# ICMP Echo

[中文]

## 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 or 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);
        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 feeds 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 does not 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 will not 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 Examples

- protocols/icmp_echo demonstrates how to implement a simple ping command line utility to test if a remote host is reachable on the IP network, using ICMP echo request packets.

- protocols/icmp/pmtu_probe demonstrates how to probe path MTU with ICMP echo requests and apply the result to the active interface using `esp_netif_set_mtu()`.

## API Reference

### Header File

- components/lwip/include/apps/ping/ping_sock.h

- This header file can be included with:

  >     #include "ping/ping_sock.h"

- This header file is a part of the API provided by the `lwip` component. To declare that your component depends on `lwip`, add the following to your CMakeLists.txt:

  >     REQUIRES lwip

  > or

  >     PRIV_REQUIRES lwip

### 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.

  Parameters:

    - config -- ping configuration

    - cbs -- a bunch of callback functions invoked by internal ping task

    - hdl_out -- handle of ping session

  Returns:

    - 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

esp_err_t esp_ping_delete_session(esp_ping_handle_t hdl)

  Delete a ping session.

  Parameters:

    hdl -- handle of ping session

  Returns:

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

    - ESP_OK: delete ping session successfully

esp_err_t esp_ping_start(esp_ping_handle_t hdl)

  Start the ping session.

  Parameters:

    hdl -- handle of ping session

  Returns:

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

    - ESP_OK: start ping session successfully

esp_err_t esp_ping_stop(esp_ping_handle_t hdl)

  Stop the ping session.

  Parameters:

    hdl -- handle of ping session

  Returns:

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

    - ESP_OK: stop ping session successfully

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.

  Parameters:

    - hdl -- handle of ping session

    - profile -- type of profile

    - data -- profile data

    - size -- profile data size

  Returns:

    - 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

### 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

  int tos

    Type of Service, a field specified in the IP header

  int ttl

    Time to Live,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:

  enumerator ESP_PING_PROF_SEQNO

    Sequence number of a ping procedure

  enumerator ESP_PING_PROF_TOS

    Type of service of a ping procedure

  enumerator ESP_PING_PROF_TTL

    Time to live of a ping procedure

  enumerator ESP_PING_PROF_REQUEST

    Number of request packets sent out

  enumerator ESP_PING_PROF_REPLY

    Number of reply packets received

  enumerator ESP_PING_PROF_IPADDR

    IP address of replied target

  enumerator ESP_PING_PROF_SIZE

    Size of received packet

  enumerator ESP_PING_PROF_TIMEGAP

    Elapsed time between request and reply packet

  enumerator ESP_PING_PROF_DURATION

    Elapsed time of the whole ping session

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