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RLP Types

RLP data type system defining bytes data, list data, and type guards for working with RLP structures.

Overview

RLP uses a discriminated union type to represent two kinds of data:

BytesData - Leaf nodes containing raw bytes
ListData - Nested arrays of RLP data

Type guards provide runtime type checking and TypeScript type narrowing for safe data access.

BrandedRlp

Core type representing RLP data structures.

export type BrandedRlp =
  | { type: "bytes"; value: Uint8Array }
  | { type: "list"; value: BrandedRlp[] }

Branded type using discriminated union pattern. The type field distinguishes between bytes and list variants. Properties:

type: "bytes" | "list" - Discriminant field
value: Uint8Array | BrandedRlp[] - Data payload

Source: BrandedRlp.ts:4-6

BytesData Variant

Represents a leaf node with raw bytes:

type BytesData = {
  type: "bytes"
  value: Uint8Array
}

Examples:

import { Rlp } from 'tevm'

// Single byte
const single: BrandedRlp = {
  type: 'bytes',
  value: new Uint8Array([0x7f])
}

// Empty bytes
const empty: BrandedRlp = {
  type: 'bytes',
  value: Bytes()
}

// Multiple bytes
const bytes: BrandedRlp = {
  type: 'bytes',
  value: new Uint8Array([1, 2, 3, 4, 5])
}

// Created via constructor
const data = Rlp(new Uint8Array([1, 2, 3]))
// => { type: 'bytes', value: Uint8Array([1, 2, 3]) }

ListData Variant

Represents a nested array of RLP data:

type ListData = {
  type: "list"
  value: BrandedRlp[]
}

Examples:

import { Rlp } from 'tevm'

// Empty list
const empty: BrandedRlp = {
  type: 'list',
  value: []
}

// List of bytes
const list: BrandedRlp = {
  type: 'list',
  value: [
    { type: 'bytes', value: new Uint8Array([1]) },
    { type: 'bytes', value: new Uint8Array([2]) }
  ]
}

// Nested lists
const nested: BrandedRlp = {
  type: 'list',
  value: [
    { type: 'bytes', value: new Uint8Array([1]) },
    {
      type: 'list',
      value: [
        { type: 'bytes', value: new Uint8Array([2]) },
        { type: 'bytes', value: new Uint8Array([3]) }
      ]
    }
  ]
}

// Created via constructor
const listData = Rlp([
  new Uint8Array([1]),
  new Uint8Array([2])
])
// => {
//   type: 'list',
//   value: [
//     { type: 'bytes', value: Uint8Array([1]) },
//     { type: 'bytes', value: Uint8Array([2]) }
//   ]
// }

Type Guards

Runtime type checking functions that narrow TypeScript types.

isData

Checks if value is any RLP data structure.

Implementation

Checks for required structure:

Value is object (not null)
Has type field
Has value field
Type is either “bytes” or “list”

function isData(value) {
  return (
    typeof value === "object" &&
    value !== null &&
    "type" in value &&
    "value" in value &&
    (value.type === "bytes" || value.type === "list")
  )
}

isBytesData

Checks if value is bytes data specifically.

Implementation

Uses isData then checks type field:

function isBytesData(value) {
  return isData(value) && value.type === "bytes"
}

isListData

Checks if value is list data specifically.

Implementation

Uses isData then checks type field:

function isListData(value) {
  return isData(value) && value.type === "list"
}

Type Patterns

Discriminated Union Pattern

RLP uses TypeScript discriminated unions for type safety:

import { Rlp } from 'tevm'

function processRlpData(data: BrandedRlp) {
  // TypeScript uses 'type' field to narrow types
  if (data.type === 'bytes') {
    // Here, TypeScript knows data.value is Uint8Array
    console.log('Bytes length:', data.value.length)
    const byte = data.value[0]  // OK
  } else {
    // Here, TypeScript knows data.value is BrandedRlp[]
    console.log('List items:', data.value.length)
    const item = data.value[0]  // OK, item is BrandedRlp
  }
}

