oak
A middleware framework for Deno’s http server, including a router middleware.
This middleware framework is inspired by Koa and middleware router inspired by @koa/router.
This README focuses on the mechanics of the oak APIs and is intended for those who are familiar with JavaScript middleware frameworks like Express and Koa as well as a decent understanding of Deno. If you aren’t familiar with these, please check out documentation on oakserver.github.io/oak.
Also, check out our FAQs and the awesome-oak site of community resources.
Warning The examples in this README pull from main
, which may not make sense
to do when you are looking to actually deploy a workload. You would want to
“pin” to a particular version which is compatible with the version of Deno you
are using and has a fixed set of APIs you would expect. https://deno.land/x/
supports using git tags in the URL to direct you at a particular version. So to
use version 3.0.0 of oak, you would want to import
https://deno.land/x/oak@v3.0.0/mod.ts
.
Application, middleware, and context
The Application
class wraps the serve()
function from the http
package. It
has two methods: .use()
and .listen()
. Middleware is added via the .use()
method and the .listen()
method will start the server and start processing
requests with the registered middleware.
A basic usage, responding to every request with Hello World!:
import { Application } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
app.use((ctx) => {
ctx.response.body = "Hello World!";
});
await app.listen({ port: 8000 });
The middleware is processed as a stack, where each middleware function can control the flow of the response. When the middleware is called, it is passed a context and reference to the “next” method in the stack.
A more complex example:
import { Application } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
// Logger
app.use(async (ctx, next) => {
await next();
const rt = ctx.response.headers.get("X-Response-Time");
console.log(`${ctx.request.method} ${ctx.request.url} - ${rt}`);
});
// Timing
app.use(async (ctx, next) => {
const start = Date.now();
await next();
const ms = Date.now() - start;
ctx.response.headers.set("X-Response-Time", `${ms}ms`);
});
// Hello World!
app.use((ctx) => {
ctx.response.body = "Hello World!";
});
await app.listen({ port: 8000 });
To provide an HTTPS server, then the app.listen()
options need to include the
options .secure
option set to true
and supply a .certFile
and a .keyFile
options as well.
An instance of application has some properties as well:
.keys
Keys to be used when signing and verifying cookies. The value can be set to an array of keys, and instance of
KeyStack
, or an object which provides the same interface asKeyStack
(e.g. an instance of keygrip). If just the keys are passed, oak will manage the keys viaKeyStack
which allows easy key rotation without requiring re-signing of data values..proxy
This defaults to
false
, but can be set via theApplication
constructor options. This is intended to indicate the application is behind a proxy and will useX-Forwarded-Proto
,X-Forwarded-Host
, andX-Forwarded-For
when processing the request, which should provide more accurate information about the request..state
A record of application state, which can be strongly typed by specifying a generic argument when constructing an
Application()
, or inferred by passing a state object (e.g.Application({ state })
).
Context
The context passed to middleware has several properties:
.app
A reference to the
Application
that is invoking this middleware..cookies
The
Cookies
instance for this context which allows you to read and set cookies..request
The
Request
object which contains details about the request..respond
Determines if when middleware finishes processing, the application should send the
.response
to the client. Iftrue
the response will be sent, and iffalse
the response will not be sent. The default istrue
but certain methods, like.upgrade()
and.sendEvents()
will set this tofalse
..response
The
Response
object which will be used to form the response sent back to the requestor..socket
This will be
undefined
if the connection has not been upgraded to a web socket. If the connection has been upgraded, the.socket
interface will be set..state
A record of application state, which can be strongly typed by specifying a generic argument when constructing an
Application()
, or inferred by passing a state object (e.g.Application({ state })
).
The context passed to middleware has some methods:
.assert()
Makes an assertion, which if not true, throws an
HTTPError
, which subclass is identified by the second argument, with the message being the third argument..send()
Stream a file to the requesting client. See Static content below for more information.
.sendEvents()
Convert the current connection into a server-sent event response and return a
ServerSentEventTarget
where messages and events can be streamed to the client. This will set.respond
tofalse
..throw()
Throws an
HTTPError
, which subclass is identified by the first argument, with the message being passed as the second..upgrade()
Attempt to upgrade the connection to a web socket connection, and resolve with an web socket interface. This will set
.respond
tofalse
.
Unlike other middleware frameworks, context
does not have a significant amount
of aliases. The information about the request is only located in .request
and
the information about the response is only located in .response
.
