HTTPS GET Ledger API

This Motoko canister performs an HTTP GET request to the Internet Computer public ledger API to retrieve a list of transactions for a specified account identifier.

Purpose

The canister demonstrates the use of HTTP outcalls in Motoko using the ic:aaaaa-aa system interface. Specifically, it issues an HTTP GET request to the ledger , parses the JSON response, and returns it to the caller.

Function Overview

public func get_transaction(account_identifier : Text, l : Nat) : async Json.Json

This function takes the following parameters:

• account_identifier: A Text value representing the principal's ICP account in its string form.
• l: A Nat indicating the number of transactions to retrieve. The value must not exceed 100.

If l > 100, the function returns a JSON string indicating that the limit has been exceeded.

HTTP GET Request Details

The function constructs an HTTPS GET request to the following endpoint:

https://ledger-api.internetcomputer.org/v2/accounts/{account_identifier}/transactions?limit={l}&sort_by=-block_height

The sort_by=-block_height parameter ensures that transactions are returned in reverse chronological order.

Request Configuration

• Method: GET

• URL: Constructed dynamically using the provided account identifier and limit.

• Headers:

  • Host: ledger-api.internetcomputer.org:443
  • Accept: application/json
  • User-Agent: motoko-canister //not required

• Body: null

• Max Response Size: null

• Cycles: 600,000,000 cycles allocated per request

Response Handling

The canister attempts to decode the response body as UTF-8 text. If decoding succeeds, it proceeds to parse the text as JSON using the mo:json library. If parsing fails, the function returns a JSON string indicating the error encountered (e.g., invalid token, unexpected EOF).

If decoding fails entirely, the function returns a JSON string stating "No value returned".

All successful responses are returned as Json.Json values.

Limitations

• The maximum number of transactions that can be fetched per request is 100.
• The function does not implement retry logic for failed HTTP requests.
• Canister must have sufficient cycles to perform the HTTP outcall.

Dependencies

• Motoko Base Library
• Motoko JSON Library

Example Usage

let result = await get_transaction(
  "aabbccddeeff00112233445566778899aabbccddeeff00112233445566778899",
  25
);

This call retrieves the 25 most recent transactions associated with the specified ICP account.