前言
最近我在钻研 COAP 协定，在尝试应用 COAP 协定找了到了一个能在ESP32上用的coap-simple库，尽管库并不欠缺对于loop解决的局部应该是没写完，然而对于第一次接触COAP的敌人来说更容易了解，不便学习，须要的敌人能够去上面下载：
https://github.com/hirotakast...
我之前应用 IOT PI 的 COAP 能和 PC node coap 通信，然而因为 coap-simple 库不欠缺，失常的无奈与 node coap 通信，只能和同样应用这个库设施通信，这次就来尝试 ESP32 之间的 M2M 通信。
获取库
应用 arduino IDE 就能下载到这个库：
如果没有看到这个库，能够去首选项增加一下附加开发板管理器网址：
https://github.com/espressif/...
具体应用能够参考的我 arduino 超具体的开发入门领导 或者间接通过我下面发的 GitHub 网址下载。
代码解析
以下代码为了不便解说，可能通过了调换了程序或者裁剪。
这个 demo 是客户端、服务端一体的，只须要注册对应的回调函数就行。
初始化局部
这部分包含了设施初始化，协定初始化等局部，重点在服务器/客户端的回调函数局部。和 SDDC 官网demo相似，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() { Serial.begin(115200); WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); } Serial.println(""); Serial.println("WiFi connected"); Serial.println("IP address: "); Serial.println(WiFi.localIP()); // LED State pinMode(9, OUTPUT); digitalWrite(9, HIGH); LEDSTATE = true; // 增加服务器url端点. // 能够增加多个端点url. // coap.server(callback_switch, "switch"); // coap.server(callback_env, "env/temp"); // coap.server(callback_env, "env/humidity"); Serial.println("Setup Callback Light"); // 其实就是注册服务器解决回调函数 // 将解决函数指针与url增加到 uri.add 中 coap.server(callback_light, "light"); // 注册客户端响应的回调函数。 // this endpoint is single callback. Serial.println("Setup Response Callback"); // 很下面一样，其实就是把回调函数指针注册到resp里 coap.response(callback_response); // 应用默认端口5683 启动 coap server/client coap.start();}void loop() { // 作为客户端时向coap服务器发送GET或PUT coap申请. // 能够发送给另外一个 ESP32 // msgid = coap.put(IPAddress(192, 168, 128, 101), 5683, "light", "0"); // msgid = coap.get(IPAddress(192, 168, 128, 101), 5683, "light"); delay(1000); coap.loop();}回调函数
// CoAP 服务器端点 URL ,对客户端发过来的命令进行解决并且回应void callback_light(CoapPacket &packet, IPAddress ip, int port) { // 这是一个模仿控灯的回调函数，通过接管的命令 Serial.println("[Light] ON/OFF"); Serial.println(packet.messageid); // 发送响应 char p[packet.payloadlen + 1]; memcpy(p, packet.payload, packet.payloadlen); p[packet.payloadlen] = NULL; String message(p); if (message.equals("0")) LEDSTATE = false; else if(message.equals("1")) LEDSTATE = true; if (LEDSTATE) { digitalWrite(9, HIGH) ; Serial.println("[Light] ON"); coap.sendResponse(ip, port, packet.messageid, "1"); } else { digitalWrite(9, LOW) ; Serial.println("[Light] OFF"); coap.sendResponse(ip, port, packet.messageid, "0"); }}// CoAP客户端响应回调void callback_response(CoapPacket &packet, IPAddress ip, int port) { Serial.println("[Coap Response got]"); char p[packet.payloadlen + 1]; memcpy(p, packet.payload, packet.payloadlen); p[packet.payloadlen] = NULL; Serial.println(p);}库代码
报文构造定义：
// 确定音讯类型，在 coap 音讯层typedef enum { COAP_CON = 0, // 牢靠传输 COAP_NONCON = 1, // 不牢靠传输 COAP_ACK = 2, // 回复 COAP_RESET = 3 // 报文异样后的被动重发申请} COAP_TYPE;// 命令执行的动作，在申请/响应层typedef enum { COAP_GET = 1, COAP_POST = 2, // 被动的重发命令 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，在申请/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 音讯层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 用于示意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须要地址，端口，端点等门路相干信息以及 COAP 申请/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; packet.type = type; packet.code = method; packet.token = token; packet.tokenlen = tokenlen; packet.payload = payload; packet.payloadlen = payloadlen; packet.optionnum = 0; packet.messageid = rand(); // use URI_HOST UIR_PATH char ipaddress[16] = ""; sprintf(ipaddress, "%d.%d.%d.%d", ip[0], ip[1], ip[2], ip[3]); packet.addOption(COAP_URI_HOST, strlen(ipaddress), (uint8_t *)ipaddress); // parse url int idx = 0; for (int i = 0; i < strlen(url); i++) { if (url[i] == '/') { packet.addOption(COAP_URI_PATH, i-idx, (uint8_t *)(url + idx)); idx = i + 1; } } if (idx <= strlen(url)) { packet.addOption(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) ; packet.addOption(COAP_CONTENT_FORMAT, 2, optionBuffer); } // send packet return this->sendPacket(packet, ip, port);}在这里的组装 coap 包音讯层的数据
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 |= (packet.type & 0x03) << 4; *p++ |= (packet.tokenlen & 0x0F); *p++ = packet.code; *p++ = (packet.messageid >> 8); *p++ = (packet.messageid & 0xFF); p = buffer + COAP_HEADER_SIZE; packetSize += 4; // make token if (packet.token != NULL && packet.tokenlen <= 0x0F) { memcpy(p, packet.token, packet.tokenlen); p += packet.tokenlen; packetSize += packet.tokenlen; } // make option header for (int i = 0; i < packet.optionnum; i++) { uint32_t optdelta; uint8_t len, delta; if (packetSize + 5 + packet.options[i].length >= COAP_BUF_MAX_SIZE) { return 0; } optdelta = packet.options[i].number - running_delta; COAP_OPTION_DELTA(optdelta, &delta); COAP_OPTION_DELTA((uint32_t)packet.options[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++ = (packet.options[i].length - 13); packetSize++; } else if (len == 14) { *p++ = (packet.options[i].length >> 8); *p++ = (0xFF & (packet.options[i].length - 269)); packetSize+=2; } memcpy(p, packet.options[i].buffer, packet.options[i].length); p += packet.options[i].length; packetSize += packet.options[i].length + 1; running_delta = packet.options[i].number; } // make payload if (packet.payloadlen > 0) { if ((packetSize + 1 + packet.payloadlen) >= COAP_BUF_MAX_SIZE) { return 0; } *p++ = 0xFF; memcpy(p, packet.payload, packet.payloadlen); packetSize += 1 + packet.payloadlen; } _udp->beginPacket(ip, port); _udp->write(buffer, packetSize); _udp->endPacket(); return packet.messageid;}因为这个库解包的loop局部没做完所以这里就先不说了
后果展现
COAP 客户端发送了ID 为20125,24157,12868的三个音讯，而后服务器端返回了这三个音讯，并带上了数据，客户端也got 到了须要的数据。
总结
感觉很怪？怪就对了，这个 demo 并不欠缺，只是这个库比较简单不便了解，同时有一个根本框架，看懂这个代码更容易了解 COAP 。