[squid-users] ICAP breaks HTTP responses with 1 octet bodies

I'm having some problems with Squid's ICAP client breaking on RESPMOD
when handling responses with a body exactly 1 octet long.

- The browser makes a request to Squid
- Squid makes a request to the web server and receives back a response
with a "Content-Length: 1" header and a 1 octet body.
- The response gets sent to the ICAP server, which replies with a "204
No Modifications".
- Squid sends the response on to the browser, with the "Content-Length:
1" header intact, but doesn't send a body. The browser sits there
indefinitely waiting for the body to appear.

As far as I can tell, the ICAP client successfully copies the body from
the virgin response to the adapted response.

The problem appears to be with
ServerStateData::handleMoreAdaptedBodyAvailable() - The API for
StoreEntry::bytesWanted() seems to be that it will return 0 if it wants
no data, or up to aRange.end-1 if more data is wanted. This means that
if aRange.end == 1, which is the case when we only have 1 octet of data,
it is always going to look like it can't accept any more data.

The fact that it can't accept a single octet is actually noted in
ServerStateData::handleMoreAdaptedBodyAvailable() in Server.cc:
   // XXX: bytesWanted API does not allow us to write just one byte!

I've resolved this problem by changing the following lines in
ServerStateData::handleMoreAdaptedBodyAvailable():
   const size_t bytesWanted = entry->bytesWanted(Range<size_t>(0,
contentSize));
   const size_t spaceAvailable = bytesWanted > 0 ? (bytesWanted + 1) : 0;

To:
   const size_t spaceAvailable = entry->bytesWanted(Range<size_t>(0,
contentSize+1));

(Patch attached)

However, I'm not sure if this is a correct fix - what effect does adding
1 to the contentSize given to bytesWanted() actually have? And is this
supposed to be handled elsewhere?

-- 
  - Steve Hill
    Technical Director
    Opendium Limited     http://www.opendium.com
Direct contacts:
    Instant messager: xmpp:steve_at_opendium.com
    Email:            steve_at_opendium.com
    Phone:            sip:steve_at_opendium.com
Sales / enquiries contacts:
    Email:            sales_at_opendium.com
    Phone:            +44-844-9791439 / sip:sales_at_opendium.com
Support contacts:
    Email:            support_at_opendium.com
    Phone:            +44-844-4844916 / sip:support_at_opendium.com