JsonStreamingParser
A Sming library for parsing potentially huge json streams on devices with scarce memory.
This library is a port of Squix78’s parser, itself a port of Salsify’s PHP based json streaming parser.
This code is available under the MIT license, which basically means that you can use, modify the distribute the code as long as you give credits to the authors and add a reference back to the original repository. Please read the enclosed LICENSE for more detail.
Comparison to ArduinoJson
ArduinoJson is a DOM parser. That is, it scans a document and builds a set of objects which reflect its content. Of course, it also allows documents to be created.
When reading larger JSON documents this requires too much memory. There are workarounds for this, but the most efficient approach is to use a SAX (streaming) parser. This type of parser processes each element and invokes a callback for each one. It is up to the application to decide what to do with the element at each stage of parsing.
How to use
Take a look in test/ReadTest.cpp for an example of how to user the parser. Here’s the main function:
BasicListener listener(output);
JSON::StreamingParser<128> parser(&listener);
auto status = parser.parse(input);
debug_i("Parser returned '%s'", JSON::toString(status).c_str());
return status == JSON::Status::EndOfDocument;
The parser requires a class inheriting from JSON::Listener, implementing these two methods:
startElement
endElement
Note that this differs from Squix’s implementation which required a separate method for each element type.
Each Element passed to these methods describes a single element, including its nesting level.
References
Used by
SoC support
esp32
esp32c2
esp32c3
esp32s2
esp32s3
esp8266
host
rp2040
rp2350