COAP协议 - arduino ESP32 M2M(端对端)通讯与代码详解
前言
最近我在研究 COAP 协议,在尝试使用 COAP 协议找了到了一个能在ESP32上用的coap-simple库,虽然库并不完善关于loop处理的部分应该是没写完,但是对于第一次接触COAP的朋友来说更容易理解,方便学习,需要的朋友可以去下面下载:
https://域名/hirotakaster/CoAP-simple-library
我之前使用 IOT PI 的 COAP 能和 PC node coap 通讯,但是因为 coap-simple 库不完善,正常的无法与 node coap 通讯,只能和同样使用这个库设备通讯,这次就来尝试 ESP32 之间的 M2M 通讯。
获取库
使用 arduino IDE 就能下载到这个库:
如果没有看到这个库,可以去首选项添加一下附加开发板管理器网址:
https://域名/espressif/arduino-esp32/releases/download/1.0.5/域名
具体使用可以参考的我 arduino 超详细的开发入门指导 或者直接通过我上面发的 GitHub 网址下载。
代码解析
以下代码为了方便讲解,可能经过了调换了顺序或者裁剪。
这个 demo 是客户端、服务端一体的,只需要注册对应的回调函数就行。
初始化部分
这部分包括了设备初始化,协议初始化等部分,重点在服务器/客户端的回调函数部分。和 SDDC 官方demo类似,在这注册回调函数之后,通过对应的端点找到对应的回调函数。
#include <WiFi.h>
#include <WiFiUdp.h>
#include <coap-simple.h>
void setup() {
域名n(115200);
域名n(ssid, password);
while (域名us() != WL_CONNECTED) {
delay(500);
域名t(".");
}
域名tln("");
域名tln("WiFi connected");
域名tln("IP address: ");
域名tln(域名lIP());
// LED State
pinMode(9, OUTPUT);
digitalWrite(9, HIGH);
LEDSTATE = true;
// 添加服务器url端点.
// 可以添加多个端点url.
// 域名er(callback_switch, "switch");
// 域名er(callback_env, "env/temp");
// 域名er(callback_env, "env/humidity");
域名tln("Setup Callback Light");
// 其实就是注册服务器处理回调函数
// 将处理函数指针与url添加到 域名 中
域名er(callback_light, "light");
// 注册客户端响应的回调函数。
// this endpoint is single callback.
域名tln("Setup Response Callback");
// 很上面一样,其实就是把回调函数指针注册到resp里
域名onse(callback_response);
// 使用默认端口5683 启动 coap server/client
域名t();
}
void loop() {
// 作为客户端时向coap服务器发送GET或PUT coap请求.
// 可以发送给另外一个 ESP32
// msgid = 域名(IPAddress(192, 168, 128, 101), 5683, "light", "0");
// msgid = 域名(IPAddress(192, 168, 128, 101), 5683, "light");
delay(1000);
域名();
}
回调函数
// CoAP 服务器端点 URL ,对客户端发过来的命令进行处理并且回应
void callback_light(CoapPacket &packet, IPAddress ip, int port)
{
// 这是一个模拟控灯的回调函数,通过接收的命令
域名tln("[Light] ON/OFF");
域名tln(域名ageid);
// 发送响应
char p[域名oadlen + 1];
memcpy(p, 域名oad, 域名oadlen);
p[域名oadlen] = NULL;
String message(p);
if (域名ls("0"))
LEDSTATE = false;
else if(域名ls("1"))
LEDSTATE = true;
if (LEDSTATE) {
digitalWrite(9, HIGH) ;
域名tln("[Light] ON");
域名Response(ip, port, 域名ageid, "1");
} else {
digitalWrite(9, LOW) ;
域名tln("[Light] OFF");
域名Response(ip, port, 域名ageid, "0");
}
}
// CoAP客户端响应回调
void callback_response(CoapPacket &packet, IPAddress ip, int port)
{
域名tln("[Coap Response got]");
char p[域名oadlen + 1];
memcpy(p, 域名oad, 域名oadlen);
p[域名oadlen] = NULL;
域名tln(p);
}
库代码
报文结构定义:
// 确定消息类型,在 coap 消息层
typedef enum {
COAP_CON = 0, // 可靠传输
COAP_NONCON = 1, // 不可靠传输
COAP_ACK = 2, // 回复
COAP_RESET = 3 // 报文异常后的被动重发请求
} COAP_TYPE;
