Handling GET/POST requests

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Overview

Canisters running on ICP can use HTTP requests in two ways: incoming and outgoing. Incoming HTTP requests refer to HTTP requests that are sent to a canister and can be used to retrieve data from a canister or send new data to the canister. Outgoing HTTP requests refer to HTT requests that the canister sends to other canisters or external services to retrieve data or send new data.

For outgoing HTTP requests, the HTTP outcalls feature should be used.

• Making HTTP requests

• How to use HTTP outcalls

• HTTP outcalls: GET

• HTTP outcalls: POST

• HTTP outcalls: technology overview

To handle incoming HTTP requests, canisters must define methods for http_requests and http_requests_update for GET and POST requests respectively.

GET requests

HTTP GET requests are used to retrieve and return existing data from an endpoint. To handle a canister's incoming GET requests, the http_request method can be exposed. Users and other services can call this method using a query call. To return HTTP response data, the following examples display how to configure the http_request to return an HTTP GET request.

Motoko

In Motoko, a case configuration can be used to return different GET responses based on the endpoint:

public query func http_request(req : HttpRequest) : async HttpResponse {
    switch (req.method, not Option.isNull(Array.find(req.headers, isGzip)), req.url) {
        case ("GET", false, "/stream") {{
        status_code = 200;
        headers = [ ("content-type", "text/plain") ];
        body = Text.encodeUtf8("Counter");
        streaming_strategy = ?#Callback({
            callback = http_streaming;
            token = {
            arbitrary_data = "start";
            }
        });
        upgrade = ?false;
        }};
        case ("GET", false, _) {{
        status_code = 200;
        headers = [ ("content-type", "text/plain") ];
        body = Text.encodeUtf8("Counter is " # Nat.toText(counter) # "\n" # req.url # "\n");
        streaming_strategy = null;
        upgrade = null;
        }};
        case ("GET", true, _) {{
        status_code = 200;
        headers = [ ("content-type", "text/plain"), ("content-encoding", "gzip") ];
        body = "\1f\8b\08\00\98\02\1b\62\00\03\2b\2c\4d\2d\aa\e4\02\00\d6\80\2b\05\06\00\00\00";
        streaming_strategy = null;
        upgrade = null;
        }};

Check out the certified cache example project to see this code in use.

Rust

use http::{Request, Response, StatusCode};

#[query]
fn respond_to(req: Request<()>) -> http::Result<Response<()>> {
    if req.uri() != "/hello" {
        return Response::builder()
            .status(StatusCode::NOT_FOUND)
            .body(())
    }

    let response_header = req.headers().contains_key("Hello!");
    let body = req.body();

}

Check out the Rust documentation for more info on query calls.

Typescript

import {
    blob,
    bool,
    Canister,
    Func,
    nat16,
    None,
    Opt,
    query,
    Record,
    text,
    Tuple,
    Variant,
    Vec
} from 'azle';

const Token = Record({
    // add whatever fields you'd like
    arbitrary_data: text
});

const StreamingCallbackHttpResponse = Record({
    body: blob,
    token: Opt(Token)
});

export const Callback = Func([text], StreamingCallbackHttpResponse, 'query');

const CallbackStrategy = Record({
    callback: Callback,
    token: Token
});

const StreamingStrategy = Variant({
    Callback: CallbackStrategy
});

type HeaderField = [text, text];
const HeaderField = Tuple(text, text);

const HttpResponse = Record({
    status_code: nat16,
    headers: Vec(HeaderField),
    body: blob,
    streaming_strategy: Opt(StreamingStrategy),
    upgrade: Opt(bool)
});

const HttpRequest = Record({
    method: text,
    url: text,
    headers: Vec(HeaderField),
    body: blob,
    certificate_version: Opt(nat16)
});

export default Canister({
    http_request: query([HttpRequest], HttpResponse, (req) => {
        return {
            status_code: 200,
            headers: [],
            body: Buffer.from('hello'),
            streaming_strategy: None,
            upgrade: None
        };
    })
});

Check out the Azle documentation for more info on HTTP requests.

Python

from kybra import blob, Func, nat16, Opt, query, Query, Record, Tuple, Variant, Vec


class HttpRequest(Record):
    method: str
    url: str
    headers: Vec["Header"]
    body: blob


class HttpResponse(Record):
    status_code: nat16
    headers: Vec["Header"]
    body: blob
    streaming_strategy: Opt["StreamingStrategy"]
    upgrade: Opt[bool]


Header = Tuple[str, str]


class StreamingStrategy(Variant):
    Callback: "CallbackStrategy"


class CallbackStrategy(Record):
    callback: "Callback"
    token: "Token"


Callback = Func(Query[["Token"], "StreamingCallbackHttpResponse"])


class StreamingCallbackHttpResponse(Record):
    body: blob
    token: Opt["Token"]


class Token(Record):
    arbitrary_data: str


@query
def http_request(req: HttpRequest) -> HttpResponse:
    return {
        "status_code": 200,
        "headers": [],
        "body": bytes(),
        "streaming_strategy": None,
        "upgrade": False,
    }

Check out the Kybra documentation for more info on HTTP requests.

