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POzlib's uncompress() strangely returning Z_BUF_ERROR
 

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  1. POzlib's uncompress() strangely returning Z_BUF_ERROR
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    <p>I'm writing Qt-based client application. It connects to remote server using <code>QTcpSocket</code>. Before sending any actual data it needs to send login info, which is zlib-compressed json.</p> <p>As far as I know from server sources, to make everything work I need to send X bytes of compressed data following 4 bytes with length of uncompressed data.</p> <p>Uncompressing on server-side looks like this:</p> <pre><code>/* look at first 32 bits of buffer, which contains uncompressed len */ unc_len = le32toh(*((uint32_t *)buf)); if (unc_len &gt; CLI_MAX_MSG) return NULL; /* alloc buffer for uncompressed data */ obj_unc = malloc(unc_len + 1); if (!obj_unc) return NULL; /* decompress buffer (excluding first 32 bits) */ comp_p = buf + 4; if (uncompress(obj_unc, &amp;dest_len, comp_p, buflen - 4) != Z_OK) goto out; if (dest_len != unc_len) goto out; memcpy(obj_unc + unc_len, &amp;zero, 1); /* null terminate */ </code></pre> <p>I'm compressing json using Qt built-in zlib (I've just downloaded headers and placed it in mingw's <code>include</code> folder):</p> <pre><code>char json[] = "{\"version\":1,\"user\":\"test\"}"; char pass[] = "test"; std::auto_ptr&lt;Bytef&gt; message(new Bytef[ // allocate memory for: sizeof(ubbp_header) // + msg header + sizeof(uLongf) // + uncompressed data size + strlen(json) // + compressed data itself + 64 // + reserve (if compressed size &gt; uncompressed size) + SHA256_DIGEST_LENGTH]);//+ SHA256 digest uLongf unc_len = strlen(json); uLongf enc_len = strlen(json) + 64; // header goes first, so server will determine that we want to login Bytef* pHdr = message.get(); // after that: uncompressed data length and data itself Bytef* pLen = pHdr + sizeof(ubbp_header); Bytef* pDat = pLen + sizeof(uLongf); // hash of compressed message updated with user pass Bytef* pSha; if (Z_OK != compress(pLen, &amp;enc_len, (Bytef*)json, unc_len)) { qDebug("Compression failed."); return false; } </code></pre> <p>Complete function code here: <a href="http://pastebin.com/hMY2C4n5" rel="nofollow">http://pastebin.com/hMY2C4n5</a></p> <p>Even though server correctly recieves uncompressed length, <code>uncompress()</code> returning <code>Z_BUF_ERROR</code>.</p> <p>P.S.: I'm actually writing pushpool's client to figure out how it's binary protocol works. I've asked this question on official bitcoin forum, but no luck there. <a href="http://forum.bitcoin.org/index.php?topic=24257.0" rel="nofollow">http://forum.bitcoin.org/index.php?topic=24257.0</a></p>
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