介绍

const Koa = require('koa');
const app = new Koa({ proxy: true });

const Koa = require('koa');
const app = new Koa();
app.proxy = true;

创建并返回一个 HTTP 服务器，将给定参数传递给 Server#listen() 。这些参数记录在 nodejs.org 上。以下是绑定到 3000 端口的无用 Koa 应用：

¥Create and return an HTTP server, passing the given arguments to Server#listen() . These arguments are documented on nodejs.org . The following is a useless Koa application bound to port 3000 :

const Koa = require('koa');
const app = new Koa();
app.listen(3000);

app.listen(...) 方法只是以下内容的语法糖：

¥The app.listen(...) method is simply sugar for the following:

const http = require('http');
const Koa = require('koa');
const app = new Koa();
http.createServer(app.callback()).listen(3000);

这意味着你可以将同一个应用启动为 HTTP 和 HTTPS，或者在多个地址上启动：

¥This means you can spin up the same application as both HTTP and HTTPS or on multiple addresses:

const http = require('http');
const https = require('https');
const Koa = require('koa');
const app = new Koa();
http.createServer(app.callback()).listen(3000);
https.createServer(app.callback()).listen(3001);

app.use(someMiddleware)
app.use(someOtherMiddleware)
app.listen(3000)

app.use(someMiddleware)
  .use(someOtherMiddleware)
  .listen(3000)

请参阅 中间件 了解更多信息。

¥See Middleware for more information.

app.keys=

设置签名的 cookie 密钥。

¥Set signed cookie keys.

这些将传递给 KeyGrip ，但是你也可以传递你自己的 KeyGrip 实例。例如，以下内容是可以接受的：

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

app.keys = ['OEK5zjaAMPc3L6iK7PyUjCOziUH3rsrMKB9u8H07La1SkfwtuBoDnHaaPCkG5Brg', 'MNKeIebviQnCPo38ufHcSfw3FFv8EtnAe1xE02xkN1wkCV1B2z126U44yk2BQVK7'];
app.keys = new KeyGrip(['OEK5zjaAMPc3L6iK7PyUjCOziUH3rsrMKB9u8H07La1SkfwtuBoDnHaaPCkG5Brg', 'MNKeIebviQnCPo38ufHcSfw3FFv8EtnAe1xE02xkN1wkCV1B2z126U44yk2BQVK7'], 'sha256');

出于安全考虑，请确保密钥足够长且随机。

¥For security reasons, please ensure that the key is long enough and random.

这些密钥可以轮换，并在使用 { signed: true } 选项签署 cookie 时使用：

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

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

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

ctx 上的许多属性都是使用 getter、setter 和 Object.defineProperty() 定义的。你只能通过在 app.context 上使用 Object.defineProperty() 来编辑这些属性（不推荐）。参见 https://github.com/koajs/koa/issues/652 。

¥Many properties on ctx are defined using getters, setters, and Object.defineProperty() . You can only edit these properties (not recommended) by using Object.defineProperty() on app.context . See https://github.com/koajs/koa/issues/652 .

已挂载的应用当前使用其父级的 ctx 和设置。因此，挂载的应用实际上只是中间件组。

¥Mounted apps currently use their parent's ctx and settings. Thus, mounted apps are really just groups of middleware.

¥Error Handling

默认情况下，除非 app.silent 是 true ，否则将所有错误输出到 stderr。当 err.status 是 404 或 err.expose 是 true 时，默认错误处理程序也不会输出错误。要执行自定义错误处理逻辑（例如集中式日志记录），你可以添加 "error" 事件监听器：

¥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)
});

如果 req/res 循环出现错误，无法响应客户端，也会传递 Context 实例：

¥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)
});

当发生错误并且仍然可以响应客户端时，即没有数据写入套接字时，Koa 将使用 500 "内部服务器错误" 进行适当响应。在任何一种情况下，都会触发应用级别 "error" 以用于记录目的。

¥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.

