MKR1400-how do I troubleshoot a POST request?

Question

I'm successfully sending a GET request (in the setup function, to load certificates,) but my POST request fails with a bunch of AT errors. I suspect this has to do with the way I'm formatting the POST. Any ideas would be appreciated.

Code follows:

// MKRGSM - Version: 1.5.0
#include <MKRGSM.h>
#include <ArduinoJson.h>
#include <Arduino_MKRGPS.h>

const char PINNUMBER[]     = "";
// APN data

const char GPRS_APN[]      = SECRET_GPRS_APN;

const char GPRS_LOGIN[]    = "";

const char GPRS_PASSWORD[] = "";

DynamicJsonDocument doc(1024);

// initialize the library instance

GSMSSLClient client;

GPRS gprs;

GSM gsmAccess(true);

// Specify IP address or hostname

char server[] = "webhook.site";
char path[] = "/ce480c43-95a8-4f1e-b996-bc02f6d1adaa";
int port = 443; 

void setup() {

  // initialize serial communications and wait for port to open:

  Serial.begin(9600);

  while (!Serial) {

    ; // wait for serial port to connect. Needed for native USB port only

  }

  // If you are using the MKR GPS as shield, change the next line to pass

  // the GPS_MODE_SHIELD parameter to the GPS.begin(...)
  delay(200);


  if (!GPS.begin()) {

    Serial.println("Failed to initialize GPS!");

    while (1);

  }
  Serial.println("Starting Arduino GSM ping.");
  // connection state
  bool connected = false;

  // After starting the modem with GSM.begin()
  // attach the shield to the GPRS network with the APN, login and password
  while (!connected)
  {
    if ((gsmAccess.begin(PINNUMBER) == GSM_READY) &&
        (gprs.attachGPRS(GPRS_APN, GPRS_LOGIN, GPRS_PASSWORD) == GPRS_READY))
    {
      connected = true;
    } 
    else 
    {
      Serial.println("Not connected");
      delay(1000);
    }
  }

  Serial.println("connecting...");

  // if you get a connection, report back via serial:
  // Use this to load Root Certs the first time
  if (client.connect(server, port)) 
  // Use this to not load Root Certs anymore as done last time and stored in modem's flash
//  if (client.connect(server, port, false)) 
  {
        Serial.println("connected");

    // Make a HTTP request:

    client.print("GET ");

    client.print(path);

    client.println(" HTTP/1.1");

    client.print("Host: ");

    client.println(server);

    client.println("Connection: close");

    client.println();
  } 
  else 
  {
    // if you didn't get a connection to the server:
    Serial.println("connection failed");
  }
}

void loop() {

  ...GPS stuff happens here

  // print GPS values

  Serial.println();

  Serial.print("Location: ");

  Serial.print(latitude, 7);

  Serial.print(", ");

  Serial.println(longitude, 7);

  Serial.print("Altitude: ");

  Serial.print(altitude);

  Serial.println("m");

  Serial.print("Number of satellites: ");

  Serial.println(satellites);

  doc["latitude"] = latitude;
  doc["longitude"] = longitude;
  doc["altitude"] = altitude;
  
  String location;
  serializeJson(doc, location);
  Serial.print("Location string: ");
  Serial.println(location);

  Serial.println();
  
  Serial.println("Starting Arduino web client.");

  // connection state
  
  if (client.available()) {
    Serial.println("Sending location");
    client.print("POST ");
    client.print(path);
    client.println(" HTTP/1.1");
    delay(5);
    client.println("Content-Type: application/json;");
    delay(5);
    client.print("Content-Length: ");
    client.println(location.length());
    client.print("Host: ");
    client.println(server);
    delay(5);
    client.println("Connection: close");
    delay(5);
    client.println();
    delay(5);
    client.println(location);
    Serial.print("Successfully sent location");

    if (!client.available() && !client.connected()) {
  
      Serial.println();
  
