Connections

Connections are essential feature of WiFi device and middleware. It is developed with strong focus on its performance and since it may interact with huge amount of data, it tries to use zero-copy (when available) feature, to decrease processing time.

GSM AT Firmware by default supports up to 5 connections being active at the same time and supports:

  • Up to 5 TCP connections active at the same time

  • Up to 5 UDP connections active at the same time

  • Up to 1 SSL connection active at a time

Note

Client or server connections are available. Same API function call are used to send/receive data or close connection.

Architecture of the connection API is using callback event functions. This allows maximal optimization in terms of responsiveness on different kind of events.

Example below shows bare minimum implementation to:

  • Start a new connection to remote host

  • Send HTTP GET request to remote host

  • Process received data in event and print number of received bytes

Client connection minimum example
  1#include "client.h"
  2#include "lwgsm/lwgsm.h"
  3#include "lwgsm/lwgsm_network_api.h"
  4
  5/* Host parameter */
  6#define CONN_HOST           "example.com"
  7#define CONN_PORT           80
  8
  9static lwgsmr_t   conn_callback_func(lwgsm_evt_t* evt);
 10
 11/**
 12 * \brief           Request data for connection
 13 */
 14static const
 15uint8_t req_data[] = ""
 16                     "GET / HTTP/1.1\r\n"
 17                     "Host: " CONN_HOST "\r\n"
 18                     "Connection: close\r\n"
 19                     "\r\n";
 20
 21/**
 22 * \brief           Start a new connection(s) as client
 23 */
 24void
 25client_connect(void) {
 26    lwgsmr_t res;
 27
 28    /* Attach to GSM network */
 29    lwgsm_network_request_attach();
 30
 31    /* Start a new connection as client in non-blocking mode */
 32    if ((res = lwgsm_conn_start(NULL, LWGSM_CONN_TYPE_TCP, "example.com", 80, NULL, conn_callback_func, 0)) == lwgsmOK) {
 33        printf("Connection to " CONN_HOST " started...\r\n");
 34    } else {
 35        printf("Cannot start connection to " CONN_HOST "!\r\n");
 36    }
 37}
 38
 39/**
 40 * \brief           Event callback function for connection-only
 41 * \param[in]       evt: Event information with data
 42 * \return          \ref lwgsmOK on success, member of \ref lwgsmr_t otherwise
 43 */
 44static lwgsmr_t
 45conn_callback_func(lwgsm_evt_t* evt) {
 46    lwgsm_conn_p conn;
 47    lwgsmr_t res;
 48    uint8_t conn_num;
 49
 50    conn = lwgsm_conn_get_from_evt(evt);          /* Get connection handle from event */
 51    if (conn == NULL) {
 52        return lwgsmERR;
 53    }
 54    conn_num = lwgsm_conn_getnum(conn);           /* Get connection number for identification */
 55    switch (lwgsm_evt_get_type(evt)) {
 56        case LWGSM_EVT_CONN_ACTIVE: {             /* Connection just active */
 57            printf("Connection %d active!\r\n", (int)conn_num);
 58            res = lwgsm_conn_send(conn, req_data, sizeof(req_data) - 1, NULL, 0); /* Start sending data in non-blocking mode */
 59            if (res == lwgsmOK) {
 60                printf("Sending request data to server...\r\n");
 61            } else {
 62                printf("Cannot send request data to server. Closing connection manually...\r\n");
 63                lwgsm_conn_close(conn, 0);        /* Close the connection */
 64            }
 65            break;
 66        }
 67        case LWGSM_EVT_CONN_CLOSE: {              /* Connection closed */
 68            if (lwgsm_evt_conn_close_is_forced(evt)) {
 69                printf("Connection %d closed by client!\r\n", (int)conn_num);
 70            } else {
 71                printf("Connection %d closed by remote side!\r\n", (int)conn_num);
 72            }
 73            break;
 74        }
 75        case LWGSM_EVT_CONN_SEND: {               /* Data send event */
 76            lwgsmr_t res = lwgsm_evt_conn_send_get_result(evt);
 77            if (res == lwgsmOK) {
 78                printf("Data sent successfully on connection %d...waiting to receive data from remote side...\r\n", (int)conn_num);
 79            } else {
 80                printf("Error while sending data on connection %d!\r\n", (int)conn_num);
 81            }
 82            break;
 83        }
 84        case LWGSM_EVT_CONN_RECV: {               /* Data received from remote side */
 85            lwgsm_pbuf_p pbuf = lwgsm_evt_conn_recv_get_buff(evt);
 86            lwgsm_conn_recved(conn, pbuf);        /* Notify stack about received pbuf */
 87            printf("Received %d bytes on connection %d..\r\n", (int)lwgsm_pbuf_length(pbuf, 1), (int)conn_num);
 88            break;
 89        }
 90        case LWGSM_EVT_CONN_ERROR: {              /* Error connecting to server */
 91            const char* host = lwgsm_evt_conn_error_get_host(evt);
 92            lwgsm_port_t port = lwgsm_evt_conn_error_get_port(evt);
 93            printf("Error connecting to %s:%d\r\n", host, (int)port);
 94            break;
 95        }
 96        default:
 97            break;
 98    }
 99    return lwgsmOK;
100}

