tinyproxy/src/utils.c

/* $Id: utils.c,v 1.40 2005-08-15 03:54:31 rjkaes Exp $
 *
 * Misc. routines which are used by the various functions to handle strings
 * and memory allocation and pretty much anything else we can think of. Also,
 * the load cutoff routine is in here. Could not think of a better place for
 * it, so it's in here.
 *
 * Copyright (C) 1998       Steven Young
 * Copyright (C) 1999-2003  Robert James Kaes (rjkaes@users.sourceforge.net)
 *
 * 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 2, 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.
 */

#include "tinyproxy.h"

#include "conns.h"
#include "heap.h"
#include "http_message.h"
#include "utils.h"

/*
 * Build the data for a complete HTTP & HTML message for the client.
 */
int
send_http_message(struct conn_s *connptr, int http_code,
                  const char *error_title, const char *message)
{
        static char *headers[] = {
                "Server: " PACKAGE "/" VERSION,
                "Content-type: text/html",
                "Connection: close"
        };

        http_message_t msg;

        msg = http_message_create(http_code, error_title);
        if (msg == NULL)
                return -1;

        http_message_add_headers(msg, headers, 3);
        http_message_set_body(msg, message, strlen(message));
        http_message_send(msg, connptr->client_fd);
        http_message_destroy(msg);

        return 0;
}

/*
 * Safely creates filename and returns the low-level file descriptor.
 */
int
create_file_safely(const char *filename, unsigned int truncate_file)
{
        struct stat lstatinfo;
        int fildes;

        /*
         * lstat() the file. If it doesn't exist, create it with O_EXCL.
         * If it does exist, open it for writing and perform the fstat()
         * check.
         */
        if (lstat(filename, &lstatinfo) < 0) {
                /*
                 * If lstat() failed for any reason other than "file not
                 * existing", exit.
                 */
                if (errno != ENOENT) {
                        fprintf(stderr,
                                "%s: Error checking file %s: %s\n",
                                PACKAGE, filename, strerror(errno));
                        return -EACCES;
                }

                /*
                 * The file doesn't exist, so create it with O_EXCL to make
                 * sure an attacker can't slip in a file between the lstat()
                 * and open()
                 */
                if ((fildes =
                     open(filename, O_RDWR | O_CREAT | O_EXCL, 0600)) < 0) {
                        fprintf(stderr,
                                "%s: Could not create file %s: %s\n",
                                PACKAGE, filename, strerror(errno));
                        return fildes;
                }
        } else {
                struct stat fstatinfo;
                int flags;

                flags = O_RDWR;
                if (!truncate_file)
                        flags |= O_APPEND;

                /*
                 * Open an existing file.
                 */
                if ((fildes = open(filename, flags)) < 0) {
                        fprintf(stderr,
                                "%s: Could not open file %s: %s\n",
                                PACKAGE, filename, strerror(errno));
                        return fildes;
                }

                /*
                 * fstat() the opened file and check that the file mode bits,
                 * inode, and device match.
                 */
                if (fstat(fildes, &fstatinfo) < 0
                    || lstatinfo.st_mode != fstatinfo.st_mode
                    || lstatinfo.st_ino != fstatinfo.st_ino
                    || lstatinfo.st_dev != fstatinfo.st_dev) {
                        fprintf(stderr,
                                "%s: The file %s has been changed before it could be opened\n",
                                PACKAGE, filename);
                        close(fildes);
                        return -EIO;
                }

                /*
                 * If the above check was passed, we know that the lstat()
                 * and fstat() were done on the same file. Now we check that
                 * there's only one link, and that it's a normal file (this
                 * isn't strictly necessary because the fstat() vs lstat()
                 * st_mode check would also find this)
                 */
                if (fstatinfo.st_nlink > 1 || !S_ISREG(lstatinfo.st_mode)) {
                        fprintf(stderr,
                                "%s: The file %s has too many links, or is not a regular file: %s\n",
                                PACKAGE, filename, strerror(errno));
                        close(fildes);
                        return -EMLINK;
                }

                /*
                 * Just return the file descriptor if we _don't_ want the file
                 * truncated.
                 */
                if (!truncate_file)
                        return fildes;

                /*
                 * On systems which don't support ftruncate() the best we can
                 * do is to close the file and reopen it in create mode, which
                 * unfortunately leads to a race condition, however "systems
                 * which don't support ftruncate()" is pretty much SCO only,
                 * and if you're using that you deserve what you get.
                 * ("Little sympathy has been extended")
                 */
#ifdef HAVE_FTRUNCATE
                ftruncate(fildes, 0);
#else
                close(fildes);
                if ((fildes =
                     open(filename, O_RDWR | O_CREAT | O_TRUNC, 0600)) < 0) {
                        fprintf(stderr,
                                "%s: Could not open file %s: %s.",
                                PACKAGE, filename, strerror(errno));
                        return fildes;
                }
#endif                          /* HAVE_FTRUNCATE */
        }

        return fildes;
}

/*
 * Write the PID of the program to the specified file.
 */
int
pidfile_create(const char *filename)
{
        int fildes;
        FILE *fd;

        /*
         * Create a new file
         */
        if ((fildes = create_file_safely(filename, TRUE)) < 0)
                return fildes;

        /*
         * Open a stdio file over the low-level one.
         */
        if ((fd = fdopen(fildes, "w")) == NULL) {
                fprintf(stderr,
                        "%s: Could not write PID file %s: %s.",
                        PACKAGE, filename, strerror(errno));
                close(fildes);
                unlink(filename);
                return -EIO;
        }

        fprintf(fd, "%ld\n", (long)getpid());
        fclose(fd);
        return 0;
}