ICMP 回显

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。

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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