New module 'freadseek'.

diff --git a/ChangeLog b/ChangeLog
index f05aa8e..32bfe85 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2008-02-29  Bruno Haible  <bruno@clisp.org>
+
+       New module 'freadseek'.
+       * modules/freadseek: New file.
+       * lib/freadseek.h: New file.
+       * lib/freadseek.c: New file.
+       * MODULES.html.sh (File stream based Input/Output): Add freadseek.
+
 2008-02-29  Sergey Poznyakoff  <gray@gnu.org.ua>
 
        * users.txt: Add anubis, cpio, mailfromd, mailutils, radius,

diff --git a/MODULES.html.sh b/MODULES.html.sh
index 5f1dc7d..16c3552 100755 (executable)
--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -2283,6 +2283,7 @@ func_all_modules ()
   func_module freadahead
   func_module freading
   func_module freadptr
+  func_module freadseek
   func_module fwritable
   func_module fwriting
   func_module getpass

diff --git a/lib/freadseek.c b/lib/freadseek.c
new file mode 100644 (file)
index 0000000..b3f2b18
--- /dev/null
+++ b/lib/freadseek.c
@@ -0,0 +1,111 @@
+/* Skipping input from a FILE stream.
+   Copyright (C) 2007-2008 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/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "freadseek.h"
+
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "freadahead.h"
+
+int
+freadseek (FILE *fp, size_t offset)
+{
+  size_t buffered;
+  int fd;
+
+  if (offset == 0)
+    return 0;
+
+  /* Increment the in-memory pointer.  This is very cheap (no system calls).  */
+  buffered = freadahead (fp);
+  if (buffered > 0)
+    {
+      size_t increment = (buffered < offset ? buffered : offset);
+
+      /* Keep this code in sync with freadahead and freadptr!  */
+#if defined _IO_ferror_unlocked     /* GNU libc, BeOS */
+      fp->_IO_read_ptr += increment;
+#elif defined __sferror             /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
+      fp->_p += increment;
+      fp->_r -= increment;
+#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, mingw */
+# if defined __sun && defined _LP64 /* Solaris/{SPARC,AMD64} 64-bit */
+#  define fp_ ((struct { unsigned char *_ptr; \
+                        unsigned char *_base; \
+                        unsigned char *_end; \
+                        long _cnt; \
+                        int _file; \
+                        unsigned int _flag; \
+                      } *) fp)
+      fp_->_ptr += increment;
+      fp_->_cnt -= increment;
+# else
+      fp->_ptr += increment;
+      fp->_cnt -= increment;
+# endif
+#elif defined __UCLIBC__            /* uClibc */
+# ifdef __STDIO_BUFFERS
+      fp->__bufpos += increment;
+# else
+      abort ();
+# endif
+#elif defined __QNX__               /* QNX */
+      fp->_Next += increment;
+#else
+ #error "Please port gnulib freadseek.c to your platform! Look at the definition of getc, getc_unlocked on your system, then report this to bug-gnulib."
+#endif
+
+      offset -= increment;
+      if (offset == 0)
+       return 0;
+    }
+
+  /* Test whether the stream is seekable or not.  */
+  fd = fileno (fp);
+  if (fd >= 0 && lseek (fd, 0, SEEK_CUR) >= 0)
+    {
+      /* FP refers to a regular file.  fseek is most efficient in this case.  */
+      return fseek (fp, offset, SEEK_CUR);
+    }
+  else
+    {
+      /* FP is a non-seekable stream, possibly not even referring to a file
+        descriptor.  Read OFFSET bytes explicitly and discard them.  */
+      char buf[4096];
+
+      do
+       {
+         size_t count = (sizeof (buf) < offset ? sizeof (buf) : offset);
+         if (fread (buf, 1, count, fp) < count)
+           {
+             if (ferror (fp))
+               /* EOF, or error before or while reading.  */
+               return EOF;
+             else
+               /* Encountered EOF.  */
+               return 0;
+           }
+         offset -= count;
+       }
+      while (offset > 0);
+
+      return 0;
+   }
+}

diff --git a/lib/freadseek.h b/lib/freadseek.h
new file mode 100644 (file)
index 0000000..7239672
--- /dev/null
+++ b/lib/freadseek.h
@@ -0,0 +1,42 @@
+/* Skipping input from a FILE stream.
+   Copyright (C) 2007-2008 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/>.  */
+
+#include <stddef.h>
+#include <stdio.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Assuming the stream STREAM is open for reading:
+
+   Read and discard OFFSET bytes from STREAM.
+
+   freadseek (STREAM, OFFSET) is the same as
+   fseek (STREAM, OFFSET, SEEK_CUR), except that the latter does not work
+   on non-seekable input streams (such as pipes).
+
+   Upon success, return 0.
+   Upon premature end of stream, return 0 (like fseek does).
+   Upon error, set the error indicator in the stream and return EOF.
+
+   STREAM must not be wide-character oriented.  */
+
+extern int freadseek (FILE *stream, size_t offset);
+
+#ifdef __cplusplus
+}
+#endif

diff --git a/modules/freadseek b/modules/freadseek
new file mode 100644 (file)
index 0000000..ce19eda
--- /dev/null
+++ b/modules/freadseek
@@ -0,0 +1,25 @@
+Description:
+freadseek() function: Read and discard input from a stream.
+
+Files:
+lib/freadseek.h
+lib/freadseek.c
+
+Depends-on:
+freadahead
+lseek
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += freadseek.c
+
+Include:
+"freadseek.h"
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible
+