Sending data

Receiving data flow is always the same. Whenever new data packet arrives, corresponding event is called to notify application layer. When it comes to sending data, application may decide between 2 options (*this is valid only for non-UDP connections):

  • Write data to temporary transmit buffer

  • Execute send command for every API function call

Temporary transmit buffer

By calling lwgsm_conn_write() on active connection, temporary buffer is allocated and input data are copied to it. There is always up to 1 internal buffer active. When it is full (or if input data length is longer than maximal size), data are immediately send out and are not written to buffer.

GSM AT Firmware allows (current revision) to transmit up to 2048 bytes at a time with single command. When trying to send more than this, application would need to issue multiple send commands on AT commands level.

Write option is used mostly when application needs to write many different small chunks of data. Temporary buffer hence prevents many send command instructions as it is faster to send single command with big buffer, than many of them with smaller chunks of bytes.

Transmit packet manually

In some cases it is not possible to use temporary buffers, mostly because of memory constraints. Application can directly start send data instructions on AT level by using lwgsm_conn_send() or lwgsm_conn_sendto() functions.

group LWGSM_CONN

Connection API functions.

Typedefs

typedef struct lwgsm_conn *lwgsm_conn_p

Pointer to lwgsm_conn_t structure.

Enums

enum lwgsm_conn_type_t

List of possible connection types.

Values:

enumerator LWGSM_CONN_TYPE_TCP

Connection type is TCP

enumerator LWGSM_CONN_TYPE_UDP

Connection type is UDP

enumerator LWGSM_CONN_TYPE_SSL

Connection type is TCP over SSL

Functions

lwgsmr_t lwgsm_conn_start(lwgsm_conn_p *conn, lwgsm_conn_type_t type, const char *const host, lwgsm_port_t port, void *const arg, lwgsm_evt_fn conn_evt_fn, const uint32_t blocking)

Start a new connection of specific type.

Parameters

  • conn – [out] Pointer to connection handle to set new connection reference in case of successful connection

  • type – [in] Connection type. This parameter can be a value of lwgsm_conn_type_t enumeration

  • host – [in] Connection host. In case of IP, write it as string, ex. “192.168.1.1”

  • port – [in] Connection port

  • arg – [in] Pointer to user argument passed to connection if successfully connected

  • conn_evt_fn – [in] Callback function for this connection

  • blocking – [in] Status whether command should be blocking or not

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

lwgsmr_t lwgsm_conn_close(lwgsm_conn_p conn, const uint32_t blocking)

Close specific or all connections.

Parameters

  • conn – [in] Connection handle to close. Set to NULL if you want to close all connections.

  • blocking – [in] Status whether command should be blocking or not

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

lwgsmr_t lwgsm_conn_send(lwgsm_conn_p conn, const void *data, size_t btw, size_t *const bw, const uint32_t blocking)

Send data on already active connection either as client or server.

Parameters

  • conn – [in] Connection handle to send data

  • data – [in] Data to send

  • btw – [in] Number of bytes to send

  • bw – [out] Pointer to output variable to save number of sent data when successfully sent. Parameter value might not be accurate if you combine lwgsm_conn_write and lwgsm_conn_send functions

  • blocking – [in] Status whether command should be blocking or not

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

lwgsmr_t lwgsm_conn_sendto(lwgsm_conn_p conn, const lwgsm_ip_t *const ip, lwgsm_port_t port, const void *data, size_t btw, size_t *bw, const uint32_t blocking)

Send data on active connection of type UDP to specific remote IP and port.

