Intermittent ProtocolException in HttpClient 3.x

[Alex, Joseph (Contractor)]

Hi,

We are getting intermittent ProtocolException " failed to respond with a valid 
HTTP response" when calling a https URL hosted in Tomcat 6.x. This is 
HTTPClient 3.x and used within an IBM JVM (JDK 6.x) Both client and server are 
within same organization, just different servers and configuration. Stacktrace 
below : 

org.apache.commons.httpclient.ProtocolException: The server a.b.com failed to 
respond with a valid HTTP response
        at 
org.apache.commons.httpclient.HttpMethodBase.readStatusLine(HttpMethodBase.java:1846)
        at 
org.apache.commons.httpclient.HttpMethodBase.readResponse(HttpMethodBase.java:1590)
        at 
org.apache.commons.httpclient.HttpMethodBase.execute(HttpMethodBase.java:995)
        at 
org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(HttpMethodDirector.java:397)
        at 
org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMethodDirector.java:170)
        at 
org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:396)
        at 
org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:324)

From HTTPClient source, this is thrown here : 

else if (s == null || count >= maxGarbageLines) {
                // Giving up
                throw new ProtocolException("The server " + conn.getHost() + 
                        " failed to respond with a valid HTTP response");
            }

I assume this means a connection has been established ,and a response returned 
, but it's just not valid and at some point it becomes null. Is this a right 
assumption, and how do we go about debugging. Is this related to the URL being 
HTTPS , and why does it happen only intermittently. During these errors, we 
don’t see entries in the server's access log, which indicates the request 
hasn't been processed.

Thanks,
Joseph


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