¥Context

Koa Context 将 Node 的 request 和 response 对象封装到一个对象中，该对象为编写 Web 应用和 API 提供了许多有用的方法。这些操作在 HTTP 服务器开发中使用得非常频繁，因此它们是在此级别添加的，而不是更高级别的框架，这将迫使中间件重新实现此通用功能。

¥A Koa Context encapsulates Node's request and response objects into a single object which provides many helpful methods for writing web applications and APIs. These operations are used so frequently in HTTP server development that they are added at this level instead of a higher level framework, which would force middleware to re-implement this common functionality.

每个请求都会创建一个 Context ，并在中间件中作为接收者或 ctx 标识符进行引用，如以下代码片段所示：

¥A Context is created per request, and is referenced in middleware as the receiver, or the ctx identifier, as shown in the following snippet:

app.use(async ctx => {
  ctx; // is the Context
  ctx.request; // is a Koa Request
  ctx.response; // is a Koa Response
});

为了方便起见，许多上下文的访问器和方法只是委托给它们的 ctx.request 或 ctx.response 等效项，并且在其他方面是相同的。例如， ctx.type 和 ctx.length 委托给 response 对象， ctx.path 和 ctx.method 委托给 request 。

¥Many of the context's accessors and methods simply delegate to their ctx.request or ctx.response equivalents for convenience, and are otherwise identical. For example ctx.type and ctx.length delegate to the response object, and ctx.path and ctx.method delegate to the request .

Context 特定方法和访问器。

¥ Context specific methods and accessors.

ctx.req

节点的 request 对象。

¥Node's request object.

ctx.res

节点的 response 对象。

¥Node's response object.

不支持绕过 Koa 的响应处理。避免使用以下节点属性：

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

res.statusCode

res.writeHead()

res.write()

res.end()

ctx.request

一个 Koa Request 对象。

¥A Koa Request object.

ctx.response

一个 Koa Response 对象。

¥A Koa Response object.

ctx.state

推荐的命名空间，用于通过中间件传递信息并将信息传递到前端视图。

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

ctx.state.user = await User.find(id);

Koa 应用扩展了内部 EventEmitter 。 ctx.app.emit 触发一个事件，其类型由第一个参数定义。对于每个事件，你可以连接 "listeners"，这是在事件触发时调用的函数。请参阅 错误处理文档 了解更多信息。

¥Koa applications extend an internal EventEmitter . ctx.app.emit emits an event with a type, defined by the first argument. For each event you can hook up "listeners", which is a function that is called when the event is emitted. Consult the error handling docs for more information.

ctx.cookies.get(name, [options])

获取 cookie name 和 options ：

¥Get cookie name with options :

signed 请求的 cookie 应该被签名

¥ signed the cookie requested should be signed

Koa 使用 cookies 模块，其中选项被简单地传递。

¥Koa uses the cookies module where options are simply passed.

ctx.cookies.set(name, value, [options])

将 cookie name 设置为 value 和 options ：

¥Set cookie name to value with options :

maxAge ：一个数字，表示从 Date.now() 到到期的毫秒数。

¥ maxAge : a number representing the milliseconds from Date.now() for expiry.

expires ：一个 Date 对象，指示 cookie 的到期日期（默认在会话结束时到期）。

¥ expires : a Date object indicating the cookie's expiration date (expires at the end of session by default).

path ：指示 cookie 路径的字符串（默认为 / ）。

¥ path : a string indicating the path of the cookie ( / by default).

domain ：指示 cookie 域的字符串（无默认值）。

¥ domain : a string indicating the domain of the cookie (no default).

secure ：一个布尔值，指示 cookie 是否仅通过 HTTPS 发送（HTTP 默认为 false ，HTTPS 默认为 true ）。 阅读有关此选项的更多信息 。

¥ secure : a boolean indicating whether the cookie is only to be sent over HTTPS ( false by default for HTTP, true by default for HTTPS). Read more about this option .

httpOnly ：一个布尔值，指示 cookie 是否仅通过 HTTP(S) 发送，而不可供客户端 JavaScript 使用（默认为 true ）。

¥ httpOnly : a boolean indicating whether the cookie is only to be sent over HTTP(S), and not made available to client JavaScript ( true by default).

partitioned ：一个布尔值，表示是否在 Chrome 中为 CHIPS 更新 （默认为 false ）对 cookie 进行分区。如果这是真的，来自嵌入式网站的 Cookie 将被分区，并且只能从创建它的同一顶层网站读取。

