ICMP Echo

Overview

ICMP (Internet Control Message Protocol) is used for diagnostic or control purposes or generated in response to errors in IP operations. The common network util ping is implemented based on the ICMP packets with the type field value of 0, also called Echo Reply.

During a ping session, the source host firstly sends out an ICMP echo request packet and wait for an ICMP echo reply with specific times. In this way, it also measures the round-trip time for the messages. After receiving a valid ICMP echo reply, the source host will generate statistics about the IP link layer (e.g. packet loss, elapsed time, etc).

It is common that IoT device needs to check whether a remote server is alive or not. The device should show the warnings to users when it got offline. It can be achieved by creating a ping session and sending/parsing ICMP echo packets periodically.

To make this internal procedure much easier for users, ESP-IDF provides some out-of-box APIs.

Create a new ping session

To create a ping session, you need to fill in the esp_ping_config_t configuration structure firstly, specifying target IP address, interval times, and etc. Optionally, you can also register some callback functions with the esp_ping_callbacks_t` structure.

Example method to create a new ping session and register callbacks:

static void test_on_ping_success(esp_ping_handle_t hdl, void *args)
{
    // optionally, get callback arguments
    // const char* str = (const char*) args;
    // printf("%s\r\n", str); // "foo"
    uint8_t ttl;
    uint16_t seqno;
    uint32_t elapsed_time, recv_len;
    ip_addr_t target_addr;
    esp_ping_get_profile(hdl, ESP_PING_PROF_SEQNO, &seqno, sizeof(seqno));
    esp_ping_get_profile(hdl, ESP_PING_PROF_TTL, &ttl, sizeof(ttl));
    esp_ping_get_profile(hdl, ESP_PING_PROF_IPADDR, &target_addr, sizeof(target_addr));
    esp_ping_get_profile(hdl, ESP_PING_PROF_SIZE, &recv_len, sizeof(recv_len));
    esp_ping_get_profile(hdl, ESP_PING_PROF_TIMEGAP, &elapsed_time, sizeof(elapsed_time));
    printf("%d bytes from %s icmp_seq=%d ttl=%d time=%d ms\n",
           recv_len, inet_ntoa(target_addr.u_addr.ip4), seqno, ttl, elapsed_time);
}

static void test_on_ping_timeout(esp_ping_handle_t hdl, void *args)
{
    uint16_t seqno;
    ip_addr_t target_addr;
    esp_ping_get_profile(hdl, ESP_PING_PROF_SEQNO, &seqno, sizeof(seqno));
    esp_ping_get_profile(hdl, ESP_PING_PROF_IPADDR, &target_addr, sizeof(target_addr));
    printf("From %s icmp_seq=%d timeout\n", inet_ntoa(target_addr.u_addr.ip4), seqno);
}

static void test_on_ping_end(esp_ping_handle_t hdl, void *args)
{
    uint32_t transmitted;
    uint32_t received;
    uint32_t total_time_ms;

    esp_ping_get_profile(hdl, ESP_PING_PROF_REQUEST, &transmitted, sizeof(transmitted));
    esp_ping_get_profile(hdl, ESP_PING_PROF_REPLY, &received, sizeof(received));
    esp_ping_get_profile(hdl, ESP_PING_PROF_DURATION, &total_time_ms, sizeof(total_time_ms));
    printf("%d packets transmitted, %d received, time %dms\n", transmitted, received, total_time_ms);
}

void initialize_ping()
{
    /* convert URL to IP address */
    ip_addr_t target_addr;
    struct addrinfo hint;
    struct addrinfo *res = NULL;
    memset(&hint, 0, sizeof(hint));
    memset(&target_addr, 0, sizeof(target_addr));
    getaddrinfo("www.espressif.com", NULL, &hint, &res) == 0);
    struct in_addr addr4 = ((struct sockaddr_in *) (res->ai_addr))->sin_addr;
    inet_addr_to_ip4addr(ip_2_ip4(&target_addr), &addr4);
    freeaddrinfo(res);

    esp_ping_config_t ping_config = ESP_PING_DEFAULT_CONFIG();
    ping_config.target_addr = target_addr;          // target IP address
    ping_config.count = ESP_PING_COUNT_INFINITE;    // ping in infinite mode, esp_ping_stop can stop it

    /* set callback functions */
    esp_ping_callbacks_t cbs;
    cbs.on_ping_success = test_on_ping_success;
    cbs.on_ping_timeout = test_on_ping_timeout;
    cbs.on_ping_end = test_on_ping_end;
    cbs.cb_args = "foo";  // arguments that will feed to all callback functions, can be NULL
    cbs.cb_args = eth_event_group;

    esp_ping_handle_t ping;
    esp_ping_new_session(&ping_config, &cbs, &ping);
}

Start and Stop ping session

You can start and stop ping session with the handle returned by esp_ping_new_session. Note that, the ping session won’t start automatically after creation. If the ping session is stopped, and restart again, the sequence number in ICMP packets will recount from zero again.

