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RLP Utilities

Helper methods for creating, measuring, flattening, and comparing RLP data structures.

Overview

Utility functions provide convenient ways to work with RLP data:

from - Create RLP data from various inputs
getEncodedLength - Calculate encoded size without encoding
flatten - Extract all bytes from nested structures
equals - Deep equality comparison

from

Create RLP data structure from various inputs with automatic type detection.

Behavior

The from method normalizes various input types into RLP data structures:

Uint8Array → Creates bytes data
BrandedRlp → Returns unchanged (idempotent)
Array → Creates list data (doesn’t recursively convert items)

Note: Arrays are not recursively converted:

import { Rlp } from 'tevm'

// Array items remain as-is (not converted to RLP data)
const list = Rlp([
  new Uint8Array([1]),  // Stays as Uint8Array
  new Uint8Array([2])   // Stays as Uint8Array
])

// To recursively convert, use encode + decode
const encoded = Rlp.encode([
  new Uint8Array([1]),
  new Uint8Array([2])
])
const decoded = Rlp.decode(encoded)
// Now fully converted to RLP data structures

Use Cases

Normalizing Input:

import { Rlp } from 'tevm'

function processRlpData(input: Uint8Array | BrandedRlp | BrandedRlp[]) {
  // Normalize to RLP data
  const data = Rlp(input)

  // Now work with consistent type
  if (data.type === 'bytes') {
    console.log('Bytes length:', data.value.length)
  } else {
    console.log('List items:', data.value.length)
  }
}

Building Structures:

import { Rlp } from 'tevm'

// Build transaction structure
const nonce = Rlp(new Uint8Array([0x00]))
const gasPrice = Rlp(new Uint8Array([0x04, 0xa8, 0x17, 0xc8]))
const gas = Rlp(new Uint8Array([0x52, 0x08]))

const transaction = Rlp([nonce, gasPrice, gas, /* ... */])

getEncodedLength

Calculate the byte length of RLP-encoded data without actually encoding it.

Algorithm

Calculates encoded size using RLP rules without allocating buffers: For Uint8Array:

// Single byte < 0x80: 1 byte (no prefix)
if (length === 1 && byte < 0x80) return 1

// Short string (< 56 bytes): 1 + length
if (length < 56) return 1 + length

// Long string: 1 + length_of_length + length
const lengthBytes = calculateLengthOfLength(length)
return 1 + lengthBytes + length

For Arrays (lists):

// Calculate total payload size
const totalLength = items.reduce((sum, item) =>
  sum + getEncodedLength(item), 0
)

// Short list (< 56 bytes): 1 + totalLength
if (totalLength < 56) return 1 + totalLength

// Long list: 1 + length_of_length + totalLength
const lengthBytes = calculateLengthOfLength(totalLength)
return 1 + lengthBytes + totalLength

Performance Benefits

Measuring without encoding saves allocation and copying:

import { Rlp } from 'tevm'

// Inefficient: encode just to check size
const encoded = Rlp.encode(data)
const size = encoded.length

// Efficient: measure directly
const size = Rlp.getEncodedLength(data)

Use Cases: Pre-sizing Buffers:

import { Rlp } from 'tevm'

// Calculate total size for multiple items
const items = [data1, data2, data3]
const totalSize = items.reduce(
  (sum, item) => sum + Rlp.getEncodedLength(item),
  0
)

// Allocate single buffer
const buffer = new Uint8Array(totalSize)

Size Validation:

import { Rlp } from 'tevm'

// Check if data will fit in block
const MAX_BLOCK_SIZE = 1000000

const size = Rlp.getEncodedLength(transactionList)
if (size > MAX_BLOCK_SIZE) {
  throw new Error('Transaction list too large for block')
}

Choosing Encoding Strategy:

import { Rlp } from 'tevm'

// Use different strategies based on size
const size = Rlp.getEncodedLength(data)

if (size < 1000) {
  // Small data: use JS encoder
  const encoded = Rlp.encode(data)
} else {
  // Large data: use WASM encoder
  const encoded = RlpWasm.encode(data)
}

flatten

Recursively extract all bytes data from nested lists (depth-first traversal).

Algorithm

Depth-first traversal that collects all bytes data:

function flatten(data) {
  const result = []

  function visit(d) {
    if (d.type === 'bytes') {
      result.push(d)
    } else {
      for (const item of d.value) {
        visit(item)
      }
    }
  }

  visit(data)
  return result
}

Use Cases

Extract Transaction Fields:

import { Rlp } from 'tevm'

// Decode transaction
const txBytes = new Uint8Array([...])
const decoded = Rlp.decode(txBytes)

// Extract all byte fields
const fields = Rlp.flatten(decoded.data)
// => [nonce, gasPrice, gas, to, value, data, v, r, s]

// Access specific fields
const [nonce, gasPrice, gas] = fields
console.log('Nonce:', nonce.value)

Count Total Bytes:

import { Rlp } from 'tevm'

function countTotalBytes(data: BrandedRlp): number {
  const flattened = Rlp.flatten(data)
  return flattened.reduce((sum, item) => sum + item.value.length, 0)
}

const nested = { /* ... */ }
const total = countTotalBytes(nested)
console.log(`Total bytes: ${total}`)

Validate Structure:

import { Rlp } from 'tevm'

function validateAllBytes(data: BrandedRlp, minLength: number) {
  const flattened = Rlp.flatten(data)

  for (const item of flattened) {
    if (item.value.length < minLength) {
      throw new Error(`Bytes too short: ${item.value.length} < ${minLength}`)
    }
  }
}

Map Over Bytes:

import { Rlp } from 'tevm'

function hashAllBytes(data: BrandedRlp): Uint8Array[] {
  const flattened = Rlp.flatten(data)
  return flattened.map(item => keccak256(item.value))
}

equals

Deep equality comparison for RLP data structures.

