Misleading `requests.UnknownHostException: Unknown host null`

[kaaveland]

Hey!

I just spent a few minutes looking for problems in the entirely wrong place. I'm making a tiny cask-app that calculates fibonacci numbers by using requests.get on version 0.9.0 to itself (for good reasons, I promise!), and I had entered the wrong port number to itself on localhost, leading to this error:

requests.UnknownHostException: Unknown host null in url http://localhost:8088/fib/4
	at requests.Requester$$anon$1.readBytesThrough(Requester.scala:291)
	at geny.Readable.writeBytesTo(Writable.scala:93)
	at geny.Readable.writeBytesTo$(Writable.scala:91)
	at requests.Requester$$anon$1.writeBytesTo(Requester.scala:191)
	at requests.Requester.apply(Requester.scala:140)
	at CamelosoServer$.fib(CamelosoServer.scala:58)
	at CamelosoServer$.$anonfun$1$$anonfun$1(CamelosoServer.scala:65)
	at cask.router.Result$Success.map(Result.scala:21)
	at CamelosoServer$.$anonfun$1(CamelosoServer.scala:65)
	at cask.router.EntryPoint.invoke(EntryPoint.scala:47)
	at cask.router.Decorator$.invoke$$anonfun$2(Decorators.scala:59)
	at cask.endpoints.WebEndpoint.wrapFunction(WebEndpoints.scala:14)
	at cask.endpoints.WebEndpoint.wrapFunction$(WebEndpoints.scala:10)
	at cask.endpoints.get.wrapFunction(WebEndpoints.scala:31)
	at cask.router.Decorator$.invoke(Decorators.scala:52)
	at cask.main.Main$DefaultHandler.handleRequest(Main.scala:123)
	at io.undertow.server.Connectors.executeRootHandler(Connectors.java:395)
	at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:861)
	at org.jboss.threads.ContextHandler$1.runWith(ContextHandler.java:18)
	at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2513)
	at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1512)
	at org.xnio.XnioWorker$WorkerThreadFactory$1$1.run(XnioWorker.java:1282)
	at java.base/java.lang.Thread.run(Thread.java:1583)

Downgrading to 0.8.3 gave me this one instead, which made it immediately obvious to me what the problem was:

java.net.ConnectException: Connection refused
	at java.base/sun.nio.ch.Net.pollConnect(Native Method)
	at java.base/sun.nio.ch.Net.pollConnectNow(Net.java:682)
	at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(NioSocketImpl.java:549)
	at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:592)
	at java.base/java.net.Socket.connect(Socket.java:751)
	at java.base/sun.net.NetworkClient.doConnect(NetworkClient.java:178)
	at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:531)
	at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:636)
	at java.base/sun.net.www.http.HttpClient.<init>(HttpClient.java:280)
	at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:386)
	at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:408)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1304)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1237)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1123)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:1052)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1675)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1599)
	at java.base/java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:531)
	at requests.Requester$$anon$1.liftedTree1$1(Requester.scala:267)
	at requests.Requester$$anon$1.readBytesThrough(Requester.scala:279)
	at geny.Readable.writeBytesTo(Writable.scala:93)
	at geny.Readable.writeBytesTo$(Writable.scala:91)
	at requests.Requester$$anon$1.writeBytesTo(Requester.scala:164)
	at requests.Requester.apply(Requester.scala:113)
	at CamelosoServer$.fib(CamelosoServer.scala:59)
	at CamelosoServer$.$anonfun$1$$anonfun$1(CamelosoServer.scala:66)
	at cask.router.Result$Success.map(Result.scala:21)
	at CamelosoServer$.$anonfun$1(CamelosoServer.scala:66)
	at cask.router.EntryPoint.invoke(EntryPoint.scala:47)
	at cask.router.Decorator$.invoke$$anonfun$2(Decorators.scala:59)
	at cask.endpoints.WebEndpoint.wrapFunction(WebEndpoints.scala:14)
	at cask.endpoints.WebEndpoint.wrapFunction$(WebEndpoints.scala:10)
	at cask.endpoints.get.wrapFunction(WebEndpoints.scala:31)
	at cask.router.Decorator$.invoke(Decorators.scala:52)
	at cask.main.Main$DefaultHandler.handleRequest(Main.scala:123)
	at io.undertow.server.Connectors.executeRootHandler(Connectors.java:395)
	at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:861)
	at org.jboss.threads.ContextHandler$1.runWith(ContextHandler.java:18)
	at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2513)
	at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1512)
	at org.xnio.XnioWorker$WorkerThreadFactory$1$1.run(XnioWorker.java:1282)
	at java.base/java.lang.Thread.run(Thread.java:1583)

I'd be happy to take a stab at patching this if you'd like! I'm guessing that 0.9.0 swallows the java.net.ConnectException somewhere.

[kaaveland]

Seems likely that this line is just mapping to the wrong thing: https://github.com/com-lihaoyi/requests-scala/blob/master/requests/src/requests/Requester.scala#L310

              case e: java.net.ConnectException     => new UnknownHostException(url, e.getMessage)

[here-abarany]

I ran into this recently as well. It would be useful to have a separate exception type, as a connection error might be handled differently for situations such as retries compared to an unknown host.