buffers.c

关于tor匿名通信的源代码

    tor_assert(buf->head);
    if (buf->head->datalen > n) {
      buf->head->datalen -= n;
      buf->head->data += n;
      buf->datalen -= n;
      return;
    } else {
      chunk_t *victim = buf->head;
      n -= victim->datalen;
      buf->datalen -= victim->datalen;
      buf->head = victim->next;
      if (buf->tail == victim)
        buf->tail = NULL;
      chunk_free(victim);
    }
  }
  check();
}

/** Create and return a new buf with default chunk capacity <b>size</b>.
 */
buf_t *
buf_new_with_capacity(size_t size)
{
  buf_t *b = buf_new();
  b->default_chunk_size = preferred_chunk_size(size);
  return b;
}

/** Allocate and return a new buffer with default capacity. */
buf_t *
buf_new(void)
{
  buf_t *buf = tor_malloc_zero(sizeof(buf_t));
  buf->magic = BUFFER_MAGIC;
  buf->default_chunk_size = 4096;
  return buf;
}

/** Remove all data from <b>buf</b>. */
void
buf_clear(buf_t *buf)
{
  chunk_t *chunk, *next;
  buf->datalen = 0;
  for (chunk = buf->head; chunk; chunk = next) {
    next = chunk->next;
    chunk_free(chunk);
  }
  buf->head = buf->tail = NULL;
}

/** Return the number of bytes stored in <b>buf</b> */
size_t
buf_datalen(const buf_t *buf)
{
  return buf->datalen;
}

/** Return the total length of all chunks used in <b>buf</b>. */
size_t
buf_allocation(const buf_t *buf)
{
  size_t total = 0;
  const chunk_t *chunk;
  for (chunk = buf->head; chunk; chunk = chunk->next) {
    total += chunk->memlen;
  }
  return total;
}

/** Return the number of bytes that can be added to <b>buf</b> without
 * performing any additional allocation. */
size_t
buf_slack(const buf_t *buf)
{
  if (!buf->tail)
    return 0;
  else
    return CHUNK_REMAINING_CAPACITY(buf->tail);
}

/** Release storage held by <b>buf</b>. */
void
buf_free(buf_t *buf)
{
  buf_clear(buf);
  buf->magic = 0xdeadbeef;
  tor_free(buf);
}

/** Append a new chunk with enough capacity to hold <b>capacity</b> bytes to
 * the tail of <b>buf</b>.  If <b>capped</b>, don't allocate a chunk bigger
 * than MAX_CHUNK_ALLOC. */
static chunk_t *
buf_add_chunk_with_capacity(buf_t *buf, size_t capacity, int capped)
{
  chunk_t *chunk;
  if (CHUNK_ALLOC_SIZE(capacity) < buf->default_chunk_size) {
    chunk = chunk_new_with_alloc_size(buf->default_chunk_size);
  } else if (capped && CHUNK_ALLOC_SIZE(capacity) > MAX_CHUNK_ALLOC) {
    chunk = chunk_new_with_alloc_size(MAX_CHUNK_ALLOC);
  } else {
    chunk = chunk_new_with_alloc_size(preferred_chunk_size(capacity));
  }
  if (buf->tail) {
    tor_assert(buf->head);
    buf->tail->next = chunk;
    buf->tail = chunk;
  } else {
    tor_assert(!buf->head);
    buf->head = buf->tail = chunk;
  }
  check();
  return chunk;
}

/** Read up to <b>at_most</b> bytes from the socket <b>fd</b> into
 * <b>chunk</b> (which must be on <b>buf</b>). If we get an EOF, set
 * *<b>reached_eof</b> to 1.  Return -1 on error, 0 on eof or blocking,
 * and the number of bytes read otherwise. */
static INLINE int
read_to_chunk(buf_t *buf, chunk_t *chunk, int fd, size_t at_most,
              int *reached_eof)
{
  ssize_t read_result;

  tor_assert(CHUNK_REMAINING_CAPACITY(chunk) >= at_most);
  read_result = tor_socket_recv(fd, CHUNK_WRITE_PTR(chunk), at_most, 0);
  if (read_result < 0) {
    int e = tor_socket_errno(fd);
    if (!ERRNO_IS_EAGAIN(e)) { /* it's a real error */
#ifdef MS_WINDOWS
      if (e == WSAENOBUFS)
        log_warn(LD_NET,"recv() failed: WSAENOBUFS. Not enough ram?");
#endif
      return -1;
    }
    return 0; /* would block. */
  } else if (read_result == 0) {
    log_debug(LD_NET,"Encountered eof on fd %d", (int)fd);
    *reached_eof = 1;
    return 0;
  } else { /* actually got bytes. */
    buf->datalen += read_result;
    chunk->datalen += read_result;
    log_debug(LD_NET,"Read %ld bytes. %d on inbuf.", (long)read_result,
              (int)buf->datalen);
    tor_assert(read_result < INT_MAX);
    return (int)read_result;
  }
}