Algorithm

Recursive comparison with type checking:

function equals(data, other) {
  // Different types
  if (data.type !== other.type) return false

  // Compare bytes
  if (data.type === 'bytes') {
    if (data.value.length !== other.value.length) return false
    for (let i = 0; i < data.value.length; i++) {
      if (data.value[i] !== other.value[i]) return false
    }
    return true
  }

  // Compare lists
  if (data.type === 'list') {
    if (data.value.length !== other.value.length) return false
    for (let i = 0; i < data.value.length; i++) {
      if (!equals(data.value[i], other.value[i])) return false
    }
    return true
  }

  return false
}

Use Cases

Deduplication:

import { Rlp } from 'tevm'

function deduplicate(items: BrandedRlp[]): BrandedRlp[] {
  const unique: BrandedRlp[] = []

  for (const item of items) {
    const isDuplicate = unique.some(u => Rlp.equals(u, item))
    if (!isDuplicate) {
      unique.push(item)
    }
  }

  return unique
}

Testing:

import { Rlp } from 'tevm'

// Test round-trip encoding
const original = {
  type: 'list',
  value: [
    { type: 'bytes', value: new Uint8Array([1]) }
  ]
}

const encoded = Rlp.encode(original)
const decoded = Rlp.decode(encoded)

console.log(Rlp.equals(original, decoded.data))  // true

Caching:

import { Rlp } from 'tevm'

const cache = new Map<string, Uint8Array>()

function encodeWithCache(data: BrandedRlp): Uint8Array {
  // Check cache
  for (const [key, cached] of cache.entries()) {
    const cachedData = JSON.parse(key)
    if (Rlp.equals(data, cachedData)) {
      return cached
    }
  }

  // Encode and cache
  const encoded = Rlp.encode(data)
  cache.set(JSON.stringify(data), encoded)
  return encoded
}

Assertions:

import { Rlp } from 'tevm'

function assertRlpEquals(
  actual: BrandedRlp,
  expected: BrandedRlp,
  message?: string
) {
  if (!Rlp.equals(actual, expected)) {
    throw new Error(message || 'RLP data not equal')
  }
}

// Usage in tests
const result = processRlpData(input)
assertRlpEquals(result, expectedOutput)

Utility Combinations

Combine utilities for powerful operations: Measure Flattened Size:

import { Rlp } from 'tevm'

function getTotalBytesSize(data: BrandedRlp): number {
  const flattened = Rlp.flatten(data)
  return flattened.reduce((sum, item) => sum + item.value.length, 0)
}

Compare After Normalization:

import { Rlp } from 'tevm'

function normalizeAndCompare(a: unknown, b: unknown): boolean {
  const dataA = Rlp(a)
  const dataB = Rlp(b)
  return Rlp.equals(dataA, dataB)
}

Validate Then Flatten:

import { Rlp } from 'tevm'

function extractAndValidate(data: BrandedRlp): Uint8Array[] {
  // Validate structure
  const size = Rlp.getEncodedLength(data)
  if (size > MAX_SIZE) {
    throw new Error('Data too large')
  }

  // Extract all bytes
  const flattened = Rlp.flatten(data)

  // Return raw byte arrays
  return flattened.map(item => item.value)
}

Types - RLP type system and guards
Encoding - Encode RLP data
Decoding - Decode RLP data
BrandedRlp - Functional API

Overview

Getting Started

Core Concepts

Skills

JSONRPCProvider

Contract

Primitives

Cryptography

EVM

Utils

Guides

Examples

Swift

Zig

Developer Documentation

Generated API (TypeDoc)

RLP Utilities

Try it Live

RLP Utilities

Overview

from

Behavior

Use Cases

getEncodedLength

Algorithm

Performance Benefits

flatten

Algorithm

Use Cases

equals

Algorithm

Use Cases

Utility Combinations

Overview

Getting Started

Core Concepts

Skills

JSONRPCProvider

Contract

Primitives

Cryptography

EVM

Utils

Guides

Examples

Swift

Zig

Developer Documentation

Generated API (TypeDoc)

Try it Live

​RLP Utilities

​Overview

​from

​Behavior

​Use Cases

​getEncodedLength

​Algorithm

​Performance Benefits

​flatten

​Algorithm

​Use Cases

​equals

​Algorithm

​Use Cases

​Utility Combinations

​Related

RLP Utilities

Overview

from

Behavior

Use Cases

getEncodedLength

Algorithm

Performance Benefits

flatten

Algorithm

Use Cases

equals

Algorithm

Use Cases

Utility Combinations

Related