text: // Copyright 2016 The Fuchsia Authors
  // Copyright (c) 2014 Travis Geiselbrecht
  //
  // Use of this source code is governed by a MIT-style
  // license that can be found in the LICENSE file or at
  // https://opensource.org/licenses/MIT
  
  #include <iovec.h>
  
  #include <assert.h>
  #include <debug.h>
  #include <err.h>
  #include <string.h>
  #include <sys/types.h>
  
  #define LOCAL_TRACE 0
  
  /*
   *  Calc total size of iovec buffers
   */
  ssize_t iovec_size(const iovec_t* iov, uint iov_cnt) {
      if (!iov) {
          return (ssize_t)ZX_ERR_INVALID_ARGS;
      }
  
      size_t c = 0;
      for (uint i = 0; i < iov_cnt; i++, iov++) {
          c += iov->iov_len;
      }
      return (ssize_t)c;
  }
  
  /*
   *  Copy out portion of iovec started from given position
   *  into single buffer
   */
  ssize_t iovec_to_membuf(uint8_t* buf, uint buf_len, const iovec_t* iov, uint iov_cnt, uint iov_pos) {
      uint buf_pos = 0;
  
      if (!buf || !iov) {
          return (ssize_t)ZX_ERR_INVALID_ARGS;
      }
  
      /* for all iovec */
      for (uint i = 0; i < iov_cnt; i++, iov++) {
  
          if (iov_pos >= iov->iov_len) {
              iov_pos -= iov->iov_len; /* skip whole chunks */
              continue;
          }
  
          /* calc number of bytes left in current iov */
          size_t to_copy = (size_t)(iov->iov_len - iov_pos);
  
          /* limit it to number of bytes left in buffer */
          if (to_copy > buf_len) {
              to_copy = buf_len;
          }
  
          /* copy data out */
          memcpy(buf + buf_pos, (uint8_t*)iov->iov_base + iov_pos, to_copy);
  
          /* advance in buffer position */
          buf_pos += to_copy;
          buf_len -= to_copy;
  
          /* check if we need to copy more data */
          if (buf_len == 0) {
              break;
          }
  
          iov_pos = 0; /* it is only possible to have fully copied iovec here */
      }
  
      return (ssize_t)buf_pos;
  }
  