¥ partitioned : a boolean indicating whether to partition the cookie in Chrome for the CHIPS Update ( false by default). If this is true, Cookies from embedded sites will be partitioned and only readable from the same top level site from which it was created.

priority ：一个字符串，表示 cookie 优先级。这可以设置为 'low' 、 'medium' 或 'high' 。

¥ priority : a string indicating the cookie priority. This can be set to 'low' , 'medium' , or 'high' .

sameSite ：一个布尔值或字符串，指示 cookie 是否为 "同一站点" cookie（默认为 false ）。可以将其设置为 'strict' 、 'lax' 、 'none' 或 true （映射到 'strict' ）。

¥ sameSite : a boolean or string indicating whether the cookie is a "same site" cookie ( false by default). This can be set to 'strict' , 'lax' , 'none' , or true (which maps to 'strict' ).

signed ：一个布尔值，指示 cookie 是否要签名（默认为 false ）。如果这是 true，则还将发送附加有 .sig 后缀的另一个同名 cookie，其中包含 27 字节 url 安全的 Base64 SHA1 值，表示 cookie-name=cookie-value 与第一个 要点 密钥的哈希值。该签名密钥用于在下次接收到 cookie 时检测篡改情况。

¥ signed : a boolean indicating whether the cookie is to be signed ( false by default). If this is true, another cookie of the same name with the .sig suffix appended will also be sent, with a 27-byte url-safe base64 SHA1 value representing the hash of cookie-name = cookie-value against the first Keygrip key. This signature key is used to detect tampering the next time a cookie is received.

overwrite ：一个布尔值，指示是否覆盖先前设置的同名 cookie（默认为 false ）。如果这是 true，则在设置此 cookie 时，在同一请求期间设置的具有相同名称（无论路径或域）的所有 cookie 都会从 Set-Cookie 标头中过滤掉。

¥ 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 使用 cookies 模块，其中选项被简单地传递。

¥Koa uses the cookies module where options are simply passed.

ctx.throw([status], [msg], [properties])

Helper 方法抛出一个错误， .status 属性默认为 500 ，这将允许 Koa 做出适当的响应。允许以下组合：

¥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:

ctx.throw(400);
ctx.throw(400, 'name required');
ctx.throw(400, 'name required', { user: user });

例如 ctx.throw(400, 'name required') 相当于：

¥For example ctx.throw(400, 'name required') is equivalent to:

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

请注意，这些是用户级错误，并用 err.expose 标记，这意味着这些消息适合客户端响应，但错误消息通常不是这种情况，因为你不想泄漏故障详细信息。

¥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.

你可以选择传递一个按原样合并到错误中的 properties 对象，这对于装饰向上游请求者报告的机器友好错误很有用。

¥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.

ctx.throw(401, 'access_denied', { user: user });

Koa 使用 http-errors 来创建错误。 status 只能作为第一个参数传递。

¥Koa uses http-errors to create errors. status should only be passed as the first parameter.

ctx.assert(value, [status], [msg], [properties])

Helper 方法在 !value 时抛出类似于 .throw() 的错误。类似于 Node 的 assert() 方法。

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

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

Koa 使用 http-assert 进行断言。

¥Koa uses http-assert for assertions.

ctx.respond

要绕过 Koa 的内置响应处理，你可以显式设置 ctx.respond = false; 。如果你想写入原始 res 对象而不是让 Koa 为你处理响应，请使用此选项。

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

请注意，Koa 不支持使用此功能。这可能会破坏 Koa 中间件和 Koa 本身的预期功能。使用此属性被认为是一种 hack，并且只是为那些希望在 Koa 中使用传统 fn(req, res) 功能和中间件的人提供便利。

¥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.

