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swift-libp2p/swift-varint 0.0.1
Google Protocol Buffer VarInt
⭐️ 0
🕓 2 weeks ago
.package(url: "https://github.com/swift-libp2p/swift-varint.git", from: "0.0.1")

VarInt encoding of 64-bit integers

Swift Package Manager compatible Build & Test (macos and linux)

Swift implementation of the Google Protocol Buffers VarInt specification

Table of Contents

Overview

It is based on the Go implementation of the Google Protocol Buffers varint specification.

  • Varints are a method of serializing integers using one or more bytes.
  • Smaller numbers take a smaller number of bytes.

For more details see

The encoding rules are:

  • Unsigned integers are serialized 7 bits at a time, starting with the least significant bits.
  • The most significant bit (msb) in each output byte indicates if there is a continuation byte.
  • Signed integers are mapped to unsigned integers using "zig-zag" encoding:
    • Positive values x are written as 2*x + 0,
    • Negative values x are written as 2*(~x) + 1
    • So, negative values are complemented and whether to complement is encoded in bit 0.

Install

Include the following dependency in your Package.swift file

let package = Package(
    ...
    dependencies: [
        ...
        .package(url: "https://github.com/swift-libp2p/swift-varint.git", .upToNextMajor(from: "0.0.1"))
    ],
    
    ...
)

Usage

Example


import VarInt

/// Create some arbitrary data
let bytes = [UInt8](https://raw.github.com/swift-libp2p/swift-varint/main/"Hello World".data(using: .utf8)!)

/// Prefix the bytes with their length so we can recover the data later
let uVarIntLengthPrefixedBytes = putUVarInt(UInt64(bytes.count)) + bytes

/// ... send the data across a network or something ...

/// Read the length prefixed data to determine the length of the payload
let lengthPrefix = uVarInt(uVarIntLengthPrefixedBytes)
print(lengthPrefix.value)     // 11 -> `Hello World` == 11 bytes
print(lengthPrefix.bytesRead) // 1  -> The value `11` fits into 1 byte

/// So dropping the first byte will result in our original data again...
let recBytes = [UInt8](https://raw.github.com/swift-libp2p/swift-varint/main/uVarIntLengthPrefixedBytes.dropFirst(lengthPrefix.bytesRead))

/// The original bytes and the recovered bytes are equal
print(bytes == recBytes) // True

API

/// Signed VarInts
public func putVarInt(_ value: Int64) -> [UInt8] 
public func varInt(_ buffer: [UInt8]) -> DecodedVarInt   // (value:  Int64, bytesRead: Int)

/// Unsigned VarInts
public func putUVarInt(_ value: UInt64) -> [UInt8]
public func uVarInt(_ buffer: [UInt8]) -> DecodedUVarInt // (value: UInt64, bytesRead: Int)

Contributing

Contributions are welcomed! This code is very much a proof of concept. I can guarantee you there's a better / safer way to accomplish the same results. Any suggestions, improvements, or even just critques, are welcome!

Let's make this code better together! 🤝

Credits

https://github.com/multiformats/go-varint

License

MIT © 2022 Breth Inc.

GitHub

link
Stars: 0
Last commit: 2 days ago
jonrohan Something's broken? Yell at me @ptrpavlik. Praise and feedback (and money) is also welcome.

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