      Serial.println("disconnecting.");
  
      client.stop();
    }
  } else {
    // if you didn't get a connection to the server:
    Serial.println("connection failed");
  }
  
}

Here's what the output looks like:

Location: 32.1208382, 35.2468376 Altitude: 640.40m Number of satellites: 5 Location string: {"latitude":32.12084,"longitude":35.24684,"altitude":640.4}

Starting Arduino web client. Sending location AT+USOWR=0,13,"504F53542068747470733A2F2F"

ERROR AT+USOWR=0,37,"2F63653438306334332D393561382D346631652D623939362D626330326636643161646161"

ERROR AT+USOWR=0,9,"20485454502F312E31"

ERROR AT+USOWR=0,2,"0D0A"

ERROR AT+USOWR=0,31,"436F6E74656E742D547970653A206170706C69636174696F6E2F6A736F6E3B"

ERROR AT+USOWR=0,2,"0D0A"

ERROR AT+USOWR=0,16,"436F6E74656E742D4C656E6774683A20"

ERROR AT+USOWR=0,2,"3539"

ERROR AT+USOWR=0,2,"0D0A"

ERROR AT+USOWR=0,6,"486F73743A20"

ERROR AT+USOWR=0,12,"776562686F6F6B2E73697465"

ERROR AT+USOWR=0,2,"0D0A"

ERROR AT+USOWR=0,17,"436F6E6E656374696F6E3A20636C6F7365"

ERROR AT+USOWR=0,2,"0D0A"

ERROR AT+USOWR=0,2,"0D0A"

ERROR AT+USOWR=0,59,"7B226C61746974756465223A33322E31323038342C226C6F6E676974756465223A33352E32343638342C22616C746974756465223A3634302E347D"

ERROR AT+USOWR=0,2,"0D0A"

ERROR

I could send the data as parameters in the GET query, but that's ugly.

reading the response is same. and the HTTP request line shouldn't have a complete URL for POST either — Juraj, Jun 22 '21 at 17:40

score 2 · Answer 1 · answered Jun 22 '21 at 16:00

2

Your HTTP request is badly formatted. You have:

POST https://webhook.site/ce480c43-95a8-4f1e-b996-bc02f6d1adaa HTTP/1.1
Content-Type: application/json

Instead the protocol is implied by the port you are connecting to, and the domain name does not go in the path on the server component - it has its own header.

Your request should look more like:

POST /ce480c43-95a8-4f1e-b996-bc02f6d1adaa HTTP/1.1
Host: webhook.site
Content-Type: application/json
Content-Length: [x]
Connection: close

[location]

Where [x] is location.length() and [location] is the content of the location string.

answered Jun 22 '21 at 16:00

Majenko

103,876
5
75
133

Thanks, I've updated the code as per your suggestions. Unfortunately, it's still failing. I'm not even seeing it go into the ```if (client.connect(server, port)) {``` block, which suggests that there is something wrong with the way I'm initializing the client. – Boris K Jun 22 '21 at 20:24
@BorisK You need to add a second newline after `Connection: close`. In HTTP the headers and content are separated by two newlines. Your original question included this `client.println();`, but your updated code omitted this. – Gerben Jun 23 '21 at 14:42
@gerben I'm not even seeing the "Sending location" output, which suggests the client is not connecting – Boris K Jun 23 '21 at 21:39
@Gerben I have swapped SIMs and am now connecting on a GET but failing on a POST. I've updated the original question. If you could take a look, I would be grateful. – Boris K Jul 20 '21 at 19:03

score 1 · Answer 2 · answered Jun 28 '21 at 15:50

1

The problem was that GSM gsmAccess; needed to be GSM gsmAccess(true). Unfortunately, while that solves the immediate problem, which is that the client was not initializing, there are other issues which deserve a separate question.

answered Jun 28 '21 at 15:50

Boris K

121
6

MKR1400-how do I troubleshoot a POST request?

2 Answers2