Cookies
The context.cookies
allows access to the values of cookies in the request, and
allows cookies to be set in the response. It automatically secures cookies if
the .keys
property is set on the application. It has several methods:
.get(key: string, options?: CookieGetOptions)
Attempts to retrieve the cookie out of the request and returns the value of the cookie based on the key. If the applications
.keys
is set, then the cookie will be verified against a signed version of the cookie. If the cookie is valid, the value will be returned. If it is invalid, the cookie signature will be set to deleted on the response. If the cookie was not signed by the current key, it will be resigned and added to the response..set(key: string, value: string, options?: CookieSetDeleteOptions)
Will set a cookie in the response based on the provided key, value and any options. If the applications
.keys
is set, then the cookie will be signed and the signature added to the response.
Request
The context.request
contains information about the request. It contains
several properties:
.hasBody
Set to
true
if the request has a body, orfalse
if it does not. It does not validate if the body is supported by the built in body parser though..headers
The headers for the request, an instance of
Headers
..method
A string that represents the HTTP method for the request.
.secure
A shortcut for
.protocol
, returningtrue
if HTTPS otherwisefalse
..serverRequest
The original
net
server request..url
An instance of
URL
which is based on the full URL for the request. This is in place of having parts of the URL exposed on the rest of the request object.
And several methods:
.accepts(...types: string[])
Negotiates the content type supported by the request for the response. If no content types are passed, the method returns a prioritized array of accepted content types. If content types are passed, the best negotiated content type is returned. If there is no content type matched, then
undefined
is returned..acceptsCharsets(...charsets: string[])
Negotiates the character encoding supported by the request for the response. If no character encodings are passed, the method returns a prioritized array of accepted character encodings. If character encodings are passed, the best negotiated charset is returned. If there are no encodings matched, then
undefined
is returned.Most browsers simply to not send a character encoding header anymore, and it is just expected UTF-8 will be used.
.acceptsEncodings(...encodings: string[])
Negotiates the content encoding supported by the request for the response. If no encodings are passed, the method returns a prioritized array of accepted encodings. If encodings are passed, the best negotiated encoding is returned. If there are no encodings matched, then
undefined
is returned..acceptsLanguages(...languages: string[])
Negotiates the language the client is able to understand. Where a locale variant takes preference. If no encodings are passed, the method returns a prioritized array of understood languages. If languages are passed, the best negotiated language is returned. If there are no languages matched, then
undefined
is returned..body(options?: BodyOptions)
The method returns a representation of the request body. When no options are passed, the request headers are used to determine the type of the body, which will be parsed and returned. The returned object contains two properties.
type
contains the type of"json"
,"text"
,"form"
,"form-data"
,"raw"
or"undefined"
.The type of the
value
can be determined by the value of thetype
property:type
value
"form"
Promise<URLSearchParams>
"form-data"
FormDataReader
"json"
Promise<unknown>
"raw"
Promise<Uint8Array>
"text"
Promise<string>
"undefined"
undefined
If there is no body, the
type
of"undefined"
is returned. If the content type of the request is not recognised, then thetype
of"raw"
is returned.You can use the option
type
to specifically request the body to be returned in a particular format. If you need access to the Deno HTTP server’s body, then you can use thetype
of"reader"
which will return the body object of type"reader"
with avalue
as aDeno.Reader
:app.use(async (ctx) => { const result = ctx.request.body({ type: "reader" }); result.type; // "reader" await Deno.readAll(result.value); // a "raw" Uint8Array of the body });
Another use case for the
type
option is if certain middleware always needs the body in a particular format, but wants other middleware to consume it in a content type resolved way:app.use(async (ctx) => { if (ctx.request.hasBody) { const result = ctx.request.body({ type: "text" }); const text = await result.value; // do some validation of the body as a string } }); app.use(async (ctx) => { const result = ctx.request.body(); // content type automatically detected if (result.type === "json") { const value = await result.value; // an object of parsed JSON } });
When specifying a
type
, it is always good to check that.request.hasBody
istrue
, as the.request.body()
will throw if the body is undefined.You can use the option
contentTypes
to set additional media types that when present as the content type for the request, the body will be parsed accordingly. The options takes possibly four keys:json
,form
,text
, andraw
. For example if you wanted JavaScript sent to the server to be parsed as text, you would do something like this:app.use(async (ctx) => { const result = ctx.request.body({ contentTypes: { text: ["application/javascript"], }, }); result.type; // "text" await result.value; // a string containing the text });
Because of the nature of how the body is parsed, once the body is requested and returned in a particular format, it can’t be requested in certain other ones, and
.request.body()
will throw if an incompatible type is requested. The type"reader"
is incompatible with all other types, bodies which are resolved as type"form-data"
or"undefined"
are incompatible with all other types. While"json"
,"form"
,"raw"
,"text"
are all compatible with each other, although if there are invalid data for that type, they may throw if coerced into that type.In particular the
contentTypes.raw
can be used to override default types that are supported that you would want the middleware to handle itself. For example if you wanted the middleware to parse all text media types itself, you would do something like this:app.use(async (ctx) => { const result = ctx.request.body({ contentTypes: { raw: ["text"], }, }); result.type; // "raw" await result.value; // a Uint8Array of all of the bytes read from the request });
Response
The context.response
contains information about the response which will be
sent back to the requestor. It contains several properties:
.body
The body of the response, which can often be handled by the automatic response body handling documented below.
