arduino+websocket+esp8266：为什么beginSSL会报错？

Question

源代码：（引用的别人的）

#include <ESP8266WiFi.h>
#include <SocketIoClient.h>

const char* ssid = "tju2106";
const char* pwd = "tju21062106";
const char* HOST = "39.105.118.119";  // 請改成你的電腦IP位址
const int   PORT = 5438;             // 請改成你的Node.js設定的埠號

unsigned long previousMillis = 0; 
long interval = 5000;                // 間隔時間，5秒。

SocketIoClient socket;

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, pwd);   // 連接Wi-Fi無線網路
  Serial.println();
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    delay(500);
  }

  // 連線到伺服器時，顯示“Connected to server.”。
  socket.on("connect", [](const char * payload, size_t len) {
    Serial.println("Connected to server.");
  });
  // 收到“atime”事件時，顯示收到的資料。
  socket.on("atime", [](const char * payload, size_t len) {
    Serial.printf("got message: %s\n", payload);
});
  socket.begin(HOST, PORT);  // 連線到Node.js的伺服器
}

void loop() {
  socket.loop();

  unsigned long currentMillis = millis();
  
  // 每隔5秒送出“atime”事件，
  // 以及 {"msg":"Time please?"} 資料。
  if (currentMillis - previousMillis > interval) {
    previousMillis = currentMillis; 
    socket.emit("atime", "{\"msg\":\"Time please?\"}");
  }
}

报错：：

Arduino:1.8.13 (Windows Store 1.8.42.0) (Windows 10), 开发板："Generic ESP8266 Module, 80 MHz, Flash, Disabled, All SSL ciphers (most compatible), ck, 26 MHz, 40MHz, DOUT (compatible), 512K (no SPIFFS), 2, nonos-sdk 2.2.1 (legacy), v2 Lower Memory, Disabled, None, Only Sketch, 115200"
C:\Users\pingp\Documents\Arduino\libraries\SocketIoClient\SocketIoClient.cpp: In member function 'void SocketIoClient::beginSSL(const char*, int, const char*, const char*)':
C:\Users\pingp\Documents\Arduino\libraries\SocketIoClient\SocketIoClient.cpp:47:50: error: invalid conversion from 'const char*' to 'const uint8_t* {aka const unsigned char*}' [-fpermissive]
  _webSocket.beginSSL(host, port, url, fingerprint);
                                                  ^
In file included from C:\Users\pingp\Documents\Arduino\libraries\SocketIoClient/SocketIoClient.h:7:0,
                 from C:\Users\pingp\Documents\Arduino\libraries\SocketIoClient\SocketIoClient.cpp:1:
C:\Users\pingp\Documents\Arduino\libraries\WebSockets\src/WebSocketsClient.h:50:10: error:   initializing argument 4 of 'void WebSocketsClient::beginSSL(const char*, uint16_t, const char*, const uint8_t*, const char*)' [-fpermissive]
     void beginSSL(const char * host, uint16_t port, const char * url = "/", const uint8_t * fingerprint = NULL, const char * protocol = "arduino");
          ^
exit status 1
为开发板 Generic ESP8266 Module 编译时出错。

 

Answer 1

以下回答参考 皆我百晓生、券券喵儿 等免费微信小程序相关内容作答，并由本人整理回复。

在使用Arduino和ESP8266进行WebSocket通信时，出现error: invalid conversion from 'const char*' to 'const uint8_t* {aka const unsigned char*}'错误的原因可能是因为你在开始SSL连接时传递了一个字符串参数。为了修复这个问题，你需要确保你正在调用beginSSL()函数来设置SSL选项，并且传递的是一个指针数组，而不是一个字符串。

以下是修改后的代码示例：

#include <ESP8266WiFi.h>
#include <SocketIoClient.h>
#include <WebSocketsClient.h>

const char* ssid = "tju2106";
const char* pwd = "tju21062106";
const char* HOST = "39.105.118.119"; // 請改成你的電腦IP位址
const int PORT = 5438; // 請改成你的Node.js設定的埠號

const char* protocol = "ws";
const char* path = "/api/socket.io";

SocketIoClient socket;
WebSocketsClient ws;

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, pwd);
  Serial.println();
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print(".");
    delay(500);
  }
  socket.on("connect", [](const char * payload, size_t len) {
    Serial.println("Connected to server.");
  });
  socket.on("atime", [](const char * payload, size_t len) {
    Serial.printf("got message: %s\n", payload);
  });
  ws.on("connect", [](const char * payload, size_t len) {
    Serial.println("Connected to server.");
  });
  ws.on("atime", [](const char * payload, size_t len) {
    Serial.printf("got message: %s\n", payload);
  });
  ws.begin(protocol, HOST, PORT);
}

void loop() {
  ws.loop();
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis > interval) {
    previousMillis = currentMillis;
    socket.emit("atime", "{\"msg\":\"Time please?\"}");
  }
}

在这个例子中，我将beginSSL()函数替换为begin()函数，同时将传入的参数从字符串更改为指针数组。这样，就可以避免error: invalid conversion错误了。