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POEncoding MessagePack objects containing Node.js Buffers
 

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    <p>I'm using <a href="https://github.com/pgriess/node-msgpack" rel="nofollow">node-msgpack</a> to encode and decode messages passed around between machines. One thing I'd like to be able to do is wrap raw Buffer data in an object and encode that with Messagepack.</p> <pre><code>msgpack = require('msgpack') buf = &lt;Buffer 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 ...&gt; obj = {foo: buf} packed = msgpack.pack(obj) </code></pre> <p>In the example above, I wanted to do a consistency check on the raw bytes of buffers nested in an object. So <code>buf</code> was obtained like so :</p> <pre><code>var buf = fs.readFileSync('some_image.png'); </code></pre> <p>In a perfect world, I would have obtained :</p> <pre><code>new Buffer(msgpack.unpack(packed).foo); #&gt; &lt;Buffer 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 ...&gt; </code></pre> <p>Instead, I end up with some random number. Digging up a little deeper, I end up with the following curiosity:</p> <pre><code>enc = 'ascii' new Buffer(buf.toString(enc), enc) #&gt; &lt;Buffer *ef bf bd* 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 ...&gt; buf #&gt; &lt;Buffer *89* 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 02 00 ...&gt; </code></pre> <p>The first byte is the problem. I tried using different encodings with no luck. What is happening here and what can I do to do circumvent the issue?</p> <h3>EDIT:</h3> <p>Originally, the <code>buf</code> was a buffer I had generated with msgpack itself, thus double-packing data. To avoid any confusion, I replaced that with another buffer obtained by reading an image, which raised the same problem.</p>
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    1. COWhere is the "ac" is coming from in your original code? > new Buffer("Hello World!") gives me "<Buffer 48 65 6c 6c 6f 20 57 6f 72 6c 64 21>" (without the "ac")
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    2. COQuoting the above, `buf = msgpack.pack("Hello World!")` :) It's a prefix msgpack puts there to know that the following bytes are raw bytes and to encode its length. That's why I'm expecting `msgpack.unpack(new Buffer(msgpack.unpack(packed).foo));` to return `"Hello World!"`.
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    3. COIt looks like you are double packing. (1) when you do buf = msgpack.pack("Hello World!") and (2) when you do packed = msgpack.pack(obj), right?
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