static int MqttClient_Publish_WritePayload(MqttClient *client,
    MqttPublish *publish, MqttPublishCb pubCb)
{
    int rc = MQTT_CODE_SUCCESS;

    if (client == NULL || publish == NULL)
        return MQTT_CODE_ERROR_BAD_ARG;

    if (pubCb) {
        word32 tmp_len = publish->buffer_len;

        do {
            /* Use the callback to get payload */
            if ((client->write.len = pubCb(publish)) < 0) {
                return MQTT_CODE_ERROR_CALLBACK;
            }

            if ((word32)client->write.len < publish->buffer_len) {
                /* Last read */
                tmp_len = (word32)client->write.len;
            }

            /* Send payload */
            do {
                if (client->write.len > client->tx_buf_len) {
                    client->write.len = client->tx_buf_len;
                }
                publish->intBuf_len = client->write.len;
                XMEMCPY(client->tx_buf, &publish->buffer[publish->intBuf_pos],
                    client->write.len);

                rc = MqttPacket_Write(client, client->tx_buf,
                        client->write.len);
                if (rc < 0) {
                    return rc;
                }

                publish->intBuf_pos += publish->intBuf_len;
                publish->intBuf_len = 0;

            } while (publish->intBuf_pos < tmp_len);

            publish->buffer_pos += publish->intBuf_pos;
            publish->intBuf_pos = 0;

        } while (publish->buffer_pos < publish->total_len);
    }
    else if (publish->buffer_pos < publish->total_len) {
        if (publish->buffer_pos > 0) {
            client->write.len = (publish->total_len - publish->buffer_pos);
            if (client->write.len > client->tx_buf_len) {
                client->write.len = client->tx_buf_len;
            }

            XMEMCPY(client->tx_buf, &publish->buffer[publish->buffer_pos],
                client->write.len);

        #ifndef WOLFMQTT_NONBLOCK
            publish->intBuf_pos += client->write.len;
        #endif
        }

        /* Send packet and payload */
    #ifdef WOLFMQTT_NONBLOCK
            rc = MqttPacket_Write(client, client->tx_buf,
                    client->write.len);
            if (rc < 0) {
                return rc;
            }

            /* ONLY if send was successful, update buffer position.
             * Otherwise, MqttPacket_Write() will resume where it left off. */
            publish->buffer_pos += client->write.len;

            /* Check if we are done sending publish message */
            if (publish->buffer_pos < publish->buffer_len) {
                return MQTT_CODE_PUB_CONTINUE;
            }
    #else
        do {
            rc = MqttPacket_Write(client, client->tx_buf,
                    client->write.len);
            if (rc < 0) {
                return rc;
            }

            publish->intBuf_pos += publish->intBuf_len;
            publish->intBuf_len = 0;

            /* Check if we are done sending publish message */
            if (publish->intBuf_pos >= publish->buffer_len) {
                rc = MQTT_CODE_SUCCESS;
                break;
            }

            /* Build packet payload to send */
            client->write.len = (publish->buffer_len - publish->intBuf_pos);
            if (client->write.len > client->tx_buf_len) {
                client->write.len = client->tx_buf_len;
            }
            publish->intBuf_len = client->write.len;
            XMEMCPY(client->tx_buf, &publish->buffer[publish->intBuf_pos],
                client->write.len);
        } while (publish->intBuf_pos < publish->buffer_len);
    #endif

        if (rc >= 0) {
            /* If transferring more chunks */
            publish->buffer_pos += publish->intBuf_pos;
            if (publish->buffer_pos < publish->total_len) {
                /* Build next payload to send */
                client->write.len = (publish->total_len - publish->buffer_pos);
                if (client->write.len > client->tx_buf_len) {
                    client->write.len = client->tx_buf_len;
                }
                rc = MQTT_CODE_PUB_CONTINUE;
            }
        }
    }
    return rc;
}
static int MqttClient_Publish_WritePayload(MqttClient *client,
    MqttPublish *publish, MqttPublishCb pubCb)
{
    int rc = MQTT_CODE_SUCCESS;

    if (client == NULL || publish == NULL)
        return MQTT_CODE_ERROR_BAD_ARG;

    if (pubCb) {
        word32 tmp_len = publish->buffer_len;

        do {
             
            if ((client->write.len = pubCb(publish)) < 0) {
                return MQTT_CODE_ERROR_CALLBACK;
            }

            if ((word32)client->write.len < publish->buffer_len) {
                 
                tmp_len = (word32)client->write.len;
            }

             
            do {
                if (client->write.len > client->tx_buf_len) {
                    client->write.len = client->tx_buf_len;
                }
                publish->intBuf_len = client->write.len;
                XMEMCPY(client->tx_buf, &publish->buffer[publish->intBuf_pos],
                    client->write.len);

                rc = MqttPacket_Write(client, client->tx_buf,
                        client->write.len);
                if (rc < 0) {
                    return rc;
                }

                publish->intBuf_pos += publish->intBuf_len;
                publish->intBuf_len = 0;

            } while (publish->intBuf_pos < tmp_len);

            publish->buffer_pos += publish->intBuf_pos;
            publish->intBuf_pos = 0;

        } while (publish->buffer_pos < publish->total_len);
    }
    else if (publish->buffer_pos < publish->total_len) {
        if (publish->buffer_pos > 0) {
            client->write.len = (publish->total_len - publish->buffer_pos);
            if (client->write.len > client->tx_buf_len) {
                client->write.len = client->tx_buf_len;
            }

            XMEMCPY(client->tx_buf, &publish->buffer[publish->buffer_pos],
                client->write.len);

        #ifndef WOLFMQTT_NONBLOCK
            publish->intBuf_pos += client->write.len;
        #endif
        }

         
    #ifdef WOLFMQTT_NONBLOCK
            rc = MqttPacket_Write(client, client->tx_buf,
                    client->write.len);
            if (rc < 0) {
                return rc;
            }

             
            publish->buffer_pos += client->write.len;

             
            if (publish->buffer_pos < publish->buffer_len) {
                return MQTT_CODE_PUB_CONTINUE;
            }
    #else
        do {
            rc = MqttPacket_Write(client, client->tx_buf,
                    client->write.len);
            if (rc < 0) {
                return rc;
            }

            publish->intBuf_pos += publish->intBuf_len;
            publish->intBuf_len = 0;

             
            if (publish->intBuf_pos >= publish->buffer_len) {
                rc = MQTT_CODE_SUCCESS;
                break;
            }

             
            client->write.len = (publish->buffer_len - publish->intBuf_pos);
            if (client->write.len > client->tx_buf_len) {
                client->write.len = client->tx_buf_len;
            }
            publish->intBuf_len = client->write.len;
            XMEMCPY(client->tx_buf, &publish->buffer[publish->intBuf_pos],
                client->write.len);
        } while (publish->intBuf_pos < publish->buffer_len);
    #endif

        if (rc >= 0) {
             
            publish->buffer_pos += publish->intBuf_pos;
            if (publish->buffer_pos < publish->total_len) {
                 
                client->write.len = (publish->total_len - publish->buffer_pos);
                if (client->write.len > client->tx_buf_len) {
                    client->write.len = client->tx_buf_len;
                }
                rc = MQTT_CODE_PUB_CONTINUE;
            }
        }
    }
    return rc;
}