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(&quot;Failed to initialize GPS!&quot;);

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(&quot;GET &quot;);

client.print(path);

client.println(&quot; HTTP/1.1&quot;);

client.print(&quot;Host: &quot;);

client.println(server);

client.println(&quot;Connection: close&quot;);

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() &amp;&amp; !client.connected()) {

  Serial.println();

  Serial.println(&quot;disconnecting.&quot;);

  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.

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

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.

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