// 命令执行的动作,在请求/响应层
typedef enum {
COAP_GET = 1,
COAP_POST = 2, // 主动的重发命令
COAP_PUT = 3,
COAP_DELETE = 4
} COAP_METHOD;
// 响应码,相当于函数返回值或者err码之类的,在请求/响应层
typedef enum {
COAP_CREATED = RESPONSE_CODE(2, 1),
COAP_DELETED = RESPONSE_CODE(2, 2),
COAP_VALID = RESPONSE_CODE(2, 3),
COAP_CHANGED = RESPONSE_CODE(2, 4),
COAP_CONTENT = RESPONSE_CODE(2, 5),
COAP_BAD_REQUEST = RESPONSE_CODE(4, 0),
COAP_UNAUTHORIZED = RESPONSE_CODE(4, 1),
COAP_BAD_OPTION = RESPONSE_CODE(4, 2),
COAP_FORBIDDEN = RESPONSE_CODE(4, 3),
COAP_NOT_FOUNT = RESPONSE_CODE(4, 4),
COAP_METHOD_NOT_ALLOWD = RESPONSE_CODE(4, 5),
COAP_NOT_ACCEPTABLE = RESPONSE_CODE(4, 6),
COAP_PRECONDITION_FAILED = RESPONSE_CODE(4, 12),
COAP_REQUEST_ENTITY_TOO_LARGE = RESPONSE_CODE(4, 13),
COAP_UNSUPPORTED_CONTENT_FORMAT = RESPONSE_CODE(4, 15),
COAP_INTERNAL_SERVER_ERROR = RESPONSE_CODE(5, 0),
COAP_NOT_IMPLEMENTED = RESPONSE_CODE(5, 1),
COAP_BAD_GATEWAY = RESPONSE_CODE(5, 2),
COAP_SERVICE_UNAVALIABLE = RESPONSE_CODE(5, 3),
COAP_GATEWAY_TIMEOUT = RESPONSE_CODE(5, 4),
COAP_PROXYING_NOT_SUPPORTED = RESPONSE_CODE(5, 5)
} COAP_RESPONSE_CODE;
// Option 编号 ,在 coap 消息层
typedef enum {
COAP_IF_MATCH = 1,
COAP_URI_HOST = 3,
COAP_E_TAG = 4,
COAP_IF_NONE_MATCH = 5,
COAP_URI_PORT = 7,
COAP_LOCATION_PATH = 8,
COAP_URI_PATH = 11,
COAP_CONTENT_FORMAT = 12,
COAP_MAX_AGE = 14,
COAP_URI_QUERY = 15,
COAP_ACCEPT = 17,
COAP_LOCATION_QUERY = 20,
COAP_PROXY_URI = 35,
COAP_PROXY_SCHEME = 39
} COAP_OPTION_NUMBER;
// 内容类型和 Accept 用于表示CoAP负载的媒体格式
typedef enum {
COAP_NONE = -1,
COAP_TEXT_PLAIN = 0,
COAP_APPLICATION_LINK_FORMAT = 40,
COAP_APPLICATION_XML = 41,
COAP_APPLICATION_OCTET_STREAM = 42,
COAP_APPLICATION_EXI = 47,
COAP_APPLICATION_JSON = 50,
COAP_APPLICATION_CBOR = 60
} COAP_CONTENT_TYPE;
class CoapOption {
public:
uint8_t number;
uint8_t length;
uint8_t *buffer;
};
class CoapPacket {
public:
uint8_t type = 0;
uint8_t code = 0;
const uint8_t *token = NULL;
uint8_t tokenlen = 0;
const uint8_t *payload = NULL;
size_t payloadlen = 0;
uint16_t messageid = 0;
uint8_t optionnum = 0;
CoapOption options[COAP_MAX_OPTION_NUM];
void addOption(uint8_t number, uint8_t length, uint8_t *opt_payload);
};
组包发送:
在这里填写包的UDP需要地址,端口,端点等路径相关信息以及 COAP 请求/响应层的信息
uint16_t Coap::send(IPAddress ip, int port, const char *url, COAP_TYPE type, COAP_METHOD method, const uint8_t *token, uint8_t tokenlen, const uint8_t *payload, size_t payloadlen, COAP_CONTENT_TYPE content_type) {
// make packet
CoapPacket packet;
域名 = type;
域名 = method;
域名n = token;
域名nlen = tokenlen;
域名oad = payload;
域名oadlen = payloadlen;
域名onnum = 0;
