source: MondoRescue/branches/stable/mindi-busybox/libbb/read.c

/* vi: set sw=4 ts=4: */
/*
 * Utility routines.
 *
 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include "libbb.h"

ssize_t safe_read(int fd, void *buf, size_t count)
{
    ssize_t n;

    do {
        n = read(fd, buf, count);
    } while (n < 0 && errno == EINTR);

    return n;
}

/*
 * Read all of the supplied buffer from a file.
 * This does multiple reads as necessary.
 * Returns the amount read, or -1 on an error.
 * A short read is returned on an end of file.
 */
ssize_t full_read(int fd, void *buf, size_t len)
{
    ssize_t cc;
    ssize_t total;

    total = 0;

    while (len) {
        cc = safe_read(fd, buf, len);

        if (cc < 0)
            return cc;  /* read() returns -1 on failure. */
        if (cc == 0)
            break;
        buf = ((char *)buf) + cc;
        total += cc;
        len -= cc;
    }

    return total;
}

// Die with an error message if we can't read the entire buffer.
void xread(int fd, void *buf, size_t count)
{
    if (count) {
        ssize_t size = full_read(fd, buf, count);
        if (size != count)
            bb_error_msg_and_die("short read");
    }
}

// Die with an error message if we can't read one character.
unsigned char xread_char(int fd)
{
    char tmp;
    xread(fd, &tmp, 1);
    return tmp;
}

// Read one line a-la fgets. Works only on seekable streams
char *reads(int fd, char *buffer, size_t size)
{
    char *p;

    if (size < 2)
        return NULL;
    size = full_read(fd, buffer, size-1);
    if ((ssize_t)size <= 0)
        return NULL;

    buffer[size] = '\0';
    p = strchr(buffer, '\n');
    if (p) {
        off_t offset;
        *p++ = '\0';
        // avoid incorrect (unsigned) widening
        offset = (off_t)(p-buffer) - (off_t)size;
        // set fd position right after '\n'
        if (offset && lseek(fd, offset, SEEK_CUR) == (off_t)-1)
            return NULL;
    }
    return buffer;
}

// Read one line a-la fgets. Reads byte-by-byte.
// Useful when it is important to not read ahead.
char *xmalloc_reads(int fd, char *buf)
{
    char *p;
    int sz = buf ? strlen(buf) : 0;

    goto jump_in;
    while (1) {
        if (p - buf == sz) {
 jump_in:
            buf = xrealloc(buf, sz + 128);
            p = buf + sz;
            sz += 128;
        }
        if (safe_read(fd, p, 1) != 1) { /* EOF/error */
            if (p == buf) {
                /* we read nothing [and buf was NULL initially] */
                free(buf);
                return NULL;
            }
            break;
        }
        if (*p == '\n')
            break;
        p++;
    }
    *p++ = '\0';
    return xrealloc(buf, p - buf);
}

ssize_t read_close(int fd, void *buf, size_t size)
{
    /*int e;*/
    size = full_read(fd, buf, size);
    /*e = errno;*/
    close(fd);
    /*errno = e;*/
    return size;
}

ssize_t open_read_close(const char *filename, void *buf, size_t size)
{
    int fd = open(filename, O_RDONLY);
    if (fd < 0)
        return fd;
    return read_close(fd, buf, size);
}

// Read (potentially big) files in one go. File size is estimated by
// lseek to end.
void *xmalloc_open_read_close(const char *filename, size_t *sizep)
{
    char *buf;
    size_t size = sizep ? *sizep : INT_MAX;
    int fd;
    off_t len;

    fd = xopen(filename, O_RDONLY);
    /* /proc/N/stat files report len 0 here */
    /* In order to make such files readable, we add small const */
    len = xlseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
    xlseek(fd, 0, SEEK_SET);
    if (len < size)
        size = len;
    buf = xmalloc(size + 1);
    size = read_close(fd, buf, size);
    if ((ssize_t)size < 0)
        bb_perror_msg_and_die("'%s'", filename);
    xrealloc(buf, size + 1);
    buf[size] = '\0';
    if (sizep)
        *sizep = size;
    return buf;
}