf, size_t count)
 {
-  ssize_t n_chars;
+  size_t total_read = 0;
 
-  if (len <= 0)
-    return len;
+  if (count > 0)
+    {
+      char *ptr = (char *) buf;
+      do
+       {
+         size_t nbytes_to_read = count;
+         ssize_t result;
+
+         /* Limit the number of bytes to read in one round, to avoid running
+            into unspecified behaviour.  But keep the file pointer block
+            aligned when doing so.  */
+         if (nbytes_to_read > MAX_BYTES_TO_READ)
+           nbytes_to_read = MAX_BYTES_TO_READ & ~8191;
 
+         result = read (fd, ptr, nbytes_to_read);
+         if (result < 0)
+           {
 #ifdef EINTR
-  do
-    {
-      n_chars = read (desc, ptr, len);
-    }
-  while (n_chars < 0 && errno == EINTR);
-#else
-  n_chars = read (desc, ptr, len);
+             if (errno == EINTR)
+               continue;
 #endif
+             return result;
+           }
+         total_read += result;
+         ptr += result;
+         count -= result;
+       }
+      while (count > 0);
+    }
 
-  return n_chars;
+  return total_read;
 }