# ICMP 回显

[English]

## 概述

网际控制报文协议 (ICMP) 通常用于诊断或控制目的，或响应 IP 操作中的错误。常用的网络工具 `ping` 的应答，即 `Echo Reply`，就是基于类型字段值为 0 的 ICMP 数据包实现的。

在 ping 会话中，首先由源主机发出请求包 (ICMP echo request)，然后等待应答包 (ICMP echo reply)，等待具有超时限制。通过这一过程，还能测量出信息的往返用时。收到有效的应答包后，源主机会生成 IP 链路层的统计数据（如失包率、运行时间等）。

IoT 设备通常需要检查远程服务器是否可用。如果服务器离线，设备应向用户发出警告。通过创建 ping 会话，定期发送或解析 ICMP echo 数据包，就能实现这一功能。

为简化这一过程方便用户操作，ESP-IDF 提供了一些好用的 API。

### 创建 ping 会话

要创建 ping 会话，首先需填写 `esp_ping_config_t`，指定目标芯片 IP 地址、间隔时间等配置。此外，还可以通过 `esp_ping_callbacks_t` 注册回调函数。

创建 ping 会话并注册回调函数示例：

    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 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);
    }

### 启动和停止 ping 会话

使用 `esp_ping_new_session` 返回的句柄可以启动或停止 ping 会话。注意，ping 会话在创建后不会自动启动。如果 ping 会话停止后重启，ICMP 数据包的序列号会归零重新计数。

### 删除 ping 会话

如果不再使用 ping 会话，可用 `esp_ping_delete_session` 将其删除。在删除 ping 会话时，确保该会话已处于停止状态（即已调用了 `esp_ping_stop` ，或该会话已完成所有步骤）。

### 获取运行时间数据

在回调函数中调用 `esp_ping_get_profile`，可获取 ping 会话的不同运行时间数据，如上文代码示例所示。

## 应用示例

- protocols/icmp_echo 演示了如何实现一个简单的 ping 命令行工具，使用 ICMP 回显请求数据包测试远程主机在 IP 网络上的可达性。

- protocols/icmp/pmtu_probe 演示了如何使用 ICMP 回显请求探测路径 MTU，并通过 `esp_netif_set_mtu()` 将探测结果应用到活动接口。

## API 参考

### 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.

  参数:

    - config -- ping configuration

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

    - hdl_out -- handle of ping session

  返回:

    - 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.

  参数:

    hdl -- handle of ping session

  返回:

    - 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.

  参数:

    hdl -- handle of ping session

  返回:

    - 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.

  参数:

    hdl -- handle of ping session

  返回:

    - 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.

  参数:

    - hdl -- handle of ping session

    - profile -- type of profile

    - data -- profile data

    - size -- profile data size

  返回:

    - 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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