ArduinoJson 不会反序列化从 HTTP GET 读取的字符串，但会反序列化字符串文字答案

【问题标题】：ArduinoJson does not deserialize string read in from an HTTP GET but does deserialize a String LiteralArduinoJson 不会反序列化从 HTTP GET 读取的字符串，但会反序列化字符串文字
【发布时间】：2019-06-26 15:41:39
【问题描述】：

我正在使用 ESP8266 向https://openaq.org/ 提供的 APi 发出 HTTP GET 请求，然后使用 ArduinoJson https://arduinojson.org/ 库反序列化数据并提取传感器读数。

我可以获取 Json 数据并打印出字符串，但是当我尝试反序列化它时，它不起作用

如果我将打印到串行监视器的输出复制并粘贴回代码中，然后将其传递给反序列化，那么它确实可以工作，请参阅当前注释掉的行

//line = "{\"meta\":{\"name\":\"openaq-api\",\"license\":\"CC BY 4.0\",\"website\":\"https://docs.openaq.org/\",\"page\":1,\"limit\":1,\"found\":1955},\"results\":[{\"location\":\"Birmingham Acocks Green\",\"parameter\":\"pm25\",\"date\":{\"utc\":\"2019-06-26T12:00:00.000Z\",\"local\":\"2019-06-26T13:00:00+01:00\"},\"value\":5,\"unit\":\"µg/m³\",\"coordinates\":{\"latitude\":52.437165,\"longitude\":-1.829999},\"country\":\"GB\",\"city\":\"Birmingham\"}]}";

起初我以为可能是 " 需要转义，但没有任何区别。我还认为可能是该字符串没有空终止符，因此无法正常工作，但尝试将字符串连接到末尾

line = line + "";

但同样没有效果

void setup() {


const char* host = "api.openaq.org";
const int httpsPort = 443;

const char* fingerprint = "47 03 D4 71 84 CD E2 47 5D 4C 04 52 61 28 83 84 E6 FF 66 53";
String url = "/v1/measurements?location=Birmingham%20Acocks%20Green&parameter=pm25&limit=1";
  // put your setup code here, to run once:
    Serial.begin(115200);

  /*
   * 
   * 
   * Connect to Wifi
   * 
   */


  Serial.println();
  Serial.print("connecting to ");
  Serial.println(ssid);
  WiFi.mode(WIFI_STA);
  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());


  //Attempt to connect to the host and port specified
  WiFiClientSecure client;
  Serial.print("Connecting to ");
  Serial.println(host);
  if (!client.connect(host, httpsPort)){
    Serial.println("Connection failed");
    return;
  }

   //Compare the Certificate returned with the one we manually obtained
   if (client.verify(fingerprint, host)) {
    Serial.println("certificate matches");
  } else {
    Serial.println("certificate doesn't match");
    return;
  }

  Serial.print("Requesting url ");
  Serial.println (url);

    client.print(String("GET ") + url + " HTTP/1.1\r\n" +
               "Host: " + host + "\r\n" +
               "User-Agent: ArduinoESP8266\r\n" +
               "Connection: close\r\n\r\n");

  Serial.println("request sent");


   // Check HTTP status
  char status[32] = {0};
  client.readBytesUntil('\r', status, sizeof(status));
  // It should be "HTTP/1.0 200 OK" or "HTTP/1.1 200 OK"
  if (strcmp(status + 9, "200 OK") != 0) {
    Serial.print(F("Unexpected response: "));
    Serial.println(status);
    return;
  }

  // Skip HTTP headers
  char endOfHeaders[] = "\r\n\r\n";
  if (!client.find(endOfHeaders)) {
    Serial.println(F("Invalid response"));
    return;
  }

  String line = client.readStringUntil('\n');
  String toReplace = "\"";
  String replacedBy = "\\\"";
  line.replace(toReplace, replacedBy);



  //line = "{\"meta\":{\"name\":\"openaq-api\",\"license\":\"CC BY 4.0\",\"website\":\"https://docs.openaq.org/\",\"page\":1,\"limit\":1,\"found\":1955},\"results\":[{\"location\":\"Birmingham Acocks Green\",\"parameter\":\"pm25\",\"date\":{\"utc\":\"2019-06-26T12:00:00.000Z\",\"local\":\"2019-06-26T13:00:00+01:00\"},\"value\":5,\"unit\":\"µg/m³\",\"coordinates\":{\"latitude\":52.437165,\"longitude\":-1.829999},\"country\":\"GB\",\"city\":\"Birmingham\"}]}";

  Serial.println(line);
  int line_len = line.length() + 1;
  char char_array[line_len];

  line.toCharArray(char_array,line_len);


  //send the String object to the input of the DeserializeJson
  DynamicJsonDocument doc(1200);
  deserializeJson(doc,char_array);
  JsonObject obj = doc.as<JsonObject>();

  String nameAQ = obj[String("meta")];

  Serial.println(nameAQ);

  JsonArray results = obj["results"];
  JsonObject results_0 = results[0];

  int results_0_value = results_0["value"];

  Serial.println(results_0_value);


}

当我 Serial.print() 我期望返回的元内容 {"name":"openaq-api","license":"CC BY 4.0","website":"https://docs.openaq.org/","page":1,"limit":1,"found":1955} 但它输出 null

当我 Serial.print() 结果_0_value int 我希望它返回 JSON 中的任何值但它输出 0

【问题讨论】：

标签： json string serialization arduino

【解决方案1】：

已设法解决此问题。我删除了这些行以转义 JSON 中的 "

  String toReplace = "\"";
  String replacedBy = "\\\"";
  line.replace(toReplace, replacedBy);

我在开发的较早时将这些放入以解决问题，我认为较早的问题是其他问题，但将它们留在了其中。它们看起来像是需要的，因为它们在 ArduinoJSon 助手https://arduinojson.org/v6/assistant/ 中显示

【讨论】：