bitcoin_wire

Bitcoin transaction and block wire formats for Gleam.

bitcoin_wire is a Gleam library for deserializing, inspecting, hashing, serializing, and performing context-free consensus checks on Bitcoin transactions and blocks. It preserves exact wire values across Erlang and JavaScript and reports malformed encodings as structured errors.

Project Status

The following Bitcoin wire-format data structures are currently implemented:

bitcoin_wire/transaction deserializes and serializes legacy and SegWit transactions, exposes their fields and output script classifications, computes their base sizes, total sizes, weights, and virtual sizes, txids, and wtxids, and runs context-free consensus checks.
bitcoin_wire/block deserializes and serializes standalone 80-byte headers and computes their block hashes. It also deserializes and serializes complete blocks; exposes their headers and transactions; computes base sizes, total sizes, weights, virtual sizes, and Merkle roots; and runs context-free consensus checks.
bitcoin_wire/hash256 provides fixed-width wire-order hashes with conversions to raw little-endian bytes and conventional Bitcoin display notation.

Additional domains may be added as the library expands.

Installation

gleam add bitcoin_wire@1

Goals and Philosophy

Correctness over convenience

Malformed or ambiguous encodings are surfaced explicitly rather than being silently normalized or accepted as partial values.

Reference-grade intent

The library is structured so it can be read alongside Bitcoin documentation as a reliable guide to wire formats and protocol data structures.

Faithful protocol modeling

Protocol distinctions and encoded forms are preserved rather than collapsed into convenience abstractions.

Cross-runtime portability

Public behavior remains consistent across the supported runtimes: Erlang and Node.js. However, native integer conversions and decode diagnostics may differ according to runtime representation limits.

Native browser builds are not currently supported. The JavaScript hashing implementation imports node:crypto, which is available in Node.js but not through native browser APIs.

Scope

This project deserializes and models caller-provided Bitcoin data. It is not a wallet, full node, RPC client, or networking library. Domain-specific documentation describes the exact deserialization, validation, and policy boundaries for each implemented module.

No security guarantees are provided.

Use Cases

Explorers and blockchain indexers: Turn externally obtained Bitcoin wire bytes into structured blocks and transactions for display, search, and downstream analysis.
Monitoring and research: Inspect caller-provided feeds and datasets for transaction shapes, script types, witness usage, block composition, Merkle roots, and context-free consensus violations.
Protocol and data tooling: Add a portable deserialization, inspection, and context-free validation layer ahead of application-specific processing.
Testing and education: Study Bitcoin wire encoding and exercise software with valid, malformed, and consensus-invalid block and transaction data.

Development

Run the unit tests on Erlang and Node.js:

gleam test -t erlang
gleam test -t javascript --runtime node

Continuous Integration

Pull requests run one workflow per project:

Workflow	Checks
`library`	Formatting and unit tests on Erlang and Node
`fuzz`	Formatting, builds, and short transaction/block fuzz runs on Erlang and Node
`benchmarks`	Formatting, builds, and selected fixture benchmark runs on Erlang and Node
`examples`	Formatting and an Erlang build

Tests, builds, and smoke runs use the compatibility baseline in the shared setup action.

Fuzz smoke runs use a fixed seed and a small number of transaction and block iterations on each runtime. Each run also verifies the original corpus before mutation begins. Benchmark smoke runs exercise fixture loading, measurement, and table reporting for transactions and blocks. They do not enforce performance thresholds; use the performance harness's comparison runner for measured regression claims.

A separate fuzz-nightly workflow runs longer transaction and block fuzz suites on Erlang and Node with a shared generated seed if main differs from its latest successful scheduled run. Unchanged successful commits are skipped, and failed runs are retried the following night.

Fuzz Testing

The standalone fuzz harness exercises transaction and block parser safety against malformed and mutated wire-format inputs. Run a selected suite with ./fuzz/run -- <suite> <iterations> [seed]; target and runtime options go before --.

Benchmarking

The standalone performance harness measures public deserialization and inspection workflows across representative inputs, scaling dimensions, and fail-fast paths. Run the complete suite with ./benchmarks/run, or pass benchmark arguments after --, for example ./benchmarks/run -- --section transaction.deserialize.fixtures.

Examples

The standalone examples project uses mempool.space raw mainnet data to demonstrate transaction JSON output, block metrics, context-free block validation, and structured transaction decode errors. Run an example from the repository root with, for example, ./examples/run -- block-metrics 0.