f(8000, () => {

  console.log("started app on " + 8000);
});

Set signed cookie keys.

These are passed to KeyGrip, however you may also pass your own KeyGrip instance. For example the following are acceptable:

f = ['im a newer secret', 'i like turtle'];
f = new KeyGrip(['im a newer secret', 'i like turtle'], 'sha256');

These keys may be rotated and are used when signing cookies with the { signed: true } option:

ctx.cookies.set('name', 'tobi', { signed: true });

the prototype from which ctx is created. You may add additional properties to ctx by editing this. This is useful for adding properties or methods to ctx to be used across your entire app, which may be more performant (no middleware) and/or easier (fewer require()s) at the expense of relying more on ctx, which could be considered an anti-pattern.

For example, to add a reference to your database from ctx:

f.db = db();

app.use(async ctx => {
  console.log(ctx.db);
});

By default outputs all errors to stderr unless app.silent is true. The default error handler also won't output errors when err.status is 404 or err.expose is true. To perform custom error-handling logic such as centralized logging you can add an "error" event listener:

app.on('error', err => {
  log.error('server error', err)
});

If an error is in the req/res cycle and it is not possible to respond to the client, the Context instance is also passed:

app.on('error', (err, ctx) => {
  log.error('server error', err, ctx)
});

When an error occurs and it is still possible to respond to the client, aka no data has been written to the socket, Koa will respond appropriately with a 500 "Internal Server Error". In either case an app-level "error" is emitted for logging purposes.

Node's response object.

Bypassing Koa's response handling is not supported. Avoid using the following node properties:

• res.statusCode
• res.writeHead()
• res.write()
• res.end()

The recommended namespace for passing information through middleware and to your frontend views.

f.user = await User.find(id);

Get cookie name with options:

• signed the cookie requested should be signed

Koa uses the cookies module where options are simply passed.

Set cookie name to value with options:

• maxAge a number representing the milliseconds from Date.now() for expiry
• signed sign the cookie value
• expires a Date for cookie expiration
• path cookie path, /' by default
• domain cookie domain
• secure secure cookie
• httpOnly server-accessible cookie, true by default
• overwrite a boolean indicating whether to overwrite previously set cookies of the same name (false by default). If this is true, all cookies set during the same request with the same name (regardless of path or domain) are filtered out of the Set-Cookie header when setting this cookie.

Koa uses the cookies module where options are simply passed.

Helper method to throw an error with a .status property defaulting to 500 that will allow Koa to respond appropriately. The following combinations are allowed:

f(400);
f(400, 'name required');
f(400, 'name required', { user: user });

For example f(400, 'name required') is equivalent to:

const err = new Error('name required');
err.status = 400;
err.expose = true;
throw err;

Note that these are user-level errors and are flagged with err.expose meaning the messages are appropriate for client responses, which is typically not the case for error messages since you do not want to leak failure details.

You may optionally pass a properties object which is merged into the error as-is, useful for decorating machine-friendly errors which are reported to the requester upstream.

f(401, 'access_denied', { user: user });

Koa uses http-errors to create errors.

Helper method to throw an error similar to .throw() when !value. Similar to node's assert() method.

f(ctx.state.user, 401, 'User not found. Please login!');

Koa uses http-assert for assertions.

To bypass Koa's built-in response handling, you may explicitly set f = false;. Use this if you want to write to the raw res object instead of letting Koa handle the response for you.

Note that using this is not supported by Koa. This may break intended functionality of Koa middleware and Koa itself. Using this property is considered a hack and is only a convenience to those wishing to use traditional fn(req, res) functions and middleware within Koa.

Set request method, useful for implementing middleware such as methodOverride().

Return request Content-Length as a number when present, or undefined.

Get origin of URL, include protocol and host.

ctx.f
// => http://example.com

Get full request URL, include protocol, host and url.

ctx.f;
// => http://example.com/foo/bar?q=1

Get raw query string void of ?.

Get raw query string with the ?.

Get hostname when present. Supports X-Forwarded-Host when app.proxy is true, otherwise Host is used.

If host is IPv6, Koa delegates parsing to WHATWG URL API, Note This may impact performance.

Get WHATWG parsed URL object.

Get request Content-Type void of parameters such as "charset".

const ct = ctx.f;
// => "image/png"

Get request charset when present, or undefined:

ctx.f;
// => "utf-8"

Get parsed query-string, returning an empty object when no query-string is present. Note that this getter does not support nested parsing.

For example "color=blue&size=small":

{
  color: 'blue',
  size: 'small'
}

Set query-string to the given object. Note that this setter does not support nested objects.

ctx.query = { next: '/login' };

Check if a request cache is "fresh", aka the contents have not changed. This method is for cache negotiation between If-None-Match / ETag, and If-Modified-Since and Last-Modified. It should be referenced after setting one or more of these response headers.

