read_file.c

/*
  Copyright 2017 Giuseppe Scrivano
  Copyright (C) Huawei Technologies., Ltd. 2018-2019. All rights reserved.
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  http://www.apache.org/licenses/LICENSE-2.0
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <stdint.h>

#include <config.h>
#include "read_file.h"

#ifndef O_CLOEXEC
#define O_CLOEXEC 02000000
#endif

#define JSON_MAX_SIZE (10LL * 1024LL * 1024LL)
#define FILE_MODE 0640

static int do_check_fread_args(const FILE *stream, const size_t *length)
{
    if (stream == NULL) {
        return -1;
    }
    if (length == NULL) {
        return -1;
    }

    return 0;
}

char *fread_file(FILE *stream, size_t *length)
{
    char *buf = NULL;
    char *tmpbuf = NULL;
    size_t off = 0;

    if (do_check_fread_args(stream, length) != 0) {
        return NULL;
    }

    while (1) {
        size_t ret, newsize, sizejudge;
        sizejudge = (JSON_MAX_SIZE - BUFSIZ) - 1;
        if (sizejudge < off) {
            goto out;
        }
        newsize = off + BUFSIZ + 1;

        tmpbuf = (char *)calloc(1, newsize);
        if (tmpbuf == NULL) {
            goto out;
        }

        if (buf != NULL) {
            (void)memcpy(tmpbuf, buf, off);

            (void)memset(buf, 0, off);

            free(buf);
        }

        buf = tmpbuf;
        tmpbuf = NULL;

        ret = fread(buf + off, 1, BUFSIZ, stream);
        if (ret == 0 && ferror(stream)) {
            goto out;
        }
        if (ret < BUFSIZ || feof(stream)) {
            *length = off + ret + 1;
            buf[*length - 1] = '\0';
            return buf;
        }

        off += BUFSIZ;
    }
out:
    free(buf);
    free(tmpbuf);
    return NULL;
}

static int do_check_args(const char *path, const size_t *length)
{
    if (path == NULL || length == NULL) {
        return -1;
    }
    if (strlen(path) > PATH_MAX) {
        return -1;
    }
    return 0;
}

char *read_file(const char *path, size_t *length)
{
    char *buf = NULL;
    char rpath[PATH_MAX + 1] = { 0 };
    int fd = -1;
    int tmperrno = -1;
    FILE *fp = NULL;

    if (do_check_args(path, length) != 0) {
        return NULL;
    }

    if (realpath(path, rpath) == NULL) {
        return NULL;
    }

    fd = open(rpath, O_RDONLY | O_CLOEXEC, FILE_MODE);
    if (fd < 0) {
        return NULL;
    }

    fp = fdopen(fd, "r");
    tmperrno = errno;
    if (fp == NULL) {
        (void)close(fd);
        errno = tmperrno;
        return NULL;
    }

    buf = fread_file(fp, length);
    (void)fclose(fp);
    return buf;
}