When I debug this, even though my write method is returning 4 bytes for every write, the caller of my output filter keeps providing me the same four bytes after the first sequence of 4 bytes.
This is boot version 1.62. Here is compiling code that illustrates:
class fixed_size_output_filter : public boost::iostreams::multichar_output_filter
{
public:
fixed_size_output_filter(std::streamsize size = 4) : mSize(size) {}
template<typename Sink>
std::streamsize write(Sink &sink, const char *s, std::streamsize n)
{
std::streamsize bytesAttempted = std::min(mSize, n);
std::streamsize bytesActual = boost::iostreams::write(sink, s, bytesAttempted);
return bytesActual;
}
private:
std::streamsize mSize;
};
BOOST_AUTO_TEST_CASE(FixedSizeOutputFilter)
{
#define BYTES 500
char sink_buffer[BYTES];
array_sink array_sink(sink_buffer, sizeof(sink_buffer));
std::streampos os_pos;
{
filtering_ostream os;
os.push(fixed_size_output_filter());
os.push(array_sink);
char buffer[BYTES];
for(char i = 0; i < sizeof(buffer); i++)
buffer[i] = i;
os.write(buffer, sizeof(buffer));
}
for(char i = 0; i < sizeof(sink_buffer); i++)
BOOST_CHECK(i == sink_buffer[i]);
}
The actual bytes that end up in the sink_buffer are as follows:
0, 1, 2, 3, 4, 5, 6, 7, 4, 5, 6, 7, 4, 5, 6, 7, 4, 5, 6, 7, ....uninitialized bytes follow through the rest of the buffer.
It would appear that the indirect_streambuf in use by the filter chain is incorrectly flushing the bytes.
Is my understanding of the library flawed? Does this appear to be a bug? Any help is greatly appreciated.
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