Merge cherrypicks of ['googleplex-android-review.googlesource.com/25558746']...

static BT_HDR* attp_build_value_cmd(uint16_t payload_size, uint8_t op_code,

                                    uint16_t handle, uint16_t offset,

                                    uint16_t len, uint8_t* p_data) {

  uint8_t *p, *pp, *p_pair_len;

  size_t pair_len;

  size_t size_now = 1;

  #define CHECK_SIZE() do {                      \

    if (size_now > payload_size) {               \

      LOG(ERROR) << "payload size too small";    \

      osi_free(p_buf);                           \

      return nullptr;                            \

    }                                            \

  } while (false)

  uint8_t *p, *pp, pair_len, *p_pair_len;

  BT_HDR* p_buf =

      (BT_HDR*)osi_malloc(sizeof(BT_HDR) + payload_size + L2CAP_MIN_OFFSET);

  p = pp = (uint8_t*)(p_buf + 1) + L2CAP_MIN_OFFSET;

  CHECK_SIZE();

  UINT8_TO_STREAM(p, op_code);

  p_buf->offset = L2CAP_MIN_OFFSET;

  p_buf->len = 1;

  if (op_code == GATT_RSP_READ_BY_TYPE) {

    p_pair_len = p;

    pair_len = len + 2;

    size_now += 1;

    CHECK_SIZE();

    // this field will be backfilled in the end of this function

    UINT8_TO_STREAM(p, pair_len);

    p_buf->len += 1;

  }

  if (op_code != GATT_RSP_READ_BLOB && op_code != GATT_RSP_READ) {

    size_now += 2;

    CHECK_SIZE();

    UINT16_TO_STREAM(p, handle);

    p_buf->len += 2;

  }

  if (op_code == GATT_REQ_PREPARE_WRITE || op_code == GATT_RSP_PREPARE_WRITE) {

    size_now += 2;

    CHECK_SIZE();

    UINT16_TO_STREAM(p, offset);

    p_buf->len += 2;

  }

  if (len > 0 && p_data != NULL && payload_size > size_now) {

  if (len > 0 && p_data != NULL) {

    /* ensure data not exceed MTU size */

    if (payload_size - size_now < len) {

      len = payload_size - size_now;

    if (payload_size - p_buf->len < len) {

      len = payload_size - p_buf->len;

      /* update handle value pair length */

      if (op_code == GATT_RSP_READ_BY_TYPE) {

        pair_len = (len + 2);

      }

      if (op_code == GATT_RSP_READ_BY_TYPE) *p_pair_len = (len + 2);

      LOG(WARNING) << StringPrintf(

          "attribute value too long, to be truncated to %d", len);

    }

    size_now += len;

    CHECK_SIZE();

    ARRAY_TO_STREAM(p, p_data, len);

    p_buf->len += len;

  }

  // backfill pair len field

  if (op_code == GATT_RSP_READ_BY_TYPE) {

    if (pair_len > UINT8_MAX) {

      LOG(ERROR) << "pair_len greater than" << UINT8_MAX;

      osi_free(p_buf);

      return nullptr;

    }

    *p_pair_len = (uint8_t) pair_len;

  }

  #undef CHECK_SIZE

  p_buf->len = (uint16_t) size_now;

  return p_buf;

}