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://github.com/hirotakast...
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://github.com/espressif/...
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
#include
#include
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;
// 添加服务器url端点.
// 可以添加多个端点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处理回调函数
// 将处理函数指针与url添加到 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");
// 很上面一样，其实就是把回调函数指针注册到resp里
coap.response(callback_response);
// 使用默认端口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请求.
// 可以发送给另外一个 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
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;
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 |= (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 。