spb

Size-prefixed blobs for encoding messages in byte streams

npm install spb
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Size-prefixed blob streams

It is often useful to treat a continuous byte stream as a series of discrete messages. This library gives you a simple but effective way to do this, by prefacing each message with the size of the message. In other words, it saves you writing a bit of fiddly parsing code if you just want to deal with whole things (e.g., JSON objects) at a time.

You can wrap streams (e.g., net.Socket) or things that look like net.Server. If you wrap a stream, then it treats incoming data as size-prefix encoded and hands you each message (without the size prefix) as a 'data' event; if you write a string or buffer, it treats it as a message and encode it with a size prefix. If you wrap a server, it provides wrapped streams in the 'connection' event.

Trivial example

> var netserver = require('net').createServer();
> var msgserver = require('spb').server(netserver);
> msgserver.on('connection', function(connection) {
... connection.on('data', function(message) {
...... // do something with the whole message
...... });
... });
> netserver.listen(5975);

Reference

spb.stream(underlying)

Wraps a Stream.

The returned stream shall parse bytes from the underlying stream and emit 'data' events consisting of whole messages (without the length prefix). Buffers or strings written to the returned stream shall be encoded with a size-prefix and written to the underlying stream.

The wrapped stream relays events ('drain', 'error', 'end', 'pipe') from the underlying stream. Aside from 'data' it is equivalent to give a callback to either the underlying stream or the wrapped stream.

Likewise, the methods pause, resume, destroy, and destroySoon for the wrapped stream simply invoke the same on the underlying stream. It is not in general safe to invoke either write or setEncoding on the underlying stream, as these interfere with the size prefixing. setEncoding on the wrapped stream does the 'right thing', in other words, it results in the messages emitted being strings.

spb.server(underlying)

Wraps a server, providing connections that are wrapped streams.

The underlying server must look like a net.Server. Specifically, it must emit the 'listening', 'close' and 'connection' events, and have a close method. It is safe to invoke methods and to supply callbacks for the above events on the underlying server; only 'connection' is not equivalent.

A note on pipes

Piping a spb stream to a byte stream will simply strip out size prefixes, effectively concatenating the messages into undelimited bytes. Piping a byte stream to a spb stream will encode as discrete messages the (probably arbitrarily delimited) packets read on the byte stream.

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