[Boost-bugs] [Boost C++ Libraries] #8309: [iostreams] bad handling of non-blocking writes for ‘indirect_streambuf’ class

Subject: [Boost-bugs] [Boost C++ Libraries] #8309: [iostreams] bad handling of non-blocking writes for ‘indirect_streambuf’ class
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-03-19 09:26:27

#8309: [iostreams] bad handling of non-blocking writes for ‘indirect_streambuf’
class
-------------------------------+--------------------------------------------
 Reporter:  fpascutti@…        |       Owner:  turkanis 
     Type:  Bugs               |      Status:  new      
Milestone:  To Be Determined   |   Component:  iostreams
  Version:  Boost 1.53.0       |    Severity:  Problem  
 Keywords:                     |  
-------------------------------+--------------------------------------------
 When a non-blocking write is done, the {{{indirect_streambuf}}} class sets
 the pointer to the start of the put area ({{{pbase()}}}) to the start of
 his own internal buffer ({{{out().buffer()}}}) offset by the number of
 bytes consumed.

 This algorithm works with a single non-blocking write but fails with
 multiple successive non-blocking writes.

 Imagine the following scenario:
 1. Initially, {{{pbase()}}}, {{{pptr()}}} and {{{out().begin()}}} point to
 address {{{0x1000}}}.
 2. 8 characters/bytes are written (assuming char as char_type).
 3. {{{pptr()}}} is set to {{{0x1008}}}.
 4. Only 2 characters are consumed downstream.
 5. {{{pbase()}}} is correctly set to {{{0x1002}}}. {{{pptr()}}} remains at
 {{{0x1008}}}.
 6. 2 more characters are consumed downstream.
 7. **{{{pbase()}}} is wrongly set to {{{0x1002}}}**. It should be set to
 {{{0x1004}}}.

 I have attached a
 [[attachment:nonblocking_indirect_streambuf_write.cpp|file containing a
 sample unit-test]] that reproduces this scenario.

 The fix looks easy as the {{{pbase()}}} pointer needs to be set to its
 previous value offset by the number of bytes consumed. I have attached a
 [[attachment:indirect_streambuf.hpp.patch|patch]] that implements this fix
 and makes the unit-test pass. However I am unable to assess the impact or
 correctness of this fix.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/8309>
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