.headers
A
Headers
instance which contains the headers for the response..status
An HTTP
Status
code that will be sent back with the response. If this is not set before responding, oak will default to200 OK
if there is a.body
, otherwise404 Not Found
..type
A media type or extension to set the
Content-Type
header for the response. For example, you can providetxt
ortext/plain
to describe the body.
And a method:
.redirect(url?: string | URL | REDIRECT_BACK, alt?: string | URL)
A method to simplify redirecting the response to another URL. It will set the
Location
header to the suppliedurl
and the status to302 Found
(unless the status is already a3XX
status). The use of symbolREDIRECT_BACK
as theurl
indicates that theReferrer
header in the request should be used as the direction, with thealt
being the alternative location if theReferrer
is not set. If neither thealt
nor theReferrer
are set, the redirect will occur to/
. A basic HTML (if the requestor supports it) or a text body will be set explaining they are being redirected.
Automatic response body handling
When the response Content-Type
is not set in the headers of the .response
,
oak will automatically try to determine the appropriate Content-Type
. First it
will look at .response.type
. If assigned, it will try to resolve the
appropriate media type based on treating the value of .type
as either the
media type, or resolving the media type based on an extension. For example if
.type
was set to "html"
, then the Content-Type
will be set to
"text/html"
.
If .type
is not set with a value, then oak will inspect the value of
.response.body
. If the value is a string
, then oak will check to see if the
string looks like HTML, if so, Content-Type
will be set to text/html
otherwise it will be set to text/plain
. If the value is an object, other than
a Uint8Array
, a Deno.Reader
, or null
, the object will be passed to
JSON.stringify()
and the Content-Type
will be set to application/json
.
If the type of body is a number, bigint or symbol, it will be coerced to a string and treated as text.
If the value of body is a function, the function will be called with no arguments. If the return value of the function is promise like, that will be await, and the resolved value will be processed as above. If the value is not promise like, it will be processed as above.
Opening the server
The application method .listen()
is used to open the server, start listening
for requests, and processing the registered middleware for each request. This
method returns a promise when the server closes.
Once the server is open, before it starts processing requests, the application
will fire a "listen"
event, which can be listened for via the
.addEventListener()
method. For example:
import { Application } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
app.addEventListener("listen", ({ hostname, port, secure }) => {
console.log(
`Listening on: ${secure ? "https://" : "http://"}${hostname ??
"localhost"}:${port}`,
);
});
// register some middleware
await app.listen({ port: 80 });
Closing the server
If you want to close the application, the application supports the option of an abort signal. Here is an example of using the signal:
import { Application } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
const controller = new AbortController();
const { signal } = controller;
// Add some middleware using `app.use()`
const listenPromise = app.listen({ port: 8000, signal });
// In order to close the sever...
controller.abort();
// Listen will stop listening for requests and the promise will resolve...
await listenPromise;
// and you can do something after the close to shutdown
Just handling requests
In situations where you don’t want the application to listen for requests on the
std/http/server
, but you still want the application to process requests, you
can use the .handle()
method. For example if you are in a serverless function
where the requests are arriving in a different way.
The .handle()
method will invoke the middleware, just like the middleware gets
invoked for each request that is processed by .listen()
. It take up to two
arguments, one being the request which conforms to the std/http/server
’s
ServerRequest
interface and an optional second argument which is if the
request is “secure” in the sense it originated from a TLS connection to the
remote client. The method resolves with a response that conforms to the
ServerResponse
interface (which can be used with the std/http/server
’s
request.respond()
method) or undefined
if the ctx.respond === true
(e.g.
the connection was upgraded to a web socket or is sending back server sent
events).