Type Narrowing with Guards

Combine type guards with TypeScript narrowing:

import { Rlp } from 'tevm'

function extractBytes(data: unknown): Uint8Array[] {
  // First check if it's RLP data at all
  if (!Rlp.isData(data)) {
    return []
  }

  // Now TypeScript knows data is BrandedRlp
  if (Rlp.isBytesData(data)) {
    // Return single item
    return [data.value]
  }

  // Must be list data
  const bytes: Uint8Array[] = []
  for (const item of data.value) {
    // Recursively extract bytes
    bytes.push(...extractBytes(item))
  }
  return bytes
}

Exhaustive Type Checking

Ensure all type variants are handled:

import { Rlp } from 'tevm'

function serializeRlp(data: BrandedRlp): string {
  switch (data.type) {
    case 'bytes':
      return `bytes(${data.value.length})`
    case 'list':
      return `list(${data.value.length})`
    default:
      // TypeScript error if new type added
      const _exhaustive: never = data
      return _exhaustive
  }
}

Working with Types

Creating RLP Data

Use Rlp() constructor for automatic type detection:

import { Rlp } from 'tevm'

// From bytes
const bytesData = Rlp(new Uint8Array([1, 2, 3]))
// => { type: 'bytes', value: Uint8Array([1, 2, 3]) }

// From array (becomes list)
const listData = Rlp([
  new Uint8Array([1]),
  new Uint8Array([2])
])
// => { type: 'list', value: [...] }

// Already RLP data (pass through)
const existing = { type: 'bytes', value: new Uint8Array([1]) }
const same = Rlp(existing)
// => Returns existing unchanged

Manual Construction

Create structures directly:

import { Rlp } from 'tevm'

// Manual bytes data
const bytes: BrandedRlp = {
  type: 'bytes',
  value: new Uint8Array([1, 2, 3])
}

// Manual list data
const list: BrandedRlp = {
  type: 'list',
  value: [bytes]
}

// Nested structure
const nested: BrandedRlp = {
  type: 'list',
  value: [
    { type: 'bytes', value: new Uint8Array([1]) },
    {
      type: 'list',
      value: [
        { type: 'bytes', value: new Uint8Array([2]) }
      ]
    }
  ]
}

Type-safe Access

Use type guards for safe access:

import { Rlp } from 'tevm'

function getFirstByte(data: BrandedRlp): number | undefined {
  if (Rlp.isBytesData(data)) {
    return data.value[0]
  }
  if (Rlp.isListData(data) && data.value.length > 0) {
    return getFirstByte(data.value[0])
  }
  return undefined
}

function countItems(data: BrandedRlp): number {
  if (Rlp.isBytesData(data)) {
    return 1
  }
  if (Rlp.isListData(data)) {
    return data.value.reduce((sum, item) => sum + countItems(item), 0)
  }
  return 0
}

Type Validation

Runtime Validation

Type guards perform runtime validation:

import { Rlp } from 'tevm'

function validateRlpData(value: unknown): asserts value is BrandedRlp {
  if (!Rlp.isData(value)) {
    throw new Error('Invalid RLP data structure')
  }

  if (value.type === 'bytes') {
    if (!(value.value instanceof Uint8Array)) {
      throw new Error('Bytes data must have Uint8Array value')
    }
  } else if (value.type === 'list') {
    if (!Array.isArray(value.value)) {
      throw new Error('List data must have array value')
    }
    // Recursively validate items
    for (const item of value.value) {
      validateRlpData(item)
    }
  }
}

// Usage
const data: unknown = JSON.parse(jsonString)
validateRlpData(data)
// Now TypeScript knows data is BrandedRlp

Type Assertions

Assert types when you know the structure:

import { Rlp } from 'tevm'

function processTransaction(data: BrandedRlp) {
  // We know transactions are lists
  if (data.type !== 'list') {
    throw new Error('Transaction must be list')
  }

  // We know list has 9 items
  if (data.value.length !== 9) {
    throw new Error('Invalid transaction')
  }

  // Access fields safely
  const [nonce, gasPrice, gas, to, value, calldata, v, r, s] = data.value

  // Each field should be bytes
  if (!Rlp.isBytesData(nonce)) {
    throw new Error('Nonce must be bytes')
  }
}

Encodable

Input type for encoding operations:

type Encodable =
  | Uint8Array
  | BrandedRlp
  | Array<Uint8Array | BrandedRlp | any>

Accepts raw bytes, RLP data, or nested arrays. See Encoding.

