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Date: Wed, 14 Mar 2001 16:50:50 -0700
From: "Mike Anderson" <MMANDERS@novell.com>
To: <tomcat-dev@jakarta.apache.org>
Subject: The available method for ServletInputStream subclasses
	(tomcat_32 branch)
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In working with some internal groups, we have some classes that perform =
file uploads (anyone heard of GroupWise Webaccess?).  One of the things =
they have done in their servlets that handle this is call the available =
method on the ServletInputStream so that they can delay the thread for a =
small amount of time if there isn't anything available to be read from the =
socket.  This allows the machine and other threads to do other processing, =
and allows the thread that wants to read the data to gracefully handle a =
client prematurely shutting down the connection.  This functionality works =
on other servlet engines (JServ, WebSphere, Novell Servlet Gateway) but =
doesn't work on Tomcat because the available() method was never implemented=
 in any of the subclasses.  So when availabe() is called, it just resolves =
down to java.io.InputStream which is documented as returning 0 because =
subclasses should override this method.  There are 2 ways to fix this:

1.  In BufferedServletInputStream, implement an available() method that =
returns limit-bytesRead or 0 whichever is greater.  The limit class =
variable is set to the value of the Content-Length header and bytesRead is =
the number of bytes read since limit was set.  (See the attached patch).  =
This is the easy fix but doesn't address the feature of available that =
says it will return the number of bytes that can be read "without =
blocking".  Obviously, if there is a large amount of data, a read will =
most likely block at some point depending on how much is asked for.

2.  Update BufferedServletInputStream to call reqA.available and then =
update the following files to provide this interface:
  Request.java
  RequestImpl.java
  HttpRequestAdapter.java
  AJP12RequestAdapter.java
  Ajp13RequestAdapter.java
  JNIRequestAdapter.java
Each of these classes would need to provide an appropriate available() =
method.

I'm willing to figure this out and implement #2 if it is deemed the better =
approach and only provided #1 because it was a "quick" fix.  I'm also =
willing to figure this out for the 3.3 tree for either implementation.  I =
would like to get it into the 3.2.2 branch since that is what most of use =
here are currently using.

Any response (other than flames:-) appreciated.


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