async-streams

async-streams

Abstract

This is basically DataInputStream/BinaryReader and DataOutputStream/BinaryWriter for Node, using Promises.

Usage

Writing streams

const AsyncStreamWriter = require('async-streams').AsyncStreamWriter;
const stream = <Some Stream>;

const writer = new AsyncStreamWriter(stream);
writer.writeInt32LE(123);
writer.writeDoubleLE(123.45);
writer.writeString("Hello World");
writer.writeJson({text: "Hello World"});

When writing more complex data, you may wish to write a size header first.

const array = [1,2,3,4,5];
writer.writeUInt32LE(array.length);
array.forEach((v) => writer.writeDoubleLE(v));

Reading streams

Each read function can be called with a callback, or used as a promise. The value returned from the callback function will override what is resolved by the promise.

const AsyncStreamReader = require('async-streams').AsyncStreamReader;
const stream = <Some Stream>;

const reader = new AsyncStreamReader(stream);
reader.readInt32LE((v) => console.log(v));
reader.readDoubleLE().then(console.log);
reader.readString((str) => str.toUpperCase())
  .then((str) => console.log(str)); // "HELLO WORLD"
reader.readJson().then((obj) => console.log(obj.text)) // "Hello World"

Promise vs. callback

When decoding complex data, it may be impossible to predict what read commands to issue until you begin reading data. In these cases, these read commands must take priority over anything previously queued up.

Promises are always resolved asyncronously, even when the data is immediately available. This makes it impossible to tell when a read command is issued as a result of another read.

Callbacks are resolved immediately when data is available. This allows the library to detect if a read command is issued as a result of another read, and prioritize it ahead of other reads.

const length = reader.readUInt32LE;
const promises = new Array(length);
for (var i = 0; i < length; i++) {
  promises[i] = reader.readDoubleLE();
}
Promise.all(promises).then((array) => console.log(array)) // [1,2,3,4,5]

AsyncStreamWriter

Constructor

• AsyncStreamWriter(stream)

Methods

• write(value, byteLength): Promise[Buffer]
• writeBoolean(value)
• writeBuffer(value)
• writeString(value)
• writeJson(value)
• writeDoubleBE(value)
• writeDoubleLE(value)
• writeFloatBE(value)
• writeFloatLE(value)
• writeInt8(value)
• writeInt16BE(value)
• writeInt16LE(value)
• writeInt32BE(value)
• writeInt32LE(value)
• writeUInt8(value)
• writeUInt16BE(value)
• writeUInt16LE(value)
• writeUInt32BE(value)
• writeUInt32LE(value)
• writeIntBE(value, byteLength)
• writeIntLE(value, byteLength)
• writeUIntBE(value, byteLength)
• writeUIntLE(value, byteLength)

AsyncStreamReader

Constructor

• AsyncStreamWriter(stream)

Methods

• read(byteLength[, callback]): Promise[Buffer]
• readBoolean([callback]): Promise[Boolean]
• readBuffer([callback]): Promise[Buffer]
• readString([callback]): Promise[String]
• readJson([callback]): Promise[Object]
• readDoubleBE([callback]): Promise[Number]
• readDoubleLE([callback]): Promise[Number]
• readFloatBE([callback]): Promise[Number]
• readFloatLE([callback]): Promise[Number]
• readInt8([callback]): Promise[Number]
• readInt16BE([callback]): Promise[Number]
• readInt16LE([callback]): Promise[Number]
• readInt32BE([callback]): Promise[Number]
• readInt32LE([callback]): Promise[Number]
• readUInt8([callback]): Promise[Number]
• readUInt16BE([callback]): Promise[Number]
• readUInt16LE([callback]): Promise[Number]
• readUInt32BE([callback]): Promise[Number]
• readUInt32LE([callback]): Promise[Number]
• readIntBE(byteLength[, callback]): Promise[Number]
• readIntLE(byteLength[, callback]): Promise[Number]
• readUIntBE(byteLength[, callback]): Promise[Number]
• readUIntLE(byteLength[, callback]): Promise[Number]

writeBuffer & readBuffer vs. write & read

write and read are meant to send and receive buffers as-is. write takes a buffer, and sends it as-is. read takes an integer and returns a buffer of that size.

writeBuffer and readBuffer are meant to send and receive buffers with size headers. writeBuffer takes a buffer and sends the length followed by the bytes. readBuffer reads the size parameter from the stream, then reads that size of bytes from the stream, and returns a buffer with those bytes.

LE (Little Endian) vs. BE (Big Endian)

See Wikipedia: Endianness for more details. What's important is to be consistent. When in doubt, use LE functions.