/** As read_to_chunk(), but return (negative) error code on error, blocking,
 * or TLS, and the number of bytes read otherwise. */
static INLINE int
read_to_chunk_tls(buf_t *buf, chunk_t *chunk, tor_tls_t *tls,
                  size_t at_most)
{
  int read_result;

  tor_assert(CHUNK_REMAINING_CAPACITY(chunk) >= at_most);
  read_result = tor_tls_read(tls, CHUNK_WRITE_PTR(chunk), at_most);
  if (read_result < 0)
    return read_result;
  buf->datalen += read_result;
  chunk->datalen += read_result;
  return read_result;
}

/** Read from socket <b>s</b>, writing onto end of <b>buf</b>.  Read at most
 * <b>at_most</b> bytes, growing the buffer as necessary.  If recv() returns 0
 * (because of EOF), set *<b>reached_eof</b> to 1 and return 0. Return -1 on
 * error; else return the number of bytes read.
 */
/* XXXX021 indicate "read blocked" somehow? */
int
read_to_buf(int s, size_t at_most, buf_t *buf, int *reached_eof)
{
  /* XXXX021 It's stupid to overload the return values for these functions:
   * "error status" and "number of bytes read" are not mutually exclusive.
   */
  int r = 0;
  size_t total_read = 0;

  check();
  tor_assert(reached_eof);
  tor_assert(s >= 0);

  while (at_most > total_read) {
    size_t readlen = at_most - total_read;
    chunk_t *chunk;
    if (!buf->tail || CHUNK_REMAINING_CAPACITY(buf->tail) < MIN_READ_LEN) {
      chunk = buf_add_chunk_with_capacity(buf, at_most, 1);
      if (readlen > chunk->memlen)
        readlen = chunk->memlen;
    } else {
      size_t cap = CHUNK_REMAINING_CAPACITY(buf->tail);
      chunk = buf->tail;
      if (cap < readlen)
        readlen = cap;
    }

    r = read_to_chunk(buf, chunk, s, readlen, reached_eof);
    check();
    if (r < 0)
      return r; /* Error */
    tor_assert(total_read+r < INT_MAX);
    total_read += r;
    if ((size_t)r < readlen) { /* eof, block, or no more to read. */
      break;
    }
  }
  return (int)total_read;
}

/** As read_to_buf, but reads from a TLS connection, and returns a TLS
 * status value rather than the number of bytes read.
 *
 * Using TLS on OR connections complicates matters in two ways.
 *
 * First, a TLS stream has its own read buffer independent of the
 * connection's read buffer.  (TLS needs to read an entire frame from
 * the network before it can decrypt any data.  Thus, trying to read 1
 * byte from TLS can require that several KB be read from the network
 * and decrypted.  The extra data is stored in TLS's decrypt buffer.)
 * Because the data hasn't been read by Tor (it's still inside the TLS),
 * this means that sometimes a connection "has stuff to read" even when
 * poll() didn't return POLLIN. The tor_tls_get_pending_bytes function is
 * used in connection.c to detect TLS objects with non-empty internal
 * buffers and read from them again.
 *
 * Second, the TLS stream's events do not correspond directly to network
 * events: sometimes, before a TLS stream can read, the network must be
 * ready to write -- or vice versa.
 */
int
read_to_buf_tls(tor_tls_t *tls, size_t at_most, buf_t *buf)
{
  int r = 0;
  size_t total_read = 0;
  check();

  while (at_most > total_read) {
    size_t readlen = at_most - total_read;
    chunk_t *chunk;
    if (!buf->tail || CHUNK_REMAINING_CAPACITY(buf->tail) < MIN_READ_LEN) {
      chunk = buf_add_chunk_with_capacity(buf, at_most, 1);
      if (readlen > chunk->memlen)
        readlen = chunk->memlen;
    } else {
      size_t cap = CHUNK_REMAINING_CAPACITY(buf->tail);
      chunk = buf->tail;
      if (cap < readlen)
        readlen = cap;
    }

    r = read_to_chunk_tls(buf, chunk, tls, readlen);
    check();
    if (r < 0)
      return r; /* Error */
    tor_assert(total_read+r < INT_MAX);
     total_read += r;
    if ((size_t)r < readlen) /* eof, block, or no more to read. */
      break;
  }
  return (int)total_read;
}

