HTTP Outcalls

Overview

This skill adds the ability to make HTTP GET and POST requests from the backend canister. Useful for integrating with external APIs and services.

Backend

For HTTP outcalls that must be performed in the backend:

There is the prefabricated module mo:caffeineai-http-outcalls/outcall.mo that that cannot be modified. It provides fundamental functionality for making HTTP GET or PUT requests in the backend.

module {
  public type TransformationInput = {
    context : Blob;
    response : IC.http_request_result;
  };
  public type TransformationOutput = IC.http_request_result;
  public type Transform = query TransformationInput -> async TransformationOutput;
  public type Header = {
    name: Text;
    value: Text;
  };

  // Helper function for the transform callback used by the IC on HTTP outcalls.
  public func transform(input : TransformationInput) : TransformationOutput;

  // HTTP GET request with a transform callback function.
  public func httpGetRequest(url : Text, extraHeaders: [Header], transform : Transform) : async Text;

  // HTTP POST request, specifying a transform callback.
  public func httpPostRequest(url : Text, extraHeaders: [Header], body : Text, transform : Transform) : async Text;
};

Usage for GET:

import OutCall "mo:caffeineai-http-outcalls/outcall";

actor {
  public query func transform(input: OutCall.TransformationInput) : async OutCall.TransformationOutput {
    OutCall.transform(input);
  };

  func makeGetOutcall(url: Text) : async Text {
    await OutCall.httpGetRequest(url, [], transform);
  };
};

Hint: JSON parsing is not directly supported in Motoko. Better tunnel JSON to frontend for parsing.

POST usage is analogous.