372 lines
10 KiB
C
372 lines
10 KiB
C
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/* Copyright (C) 2007 Eric Blake
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* Permission to use, copy, modify, and distribute this software
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* is freely granted, provided that this notice is preserved.
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*/
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/*
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FUNCTION
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<<fmemopen>>---open a stream around a fixed-length string
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INDEX
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fmemopen
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ANSI_SYNOPSIS
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#include <stdio.h>
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FILE *fmemopen(void *restrict <[buf]>, size_t <[size]>,
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const char *restrict <[mode]>);
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DESCRIPTION
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<<fmemopen>> creates a seekable <<FILE>> stream that wraps a
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fixed-length buffer of <[size]> bytes starting at <[buf]>. The stream
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is opened with <[mode]> treated as in <<fopen>>, where append mode
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starts writing at the first NUL byte. If <[buf]> is NULL, then
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<[size]> bytes are automatically provided as if by <<malloc>>, with
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the initial size of 0, and <[mode]> must contain <<+>> so that data
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can be read after it is written.
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The stream maintains a current position, which moves according to
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bytes read or written, and which can be one past the end of the array.
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The stream also maintains a current file size, which is never greater
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than <[size]>. If <[mode]> starts with <<r>>, the position starts at
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<<0>>, and file size starts at <[size]> if <[buf]> was provided. If
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<[mode]> starts with <<w>>, the position and file size start at <<0>>,
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and if <[buf]> was provided, the first byte is set to NUL. If
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<[mode]> starts with <<a>>, the position and file size start at the
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location of the first NUL byte, or else <[size]> if <[buf]> was
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provided.
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When reading, NUL bytes have no significance, and reads cannot exceed
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the current file size. When writing, the file size can increase up to
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<[size]> as needed, and NUL bytes may be embedded in the stream (see
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<<open_memstream>> for an alternative that automatically enlarges the
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buffer). When the stream is flushed or closed after a write that
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changed the file size, a NUL byte is written at the current position
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if there is still room; if the stream is not also open for reading, a
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NUL byte is additionally written at the last byte of <[buf]> when the
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stream has exceeded <[size]>, so that a write-only <[buf]> is always
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NUL-terminated when the stream is flushed or closed (and the initial
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<[size]> should take this into account). It is not possible to seek
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outside the bounds of <[size]>. A NUL byte written during a flush is
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restored to its previous value when seeking elsewhere in the string.
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RETURNS
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The return value is an open FILE pointer on success. On error,
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<<NULL>> is returned, and <<errno>> will be set to EINVAL if <[size]>
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is zero or <[mode]> is invalid, ENOMEM if <[buf]> was NULL and memory
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could not be allocated, or EMFILE if too many streams are already
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open.
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PORTABILITY
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This function is being added to POSIX 200x, but is not in POSIX 2001.
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Supporting OS subroutines required: <<sbrk>>.
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*/
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#include <sys/lock.h>
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#include "local.h"
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/* Describe details of an open memstream. */
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typedef struct fmemcookie {
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void *storage; /* storage to free on close */
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char *buf; /* buffer start */
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size_t pos; /* current position */
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size_t eof; /* current file size */
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size_t max; /* maximum file size */
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char append; /* nonzero if appending */
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char writeonly; /* 1 if write-only */
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char saved; /* saved character that lived at pos before write-only NUL */
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} fmemcookie;
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/* Read up to non-zero N bytes into BUF from stream described by
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COOKIE; return number of bytes read (0 on EOF). */
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static _READ_WRITE_RETURN_TYPE
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_DEFUN(fmemreader, (ptr, cookie, buf, n),
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struct _reent *ptr _AND
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void *cookie _AND
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char *buf _AND
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int n)
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{
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fmemcookie *c = (fmemcookie *) cookie;
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/* Can't read beyond current size, but EOF condition is not an error. */
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if (c->pos > c->eof)
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return 0;
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if (n >= c->eof - c->pos)
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n = c->eof - c->pos;
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memcpy (buf, c->buf + c->pos, n);
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c->pos += n;
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return n;
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}
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/* Write up to non-zero N bytes of BUF into the stream described by COOKIE,
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returning the number of bytes written or EOF on failure. */
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static _READ_WRITE_RETURN_TYPE
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_DEFUN(fmemwriter, (ptr, cookie, buf, n),
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struct _reent *ptr _AND
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void *cookie _AND
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const char *buf _AND
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int n)
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{
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fmemcookie *c = (fmemcookie *) cookie;
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int adjust = 0; /* true if at EOF, but still need to write NUL. */
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/* Append always seeks to eof; otherwise, if we have previously done
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a seek beyond eof, ensure all intermediate bytes are NUL. */
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if (c->append)
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c->pos = c->eof;
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else if (c->pos > c->eof)
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memset (c->buf + c->eof, '\0', c->pos - c->eof);
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/* Do not write beyond EOF; saving room for NUL on write-only stream. */
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if (c->pos + n > c->max - c->writeonly)
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{
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adjust = c->writeonly;
