如何修复Scala HTTP请求addHeader不生效 跨请求复制请求头问题

Akka HTTP 框架中HttpRequest属于不可变值类，所有修改类方法（包括addHeader）不会直接修改当前实例，而是返回携带修改结果的全新对象。
原代码循环调用request.addHeader(h)时，没有将方法返回的新实例重新赋值，原请求对象的headers始终保留初始化时传入的空列表Nil，因此后续打印日志时看不到任何已添加的请求头。

跨请求复制请求头时，需要主动过滤和单次请求强绑定、无法跨请求透传的头部，避免触发HTTP协议解析错误，需要过滤的头部包括：Host、Content-Length、Connection、Transfer-Encoding、Keep-Alive。

实现代码示例 #

private def apiPostRequest(path: String, host: HostStoreInfo, byteString: ByteString, prevRequest: HttpRequest): Future[HttpResponse] = {
  // 定义不可透传的头部列表
  val excludedHeaders = Set("Host", "Content-Length", "Connection", "Transfer-Encoding", "Keep-Alive")
  // 从旧请求中筛选可复制的头部
  val copiedHeaders = Option(prevRequest)
    .map(_.headers.filterNot(h => excludedHeaders.contains(h.name)))
    .getOrElse(Nil)

  // 初始化新请求时直接传入筛选后的请求头
  val request = HttpRequest(
    method = HttpMethods.POST,
    uri = s"http://${host.host}:${host.port}$path",
    headers = copiedHeaders,
    entity = HttpEntity.apply(byteString)
  )

  logger.info("Previous request  " + prevRequest)
  logger.info("Here are the headers  " + request.headers)
  Http().singleRequest(request)
}

如果需要基于旧请求的其他属性做调整，也可以借助copy方法构造新实例：

private def apiPostRequest(path: String, host: HostStoreInfo, byteString: ByteString, prevRequest: HttpRequest): Future[HttpResponse] = {
  val excludedHeaders = Set("Host", "Content-Length", "Connection", "Transfer-Encoding", "Keep-Alive")
  if (prevRequest == null) {
    val request = HttpRequest(
      method = HttpMethods.POST,
      uri = s"http://${host.host}:${host.port}$path",
      entity = HttpEntity.apply(byteString)
    )
    return Http().singleRequest(request)
  }
  // 筛选合法可复制的头部
  val validHeaders = prevRequest.headers.filterNot(h => excludedHeaders.contains(h.name))
  // 复制旧请求对象，覆盖需要调整的属性
  val newRequest = prevRequest.copy(
    method = HttpMethods.POST,
    uri = s"http://${host.host}:${host.port}$path",
    headers = validHeaders,
    entity = HttpEntity.apply(byteString)
  )
  Http().singleRequest(newRequest)
}

• 不建议全量复制所有请求头，否则会因新旧Host、请求体元数据冲突，被Akka HTTP客户端拦截抛出协议异常
• 仅需要透传少量自定义业务头时，使用头部白名单的方式比全量过滤更安全可控

内容的提问来源于stack exchange，提问作者hareendra reddy