/** Helper for flush_buf(): try to write <b>sz</b> bytes from chunk
 * <b>chunk</b> of buffer <b>buf</b> onto socket <b>s</b>.  On success, deduct
 * the bytes written from *<b>buf_flushlen</b>.  Return the number of bytes
 * written on success, 0 on blocking, -1 on failure.
 */
static INLINE int
flush_chunk(int s, buf_t *buf, chunk_t *chunk, size_t sz,
            size_t *buf_flushlen)
{
  ssize_t write_result;

  tor_assert(sz <= chunk->datalen);
  write_result = tor_socket_send(s, chunk->data, sz, 0);
  if (write_result < 0) {
    int e = tor_socket_errno(s);
    if (!ERRNO_IS_EAGAIN(e)) { /* it's a real error */
#ifdef MS_WINDOWS
      if (e == WSAENOBUFS)
        log_warn(LD_NET,"write() failed: WSAENOBUFS. Not enough ram?");
#endif
      return -1;
    }
    log_debug(LD_NET,"write() would block, returning.");
    return 0;
  } else {
    *buf_flushlen -= write_result;
    buf_remove_from_front(buf, write_result);
    tor_assert(write_result < INT_MAX);
    return (int)write_result;
  }
}

/** Helper for flush_buf_tls(): try to write <b>sz</b> bytes from chunk
 * <b>chunk</b> of buffer <b>buf</b> onto socket <b>s</b>.  (Tries to write
 * more if there is a forced pending write size.)  On success, deduct the
 * bytes written from *<b>buf_flushlen</b>.  Return the number of bytes
 * written on success, and a TOR_TLS error code on failue or blocking.
 */
static INLINE int
flush_chunk_tls(tor_tls_t *tls, buf_t *buf, chunk_t *chunk,
                size_t sz, size_t *buf_flushlen)
{
  int r;
  size_t forced;
  char *data;

  forced = tor_tls_get_forced_write_size(tls);
  if (forced > sz)
    sz = forced;
  if (chunk) {
    data = chunk->data;
    tor_assert(sz <= chunk->datalen);
  } else {
    data = NULL;
    tor_assert(sz == 0);
  }
  r = tor_tls_write(tls, data, sz);
  if (r < 0)
    return r;
  if (*buf_flushlen > (size_t)r)
    *buf_flushlen -= r;
  else
    *buf_flushlen = 0;
  buf_remove_from_front(buf, r);
  log_debug(LD_NET,"flushed %d bytes, %d ready to flush, %d remain.",
            r,(int)*buf_flushlen,(int)buf->datalen);
  return r;
}

/** Write data from <b>buf</b> to the socket <b>s</b>.  Write at most
 * <b>sz</b> bytes, decrement *<b>buf_flushlen</b> by
 * the number of bytes actually written, and remove the written bytes
 * from the buffer.  Return the number of bytes written on success,
 * -1 on failure.  Return 0 if write() would block.
 */
int
flush_buf(int s, buf_t *buf, size_t sz, size_t *buf_flushlen)
{
  /* XXXX021 It's stupid to overload the return values for these functions:
   * "error status" and "number of bytes flushed" are not mutually exclusive.
   */
  int r;
  size_t flushed = 0;
  tor_assert(buf_flushlen);
  tor_assert(s >= 0);
  tor_assert(*buf_flushlen <= buf->datalen);
  tor_assert(sz <= *buf_flushlen);

  check();
  while (sz) {
    size_t flushlen0;
    tor_assert(buf->head);
    if (buf->head->datalen >= sz)
      flushlen0 = sz;
    else
      flushlen0 = buf->head->datalen;

    r = flush_chunk(s, buf, buf->head, flushlen0, buf_flushlen);
    check();
    if (r < 0)
      return r;
    flushed += r;
    sz -= r;
    if (r == 0 || (size_t)r < flushlen0) /* can't flush any more now. */
      break;
  }
  tor_assert(flushed < INT_MAX);
  return (int)flushed;
}

/** As flush_buf(), but writes data to a TLS connection.  Can write more than
 * <b>flushlen</b> bytes.
 */
int
flush_buf_tls(tor_tls_t *tls, buf_t *buf, size_t flushlen,
              size_t *buf_flushlen)
{
  int r;
  size_t flushed = 0;
  ssize_t sz;
  tor_assert(buf_flushlen);
  tor_assert(*buf_flushlen <= buf->datalen);
  tor_assert(flushlen <= *buf_flushlen);
  sz = (ssize_t) flushlen;

  /* we want to let tls write even if flushlen is zero, because it might
   * have a partial record pending */
  check_no_tls_errors();

  check();
  do {
    size_t flushlen0;
    if (buf->head) {
      if ((ssize_t)buf->head->datalen >= sz)
        flushlen0 = sz;
      else
        flushlen0 = buf->head->datalen;
    } else {
      flushlen0 = 0;
    }

    r = flush_chunk_tls(tls, buf, buf->head, flushlen0, buf_flushlen);
    check();
    if (r < 0)
      return r;
    flushed += r;
    sz -= r;
    if (r == 0) /* Can't flush any more now. */
      break;
  } while (sz > 0);
  tor_assert(flushed < INT_MAX);
  return (int)flushed;
}

/** Append <b>string_len</b> bytes from <b>string</b> to the end of
 * <b>buf</b>.
 *
 * Return the new length of the buffer on success, -1 on failure.
 */
int
write_to_buf(const char *string, size_t string_len, buf_t *buf)