¥Request aliases

以下访问器和别名 请求 等效项：

¥The following accessors and alias Request equivalents:

ctx.header

ctx.headers

ctx.method

ctx.method=

ctx.url

ctx.url=

ctx.originalUrl

ctx.origin

ctx.href

ctx.path

ctx.path=

ctx.query

ctx.query=

ctx.querystring

ctx.querystring=

ctx.host

ctx.hostname

ctx.fresh

ctx.stale

ctx.socket

ctx.protocol

ctx.secure

ctx.ip

ctx.ips

ctx.subdomains

ctx.is()

ctx.accepts()

ctx.acceptsEncodings()

ctx.acceptsCharsets()

ctx.acceptsLanguages()

ctx.get()

¥Response aliases

以下访问器和别名 响应 等效项：

¥The following accessors and alias Response equivalents:

ctx.body

ctx.body=

ctx.has()

ctx.status

ctx.status=

ctx.message

ctx.message=

ctx.length=

ctx.length

ctx.type=

ctx.type

ctx.vary()

ctx.headerSent

ctx.redirect()

ctx.attachment()

ctx.set()

ctx.append()

ctx.remove()

ctx.lastModified=

ctx.etag=

ctx.writable

¥Request

Koa Request 对象是 Node 的普通请求对象之上的抽象，提供对日常 HTTP 服务器开发有用的附加功能。

¥A Koa Request object is an abstraction on top of Node's vanilla request object, providing additional functionality that is useful for every day HTTP server development.

request.header

请求标头对象。这与节点的 http.IncomingMessage 上的 headers 字段相同。

¥Request header object. This is the same as the headers field on Node's http.IncomingMessage .

request.header=

设置请求头对象。

¥Set request header object.

request.headers

请求标头对象。别名为 request.header 。

¥Request header object. Alias as request.header .

request.headers=

设置请求头对象。别名为 request.header= 。

¥Set request header object. Alias as request.header= .

request.method

请求方法。

¥Request method.

request.method=

设置请求方法，对于实现 methodOverride() 等中间件很有用。

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

request.length

将请求内容长度返回为数字（如果存在）或 undefined 。

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

request.url

获取请求 URL。

¥Get request URL.

request.url=

设置请求 URL，对于 url 重写很有用。

¥Set request URL, useful for url rewrites.

request.originalUrl

获取请求原始 URL。

¥Get request original URL.

request.origin

获取 URL 的来源，包括 protocol 和 host 。

¥Get origin of URL, include protocol and host .

ctx.request.origin
// => http://example.com

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

如果 host 是 IPv6，Koa 将解析委托给 WHATWG URL API ，注意这可能会影响性能。

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

request.URL

获取 WHATWG 解析的 URL 对象。

¥Get WHATWG parsed URL object.

request.type

获取请求 Content-Type 不含 "charset" 等参数。

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

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

ctx.request.charset;
// => "utf-8"

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

// freshness check requires status 20x or 304
ctx.status = 200;
ctx.set('ETag', '123');
// cache is ok
if (ctx.fresh) {
  ctx.status = 304;
  return;
// cache is stale
// fetch new data
ctx.body = await db.find('something');

const app = new Koa({
  proxy: true,
  proxyIpHeader: 'X-Real-IP',
});

const app = new Koa({
  proxy: true,
  maxIpsCount: 1, // only one proxy in front of the server
// request.header['X-Forwarded-For'] === [ '127.0.0.1', '127.0.0.2' ];
// ctx.ips === [ '127.0.0.2' ];

// 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

if (ctx.is('image/*')) {
  // process
} else {
  ctx.throw(415, 'images only!');
¥Content Negotiation
Koa 的 request 对象包括由 accepts 和 negotiator 提供支持的有用的内容协商实用程序。这些实用程序是：
¥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)
如果未提供类型，则返回所有可接受的类型。
¥If no types are supplied, all acceptable types are returned.
如果提供多种类型，将返回最佳匹配。如果未找到匹配项，则返回 false，并且你应该向客户端发送 406 "Not Acceptable" 响应。
¥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.
如果缺少可接受任何类型的接受标头，则将返回第一个类型。因此，你提供的类型的顺序很重要。
¥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.
request.accepts(types)
检查给定的 type(s) 是否可接受，为 true 时返回最佳匹配，否则返回 false。type 值可以是一个或多个 mime 类型字符串（例如 "application/json"）、扩展名（例如 "json"）或数组 ["json", "html", "text/plain"]。
¥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"
你可以根据需要多次调用 ctx.accepts()，或者使用开关：
¥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');
request.acceptsEncodings(encodings)
检查 encodings 是否可接受，为真时返回最佳匹配，否则返回 false。请注意，你应该包含 identity 作为编码之一！
¥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"
当没有给出参数时，所有接受的编码都作为数组返回：
¥When no arguments are given all accepted encodings
are returned as an array:
// Accept-Encoding: gzip, deflate
ctx.acceptsEncodings();
// => ["gzip", "deflate", "identity"]
请注意，如果客户端显式发送 identity;q=0，则 identity 编码（意味着无编码）可能不可接受。尽管这是一种边缘情况，但你仍然应该处理此方法返回 false 的情况。
¥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.
request.acceptsCharsets(charsets)
检查 charsets 是否可接受，为真时返回最佳匹配，否则返回 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"
当没有给出参数时，所有接受的字符集都作为数组返回：
¥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"]

