Mark Slater created HTTPCLIENT-2352:
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Summary: Race condition causing java.lang.ArithmeticException:
Update causes flow control window to exceed 2147483647
Key: HTTPCLIENT-2352
URL: https://issues.apache.org/jira/browse/HTTPCLIENT-2352
Project: HttpComponents HttpClient
Issue Type: Bug
Components: HttpClient (async)
Affects Versions: 5.3.1
Reporter: Mark Slater
I’m getting {{java.lang.ArithmeticException: Update causes flow control window
to exceed 2147483647}} intermittently when making HTTP/2 requests using HTTP
Client 5.3.1 as the engine for the [Ktor HTTP Client
3.0.3|https://github.com/ktorio/ktor/tree/3.0.3]. It occurs in about 10% of
requests to some addresses from my desktop.
I’ve found what seems to be a race condition that appears to be the root cause
of the problem in
{{[org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer|https://github.com/apache/httpcomponents-core/blob/rel/v5.2.4/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java]}}
(version 5.2.4 is used by this version of HTTP Client).
This is the stack trace I get:
{code:java}
Caused by: java.lang.ArithmeticException: Update causes flow control window to
exceed 2147483647
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.updateWindow(AbstractH2StreamMultiplexer.java:215)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.updateInputWindow(AbstractH2StreamMultiplexer.java:225)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.incrementInputCapacity(AbstractH2StreamMultiplexer.java:385)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.access$1200(AbstractH2StreamMultiplexer.java:94)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer$H2StreamChannelImpl.update(AbstractH2StreamMultiplexer.java:1448)
at
io.ktor.client.engine.apache5.ApacheResponseConsumer.updateCapacity(ApacheResponseConsumer.kt:131)
at
io.ktor.client.engine.apache5.BasicResponseConsumer.updateCapacity(ApacheResponseConsumer.kt:54)
at
org.apache.hc.client5.http.impl.async.HttpAsyncMainClientExec$1.updateCapacity(HttpAsyncMainClientExec.java:233)
at
org.apache.hc.core5.http2.impl.nio.ClientH2StreamHandler.updateInputCapacity(ClientH2StreamHandler.java:226)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer$H2Stream.produceInputCapacityUpdate(AbstractH2StreamMultiplexer.java:1662)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.consumeDataFrame(AbstractH2StreamMultiplexer.java:1030)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.consumeFrame(AbstractH2StreamMultiplexer.java:735)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.onInput(AbstractH2StreamMultiplexer.java:446)
at
org.apache.hc.core5.http2.impl.nio.AbstractH2IOEventHandler.inputReady(AbstractH2IOEventHandler.java:65)
at
org.apache.hc.core5.http2.impl.nio.ClientH2IOEventHandler.inputReady(ClientH2IOEventHandler.java:39)
at
org.apache.hc.core5.reactor.ssl.SSLIOSession.decryptData(SSLIOSession.java:609)
at
org.apache.hc.core5.reactor.ssl.SSLIOSession.access$200(SSLIOSession.java:74)
at
org.apache.hc.core5.reactor.ssl.SSLIOSession$1.inputReady(SSLIOSession.java:202)
at
org.apache.hc.core5.reactor.InternalDataChannel.onIOEvent(InternalDataChannel.java:142)
at
org.apache.hc.core5.reactor.InternalChannel.handleIOEvent(InternalChannel.java:51)
... 5 more
{code}
The problem is in the
{{[updateWindow|https://github.com/apache/httpcomponents-core/blob/rel/v5.2.4/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java#L202]}}
method, which attempts to adjust the flow control window by a delta computed
previously. The method caters for the window size changing concurrently with
the computation and validation of the new size by aborting and retrying
conflicted calls. However, it doesn’t cater for the consequences of
out-of-order deltas.
On connect, the size of {{connInputWindow}} is increased by the
{{[maximizeConnWindow|https://github.com/apache/httpcomponents-core/blob/rel/v5.2.4/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java#L1049]}}
method to {{{}Integer.MAX_VALUE{}}}, the largest permitted size. As data is
consumed and received, the
{{[updateWindow|https://github.com/apache/httpcomponents-core/blob/rel/v5.2.4/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java#L202]}}
method is called with positive and negative deltas to reflect the changes in
available capacity. However, the order in which these updates are applied is
not guaranteed. If a negative delta due to the receipt of data is applied
after the positive delta due to some of that data being consumed, the window
size will be increased beyond {{Integer.MAX_VALUE,}} and
{{ArithmeticException}} will be thrown.
It would be possible to mitigate this somewhat (perhaps entirely) if
{{[maximizeConnWindow|https://github.com/apache/httpcomponents-core/blob/rel/v5.2.4/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java#L1049]}}
could be configured to use a maximum size somewhat less than
{{{}Integer.MAX_VALUE{}}}, but I’m not familiar enough with HTTP/2 to know if
this would have wider consequences.
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