Very long response headers and java.net.http.HttpClient?

Wed Jul 24 21:30:44 UTC 2024

A proper list would be net-dev at openjdk.java.net.

> On 24 Jul 2024, at 21:13, Andy Boothe <andy.boothe at gmail.com> wrote:
>
> Hello,
>
> I'm documenting some guidelines for using java.net.http.HttpClient defensively for my team. For example: "Always set a request timeout", "Don't assume HTTP response entities are small and/or will fit in memory", etc.
>
> One guideline I'd like to document is "Set a maximum for HTTP response header size." However, I can't seem to find a way to set that limit, either in documentation or in OpenJDK code.
>
> I tried my best to search the archives for this mailing list for any mentions, but came up empty.
>
> To make sure my head is on straight and there isn't an undocumented limit set by default, I wrote the attached (very quick and dirty) client and server programs. LongResponseHeaderDemoServer opens a raw server socket and reads (what it assumes is) a well-formed HTTP request, and then prints an HTTP response which includes a response header of infinite length. LongResponseHeaderDemoHttpClient uses java.net.http.HttpClient to make a request and print the response body.
>
> When I run LongResponseHeaderDemoServer in one terminal and make a curl request to the server in another terminal, this is what curl spits out:
>
> $ curl -vvv -D - http://localhost:3000
> * Host localhost:3000 was resolved.
> * IPv6: ::1
> * IPv4: 127.0.0.1
> *   Trying [::1]:3000...
> * Connected to localhost (::1) port 3000
> > GET / HTTP/1.1
> > Host: localhost:3000
> > User-Agent: curl/8.6.0
> > Accept: */*
> >
> < HTTP/1.1 200 OK
> HTTP/1.1 200 OK
> < Content-Type: text/plain
> Content-Type: text/plain
> < Connection: close
> Connection: close
> < Content-Length: 3
> Content-Length: 3
> * Closing connection
> curl: (100) A value or data field grew larger than allowed
>
> So curl detects the long response header and bails out. Safe and sane.
>
> However, when I run LongResponseHeaderDemoServer in one terminal and run LongResponseHeaderDemoHttpClient in another terminal, this is what happens:
>
> $ java LongResponseHeaderDemoHttpClient
> Exception in thread "main" java.io.IOException: Requested array size exceeds VM limit
> at java.net.http/jdk.internal.net.http.HttpClientImpl.send(HttpClientImpl.java:966)
> at java.net.http/jdk.internal.net.http.HttpClientFacade.send(HttpClientFacade.java:133)
> at LongResponseHeaderDemoHttpClient.main(LongResponseHeaderDemoHttpClient.java:13)
> Caused by: java.lang.OutOfMemoryError: Requested array size exceeds VM limit
> at java.base/java.util.Arrays.copyOf(Arrays.java:3541)
> at java.base/java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:242)
> at java.base/java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:806)
> at java.base/java.lang.StringBuilder.append(StringBuilder.java:246)
> at java.net.http/jdk.internal.net.http.Http1HeaderParser.readResumeHeader(Http1HeaderParser.java:250)
> at java.net.http/jdk.internal.net.http.Http1HeaderParser.parse(Http1HeaderParser.java:124)
> at java.net.http/jdk.internal.net.http.Http1Response$HeadersReader.handle(Http1Response.java:605)
> at java.net.http/jdk.internal.net.http.Http1Response$HeadersReader.handle(Http1Response.java:536)
> at java.net.http/jdk.internal.net.http.Http1Response$Receiver.accept(Http1Response.java:527)
> at java.net.http/jdk.internal.net.http.Http1Response$HeadersReader.tryAsyncReceive(Http1Response.java:583)
> at java.net.http/jdk.internal.net.http.Http1AsyncReceiver.flush(Http1AsyncReceiver.java:233)
> at java.net.http/jdk.internal.net.http.Http1AsyncReceiver$$Lambda/0x00000008010dbd50.run(Unknown Source)
> at java.net.http/jdk.internal.net.http.common.SequentialScheduler$LockingRestartableTask.run(SequentialScheduler.java:182)
> at java.net.http/jdk.internal.net.http.common.SequentialScheduler$CompleteRestartableTask.run(SequentialScheduler.java:149)
> at java.net.http/jdk.internal.net.http.common.SequentialScheduler$SchedulableTask.run(SequentialScheduler.java:207)
> at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
> at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
> at java.base/java.lang.Thread.runWith(Thread.java:1596)
> at java.base/java.lang.Thread.run(Thread.java:1583)
>
> Ostensibly, HttpClient just keeps on reading the never-ending header until it OOMs. This seems to confirm that there is no default limit to header size. It also seems like A Very Bad Thing to me. This suggests that any time a program makes an HTTP request to an untrusted source using HttpClient, for example when crawling the web, they are at risk of an OOM.
>
> For grins, I also wrote an application LongResponseHeaderDemoHttpURLConnection that does the same thing as LongResponseHeaderDemoHttpClient, just using HttpURLConnection instead of HttpClient. When I run LongResponseHeaderDemoServer in one terminal and LongResponseHeaderDemoHttpURLConnection in another terminal, this is what happens:
>
> $ java LongResponseHeaderDemoHttpURLConnection
> Exception in thread "main" java.lang.NegativeArraySizeException: -1610612736
> at java.base/sun.net.www.MessageHeader.mergeHeader(MessageHeader.java:526)
> at java.base/sun.net.www.MessageHeader.parseHeader(MessageHeader.java:481)
> at java.base/sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:804)
> at java.base/sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:726)
> at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1688)
> at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1589)
> at java.base/java.net.URL.openStream(URL.java:1161)
> at LongResponseHeaderDemoHttpURLConnection.main(LongResponseHeaderDemoHttpURLConnection.java:12)
>
> So HttpURLConnection doesn't handle things gracefully either, but at least it doesn't OOM. That seems like a bug, too, but perhaps less severe.
>
> For reference, here's my java version:
>
> $ java -version
> openjdk version "21.0.2" 2024-01-16 LTS
> OpenJDK Runtime Environment Corretto-21.0.2.13.1 (build 21.0.2+13-LTS)
> OpenJDK 64-Bit Server VM Corretto-21.0.2.13.1 (build 21.0.2+13-LTS, mixed mode, sharing)
>
> Can anyone check my work, and maybe reproduce? And ideally, can someone with more knowledge than me about java.net.http.HttpClient and/or java.net.HttpURLConnection please comment? Is this real, or have I made a mistake somewhere along the way? If it's real, what's next? A bug report?
>
> Andy Boothe
> Email: andy.boothe at gmail.com
> Mobile: (979) 574-1089

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