request.acceptsLanguages(langs)
检查 langs 是否可接受，为真时返回最佳匹配，否则返回 false。
¥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"
当没有给出参数时，所有接受的语言都作为数组返回：
¥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"]

request.idempotent
检查请求是否幂等。
¥Check if the request is idempotent.
request.socket
返回请求套接字。
¥Return the request socket.
request.get(field)
返回请求头，不区分大小写 field。
¥Return request header with case-insensitive field.
¥Response
Koa Response 对象是 Node 的普通响应对象之上的抽象，提供对日常 HTTP 服务器开发有用的附加功能。
¥A Koa Response object is an abstraction on top of Node's vanilla response object,
providing additional functionality that is useful for every day HTTP server
development.
response.header
响应头对象。
¥Response header object.
response.headers
响应头对象。别名为 response.header。
¥Response header object. Alias as response.header.
response.socket
响应套接字。指向 request.socket 的 net.Socket 实例。
¥Response socket. Points to net.Socket instance as request.socket.
response.status
获取响应状态。默认情况下，response.status 设置为 404，与 Node 的 res.statusCode 默认设置为 200 不同。
¥Get response status. By default, response.status is set to 404 unlike Node's res.statusCode which defaults to 200.
response.status=
通过数字代码设置响应状态：
¥Set response status via numeric code:
100 "继续"
¥100 "continue"
101 "切换协议"
¥101 "switching protocols"
102 "处理中"
¥102 "processing"
200 "ok"
201 "已创建"
¥201 "created"
202 "已接受"
¥202 "accepted"
203 "非权威信息"
¥203 "non-authoritative information"
204 "无内容"
¥204 "no content"
205 "重置内容"
¥205 "reset content"
206 "部分内容"
¥206 "partial content"
207 "多状态"
¥207 "multi-status"
208 "已上报"
¥208 "already reported"
226 "已使用"
¥226 "im used"
300 "多项选择"
¥300 "multiple choices"
301 "永久移动"
¥301 "moved permanently"
302 "已找到"
¥302 "found"
303 "查看其他"
¥303 "see other"
304 "未修改"
¥304 "not modified"
305 "使用代理服务器"
¥305 "use proxy"
307 "临时重定向"
¥307 "temporary redirect"
308 "永久重定向"
¥308 "permanent redirect"
400 "错误的请求"
¥400 "bad request"
401 "未授权"
¥401 "unauthorized"
402 "需要付款"
¥402 "payment required"
403 "已禁止"
¥403 "forbidden"
404 "未找到"
¥404 "not found"
405 "方法不允许"
¥405 "method not allowed"
406 "不被接受的"
¥406 "not acceptable"
407 "需要代理身份验证"
¥407 "proxy authentication required"
408 "请求超时"
¥408 "request timeout"
409 "冲突"
¥409 "conflict"
410 "已失去"
¥410 "gone"
411 "需要长度"
¥411 "length required"
412 "前提条件失败"
¥412 "precondition failed"
413 "有效载荷太大"
¥413 "payload too large"
414 "uri 太长"
¥414 "uri too long"
415 "不支持的媒体类型"
¥415 "unsupported media type"
416 "范围不满足"
¥416 "range not satisfiable"
417 "期望失败"
¥417 "expectation failed"
418 "我是茶壶"
¥418 "I'm a teapot"
422 "不可处理的实体"
¥422 "unprocessable entity"
423 "已上锁"
¥423 "locked"
424 "失败的依赖"
¥424 "failed dependency"
426 "需要升级"
¥426 "upgrade required"
428 "需要先决条件"
¥428 "precondition required"
429 "请求太多"
¥429 "too many requests"
431 "请求头字段太大"
¥431 "request header fields too large"
500 "内部服务器错误"
¥500 "internal server error"
501 "未实现"
¥501 "not implemented"
502 "错误的网关"
¥502 "bad gateway"
503 "暂停服务"
¥503 "service unavailable"
504 "网关超时"
¥504 "gateway timeout"
505 "不支持 http 版本"
¥505 "http version not supported"
506 "变体也协商"
¥506 "variant also negotiates"
507 "存储空间不足"
¥507 "insufficient storage"
508 "检测到循环"
¥508 "loop detected"
510 "未扩展"
¥510 "not extended"
511 "需要网络认证"
¥511 "network authentication required"
注意：不要太担心记住这些字符串，如果你有拼写错误，将会抛出错误，显示此列表以便你可以进行更正。
¥NOTE: don't worry too much about memorizing these strings,
if you have a typo an error will be thrown, displaying this list
so you can make a correction.
由于 response.status 默认设置为 404，因此要发送不带正文且具有不同状态的响应，请按如下方式完成：
¥Since response.status default is set to 404, to send a response
without a body and with a different status is to be done like this:
ctx.response.status = 200;
// Or whatever other status
ctx.response.status = 204;