域名ageid = rand();
// use URI_HOST UIR_PATH
char ipaddress[16] = "";
sprintf(ipaddress, "%d.%d.%d.%d", ip[0], ip[1], ip[2], ip[3]);
域名ption(COAP_URI_HOST, strlen(ipaddress), (uint8_t *)ipaddress);
// parse url
int idx = 0;
for (int i = 0; i < strlen(url); i++) {
if (url[i] == \'/\') {
域名ption(COAP_URI_PATH, i-idx, (uint8_t *)(url + idx));
idx = i + 1;
}
}
if (idx <= strlen(url)) {
域名ption(COAP_URI_PATH, strlen(url)-idx, (uint8_t *)(url + idx));
}
// if Content-Format option
uint8_t optionBuffer[2] {0};
if (content_type != COAP_NONE) {
optionBuffer[0] = ((uint16_t)content_type & 0xFF00) >> 8;
optionBuffer[1] = ((uint16_t)content_type & 0x00FF) ;
域名ption(COAP_CONTENT_FORMAT, 2, optionBuffer);
}
// send packet
return this->sendPacket(packet, ip, port);
}
在这里的组装 coap 包消息层的数据
uint16_t Coap::sendPacket(CoapPacket &packet, IPAddress ip, int port) {
uint8_t buffer[COAP_BUF_MAX_SIZE];
uint8_t *p = buffer;
uint16_t running_delta = 0;
uint16_t packetSize = 0;
// 制作coap包基头
*p = 0x01 << 6;
*p |= (域名 & 0x03) << 4;
*p++ |= (域名nlen & 0x0F);
*p++ = 域名;
*p++ = (域名ageid >> 8);
*p++ = (域名ageid & 0xFF);
p = buffer + COAP_HEADER_SIZE;
packetSize += 4;
// make token
if (域名n != NULL && 域名nlen <= 0x0F) {
memcpy(p, 域名n, 域名nlen);
p += 域名nlen;
packetSize += 域名nlen;
}
// make option header
for (int i = 0; i < 域名onnum; i++) {
uint32_t optdelta;
uint8_t len, delta;
if (packetSize + 5 + 域名ons[i].length >= COAP_BUF_MAX_SIZE) {
return 0;
}
optdelta = 域名ons[i].number - running_delta;
COAP_OPTION_DELTA(optdelta, &delta);
COAP_OPTION_DELTA((uint32_t)域名ons[i].length, &len);
*p++ = (0xFF & (delta << 4 | len));
if (delta == 13) {
*p++ = (optdelta - 13);
packetSize++;
} else if (delta == 14) {
*p++ = ((optdelta - 269) >> 8);
*p++ = (0xFF & (optdelta - 269));
packetSize+=2;
} if (len == 13) {
*p++ = (域名ons[i].length - 13);
packetSize++;
} else if (len == 14) {
*p++ = (域名ons[i].length >> 8);
*p++ = (0xFF & (域名ons[i].length - 269));
packetSize+=2;
}
memcpy(p, 域名ons[i].buffer, 域名ons[i].length);
p += 域名ons[i].length;
packetSize += 域名ons[i].length + 1;
running_delta = 域名ons[i].number;
}
// make payload
if (域名oadlen > 0) {
if ((packetSize + 1 + 域名oadlen) >= COAP_BUF_MAX_SIZE) {
return 0;
}
*p++ = 0xFF;
memcpy(p, 域名oad, 域名oadlen);
packetSize += 1 + 域名oadlen;
}
_udp->beginPacket(ip, port);
_udp->write(buffer, packetSize);
_udp->endPacket();
return 域名ageid;
}
因为这个库解包的loop部分没做完所以这里就先不说了
结果展示
COAP 客户端发送了ID 为20125,24157,12868的三个消息,然后服务器端返回了这三个消息,并带上了数据,客户端也got 到了需要的数据。
总结
感觉很怪?怪就对了,这个 demo 并不完善,只是这个库比较简单方便理解,同时有一个基本框架,看懂这个代码更容易理解 COAP 。