在异步工作流中捕获 HttpClient 超时

Question

我正在通过 Async.AwaitTask 呼叫 HttpClient，是从代理 (MailboxProcessor) 中呼叫的。我想在 HTTP 调用期间捕获错误，因此在异步工作流中使用了 try...with，但它完全没有捕获到客户端超时异常，这会导致代理崩溃。

最小复制：

#r "System.Net.Http"
open System
open System.Net.Http

let client = new HttpClient()
client.Timeout <- TimeSpan.FromSeconds(1.)
async {
    try
        let! content = Async.AwaitTask <| client.GetStringAsync("http://fake-response.appspot.com/?sleep=30")
        return content
    with ex ->
        // Does not catch client-side timeout exception
        return "Caught it!"
}
|> Async.RunSynchronously
// Throws System.OperationCanceledException: The operation was canceled

我可以通过使它完全同步来修复它，但我更愿意保持整个堆栈异步，因为可能运行许多并行：

#r "System.Net.Http"
open System
open System.Net.Http

let client = new HttpClient()
client.Timeout <- TimeSpan.FromSeconds(1.)
try
    Async.AwaitTask <| client.GetStringAsync("http://fake-response.appspot.com/?sleep=30")
    |> Async.RunSynchronously
with ex ->
    "Caught it!"
// Returns "Caught it!"

是否有在异步上下文中捕获 OperationCanceledException 的有效方法？

Answer 1

发生这种情况是因为 HttpClient.GetStringAsync 任务将被取消，而不是因 TimeoutException 而失败，从而促使异步机制触发其取消继续，这是无法处理的。解决此问题的简单方法如下：

async {
    try
        let! content = 
            client.GetStringAsync("http://fake-response.appspot.com/?sleep=30")
                  .ContinueWith(fun (t:Task<string>) -> t.Result)
            |> Async.AwaitTask
        return content
    with ex ->
        // Does not catch client-side timeout exception
        return "Caught it!"
}

在异步工作流中捕获 HttpClient 超时

Catching HttpClient timeouts within an async workflow

f#

dotnet-httpclient

f#-async