response.message
获取响应状态消息。默认情况下，response.message 与 response.status 关联。
¥Get response status message. By default, response.message is
associated with response.status.
response.message=
将响应状态消息设置为给定值。
¥Set response status message to the given value.
response.length=
将响应内容长度设置为给定值。
¥Set response Content-Length to the given value.
response.length
如果存在，则以数字形式返回响应内容长度，或者在可能的情况下从 ctx.body 或 undefined 中推导出来。
¥Return response Content-Length as a number when present, or deduce
from ctx.body when possible, or undefined.
response.body
获取响应正文。
¥Get response body.
response.body=
将响应正文设置为以下内容之一：
¥Set response body to one of the following:
string 已写

¥string written
Buffer 已写

¥Buffer written
Stream 管道式

¥Stream piped
Object || Array json-stringified

null || undefined 无内容响应

¥null || undefined no content response
如果没有设置 response.status，Koa 会根据 response.body 自动将状态设置为 200 或 204。具体来说，如果 response.body 没有设置或者已经设置为 null 或 undefined，Koa 会自动将 response.status 设置为 204。如果你确实想发送其他状态的无内容响应，则应按以下方式覆盖 204 状态：
¥If response.status has not been set, Koa will automatically set the status to 200 or 204 depending on response.body. Specifically, if response.body has not been set or has been set as null or undefined, Koa will automatically set response.status to 204. If you really want to send no content response with other status, you should override the 204 status as the following way:
// This must be always set first before status, since null | undefined
// body automatically sets the status to 204
ctx.body = null;
// Now we override the 204 status with the desired one
ctx.status = 200;
Koa 并不防范所有可以作为响应主体的内容 - 函数没有有意义的序列化，根据你的应用返回一个布尔值可能有意义，并且虽然错误有效，但它可能不会像某些人预期的那样工作 错误的属性是不可枚举的。我们建议在你的应用中添加中间件来断言每个应用的正文类型。示例中间件可能是：
¥Koa doesn't guard against everything that could be put as a response body -- a function doesn't serialise meaningfully, returning a boolean may make sense based on your application, and while an error works, it may not work as intended as some properties of an error are not enumerable.  We recommend adding middleware in your app that asserts body types per app.  A sample middleware might be:
app.use(async (ctx, next) => {
  await next()
  ctx.assert.equal('object', typeof ctx.body, 500, 'some dev did something wrong')
¥String
Content-Type 默认为 text/html 或 text/plain，两者的默认字符集均为 utf-8。还设置了内容长度字段。
¥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.
¥Buffer
Content-Type 默认为 application/octet-stream，并且还设置了 Content-Length。
¥The Content-Type is defaulted to application/octet-stream, and Content-Length
is also set.
¥Stream
Content-Type 默认为 application/octet-stream。
¥The Content-Type is defaulted to application/octet-stream.
每当将流设置为响应正文时，.onerror 就会自动添加为 error 事件的监听器以捕获任何错误。此外，每当请求关闭（甚至过早）时，流都会被销毁。如果你不需要这两个功能，请不要直接将流设置为正文。例如，当将主体设置为代理中的 HTTP 流时，你可能不希望这样做，因为这会破坏底层连接。
¥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.
看：https://github.com/koajs/koa/pull/612 了解更多信息。
¥See: https://github.com/koajs/koa/pull/612 for more information.
下面是一个在不自动销毁流的情况下进行流错误处理的示例：
¥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', (err) => ctx.onerror(err)).pipe(PassThrough());
¥Object
Content-Type 默认为 application/json。这包括普通对象 { foo: 'bar' } 和数组 ['foo', 'bar']。
¥The Content-Type is defaulted to application/json. This includes plain objects { foo: 'bar' } and arrays ['foo', 'bar'].
response.get(field)
获取响应头字段值，不区分大小写 field。
¥Get a response header field value with case-insensitive field.
const etag = ctx.response.get('ETag');

