Context

包路径: github.com/caicloud/nirvana/service

在 Nirvana 中，Context 用于传递请求的上下文。Context 中包含 HTTP 的 Request 和 ResponseWriter。可是使用 service 包的 HTTPContextFrom() 方法获得 HTTP Context。HTTP Context 相关接口如下：

// ValueContainer contains values from a request.
type ValueContainer interface {
    // Path returns path value by key.
    Path(key string) (string, bool)
    // Query returns value from query string.
    Query(key string) ([]string, bool)
    // Header returns value by header key.
    Header(key string) ([]string, bool)
    // Form returns value from request. It is valid when
    // http "Content-Type" is "application/x-www-form-urlencoded"
    // or "multipart/form-data".
    Form(key string) ([]string, bool)
    // File returns a file reader when "Content-Type" is "multipart/form-data".
    File(key string) (multipart.File, bool)
    // Body returns a reader to read data from request body.
    // The reader only can read once.
    Body() (reader io.ReadCloser, contentType string, ok bool)
}

// ResponseWriter extends http.ResponseWriter.
type ResponseWriter interface {
    http.ResponseWriter
    // HeaderWritable can check whether WriteHeader() has
    // been called. If the method returns false, you should
    // not recall WriteHeader().
    HeaderWritable() bool
    // StatusCode returns status code.
    StatusCode() int
    // ContentLength returns the length of written content.
    ContentLength() int
}

// HTTPContext describes an http context.
type HTTPContext interface {
    Request() *http.Request
    ResponseWriter() ResponseWriter
    ValueContainer() ValueContainer
    RoutePath() string
}

Nirvana 框架会为每个请求构建这样的 HTTPContext。如有必要，可以通过这些接口拿到与请求相关的所有数据。

在一个请求路由匹配成功后，Nirvana 会把对应的 HTTPContext 传递给中间件，然后由中间件调用链继续传递。最终经由 ContextPrefab 传递给业务函数。

中间件不应该修改 HTTPContext，除非您明确知道如何修改。