Note

In case IP and port values are not set, it will behave as normal send function (suitable for TCP too)

Parameters

  • conn – [in] Connection handle to send data

  • ip – [in] Remote IP address for UDP connection

  • port – [in] Remote port connection

  • data – [in] Pointer to data to send

  • btw – [in] Number of bytes to send

  • bw – [out] Pointer to output variable to save number of sent data when successfully sent

  • blocking – [in] Status whether command should be blocking or not

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

lwgsmr_t lwgsm_conn_set_arg(lwgsm_conn_p conn, void *const arg)

Set argument variable for connection.

See

lwgsm_conn_get_arg

Parameters

  • conn – [in] Connection handle to set argument

  • arg – [in] Pointer to argument

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

void *lwgsm_conn_get_arg(lwgsm_conn_p conn)

Get user defined connection argument.

See

lwgsm_conn_set_arg

Parameters

conn – [in] Connection handle to get argument

Returns

User argument

uint8_t lwgsm_conn_is_client(lwgsm_conn_p conn)

Check if connection type is client.

Parameters

conn – [in] Pointer to connection to check for status

Returns

1 on success, 0 otherwise

uint8_t lwgsm_conn_is_active(lwgsm_conn_p conn)

Check if connection is active.

Parameters

conn – [in] Pointer to connection to check for status

Returns

1 on success, 0 otherwise

uint8_t lwgsm_conn_is_closed(lwgsm_conn_p conn)

Check if connection is closed.

Parameters

conn – [in] Pointer to connection to check for status

Returns

1 on success, 0 otherwise

int8_t lwgsm_conn_getnum(lwgsm_conn_p conn)

Get the number from connection.

Parameters

conn – [in] Connection pointer

Returns

Connection number in case of success or -1 on failure

lwgsmr_t lwgsm_get_conns_status(const uint32_t blocking)

Gets connections status.

Parameters

blocking – [in] Status whether command should be blocking or not

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

lwgsm_conn_p lwgsm_conn_get_from_evt(lwgsm_evt_t *evt)

Get connection from connection based event.

Parameters

evt – [in] Event which happened for connection

Returns

Connection pointer on success, NULL otherwise

lwgsmr_t lwgsm_conn_write(lwgsm_conn_p conn, const void *data, size_t btw, uint8_t flush, size_t *const mem_available)

Write data to connection buffer and if it is full, send it non-blocking way.

Note

This function may only be called from core (connection callbacks)

Parameters

  • conn – [in] Connection to write

  • data – [in] Data to copy to write buffer

  • btw – [in] Number of bytes to write

  • flush – [in] Flush flag. Set to 1 if you want to send data immediately after copying

  • mem_available – [out] Available memory size available in current write buffer. When the buffer length is reached, current one is sent and a new one is automatically created. If function returns lwgsmOK and *mem_available = 0, there was a problem allocating a new buffer for next operation

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

lwgsmr_t lwgsm_conn_recved(lwgsm_conn_p conn, lwgsm_pbuf_p pbuf)

Notify connection about received data which means connection is ready to accept more data.

Once data reception is confirmed, stack will try to send more data to user.

Note

Since this feature is not supported yet by AT commands, function is only prototype and should be used in connection callback when data are received

Note

Function is not thread safe and may only be called from connection event function

Parameters

  • conn – [in] Connection handle

  • pbuf – [in] Packet buffer received on connection

Returns

lwgsmOK on success, member of lwgsmr_t enumeration otherwise

size_t lwgsm_conn_get_total_recved_count(lwgsm_conn_p conn)

Get total number of bytes ever received on connection and sent to user.

Parameters

conn – [in] Connection handle

Returns

Count of received bytes on connection

uint8_t lwgsm_conn_get_remote_ip(lwgsm_conn_p conn, lwgsm_ip_t *ip)

Get connection remote IP address.

Parameters

  • conn – [in] Connection handle

  • ip – [out] Pointer to IP output handle

Returns

1 on success, 0 otherwise

lwgsm_port_t lwgsm_conn_get_remote_port(lwgsm_conn_p conn)

Get connection remote port number.

Parameters

conn – [in] Connection handle

Returns

Port number on success, 0 otherwise

lwgsm_port_t lwgsm_conn_get_local_port(lwgsm_conn_p conn)

Get connection local port number.

Parameters

conn – [in] Connection handle

Returns

Port number on success, 0 otherwise