// freshness check requires status 20x or 304
ctx.status = 200;
ctx.set('ETag', '123');

// cache is ok
if (ctx.f) {
  ctx.status = 304;
  return;
}

// cache is stale
// fetch new data
ctx.body = await db.find('something');

Inverse of request.fresh.

Request remote address. Supports X-Forwarded-For when app.proxy is true.

Return subdomains as an array.

Subdomains are the dot-separated parts of the host before the main domain of the app. By default, the domain of the app is assumed to be the last two parts of the host. This can be changed by setting app.subdomainOffset.

For example, if the domain is "tobi.ferrets.example.com": If app.subdomainOffset is not set, ctx.subdomains is ["ferrets", "tobi"]. If app.subdomainOffset is 3, ctx.subdomains is ["tobi"].

Check if the incoming request contains the "Content-Type" header field, and it contains any of the give mime types. If there is no request body, null is returned. If there is no content type, or the match fails false is returned. Otherwise, it returns the matching content-type.

// With Content-Type: text/html; charset=utf-8
ctx.is('html'); // => 'html'
ctx.is('text/html'); // => 'text/html'
ctx.is('text/*', 'text/html'); // => 'text/html'

// When Content-Type is application/json
ctx.is('json', 'urlencoded'); // => 'json'
ctx.is('application/json'); // => 'application/json'
ctx.is('html', 'application/*'); // => 'application/json'

ctx.is('html'); // => false

For example if you want to ensure that only images are sent to a given route:

if (ctx.is('image/*')) {
  // process
} else {
  ctx.throw(415, 'images only!');
}

Content Negotiation

Koa's request object includes helpful content negotiation utilities powered by accepts and negotiator. These utilities are:

• request.accepts(types)
• request.acceptsEncodings(types)
• request.acceptsCharsets(charsets)
• request.acceptsLanguages(langs)

If no types are supplied, all acceptable types are returned.

If multiple types are supplied, the best match will be returned. If no matches are found, a false is returned, and you should send a 406 "Not Acceptable" response to the client.

In the case of missing accept headers where any type is acceptable, the first type will be returned. Thus, the order of types you supply is important.

Check if the given type(s) is acceptable, returning the best match when true, otherwise false. The type value may be one or more mime type string such as "application/json", the extension name such as "json", or an array ["json", "html", "text/plain"].

// Accept: text/html
ctx.accepts('html');
// => "html"

// Accept: text/*, application/json
ctx.accepts('html');
// => "html"
ctx.accepts('text/html');
// => "text/html"
ctx.accepts('json', 'text');
// => "json"
ctx.accepts('application/json');
// => "application/json"

// Accept: text/*, application/json
ctx.accepts('image/png');
ctx.accepts('png');
// => false

// Accept: text/*;q=.5, application/json
ctx.accepts(['html', 'json']);
ctx.accepts('html', 'json');
// => "json"

// No Accept header
ctx.accepts('html', 'json');
// => "html"
ctx.accepts('json', 'html');
// => "json"

You may call ctx.accepts() as many times as you like, or use a switch:

switch (ctx.accepts('json', 'html', 'text')) {
  case 'json': break;
  case 'html': break;
  case 'text': break;
  default: ctx.throw(406, 'json, html, or text only');
}

Check if encodings are acceptable, returning the best match when true, otherwise false. Note that you should include identity as one of the encodings!

// Accept-Encoding: gzip
ctx.acceptsEncodings('gzip', 'deflate', 'identity');
// => "gzip"

ctx.acceptsEncodings(['gzip', 'deflate', 'identity']);
// => "gzip"

When no arguments are given all accepted encodings are returned as an array:

// Accept-Encoding: gzip, deflate
ctx.acceptsEncodings();
// => ["gzip", "deflate", "identity"]

Note that the identity encoding (which means no encoding) could be unacceptable if the client explicitly sends identity;q=0. Although this is an edge case, you should still handle the case where this method returns false.

Check if charsets are acceptable, returning the best match when true, otherwise false.

// Accept-Charset: utf-8, iso-8859-1;q=0.2, utf-7;q=0.5
ctx.acceptsCharsets('utf-8', 'utf-7');
// => "utf-8"

ctx.acceptsCharsets(['utf-7', 'utf-8']);
// => "utf-8"

When no arguments are given all accepted charsets are returned as an array:

// Accept-Charset: utf-8, iso-8859-1;q=0.2, utf-7;q=0.5
ctx.acceptsCharsets();
// => ["utf-8", "utf-7", "iso-8859-1"]

Check if langs are acceptable, returning the best match when true, otherwise false.

// Accept-Language: en;q=0.8, es, pt
ctx.acceptsLanguages('es', 'en');
// => "es"

ctx.acceptsLanguages(['en', 'es']);
// => "es"

When no arguments are given all accepted languages are returned as an array:

// Accept-Language: en;q=0.8, es, pt
ctx.acceptsLanguages();
// => ["es", "pt", "en"]

Response header object.

Response header object.

