Re: [boost] [iostreams] Inconsistency of "faiture" of writes in Sinks and filters

Subject: Re: [boost] [iostreams] Inconsistency of "faiture" of writes in Sinks and filters
From: Artyom (artyomtnk_at_[hidden])
Date: 2010-10-31 02:28:57

Hello,

Bump...

Anybody has an opinion about this?

Artyom

----- Original Message ----
> From: Artyom <artyomtnk_at_[hidden]>
> To: boost_at_[hidden]
> Sent: Sat, October 23, 2010 9:29:30 PM
> Subject: [boost] [iostreams] Inconsistency of "failure" of writes in Sinks and 
>filters
> 
> Hello,
> 
> I implement the sink device that sometimes may fail on  writes.
> 
> When Sink is implemented it should throw an exception on fault.  To notify
> the stream on error.
> 
> However it is not always works this  way. I've got the exception to "leak" to 
>the
> main program when I combine in  the filter gzip_comressor() filter that writes
> to output device that its Sink  is full. When I call reset on the filter
> the exception in leaking to the  program instead of being caught.
> 
> Is it bug or (accidental)  feature?
> 
> On the other hand, if I don't throw but rather return 0, I get  into infinite 
> loop
> in the boost::iostreams::non_blocking_adapter::write  when I call 
>filter.reset().
> 
> So I how can I write a sink device that  reports errors?
> 
> In following example the exception is caught when  filter.reset() is called:
> 
>     #include  <boost/iostreams/stream.hpp>
>     #include  <boost/iostreams/filtering_stream.hpp>
>     #include  <boost/iostreams/filter/gzip.hpp>
>     #include  <boost/iostreams/tee.hpp>
>     #include  <iostream>
> 
>     class my_small_device : public  boost::iostreams::sink
>     {
>         int  count;
>     public:
>         my_small_device()  : count(1000) {}
>         std::streamsize write(char const  *d,std::streamsize n)
>         {
>              if(count < n)
>                  throw std::runtime_error("Device is full");
>              count-=n;
>              return n;
>         }
>      };
> 
>     int main()
>     {
>          try {
>             using namespace  boost::iostreams;
>              boost::iostreams::stream<my_small_device> 
> output(my_small_device(),10);
>              {
>                  boost::iostreams::filtering_ostream filter;
>                  filter.push(gzip_compressor());
>                  filter.push(output);
>                  for(int i=0;i<10000000;i++)  {
>                      if(!(filter << i << '\n')) {
>                          std::cerr << "Fail!"  << std::endl;
>                          break;
>                      }
>                  }
>                  std::cout << "Closing filter" << std::endl;
>                  filter.reset();
>              }
> 
>              std::cout << "ok" << std::endl;
>              return 0;
>         }catch(std::exception  const &e) {
>             std::cerr <<  "Catched " << e.what() << std::endl;
>              return 1;
>         }
>      }
> 
> Thanks,
>    Artyom
> 
> 
>       
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