POST requests

HTTP POST requests are used to send data to an endpoint with the intention of retaining that data. To handle incoming POST requests, the htt_request_update method can be used. This method uses an update call, which can be used to change a canister's state. The following examples display how to configure http_request_update method within your canister.

Motoko

In Motoko, a case configuration can be used to return different POST responses based on the endpoint:

  public func http_request_update(req : HttpRequest) : async HttpResponse {
    switch (req.method, not Option.isNull(Array.find(req.headers, isGzip))) {
      case ("POST", false) {
        counter += 1;
        {
          status_code = 201;
          headers = [ ("content-type", "text/plain") ];
          body = Text.encodeUtf8("Counter updated to " # Nat.toText(counter) # "\n");
          streaming_strategy = null;
          upgrade = null;
        }
      };
      case ("POST", true) {
        counter += 1;
        {
          status_code = 201;
          headers = [ ("content-type", "text/plain"), ("content-encoding", "gzip") ];
          body = "\1f\8b\08\00\37\02\1b\62\00\03\2b\2d\48\49\2c\49\e5\02\00\a8\da\91\6c\07\00\00\00";

          streaming_strategy = null;
          upgrade = null;
        }
      };

Check out the certified cache example project to see this code in use.

Rust

use http::{Request, Response, StatusCode};

#[update]
fn respond_to(req: Request<()>) -> http::Result<Response<()>> {
    let mut builder = Response::builder()
        .header("Hello!")
        .status(StatusCode::OK);

    if req.headers().contains_key("Another-Header") {
        builder = builder.header("Another-Header", "Ack");
    }

    builder.body(())
}

Check out the Rust documentation for more info on update calls.

Typescript

import {
    blob,
    bool,
    Canister,
    Func,
    nat16,
    None,
    Opt,
    Record,
    text,
    Tuple,
    update,
    Variant,
    Vec
} from 'azle';

const Token = Record({
    // add whatever fields you'd like
    arbitrary_data: text
});

const StreamingCallbackHttpResponse = Record({
    body: blob,
    token: Opt(Token)
});

export const Callback = Func([text], StreamingCallbackHttpResponse, 'query');

const CallbackStrategy = Record({
    callback: Callback,
    token: Token
});

const StreamingStrategy = Variant({
    Callback: CallbackStrategy
});

type HeaderField = [text, text];
const HeaderField = Tuple(text, text);

const HttpResponse = Record({
    status_code: nat16,
    headers: Vec(HeaderField),
    body: blob,
    streaming_strategy: Opt(StreamingStrategy),
    upgrade: Opt(bool)
});

const HttpRequest = Record({
    method: text,
    url: text,
    headers: Vec(HeaderField),
    body: blob,
    certificate_version: Opt(nat16)
});

export default Canister({
    http_request_update: update([HttpRequest], HttpResponse, (req) => {
        return {
            status_code: 200,
            headers: [],
            body: Buffer.from('hello'),
            streaming_strategy: None,
            upgrade: None
        };
    })
});

Check out the Azle documentation for more info on HTTP requests.

Python

from kybra import blob, Func, nat16, Opt, query, Query, Record, Tuple, Variant, Vec


class HttpRequest(Record):
    method: str
    url: str
    headers: Vec["Header"]
    body: blob


class HttpResponse(Record):
    status_code: nat16
    headers: Vec["Header"]
    body: blob
    streaming_strategy: Opt["StreamingStrategy"]
    upgrade: Opt[bool]


Header = Tuple[str, str]


class StreamingStrategy(Variant):
    Callback: "CallbackStrategy"


class CallbackStrategy(Record):
    callback: "Callback"
    token: "Token"


Callback = Func(Query[["Token"], "StreamingCallbackHttpResponse"])


class StreamingCallbackHttpResponse(Record):
    body: blob
    token: Opt["Token"]


class Token(Record):
    arbitrary_data: str


@query
def http_request_update(req: HttpRequest) -> HttpResponse:
    return {
        "status_code": 200,
        "headers": [],
        "body": bytes(),
        "streaming_strategy": None,
        "upgrade": False,
    }

Check out the Kybra documentation for more info on HTTP requests.

Resources

• Making HTTP requests

• How to use HTTP outcalls

• HTTP outcalls: GET

• HTTP outcalls: POST

• HTTP outcalls: technology overview

• Motoko certified cache example

• Rust documentation

• Azle documentation

• Kybra documentation