Decoded

Output type from decoding operations:

type Decoded = {
  data: BrandedRlp
  remainder: Uint8Array
}

Contains decoded RLP data and remaining bytes. See Decoding.

Type Examples

Transaction Type

import { Rlp } from 'tevm'

type Transaction = {
  nonce: Uint8Array
  gasPrice: Uint8Array
  gas: Uint8Array
  to: Uint8Array
  value: Uint8Array
  data: Uint8Array
  v: Uint8Array
  r: Uint8Array
  s: Uint8Array
}

function toRlp(tx: Transaction): BrandedRlp {
  return {
    type: 'list',
    value: [
      { type: 'bytes', value: tx.nonce },
      { type: 'bytes', value: tx.gasPrice },
      { type: 'bytes', value: tx.gas },
      { type: 'bytes', value: tx.to },
      { type: 'bytes', value: tx.value },
      { type: 'bytes', value: tx.data },
      { type: 'bytes', value: tx.v },
      { type: 'bytes', value: tx.r },
      { type: 'bytes', value: tx.s }
    ]
  }
}

function fromRlp(data: BrandedRlp): Transaction {
  if (data.type !== 'list' || data.value.length !== 9) {
    throw new Error('Invalid transaction')
  }

  const [nonce, gasPrice, gas, to, value, calldata, v, r, s] = data.value

  if (!data.value.every(Rlp.isBytesData)) {
    throw new Error('All fields must be bytes')
  }

  return {
    nonce: nonce.value,
    gasPrice: gasPrice.value,
    gas: gas.value,
    to: to.value,
    value: value.value,
    data: calldata.value,
    v: v.value,
    r: r.value,
    s: s.value
  }
}

Merkle Proof Type

import { Rlp } from 'tevm'

type MerkleProof = Uint8Array[]

function proofToRlp(proof: MerkleProof): BrandedRlp {
  return {
    type: 'list',
    value: proof.map(node => ({
      type: 'bytes',
      value: node
    }))
  }
}

function proofFromRlp(data: BrandedRlp): MerkleProof {
  if (data.type !== 'list') {
    throw new Error('Proof must be list')
  }

  if (!data.value.every(Rlp.isBytesData)) {
    throw new Error('All proof nodes must be bytes')
  }

  return data.value.map(node => node.value)
}

Encoding - Encode typed data to RLP
Decoding - Decode RLP to typed structures
Utilities - Helper functions for working with types
Branded Types - Type branding pattern

Documentation Index

Try it Live

​RLP Types

​Overview

​BrandedRlp

​BytesData Variant

​ListData Variant

​Type Guards

​isData

​Implementation

​isBytesData

​Implementation

​isListData

​Implementation

​Type Patterns

​Discriminated Union Pattern

​Type Narrowing with Guards

​Exhaustive Type Checking

​Working with Types

​Creating RLP Data

​Manual Construction

​Type-safe Access

​Type Validation

​Runtime Validation

​Type Assertions

​Related Types

​Encodable

​Decoded

​Type Examples

​Transaction Type

​Merkle Proof Type

​Related

RLP Types

Overview

BrandedRlp

BytesData Variant

ListData Variant

Type Guards

isData

Implementation

isBytesData

Implementation

isListData

Implementation

Type Patterns

Discriminated Union Pattern

Type Narrowing with Guards

Exhaustive Type Checking

Working with Types

Creating RLP Data

Manual Construction

Type-safe Access

Type Validation

Runtime Validation

Type Assertions

Related Types

Encodable

Decoded

Type Examples

Transaction Type

Merkle Proof Type

Related