[HTTPCLIENT-2313] NPE NullPointerException in PoolingHttpClientConnectionManager when debug logging is enabled

• Type: Bug
• Status: Resolved
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 5.3
• Fix Version/s: 5.3.1
• Component/s: HttpClient (classic)
• Assignee: Unassigned
• Reporter: Sven Haster
• Created: 19/Dec/23 09:05
• Updated: 19/Dec/23 12:41
• Resolved: 19/Dec/23 09:40

Description

If you enable debug logging, HttpClient5 will give you free NPEs in certain classes, such as PoolingHttpClientConnectionManager.

On line 410-413 of this class there is the following code:

} else {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("{} connection is not kept alive(isConsistent:{})", ConnPoolSupport.getId(endpoint), conn.isConsistent());
                }
            }

This else is related to the boolean `reusable` being false. However, one of the possible causes of this boolean being false is `conn` being `null`:

boolean reusable = conn != null && conn.isOpen() && conn.isConsistent();

If `conn` is `null` then `conn.isConsistent()` throws an NPE during the creation of the debug message.

java.lang.NullPointerException: Cannot invoke "org.apache.hc.client5.http.io.ManagedHttpClientConnection.isConsistent()" because "conn" is null
	at org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager.release(PoolingHttpClientConnectionManager.java:412)
	at org.apache.hc.client5.http.impl.classic.InternalExecRuntime.discardEndpoint(InternalExecRuntime.java:246)
	at org.apache.hc.client5.http.impl.classic.InternalExecRuntime.releaseEndpoint(InternalExecRuntime.java:260)
	at org.apache.hc.client5.http.impl.classic.ResponseEntityProxy.releaseConnection(ResponseEntityProxy.java:80)
	at org.apache.hc.client5.http.impl.classic.ResponseEntityProxy.eofDetected(ResponseEntityProxy.java:115)
	at org.apache.hc.core5.http.io.EofSensorInputStream.checkEOF(EofSensorInputStream.java:199)
	at org.apache.hc.core5.http.io.EofSensorInputStream.read(EofSensorInputStream.java:136)
	at java.base/sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:270)
	at java.base/sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:313)
	at java.base/sun.nio.cs.StreamDecoder.read(StreamDecoder.java:188)
	at java.base/java.io.InputStreamReader.read(InputStreamReader.java:177)
	at java.base/java.io.Reader.read(Reader.java:250)
	at org.apache.hc.core5.http.io.entity.EntityUtils.toCharArrayBuffer(EntityUtils.java:188)
	at org.apache.hc.core5.http.io.entity.EntityUtils.toString(EntityUtils.java:231)
	at org.apache.hc.core5.http.io.entity.EntityUtils.toString(EntityUtils.java:292)
	at org.apache.hc.core5.http.io.entity.EntityUtils.toString(EntityUtils.java:253)
	at com.github.tomakehurst.wiremock.common.HttpClientUtils.getEntityAsStringAndCloseStream(HttpClientUtils.java:35)
	at com.github.tomakehurst.wiremock.client.HttpAdminClient.safelyExecuteRequest(HttpAdminClient.java:535)
	at com.github.tomakehurst.wiremock.client.HttpAdminClient.executeRequest(HttpAdminClient.java:507)
	at com.github.tomakehurst.wiremock.client.HttpAdminClient.executeRequest(HttpAdminClient.java:483)
	at com.github.tomakehurst.wiremock.client.HttpAdminClient.addStubMapping(HttpAdminClient.java:150)
	at com.github.tomakehurst.wiremock.client.WireMock.register(WireMock.java:446)
	at com.github.tomakehurst.wiremock.client.WireMock.register(WireMock.java:441)
	at com.github.tomakehurst.wiremock.client.WireMock.givenThat(WireMock.java:130)
	at com.github.tomakehurst.wiremock.client.WireMock.stubFor(WireMock.java:134)