Delete a ping session

If a ping session won’t be used any more, you can delete it with esp_ping_delete_session. Please make sure the ping session is in stop state (i.e. you have called esp_ping_stop before or the ping session has finished all the procedures) when you call this function.

Get runtime statistics

As the example code above, you can call esp_ping_get_profile to get different runtime statistics of ping session in the callback function.

Application Example

ICMP echo example: protocols/icmp_echo

API Reference

Header File

• lwip/include/apps/ping/ping_sock.h

Functions

esp_err_t esp_ping_new_session(const esp_ping_config_t *config, const esp_ping_callbacks_t *cbs, esp_ping_handle_t *hdl_out)

Create a ping session.

Return

• ESP_ERR_INVALID_ARG: invalid parameters (e.g. configuration is null, etc)

• ESP_ERR_NO_MEM: out of memory

• ESP_FAIL: other internal error (e.g. socket error)

• ESP_OK: create ping session successfully, user can take the ping handle to do follow-on jobs

Parameters

• config: ping configuration

• cbs: a bunch of callback functions invoked by internal ping task

• hdl_out: handle of ping session

esp_err_t esp_ping_delete_session(esp_ping_handle_t hdl)

Delete a ping session.

Return

• ESP_ERR_INVALID_ARG: invalid parameters (e.g. ping handle is null, etc)

• ESP_OK: delete ping session successfully

Parameters

• hdl: handle of ping session

esp_err_t esp_ping_start(esp_ping_handle_t hdl)

Start the ping session.

Return

• ESP_ERR_INVALID_ARG: invalid parameters (e.g. ping handle is null, etc)

• ESP_OK: start ping session successfully

Parameters

• hdl: handle of ping session

esp_err_t esp_ping_stop(esp_ping_handle_t hdl)

Stop the ping session.

Return

• ESP_ERR_INVALID_ARG: invalid parameters (e.g. ping handle is null, etc)

• ESP_OK: stop ping session successfully

Parameters

• hdl: handle of ping session

esp_err_t esp_ping_get_profile(esp_ping_handle_t hdl, esp_ping_profile_t profile, void *data, uint32_t size)

Get runtime profile of ping session.

Return

• ESP_ERR_INVALID_ARG: invalid parameters (e.g. ping handle is null, etc)

• ESP_ERR_INVALID_SIZE: the actual profile data size doesn’t match the “size” parameter

• ESP_OK: get profile successfully

Parameters

• hdl: handle of ping session

• profile: type of profile

• data: profile data

• size: profile data size

Structures

struct esp_ping_callbacks_t

Type of “ping” callback functions.

Public Members

void *cb_args

arguments for callback functions

void (*on_ping_success)(esp_ping_handle_t hdl, void *args)

Invoked by internal ping thread when received ICMP echo reply packet.

void (*on_ping_timeout)(esp_ping_handle_t hdl, void *args)

Invoked by internal ping thread when receive ICMP echo reply packet timeout.

void (*on_ping_end)(esp_ping_handle_t hdl, void *args)

Invoked by internal ping thread when a ping session is finished.

struct esp_ping_config_t

Type of “ping” configuration.

Public Members

uint32_t count

A “ping” session contains count procedures

uint32_t interval_ms

Milliseconds between each ping procedure

uint32_t timeout_ms

Timeout value (in milliseconds) of each ping procedure

uint32_t data_size

Size of the data next to ICMP packet header

uint8_t tos

Type of Service, a field specified in the IP header

ip_addr_t target_addr

Target IP address, either IPv4 or IPv6

uint32_t task_stack_size

Stack size of internal ping task

uint32_t task_prio

Priority of internal ping task

uint32_t interface

Netif index, interface=0 means NETIF_NO_INDEX

Macros

ESP_PING_DEFAULT_CONFIG()

Default ping configuration.

ESP_PING_COUNT_INFINITE

Set ping count to zero will ping target infinitely

Type Definitions

typedef void *esp_ping_handle_t

Type of “ping” session handle.

Enumerations

enum esp_ping_profile_t

Profile of ping session.

Values:

ESP_PING_PROF_SEQNO

Sequence number of a ping procedure

ESP_PING_PROF_TTL

Time to live of a ping procedure

ESP_PING_PROF_REQUEST

Number of request packets sent out

ESP_PING_PROF_REPLY

Number of reply packets received

ESP_PING_PROF_IPADDR

IP address of replied target

ESP_PING_PROF_SIZE

Size of received packet

ESP_PING_PROF_TIMEGAP

Elapsed time between request and reply packet

ESP_PING_PROF_DURATION

Elapsed time of the whole ping session

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