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n = c->max - c->pos;
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}
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/* Now n is the number of bytes being modified, and adjust is 1 if
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the last byte is NUL instead of from buf. Write a NUL if
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write-only; or if read-write, eof changed, and there is still
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room. When we are within the file contents, remember what we
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overwrite so we can restore it if we seek elsewhere later. */
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if (c->pos + n > c->eof)
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{
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c->eof = c->pos + n;
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if (c->eof - adjust < c->max)
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c->saved = c->buf[c->eof - adjust] = '\0';
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}
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else if (c->writeonly)
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{
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if (n)
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{
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c->saved = c->buf[c->pos + n - adjust];
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c->buf[c->pos + n - adjust] = '\0';
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}
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else
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adjust = 0;
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}
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c->pos += n;
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if (n - adjust)
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memcpy (c->buf + c->pos - n, buf, n - adjust);
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else
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{
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ptr->_errno = ENOSPC;
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return EOF;
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}
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return n;
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}
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/* Seek to position POS relative to WHENCE within stream described by
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COOKIE; return resulting position or fail with EOF. */
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static _fpos_t
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_DEFUN(fmemseeker, (ptr, cookie, pos, whence),
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struct _reent *ptr _AND
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void *cookie _AND
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_fpos_t pos _AND
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int whence)
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{
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fmemcookie *c = (fmemcookie *) cookie;
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#ifndef __LARGE64_FILES
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off_t offset = (off_t) pos;
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#else /* __LARGE64_FILES */
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_off64_t offset = (_off64_t) pos;
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#endif /* __LARGE64_FILES */
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if (whence == SEEK_CUR)
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offset += c->pos;
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else if (whence == SEEK_END)
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offset += c->eof;
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if (offset < 0)
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{
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ptr->_errno = EINVAL;
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offset = -1;
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}
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else if (offset > c->max)
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{
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ptr->_errno = ENOSPC;
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offset = -1;
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}
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#ifdef __LARGE64_FILES
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else if ((_fpos_t) offset != offset)
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{
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ptr->_errno = EOVERFLOW;
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offset = -1;
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}
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#endif /* __LARGE64_FILES */
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else
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{
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if (c->writeonly && c->pos < c->eof)
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{
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c->buf[c->pos] = c->saved;
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c->saved = '\0';
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}
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c->pos = offset;
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if (c->writeonly && c->pos < c->eof)
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{
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c->saved = c->buf[c->pos];
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c->buf[c->pos] = '\0';
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}
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}
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return (_fpos_t) offset;
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}
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/* Seek to position POS relative to WHENCE within stream described by
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COOKIE; return resulting position or fail with EOF. */
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#ifdef __LARGE64_FILES
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static _fpos64_t
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_DEFUN(fmemseeker64, (ptr, cookie, pos, whence),
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struct _reent *ptr _AND
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void *cookie _AND
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_fpos64_t pos _AND
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int whence)
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{
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_off64_t offset = (_off64_t) pos;
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fmemcookie *c = (fmemcookie *) cookie;
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if (whence == SEEK_CUR)
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offset += c->pos;
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else if (whence == SEEK_END)
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offset += c->eof;
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if (offset < 0)
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{
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ptr->_errno = EINVAL;
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offset = -1;
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}
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else if (offset > c->max)
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{
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ptr->_errno = ENOSPC;
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offset = -1;
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}
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else
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{
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if (c->writeonly && c->pos < c->eof)
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{
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c->buf[c->pos] = c->saved;
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c->saved = '\0';
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}
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c->pos = offset;
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if (c->writeonly && c->pos < c->eof)
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{
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c->saved = c->buf[c->pos];
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c->buf[c->pos] = '\0';
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}
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}
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return (_fpos64_t) offset;
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}
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#endif /* __LARGE64_FILES */
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/* Reclaim resources used by stream described by COOKIE. */
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static int
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_DEFUN(fmemcloser, (ptr, cookie),
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struct _reent *ptr _AND
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void *cookie)
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{
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fmemcookie *c = (fmemcookie *) cookie;
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_free_r (ptr, c->storage);
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return 0;
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}
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/* Open a memstream around buffer BUF of SIZE bytes, using MODE.