Set response status via numeric code:

100 "continue", 101 "switching protocols", 102 "processing", 200 "ok", 201 "created", 202 "accepted", 203 "non-authoritative information", 204 "no content", 205 "reset content", 206 "partial content", 207 "multi-status", 208 "already reported", 226 "im used", 300 "multiple choices", 301 "moved permanently", 302 "found", 303 "see other", 304 "not modified", 305 "use proxy", 307 "temporary redirect", 308 "permanent redirect", 400 "bad request", 401 "unauthorized", 402 "payment required", 403 "forbidden", 404 "not found", 405 "method not allowed", 406 "not acceptable", 407 "proxy authentication required", 408 "request timeout", 409 "conflict", 410 "gone", 411 "length required", 412 "precondition failed", 413 "payload too large", 414 "uri too long", 415 "unsupported media type", 416 "range not satisfiable", 417 "expectation failed", 418 "I'm a teapot", 422 "unprocessable entity", 423 "locked", 424 "failed dependency", 426 "upgrade required", 428 "precondition required", 429 "too many requests", 431 "request header fields too large", 500 "internal server error", 501 "not implemented", 502 "bad gateway", 503 "service unavailable", 504 "gateway timeout", 505 "http version not supported", 506 "variant also negotiates", 507 "insufficient storage", 508 "loop detected", 510 "not extended", 511 "network authentication required"

Set response status message to the given value.

Set response Content-Length to the given value.

Return response Content-Length as a number when present, or deduce from ctx.body when possible, or undefined.

Get response body.

Set response body to one of the following:

• string written
• Buffer written
• Stream piped
• Object || Array json-stringified
• null no content response

If response.status has not been set, Koa will automatically set the status to 200 or 204.

The Content-Type is defaulted to text/html or text/plain, both with a default charset of utf-8. The Content-Length field is also set.

The Content-Type is defaulted to application/octet-stream, and Content-Length is also set.

The Content-Type is defaulted to application/octet-stream.

Whenever a stream is set as the response body, .onerror is automatically added as a listener to the error event to catch any errors. In addition, whenever the request is closed (even prematurely), the stream is destroyed. If you do not want these two features, do not set the stream as the body directly. For example, you may not want this when setting the body as an HTTP stream in a proxy as it would destroy the underlying connection.

See: https://github.com/koajs/koa/pull/612 for more information.

Here's an example of stream error handling without automatically destroying the stream:

const PassThrough = require('stream').PassThrough;

app.use(async ctx => {
  ctx.body = someHTTPStream.on('error', ctx.onerror).pipe(PassThrough());
});

The Content-Type is defaulted to application/json. This includes plain objects { foo: 'bar' } and arrays ['foo', 'bar'].

Get a response header field value with case-insensitive field.

const etag = ctx.response.get('ETag');

Set response header field to value:

ctx.set('Cache-Control', 'no-cache');

Append additional header field with value val.

ctx.append('Link', '<http://127.0.0.1/>');

Set several response header fields with an object:

ctx.set({
  'Etag': '1234',
  'Last-Modified': date
});

Remove header field.

Get response Content-Type void of parameters such as "charset".

const ct = ctx.type;
// => "image/png"

Set response Content-Type via mime string or file extension.

ctx.type = 'text/plain; charset=utf-8';
ctx.type = 'image/png';
ctx.type = '.png';
ctx.type = 'png';

Note: when appropriate a charset is selected for you, for example response.type = 'html' will default to "utf-8". If you need to overwrite charset, use ctx.set('Content-Type', 'text/html') to set response header field to value directly.

Very similar to ctx.request.is(). Check whether the response type is one of the supplied types. This is particularly useful for creating middleware that manipulate responses.

For example, this is a middleware that minifies all HTML responses except for streams.

const minify = require('html-minifier');

app.use(async (ctx, next) => {
  await next();

  if (!ctx.response.is('html')) return;

  let body = ctx.body;
  if (!body || body.pipe) return;

  if (Buffer.isBuffer(body)) body = body.toString();
  ctx.body = minify(body);
});

Perform a [302] redirect to url.

The string "back" is special-cased to provide Referrer support, when Referrer is not present alt or "/" is used.

ctx.redirect('back');
ctx.redirect('back', '/index.html');
ctx.redirect('/login');
ctx.redirect('http://google.com');

To alter the default status of 302, simply assign the status before or after this call. To alter the body, assign it after this call:

ctx.status = 301;
ctx.redirect('/cart');
ctx.body = 'Redirecting to shopping cart';

Set Content-Disposition to "attachment" to signal the client to prompt for download. Optionally specify the filename of the download.

Check if a response header has already been sent. Useful for seeing if the client may be notified on error.

Return the Last-Modified header as a Date, if it exists.

Set the Last-Modified header as an appropriate UTC string. You can either set it as a Date or date string.

ctx.response.lastModified = new Date();

Set the ETag of a response including the wrapped "s. Note that there is no corresponding response.etag getter.

ctx.response.etag = crypto.createHash('md5').update(ctx.body).digest('hex');