NullPointerException in jdk.incubator.httpclient

Question

I'm trying to new use new shiny httpclient from JDK10. Code is pretty simple. I use synchronous HTTP call form multiple threads:

private final HttpClient httpClient = HttpClient.newBuilder()
        .executor(Utils.newFixedThreadPoolExecutor(1, "HttpClient"))
        .build();

private JsonObject useHttpClient(URL url, String params) throws Exception {
    HttpRequest req = HttpRequest.newBuilder()
            .uri(url.toURI())
            .setHeader("Connection", "keep-alive")
            .setHeader("Accept-Encoding", "gzip")
            .timeout(timeout)
            .POST(HttpRequest.BodyPublisher.fromString(params))
            .build();
    HttpResponse<InputStream> response = httpClient.send(req, HttpResponse.BodyHandler.asInputStream());
    if (response.statusCode() != 200) {
        throw new IOException("Server returned " + response.statusCode());
    }
    String encoding = response.headers().firstValue("content-encoding").orElse("");
    return parseResponseStream(encoding, response.body());
}

Sometimes I get NPEs:

java.lang.NullPointerException: null
at jdk.incubator.http.internal.hpack.HeaderTable$Table.remove(HeaderTable.java:455) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.hpack.HeaderTable.evictEntry(HeaderTable.java:264) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.hpack.HeaderTable.put(HeaderTable.java:233) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.hpack.HeaderTable.put(HeaderTable.java:215) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.hpack.Decoder.resumeLiteralWithIndexing(Decoder.java:464) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.hpack.Decoder.proceed(Decoder.java:268) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.hpack.Decoder.decode(Decoder.java:246) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.Http2Connection.decodeHeaders(Http2Connection.java:471) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.Http2Connection.processFrame(Http2Connection.java:635) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.frame.FramesDecoder.decode(FramesDecoder.java:156) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.Http2Connection$FramesController.processReceivedData(Http2Connection.java:195) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.Http2Connection.asyncReceive(Http2Connection.java:528) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.Http2Connection$Http2TubeSubscriber.processQueue(Http2Connection.java:1054) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.common.SequentialScheduler$SynchronizedRestartableTask.run(SequentialScheduler.java:175) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.common.SequentialScheduler$CompleteRestartableTask.run(SequentialScheduler.java:147) ~[jdk.incubator.httpclient:?]
at jdk.incubator.http.internal.common.SequentialScheduler$SchedulableTask.run(SequentialScheduler.java:198) ~[jdk.incubator.httpclient:?]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135) [?:?]

Are there any problem in my code? What can be reason for this exception?

C:\Program Files\Java\jdk-10\bin>java -version
java version "10" 2018-03-20
Java(TM) SE Runtime Environment 18.3 (build 10+46)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10+46, mixed mode)

Answer 1

Are there any problem in my code?

As someone familiar with the JDK HTTP Client API, I cannot see any specific issues with the code you posted.

What can be reason for this exception?

The reason for the exception is a bug in the JDK HTTP Client HPACK code. There is nothing that you can do, in your code, to workaround it.

Specific information on the JDK HPACK bug can be found at https://bugs.openjdk.java.net/browse/JDK-8200625 ( duplicating technical information, from the aforementioned OpenJDK JIRA issue, here will not add value, and likely to become stale quickly )