Walkable Buffer

🚶🛡️ A class for easily reading data from binary Buffers

Install

npm install walkable-buffer

• Supported Node versions aim to be Latest current and LTS as well as trying to keep up to date with the latest supported node in Google cloud functions.

Usage

• Instance defaults
  • Defaults in Constructor
  • Set/get defaults on existing instance
• Cursor
  • initialCursor in constructor
  • Manipulage Cursor
• Read Integers
• Read Strings
• Buffer
• Size

import fs from "fs";
import WalkableBuffer from "walkable-buffer";

const buffer = fs.readFileSync("./temp");
const wb = new WalkableBuffer({
    buffer,
    // Set instance defaults for `endianness`, `encoding` and `signed`
    // The instance default can be overridden for each operation
    endianness: "LE",
    encoding: "utf8",
    signed: true,
});

const v = wb.get(
    6 /* byteLength */,
    "BE" /* endianness - Override instance default for this operation */,
); // => 140 737 488 355 327

const s = wb.getString(
    16 /* byteLength */,
    "utf16le" /* encoding - overrides instance default */,
); // => "Hellö höw åre yö"

const b = wb.getBigInt(
    null /* endianness - null/undefined to use instance default */,
    false /* signed - override isntance default */,
); // 18_446_744_073_709_551_615n

Instance defaults

The instance defaults include endianness, encoding and signed controlling how to read the binary data into integers and text.

The effect of this is that the operations get/peek - BigInt/String/SizedString will use the configured settings if none is provided.

Config	Default Value
endianness	"LE"
encoding	"utf8"
signed	true (Signed integers)

Defaults in Constructor

You can set the instance defaults when creating the instance by configuring it in the WalkableBufferOptions provided to the constructor.

import WalkableBuffer from "walkable-buffer";

const wb = new WalkableBuffer({
    buffer,
    endianness: "LE",
    encoding: "utf8",
    signed: true,
});

Set/get defaults on existing instance

You can also use set/get - Endianness/Encoding/Signed.

import WalkableBuffer from "walkable-buffer";

const wb = new WalkableBuffer({ buffer });

wb.getEndianness(); // => "LE" (the default)
wb.setEndianness("BE");
wb.getEndianness(); // => "BE"

wb.getEncoding(); // "utf8" (the default)
wb.setEncoding("ascii");
wb.getEncoding(); // => "ascii"

wb.getSigned(); // true (for signed integers, the default)
wb.setSigned(false);
wb.getSigned(); // false (for unsigned integers)

Cursor

The "cursor" is the byteOffset that the walkable buffer has currently "walked". It is the default position to read data from, and it advances whenever a get operation is completed successfully.

By default, the WalkableBuffer will start with the cursor at 0.

initialCursor in constructor

import WalkableBuffer from "walkable-buffer";

const wb = new WalkableBuffer({
    buffer,
    initialCursor: 8, // First `get` operation will start at byteOffset 8
});

Manipulate Cursor

The following "walking" operations will advance the cursor to the first byte after data is read:

• get()
• getBigInt()
• getString()
• getSizedString()

The following operations will read data without manipulating the cursor:

• peek()
• peekBigInt()
• peekString()
• peekSizedString()

To manipulate the position of the cursor you can also

• skip(byteLength) to skip byteLength of bytes.
• goTo(byteOffset) to move cursor to a specific offset of the buffer.

And to get the current position of the cursor, use getCurrentPos().

Read Integers

• get(byteLength, endianness, signed) - Read byteLength as a signed/unsigned integer, reading with endianness, and advancing cursor byteLength.

• peek(byteLength, byteOffset, endianness, signed) - Read byteLength at cursor + byteOffset as a signed/unsigned integer, without manipulating the cursor.

• getBigInt(endianness, signed) - Read the next 8 bytes as a signed/unsigned BigInt , reading with endianness, and advancing cursor 8 steps.

• peekBigInt(byteOffset, endianness, signed) - Read 8 bytes at byteOffset as a signed/unsigned BigInt , reading with endianness, without manipulating the cursor.

Read Strings

• getString(byteLength, encoding) - Read the next byteLength bytes as a string, using encoding, and advances cursor byteLength.

• peekString(byteLength, byteOffset, encoding) - Read the byteLength bytes at cursor - byteOffset as a string, using encoding, without manipulating the cursor.

• getSizedString(sizeOfSize, endianness, encoding) - Read the next sizeOfSize as an unsigned integer with endianness to get byte-length, then reads that many bytes as a string with encoding.

Buffer

You can get the entire Buffer of WalkableBuffer back by running getSourceBuffer().

You can also get Buffer of a specific byteLength from current cursor by running getBuffer(byteLength). If called without byteLength, returns a buffer being a split from current cursor position to end of buffer.

Size

You can get the size of the Buffer with size(), and get the number of bytes from current cursor position to the end of the buffer, sizeRemainingBuffer().

License

MIT © Oscar Busk