Nimlang:异步程序不编译

Question

我正在编写一个HTTP服务器，它发送HTTP请求并将内容返回给客户端。

以下是代码：

import asynchttpserver, asyncdispatch
import httpClient

let client = newHttpClient()

var server = newAsyncHttpServer()

proc cb(req: Request) {.async.} =

  let content = client.getContent("http://google.com")
  await req.respond(Http200, content)

waitFor server.serve(Port(8080), cb)

但是，我获得了以下编译错误消息(nim v1.0.0)：

Error: type mismatch: got <AsyncHttpServer, Port, proc (req: Request): Future[system.void]{.locks: <unknown>.}>
but expected one of:
proc serve(server: AsyncHttpServer; port: Port;
          callback: proc (request: Request): Future[void] {.closure, gcsafe.};
          address = ""): owned(Future[void])
  first type mismatch at position: 3
  required type for callback: proc (request: Request): Future[system.void]{.closure, gcsafe.}
  but expression 'cb' is of type: proc (req: Request): Future[system.void]{.locks: <unknown>.}
  This expression is not GC-safe. Annotate the proc with {.gcsafe.} to get extended error information.

expression: serve(server, Port(8080), cb)

serve函数需要另一个表达式，但不知道如何修复它。令人惊讶的是，当我从服务器回调"cb“中删除HTTP请求时，代码编译得非常好。这是否意味着serve函数期望不同的回调表达式(取决于回调体)？

Answer 1

问题是，HttpClient是一个全局变量，用于回调函数"cb“。因此，回调函数不是GC安全的。

因此，在回调函数中实例化HttpClient就足够了：

import asynchttpserver, asyncdispatch
import httpClient



var server = newAsyncHttpServer()

proc cb(req: Request) {.async.} =

  let client = newHttpClient()

  let content = client.getContent("https://google.com")

  await req.respond(Http200, content)

waitFor server.serve(Port(8080), cb)