Retrieving Data from APIs using Mustache Templates (optional)

Retrieving Data from APIs using Mustache Templates

Overview

• This is an optional step where you filter the JSON response in the Particle cloud before sending the JSON resposne to the Photon 2
• This saves processing and bandwidth because you are only sending the Photon 2 the exact JSON data you want, not the whole JSON response
• This is a good practice, but not explicitly required in our class.

Part 3: Subscribe to JSON response from Weather Stack

Photon 2 firmware

void setup() {
  // Subscribe to the integration response event
  Particle.subscribe("hook-response/JSONWeatherStack",
                      jsonSubscriptionHandler, MY_DEVICES);
}

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Part 4 : Create Mustache template

• Often we might only want a few items from the JSON, but the webserver sends the entire message
• This extra data can waste time, bandwidth, power, and the response size can create errors
• Instead, we can have Particle webserver send us only the data we actually want by creating Mustache templates

Example: Entire Weather Stack JSON Response

Example: What if we only want the temperature?

Creating Mustache Webhook Response Templates

Particle Console Webhook

Example: Mustache Format

• If we are only interested in the temperature value which is nested in the current object, we could create a template like the following

  {"temp":"}"}

• Now instead of the server sending entire JSON response, it will only send the following

  {"temp":"61"}
  

• For webhook response templates, make sure the template will always result in valid JSON (i.e. {"name":"value"})

Part 5: Creating the function handler to receive and parse the JSON

• The last step is to create Photon 2 code to handle / parse the JSON response
• While it is possible to manually parse JSON in C++, it is considered unsafe due to potential for security vulnerabilities
• Instead, use a library
• Instruction and examples for parsing JSON with ArduinoJson

Resources

• Mustache Tester
• Mustache Variable Reference
• JSON Validator and formatter
• Weatherstack documentation

Credits

• Photo by Inset Agency on Unsplash