146 lines
3.3 KiB
Markdown
146 lines
3.3 KiB
Markdown
# Context
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A Koa Context encapsulates node's `request` and `response` objects
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into a single object which provides many helpful methods for writing
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web applications and APIs.
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Many accesors and methods simply delegate to their `ctx.request` or `ctx.response`
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equivalents for convenience, and are otherwise identical.
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These operations are used so frequently in HTTP server development
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that they are added at this level, instead of a higher level framework,
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which would force middlware to re-implement this common functionality.
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A `Context` is created _per_ request, and is referenced in middleware
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as the receiver, or the `this` identifier, as shown in the following
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snippet:
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```js
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app.use(function *(){
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this; // is the Context
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this.request; // is a koa Request
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this.response; // is a koa Response
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});
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```
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## Request aliases
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The following accessors and alias [Request](request.md) equivalents:
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- `ctx.header`
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- `ctx.method`
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- `ctx.method=`
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- `ctx.url`
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- `ctx.url=`
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- `ctx.path`
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- `ctx.path=`
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- `ctx.query`
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- `ctx.query=`
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- `ctx.querystring`
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- `ctx.querystring=`
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- `ctx.length`
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- `ctx.host`
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- `ctx.fresh`
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- `ctx.stale`
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- `ctx.socket`
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- `ctx.protocol`
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- `ctx.secure`
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- `ctx.ip`
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- `ctx.ips`
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- `ctx.subdomains`
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- `ctx.is()`
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- `ctx.accepts()`
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- `ctx.acceptsEncodings()`
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- `ctx.acceptsCharsets()`
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- `ctx.acceptsLanguages()`
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- `ctx.get()`
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## Response aliases
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The following accessors and alias [Response](response.md) equivalents:
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- `ctx.body`
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- `ctx.body=`
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- `ctx.status`
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- `ctx.status=`
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- `ctx.length=`
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- `ctx.type`
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- `ctx.type=`
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- `ctx.headerSent`
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- `ctx.redirect()`
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- `ctx.attachment()`
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- `ctx.set()`
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- `ctx.remove()`
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- `ctx.lastModified=`
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- `ctx.etag=`
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## API
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`Context` specific methods and accessors.
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### ctx.req
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Node's `request` object.
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### ctx.res
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Node's `response` object.
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### ctx.request
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A koa `Request` object.
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### ctx.response
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A koa `Response` object.
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### ctx.app
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Application instance reference.
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### ctx.cookies.get(name, [options])
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Get cookie `name` with `options`:
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- `signed` the cookie requested should be signed
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Note: koa uses the [cookies](https://github.com/jed/cookies) module where options are simply passed.
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### ctx.cookies.set(name, value, [options])
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Set cookie `name` to `value` with `options`:
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- `signed` sign the cookie value
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- `expires` a `Date` for cookie expiration
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- `path` cookie path, `/'` by default
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- `domain` cookie domain
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- `secure` secure cookie
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- `httpOnly` server-accessible cookie, __true__ by default
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Note: koa uses the [cookies](https://github.com/jed/cookies) module where options are simply passed.
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### ctx.throw(msg, [status])
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Helper method to throw an error with a `.status` property
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defaulting to `500` that will allow Koa to respond appropriately.
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The following combinations are allowed:
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```js
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this.throw(403)
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this.throw('name required', 400)
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this.throw('something exploded')
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```
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For example `this.throw('name required', 400)` is equivalent to:
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```js
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var err = new Error('name required');
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err.status = 400;
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throw err;
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```
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Note that these are user-level errors and are flagged with
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`err.expose` meaning the messages are appropriate for
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client responses, which is typically not the case for
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error messages since you do not want to leak failure
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details.
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