Parsing JSON response from Stream

Question

I want to parse JSON response from a GET Request. I do this usually by using a String variable to store the response and later parse this string using ArduinoJSON library like shown below:

#include <Arduino.h>
#include "OTA.h"
#include "Credentials.h"
#include <HTTPClient.h>
#include <ArduinoJson.h>
const char url[] = "http://date.jsontest.com/";
HTTPClient getClient;
void getRequest(String &payload)
{
 getClient.begin(url);
 int httpCode = getClient.GET();
 if (httpCode > 0)
 {
 payload = getClient.getString();
 // Serial.print("HTTP Status: ");
 // Serial.println(httpCode);
 }
 else
 {
 Serial.println("Error on HTTP request");
 }
 getClient.end();
}
void parseResponse(String &payload)
{
 StaticJsonDocument<128> doc;
 DeserializationError error = deserializeJson(doc, payload);
 if (error)
 {
 Serial.print("deserializeJson() failed: ");
 Serial.println(error.c_str());
 return;
 }
 const char *time = doc["time"]; // "03:53:25 AM"
 // unsigned long *epoch = doc["milliseconds_since_epoch"]; // 1362196405309
 const char *date = doc["date"]; // "03-02-2013"
 Serial.println(date);
}
void setup()
{
 setupOTA("ESP-N2", mySSID, myPASSWORD);
 Serial.begin(115200);
}
void loop()
{
 ArduinoOTA.handle();
 unsigned long newTime = millis();
 static unsigned long oldTime = 0;
 String payload;
 if (newTime - oldTime >= 5000)
 {
 oldTime = newTime;
 getRequest(payload);
 parseResponse(payload);
 Serial.println();
 }
}

I want to avoid using String and ArduinoJSON offician reference page mentions that it's possible to deserialize directly from input Stream e.g. wifiClient, ethernetclient or serial but I couldn't find any example showing it's usage. So I am curious to learn how to use it.

From my basic understanding of a Stream, I suppose I need define a buffer or memory location that will hold the incoming bytes and using the address of this buffer need to read data bit by bit. So do I need to do something like this:

char buffer[]= httpClient.getStream();

and then pass this buffer as input to deserialize function? or have I gotten it completely wrong?

• Mat: arduinojson.org/v6/how-to/use-arduinojson-with-httpclient

Answer 1

httpClient.getStream() returns an instance of Stream that you can pass to deserializeJson(), like so:

deserializeJson(doc, httpClient.getStream());

However, by doing so, you bypass the code in HTTPClient that handles chunked transfer encoding, so you must call httpClient.useHTTP10(true) before calling GET to make sure the server won't return a chunked response.

See How to use ArduinoJson with HTTPClient?

• Zaffresky: Thanks a lot for the explanation. I am happy to learn the Stream usage. It works well but I also get [D][HTTPClient.cpp:378] disconnect(): still data in buffer (1), clean up. [D][HTTPClient.cpp:387] disconnect(): tcp stop. Since I am reading all the stream data, which data it might be referring to? Can it cause an issue like memory leakage or fragmentation?
• Juraj: I added ChunkedStreamReader to my StreamLib. it wraps an input Stream and decodes the chunked input: github.com/jandrassy/StreamLib/blob/…
• seddouguim: I followed the approach mentioned in the docs but it seems that my GET requests fail when I use http1.0. My server is running on aws (amplify) and uses http2. What should I do in this case?