An example:
import { listenAndServe } from "https://deno.land/std/http/server.ts";
import { Application } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
app.use((ctx) => {
ctx.response.body = "Hello World!";
});
await listenAndServe({ port: 8000 }, async (request) => {
const response = await app.handle(request);
if (response) {
request.respond(response);
}
});
Error handling
Middleware can be used to handle other errors with middleware. Awaiting other middleware to execute while trapping errors works. So if you had an error handling middleware that provides a well managed response to errors would work like this:
import {
Application,
isHttpError,
Status,
} from "https://deno.land/x/oak/mod.ts";
const app = new Application();
app.use(async (ctx, next) => {
try {
await next();
} catch (err) {
if (isHttpError(err)) {
switch (err.status) {
case Status.NotFound:
// handle NotFound
break;
default:
// handle other statuses
}
} else {
// rethrow if you can't handle the error
throw err;
}
}
});
Uncaught middleware exceptions will be caught by the application. Application
extends the global EventTarget
in Deno, and when uncaught errors occur in the
middleware or sending of responses, an EventError
will be dispatched to the
application. To listen for these errors, you would add an event handler to the
application instance:
import { Application } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
app.addEventListener("error", (evt) => {
// Will log the thrown error to the console.
console.log(evt.error);
});
app.use((ctx) => {
// Will throw a 500 on every request.
ctx.throw(500);
});
await app.listen({ port: 80 });
Router
The Router
class produces middleware which can be used with an Application
to enable routing based on the pathname of the request.
Basic usage
The following example serves up a RESTful service of a map of books, where
http://localhost:8000/book/
will return an array of books and
http://localhost:8000/book/1
would return the book with ID "1"
:
import { Application, Router } from "https://deno.land/x/oak/mod.ts";
const books = new Map<string, any>();
books.set("1", {
id: "1",
title: "The Hound of the Baskervilles",
author: "Conan Doyle, Arthur",
});
const router = new Router();
router
.get("/", (context) => {
context.response.body = "Hello world!";
})
.get("/book", (context) => {
context.response.body = Array.from(books.values());
})
.get("/book/:id", (context) => {
if (context.params && context.params.id && books.has(context.params.id)) {
context.response.body = books.get(context.params.id);
}
});
const app = new Application();
app.use(router.routes());
app.use(router.allowedMethods());
await app.listen({ port: 8000 });
A route passed is converted to a regular expression using
path-to-regexp, which means
parameters expressed in the pattern will be converted. path-to-regexp
has
advanced usage which can create complex patterns which can be used for matching.
Check out the
documentation for that library
if you have advanced use cases.
Static content
The function send()
is designed to serve static content as part of a
middleware function. In the most straight forward usage, a root is provided and
requests provided to the function are fulfilled with files from the local file
system relative to the root from the requested path.
A basic usage would look something like this:
import { Application, send } from "https://deno.land/x/oak/mod.ts";
const app = new Application();
app.use(async (context) => {
await send(context, context.request.url.pathname, {
root: `${Deno.cwd()}/examples/static`,
index: "index.html",
});
});
await app.listen({ port: 8000 });
Helpers
The mod.ts
also exports a variable named helpers
which contains functions
that help with managing contexts.
getQuery(ctx, options?)
The helpers.getQuery()
function is designed to make it easier to determine
what a request might be querying in the middleware. It takes the supplied
context’s .request.url.searchParams
and converts it to a record object of the
keys and values. For example, it would convert the following request:
https://localhost/resource/?foo=bar&baz=qat
Into an object like this:
{
foo: "bar",
baz: "qat"
}
The function can take a couple of options. The asMap
will result in a Map
being returned instead of an object. The mergeParams
will merge in parameters
that were parsed out of the route. This only works with router contexts, and any
params will be overwritten by the request’s search params. If the following URL
was requested:
https://localhost/book/1234/page/23?page=32&size=24
And the following was the router middleware:
router.get("/book/:id/page/:page", (ctx) => {
getQuery(ctx, { mergeParams: true });
});
Would result in the return value being:
{
id: "1234",
page: "32",
size: "24"
}
There are several modules that are directly adapted from other modules. They have preserved their individual licenses and copyrights. All of the modules, including those directly adapted are licensed under the MIT License.
All additional work is copyright 2018 - 2020 the oak authors. All rights reserved.