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Return the new stream, or fail with NULL. */
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FILE *
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_DEFUN(_fmemopen_r, (ptr, buf, size, mode),
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struct _reent *ptr _AND
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void *buf _AND
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size_t size _AND
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const char *mode)
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{
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FILE *fp;
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fmemcookie *c;
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int flags;
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int dummy;
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if ((flags = __sflags (ptr, mode, &dummy)) == 0)
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return NULL;
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if (!size || !(buf || flags & __SAPP))
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{
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ptr->_errno = EINVAL;
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return NULL;
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}
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if ((fp = __sfp (ptr)) == NULL)
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return NULL;
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if ((c = (fmemcookie *) _malloc_r (ptr, sizeof *c + (buf ? 0 : size)))
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== NULL)
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{
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__sfp_lock_acquire ();
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fp->_flags = 0; /* release */
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#ifndef __SINGLE_THREAD__
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__lock_close_recursive (fp->_lock);
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#endif
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__sfp_lock_release ();
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return NULL;
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}
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c->storage = c;
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c->max = size;
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/* 9 modes to worry about. */
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/* w/a, buf or no buf: Guarantee a NUL after any file writes. */
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c->writeonly = (flags & __SWR) != 0;
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c->saved = '\0';
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if (!buf)
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{
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/* r+/w+/a+, and no buf: file starts empty. */
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c->buf = (char *) (c + 1);
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*(char *) buf = '\0';
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c->pos = c->eof = 0;
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c->append = (flags & __SAPP) != 0;
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}
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else
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{
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c->buf = (char *) buf;
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switch (*mode)
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{
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case 'a':
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/* a/a+ and buf: position and size at first NUL. */
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buf = memchr (c->buf, '\0', size);
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c->eof = c->pos = buf ? (char *) buf - c->buf : size;
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if (!buf && c->writeonly)
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/* a: guarantee a NUL within size even if no writes. */
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c->buf[size - 1] = '\0';
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c->append = 1;
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break;
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case 'r':
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/* r/r+ and buf: read at beginning, full size available. */
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c->pos = c->append = 0;
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c->eof = size;
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break;
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case 'w':
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/* w/w+ and buf: write at beginning, truncate to empty. */
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c->pos = c->append = c->eof = 0;
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*c->buf = '\0';
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break;
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default:
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abort ();
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}
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}
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_flockfile (fp);
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fp->_file = -1;
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fp->_flags = flags;
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fp->_cookie = c;
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fp->_read = flags & (__SRD | __SRW) ? fmemreader : NULL;
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fp->_write = flags & (__SWR | __SRW) ? fmemwriter : NULL;
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fp->_seek = fmemseeker;
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#ifdef __LARGE64_FILES
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fp->_seek64 = fmemseeker64;
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fp->_flags |= __SL64;
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#endif
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fp->_close = fmemcloser;
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_funlockfile (fp);
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return fp;
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}
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#ifndef _REENT_ONLY
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FILE *
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_DEFUN(fmemopen, (buf, size, mode),
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void *buf _AND
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size_t size _AND
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const char *mode)
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{
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return _fmemopen_r (_REENT, buf, size, mode);
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}
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#endif /* !_REENT_ONLY */
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