Problem with the "String.toCharArray()"

Projects Programming
1

Hi guys, I'm trying to parse a json response from my web api:

This is a chunk, here I send the GET request, and I capture the response from the server:

 if (client.connect(server, 80)) {
    //Send the HTTP Request
    Serial.println("Fetching Data...");
    Serial.println();
    client.println("GET "+path+" HTTP/1.1");
    client.println("Host: localhost");
    client.println("User-Agent: ArduinoWiFi/1.1");
    client.println("Connection: close");
    client.println(); 

    //Capture the response
    while (!rcvResponse){
      if (client.available()){
        rcvResponse=true;
        while (client.available()){
          char c = client.read();
          http_response += c;  
        }
      }
    }

    client.stop();

    Serial.println("Website response STRING: ");
    Serial.println(http_response);
    Serial.println();

This is the output in JSON:

Website response STRING:
HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 195
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/8.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Mon, 24 Nov 2014 14:33:11 GMT
Connection: close

{"Success":true,"ErrorDescription":null,"ErrorCode":null,"Data":{"DaysList":[{"EventId":2,"DayId":5,"NumberOfVisitors":0,"Done":false},{"EventId":2,"DayId":6,"NumberOfVisitors":0,"Done":false}]}}

Then I try to parse the response, in this way:

    char httpJSON[http_response.length()+1];
    http_response.toCharArray(httpJSON, http_response.length()+1);   

    Serial.println("Website response CHAR-ARRAY: ");
    Serial.write(httpJSON);
    Serial.println(); 

    aJsonObject* root = aJson.parse(httpJSON);

    if (root != NULL) {
      Serial.println("OK: JSON Object obtained");
    }
    else{
      Serial.println("ERROR: Unable to get the root.");
    }

And then, the output:

HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 195
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/8.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Mon, 24 Nov 2014 14:33:11 GMT
Connection: close

{"Success":true,"ErrorDescription":null,"ErrorCode":null,"Data":{"DaysList":[{"EventId":2,"DayI´×þûHTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 195
Content-Typ
ERROR: Unable to get the root.

As you can see, when I convert the string into a array of chars, I obtain an incomplete output, with strange chars...somebody can help me?

2 
    char httpJSON[http_response.length()+1];

What is http_response.length() returning? After you've pissed away and fragmented memory all to hell using the String class, do you really have enough memory left to allocate this array?

3

If you insist on using the String class, you could use it more directly (without copying to another string) with http_response.c_str().

4

Hi guys,
Many thanks for the advices, and I decided to solve the problem of the memory it this way:

First of all, I have split the code, because I don't love the "monolithic style" xD

This is the loop, where I capture ONLY THE MODEL from the response:

void loop() {  
  if (client.available()){
    model = "";
    while (client.available()){
      char c = client.read();
      //Check if the model begins
      if (c == '{')
        storeJSON = true;  

      if (storeJSON)
        model += c;                        
    }
    parserJSON(model);
    storeJSON=false;
  }
  
  // if twenty seconds have passed since your last connection,
  // then connect again and send data:
  if (millis() - lastConnectionTime > postingInterval) {
    GetData("/GuestCounter/api/event/getDay?DayId=3");
  }
}

This is my HTTP Request:

void GetData(String path) { 
  client.stop();
  client.flush();
  Serial.flush();

  if (client.connect(server, 80)) {
    //Send the HTTP Request
    Serial.println("Fetching Data...");
    Serial.println();
    client.println("GET "+path+" HTTP/1.1");
    client.println("Host: localhost");
    client.println("User-Agent: ArduinoWiFi/1.1");
    client.println("Connection: close");
    client.println(); 
  }
  else{
    Serial.println("connection failed");
  }
  // note the time that the connection was made:
  lastConnectionTime = millis();
}

And this is my function for parsing the string containing the model.

void parserJSON(String model){
  length=model.length()+1;
  char* httpJSON = (char *) calloc(length,sizeof(char));  
  model.toCharArray(httpJSON, length); 

  client.flush();
  Serial.flush();

  Serial.println("MODEL:");
  Serial.print(httpJSON);
  Serial.println();

  aJsonObject* root = aJson.parse(httpJSON);  

  if (root != NULL) {
    aJsonObject* data = aJson.getObjectItem(root, "Data");
    if (data != NULL) {
      aJsonObject* DayId = aJson.getObjectItem(data, "DayId");
      if (DayId != NULL) {
        Serial.println("Day ID:");
        int id=(int)DayId->valuestring;
        Serial.print(id);
        Serial.println();
      }
    }
  }
  else{
    Serial.println("ERROR: Unable to get the root.");
  }
  free(httpJSON);
  free(root);
}

But now I have a different problem...When I run this sketch I obtain this output:

Fetching Data...
MODEL: {"Success":true,"ErrorDescription":null,"ErrorCode":null,"Data":{"EventId":1,"DayId":3,"NumberOfVisitors":0,"Done":false}}
Day ID: 3

Fetching Data...
MODEL: {"Success":true,"ErrorDescription":null,"ErrorCode":null,"Data":{"EventId":1,"DayId":3,"NumberOfVisitors":0,"Done":false}}
Day ID:3

Fetching Data...
MODEL: {"Success":true,"ErrorDescription":null,"ErrorCode":null,"Data":{"EventId":1,"DayId":3,"NumberOfVisitors":0,"Done":false}}
ERROR: Unable to get the root.

Fetching Data...
MODEL: {"Success":true,"ErrorDescription":null,"ErrorCode":null,"Data":{"EventId":1,"DayId":3,"NumberOfVisitors":0,"Done":false}}
ERROR: Unable to get the root.

I can get the root, and then parse the string only twice, then begins to fail parsing...what can I do?
any Ideas?

Thank you boys! :slight_smile:

5

Well, if you get four captures and then no more, then you code probably does not release the four sockets available after use.