5、Ktor学习-生成HTTP响应;

Melrose
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  处理路径或直接拦截管道时，将获得ApplicationCall的上下文。 该调用包含一个名为response的属性，允许发出响应。

上下文

  使用路由功能时，您可以访问路由处理程序中的call属性：

routing {
    get("/") {
        call.respondText("Request uri: ${call.request.uri}")
    } 
}

当拦截请求时，拦截中的lambda处理程序也具有可用的call属性：

intercept(ApplicationCallPipeline.Call) { 
    if (call.request.uri == "/") {
        call.respondText("Test String")
    }
}

控制HTTP headers和status

  您可以控制响应的生成方式，HTTP status，headers，cookie等。

  作为响应的一部分，您可以访问其内部上下文：

val call: ApplicationCall = response.call
val pipeline: ApplicationSendPipeline = response.pipeline

  headers:

val headers: ResponseHeaders = response.headers

  用于设置Set-Cookie标头的便捷cookie实例：

val cookies: ResponseCookies = response.cookies

  获取和更改HTTP status：

response.status(HttpStatusCode.OK) - Sets the HttpStatusCode to a predefined standard one
response.status(HttpStatusCode(418, "I'm a tea pot")) - Sets the HttpStatusCode to a custom status code
val status: HttpStatusCode? = response.status() - Gets the currently set HttpStatusCode if set

response.contentType(ContentType.Text.Plain.withCharset(Charsets.UTF_8)) - Typed way for setting the Content-Type (for ContentType.Application.Json the default charset is UTF_8 without making it explicit)
response.contentType("application/json; charset=UTF-8") - Untyped way for setting the Content-Type header

  自定义headers:

response.header("X-My-Header", "my value") - Appends a custom header
response.header("X-My-Times", 1000) - Appends a custom header
response.header("X-My-Times", 1000L) - Appends a custom header
response.header("X-My-Date", Instant.EPOCH) - Appends a custom header

  设置标头的便捷方法：

response.etag("33a64df551425fcc55e4d42a148795d9f25f89d4") - Sets the ETag used for caching
response.lastModified(ZonedDateTime.now()) - Sets the Last-Modified header
response.contentLength(1024L) - Sets the Content-Length. This is generally automatically set when sending the payload
response.cacheControl(CacheControl.NoCache(CacheControl.Visibility.Private)) - Sets the Cache-Control header in a typed way
response.expires(LocalDateTime.now()) - Sets the Expires header
response.contentRange(1024L until 2048L, 4096L) - Sets the Content-Range header (check the PartialContent feature)

HTTP/2 Pushing和HTTP/1链接头

  call支持Pushing功能。

  • 在HTTP/2中，使用Pushing功能
  • 在HTTP/1.2中，它将链接头添加为一个提示
routing {
    get("/") {
        call.push("/style.css")
    }
}

注：Pushing减少了请求和页面显示之间的时间。但请注意，事先发送内容可能会发送已由客户端缓存的内容。

重定向

  您可以使用respondRedirect方法轻松生成重定向响应，使用Location标头发送301 Moved Permanently或302 Found重定向。

call.respondRedirect("/moved/here", permanent = true)

发送响应内容

  发送通用内容（与Content negotiation兼容）：

call.respond(MyDataClass("hello", "world")) - Check the Content Negotiation section
call.respond(HttpStatusCode.NotFound, MyDataClass("hello", "world")) - Specifies a status code, and sends a payload in a single call. Check StatusPages

  发送文本信息：

call.respondText("text") - Just a string with the body
call.respondText("p { background: red; }", contentType = ContentType.Text.CSS, status = HttpStatusCode.OK) { ... } - Sending a text specifying the ContentType, the HTTP Status and configuring the OutgoingContent
call.respondText { "string" } - Responding a string with a suspend provider
call.respondText(contentType = ..., status = ...) { "string" } - Responding a string with a suspend provider
call.respond(TextContent("{}", ContentType.Application.Json)) - Responding a string without adding a charset to the Content-Type

  发送byte数组：

call.respondBytes(byteArrayOf(1, 2, 3)) - A ByteArray with a binary body

发送文件：

call.respondFile(File("/path/to/file")) - Sends a file
call.respondFile(File("basedir"), "filename") { ... } - Send a file and configures the OutgoingContent

  发送URL编码的表单（application/x-www-form-urlencoded）：

Use Parameters.formUrlEncode. Check the Utilities page for more information about this.

  使用Writer发送分块内容：

call.respondWrite { write("hello"); write("world") } - Sends text using a writer. This is used with the HTML DSL
call.respondWrite(contentType = ..., status = ...) { write("hello"); write("world") } - Sends text using a writer and specifies a contentType and a status

使文件可下载

  您可以通过添加Content-Disposition标头使文件“可下载”。以无类型的方式，您可以执行以下操作：

call.response.header(HttpHeaders.ContentDisposition, "attachment; filename=\"myfilename.bin\"")

  但是Ktor还提供了一种带有正确转义的类型化方法来生成此标头：

call.response.header(HttpHeaders.ContentDisposition, ContentDisposition.Attachment.withParameter(ContentDisposition.Parameters.FileName, "myfilename.bin").toString())

Content negotiation(介绍)

  在配置用于Content negotiation的插件时，管道可以接受call.respond方法的其他类型。

  1. 发送 HTML DSL
  2. 发送 HTMLFreeMarker
  3. 发送data class生成的json
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