response.has(field)
如果当前在传出标头中设置了由名称标识的标头，则返回 true。标头名称匹配不区分大小写。
¥Returns true if the header identified by name is currently set in the outgoing headers.
The header name matching is case-insensitive.
const rateLimited = ctx.response.has('X-RateLimit-Limit');

response.set(field, value)
将响应标头 field 设置为 value：
¥Set response header field to value:
ctx.set('Cache-Control', 'no-cache');

response.append(field, value)
附加带有值 val 的附加标头 field。
¥Append additional header field with value val.
ctx.append('Link', 'http://127.0.0.1');

response.set(fields)
用一个对象设置几个响应头 fields：
¥Set several response header fields with an object:
ctx.set({
  'Etag': '1234',
  'Last-Modified': date
});
这委托给 setHeader，它通过指定的键设置或更新标头，并且不会重置整个标头。
¥This delegates to setHeader which sets or updates headers by specified keys and doesn't reset the entire header.
response.remove(field)
删除标头 field。
¥Remove header field.
response.type
获取响应 Content-Type，不含 "charset" 等参数。
¥Get response Content-Type void of parameters such as "charset".
const ct = ctx.type;
// => "image/png"

response.type=
通过 mime 字符串或文件扩展名设置响应 Content-Type。
¥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';
注意：如果合适，会为你选择 charset，例如 response.type = 'html' 将默认为 "utf-8"。如果需要覆盖 charset，可以使用 ctx.set('Content-Type', 'text/html') 直接将响应头字段设置为值。
¥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.
response.is(types...)
与 ctx.request.is() 非常相似。检查响应类型是否是提供的类型之一。这对于创建操纵响应的中间件特别有用。
¥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.
例如，这是一个缩小除流之外的所有 HTML 响应的中间件。
¥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);
response.redirect(url, [alt])
执行 [302] 重定向到 url。
¥Perform a [302] redirect to url.
字符串 "back" 是特殊大小写的，用于在引用者不存在时提供引用者支持，而使用 alt 或 "/"。
¥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');
要更改 302 的默认状态，只需在调用之前或之后指定状态即可。要更改主体，请在此调用后分配它：
¥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';

response.attachment([filename], [options])
将 Content-Disposition 设置为 "attachment" 以指示客户端提示下载。可以选择指定下载的 filename 和一些 options。
¥Set Content-Disposition to "attachment" to signal the client
to prompt for download. Optionally specify the filename of the
download and some options.
response.headerSent
检查响应标头是否已发送。对于查看是否可以通知客户端错误很有用。
¥Check if a response header has already been sent. Useful for seeing
if the client may be notified on error.
response.lastModified
将 Last-Modified 标头作为 Date 返回（如果存在）。
¥Return the Last-Modified header as a Date, if it exists.
response.lastModified=
将 Last-Modified 标头设置为适当的 UTC 字符串。你可以将其设置为 Date 或日期字符串。
¥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();

response.etag=
设置包含封装的 " 的响应的 ETag。请注意，没有相应的 response.etag getter。
¥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');

response.vary(field)
随 field 变化。
¥Vary on field.