Received: (qmail 23699 invoked by uid 2012); 27 Jul 1998 15:50:54 -0000
Message-Id: <19980727155054.23698.qmail@hyperreal.org>
Date: 27 Jul 1998 15:50:54 -0000
From: Jesse Pelton <jsp@pkc.com>
Reply-To: jsp@pkc.com
To: apbugs@hyperreal.org
Subject: ISAPI: loss of POSTed data
X-Send-Pr-Version: 3.2

>Number:         2720
>Category:       mod_isapi
>Synopsis:       ISAPI: loss of POSTed data
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          closed
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Mon Jul 27 10:10:00 PDT 1998
>Closed-Date:    Tue Sep 26 09:44:05 PDT 2000
>Last-Modified:  Tue Sep 26 09:44:05 PDT 2000
>Originator:     jsp@pkc.com
>Release:        1.3.1
>Organization:
>Environment:
Windows NT Workstation 4.0 SP3
MSVC++ 5.0
Netscape Navigator 3.0, 4.05
Internet Explorer 4.0 (4.72.3110.8)
>Description:
If the data POSTed by a browser exceeds some size, the call to
ap_get_client_block() in isapi_handler() only retrieves the first part of the
data.  The size is not fixed; I've observed the problem with Navigator with
POSTs in the 13K-18K range (of which about 9K-13K was read), and with IE with
POSTs in the 18K range (of which roughly 16K was read).

The browsers are apparently sending the data in chunks, because a subsequent
call to ap_get_client_block() fetches more bytes.
>How-To-Repeat:
POST a lot of data from a form to an ISAPI DLL.  It doesn't seem to make much
difference whether you use a few large inputs or a lot of small ones.  You can
use any valid ISAPI DLL, since the problem is entirely on the server side.
>Fix:
Replace the following code in isapi_handler():

	if ((read = ap_get_client_block(r, ecb->lpbData, to_read)) < 0) {
	    if (isapi_term) (*isapi_term)(HSE_TERM_MUST_UNLOAD);
	    FreeLibrary(isapi_handle);
	    return SERVER_ERROR;
	}

with something like the following:

	read = 0;

	while (to_read - read > 0)
	{
	    long this_read;

	    if ((this_read = ap_get_client_block(r, ecb->lpbData + read, to_read - read)) <= 0) {
		if (isapi_term) (*isapi_term)(HSE_TERM_MUST_UNLOAD);
		FreeLibrary(isapi_handle);
		return SERVER_ERROR;
	    }
	    read += this_read;
	}

This code works, but may not comply with your coding style.
>Release-Note:
>Audit-Trail:
Category-Changed-From-To: os-windows-mod_isapi
Category-Changed-By: wrowe
Category-Changed-When: Thu Jun 15 13:24:49 PDT 2000

State-Changed-From-To: open-closed
State-Changed-By: wrowe
State-Changed-When: Tue Sep 26 09:44:03 PDT 2000
State-Changed-Why:

This problem should now be resolved with the 1.3.13 release
of Apache.  You may wish to check out the current sources,
build and test that the issue is resolved.

Note that Apache 1.3.13 now supports ISAPIReadAheadBuffer
to define the max size of the initial request block, and
ReadClient to retrieve the rest of the request.

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