HttpClient API expectations for connection failures

[Jaikiran Pai]

Any thoughts?

-Jaikiran

On Sunday, June 3, 2018, Jaikiran Pai <jai.forums2013 at gmail.com> wrote:
> Consider the following code:
>
> public class HttpClientTest {
>     public static void main(final String[] args) {
>         final HttpClient httpClient = HttpClient.newBuilder().build();
>         final String targetURL = "http://unknown.host.foo.bar.com.nowhere
";
>         final HttpRequest request =
HttpRequest.newBuilder().uri(URI.create(targetURL))
>                                 .method("HEAD",
HttpRequest.BodyPublishers.noBody())
>                                 .build();
>         try {
>             httpClient.send(request,
HttpResponse.BodyHandlers.discarding());
>         } catch(IOException | InterruptedException e) {
>             // intentionally ignore
>             System.out.println("Caught an intentionally ignored
exception");
>         } catch (Exception e) {
>             e.printStackTrace();
>         }
>     }
> }
>
> which tries to send a request to (in this case an intentional)
non-existent address. The exception that gets thrown is:
>
>
> java.nio.channels.UnresolvedAddressException
>     at java.base/sun.nio.ch.Net.checkAddress(Net.java:130)
>     at
java.base/sun.nio.ch.SocketChannelImpl.connect(SocketChannelImpl.java:674)
>     at
java.net.http/jdk.internal.net.http.PlainHttpConnection.lambda$connectAsync$0(PlainHttpConnection.java:113)
>     at java.base/java.security.AccessController.doPrivileged(Native
Method)
>     at
java.net.http/jdk.internal.net.http.PlainHttpConnection.connectAsync(PlainHttpConnection.java:115)
>     at
java.net.http/jdk.internal.net.http.Http1Exchange.sendHeadersAsync(Http1Exchange.java:261)
>     at
java.net.http/jdk.internal.net.http.Exchange.lambda$responseAsyncImpl0$8(Exchange.java:385)
>     at
java.net.http/jdk.internal.net.http.Exchange.checkFor407(Exchange.java:320)
>     at
java.net.http/jdk.internal.net.http.Exchange.lambda$responseAsyncImpl0$9(Exchange.java:389)
>     at
java.base/java.util.concurrent.CompletableFuture.uniHandle(CompletableFuture.java:930)
>     at
java.base/java.util.concurrent.CompletableFuture.uniHandleStage(CompletableFuture.java:946)
>     at
java.base/java.util.concurrent.CompletableFuture.handle(CompletableFuture.java:2266)
>     at
java.net.http/jdk.internal.net.http.Exchange.responseAsyncImpl0(Exchange.java:389)
>     at
java.net.http/jdk.internal.net.http.Exchange.responseAsyncImpl(Exchange.java:299)
>     at
java.net.http/jdk.internal.net.http.Exchange.responseAsync(Exchange.java:291)
>     at
java.net.http/jdk.internal.net.http.MultiExchange.responseAsyncImpl(MultiExchange.java:240)
>     at
java.net.http/jdk.internal.net.http.MultiExchange.lambda$responseAsync0$1(MultiExchange.java:205)
>     at
java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1072)
>     at
java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
>     at
java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1705)
>     at
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
>     at
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
>     at java.base/java.lang.Thread.run(Thread.java:832)
>
>
> It's a different matter that this stacktrace is missing the caller's
stack frames and that's being tracked in [1]. The javadoc of send method
doesn't mention anything about what specific exception gets thrown in case
of connection failures. It does say:
>
>      * @throws IllegalArgumentException if the {@code request} argument
is not
>      *         a request that could have been validly built as specified
by {@link
>      *         HttpRequest.Builder HttpRequest.Builder}.
>
> and the thrown java.nio.channels.UnresolvedAddressException indeed
extends IllegalArgumentException. However, given that the API itself
doesn't say anything about exceptions that get thrown on connection
failures, adding a catch block specifically for
java.nio.channels.UnresolvedAddressException seems like relying on the
implementation detail. Can these APIs make it explicit what exception(s)
can be expected to be thrown in case of connection failures, so that it's
part of the contract?
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8203298
>
> -Jaikiran
>
>
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