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copied!<p>Looking through <a href="http://svn.php.net/viewvc/php/php-src/trunk/ext/zlib/zlib_filter.c?revision=316627&view=markup" rel="nofollow">the C source code</a>, the problem is that the filter always lets <a href="http://zlib.net/manual.html#Basic" rel="nofollow">zlib's <code>deflate()</code> function</a> decide how much data to accumulate before producing compressed output. The deflate filter does not create a new data bucket to pass on unless <code>deflate()</code> outputs some data (see line 235) or the <code>PSFS_FLAG_FLUSH_CLOSE</code> flag bit is set (line 250). That's why you only see the header bytes until you close <code>$in</code>; the first call to <code>deflate()</code> outputs the two header bytes, so <code>data->strm.avail_out</code> is 2 and a new bucket is created for these two bytes to pass on.</p> <p>Note that <code>fflush()</code> does not work because of a known issue with the zlib filter. See: <a href="https://bugs.php.net/bug.php?id=48725" rel="nofollow">Bug #48725 Support for flushing in zlib stream</a>.</p> <p>Unfortunately, there does not appear to be a nice work-around to this. I started writing a filter in PHP by extending <code>php_user_filter</code>, but quickly ran into the problem that <code>php_user_filter</code> does not expose the flag bits, only whether <code>flags & PSFS_FLAG_FLUSH_CLOSE</code> (the fourth parameter to the <code>filter()</code> method, a boolean argument commonly named <code>$closing</code>). You would need to modify the C sources yourself to fix Bug #48725. Alternatively, re-write it.</p> <p>Personally I would consider re-writing it because there seems to be a few eyebrow-raising issues with the code:</p> <ul> <li><code>status = deflate(&(data->strm), flags & PSFS_FLAG_FLUSH_CLOSE ? Z_FULL_FLUSH : (flags & PSFS_FLAG_FLUSH_INC ? Z_SYNC_FLUSH : Z_NO_FLUSH));</code> seems odd because when writing, I don't know why <code>flags</code> would be anything other than <code>PSFS_FLAG_NORMAL</code>. Is it possible to write & flush at the same time? In any case, handling the flags should be done outside of the <code>while</code> loop through the "in" bucket brigade, like how <code>PSFS_FLAG_FLUSH_CLOSE</code> is handled outside of this loop.</li> <li><p>Line 221, the <code>memcpy</code> to <code>data->strm.next_in</code> seems to ignore the fact that <code>data->strm.avail_in</code> may be non-zero, so the compressed output might skip some data of a write. See, for example, the following text from the zlib manual:</p> <blockquote> <p>If not all input can be processed (because there is not enough room in the output buffer), <code>next_in</code> and <code>avail_in</code> are updated and processing will resume at this point for the next call of <code>deflate()</code>.</p> </blockquote> <p>In other words, it is possible that <code>avail_in</code> is non-zero.</p></li> <li>The <code>if</code> statement on line 235, <code>if (data->strm.avail_out < data->outbuf_len)</code> should probably be <code>if (data->strm.avail_out)</code> or perhaps <code>if (data->strm.avail_out > 2)</code>.</li> <li><s>I'm not sure why <code>*bytes_consumed = consumed;</code> isn't <code>*bytes_consumed += consumed;</code>. The example streams at <a href="http://www.php.net/manual/en/function.stream-filter-register.php" rel="nofollow">http://www.php.net/manual/en/function.stream-filter-register.php</a> all use <code>+=</code> to update <code>$consumed</code>.</s></li> </ul> <p><strong>EDIT:</strong> <code>*bytes_consumed = consumed;</code> is correct. <a href="http://svn.php.net/viewvc/php/php-src/trunk/ext/standard/filters.c?revision=316627&view=markup" rel="nofollow">The standard filter implementations</a> all use <code>=</code> rather than <code>+=</code> to update the <code>size_t</code> value pointed to by the fifth parameter. Also, even though <code>$consumed += ...</code> on the PHP side effectively translates to <code>+=</code> on the <code>size_t</code> (see lines 206 and 231 of <a href="http://svn.php.net/viewvc/php/php-src/trunk/ext/standard/user_filters.c?revision=316627&view=markup" rel="nofollow"><code>ext/standard/user_filters.c</code></a>), the native filter function is called with either a <code>NULL</code> pointer or a pointer to a <code>size_t</code> set to 0 for the fifth argument (see lines 361 and 452 of <a href="http://svn.php.net/viewvc/php/php-src/trunk/main/streams/filter.c?revision=316627&view=markup" rel="nofollow"><code>main/streams/filter.c</code></a>).</p>

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