arduino json on the serial stream - arduino

Question

Im using the BLuno arduino,
Its connecting fine to my iOS phone, sending and receiving messages.
Now I want to use arduino json to parse messages from my phone,
The serial connection receives data fine, but Im doing something wrong taking the stream to parse with the json library...
I get the error:
deserializeJson() failed: InvalidInput
The code:
#include <ArduinoJson.h>
StaticJsonDocument<400> doc;
void setup() {
Serial.begin(115200);
}
void loop()
{
if (Serial.available() > 0)
{
String s = Serial.readStringUntil("#"); // Until CR (Carriage Return)
s.replace("#", "");
Serial.println(s);
DeserializationError error = deserializeJson(doc, s);
if (error) {
Serial.print(F("deserializeJson() failed: "));
Serial.println(error.c_str());
return;
}
int value = doc["value"];
Serial.println(Serial.println(value));
IS
deserializeJson(doc, s);
correct?, I try to send different values, from the phone:
I just need to parse a key value pair, but none of the following ways worked:
{'a':'b'}
or
"{"a":"b"}"
or
{\"a\":\"b\"}
Where is my problem please?
how to format the {"a":"b"}
so the serial likes it for parsing?

Answer 1

There is nothing wrong with your code and ArduinoJson method, the
{'a':'b'} "{"a":"b"}" {\"a\":\"b\"}
is not a valid JSON object nor a serialised string representation of a JSON object.
If you JSON consists of multiple objects, the correct format should be:
[{"a": "b"},{"a": "b"},{"a": "b"}]
and with the serialised string representation should be like this:
"[{\"a\": \"b\"},{\"a\": \"b\"},{\"a\": \"b\"}]"
It is always a good idea to utilise one of those online JSON Validator to valid your JSON object during your development.
Update
Looks like that you had updated your question, based on your update, there are two problems in your code:
if the JSON object is {"a":"b"}, then there is no doc["value"] in the deserialised data, it should be doc["a"] to access the value "b".
the doc["a"] will not be int as in your int value = doc["value"], doc["value"] return a pointer to a char.
Here will be the code that produce the correct value.
void loop() {
char s[] = "{\"a\":\"b\"}";
StaticJsonDocument<200> doc;
DeserializationError error = deserializeJson(doc, s);
if (error) {
Serial.print(F("deserializeJson() failed: "));
Serial.println(error.c_str());
return;
}
const char* value = doc["a"];
Serial.println(value);
while(1) {};
}