Bitcoin RPC Proxy

Finer-grained permission management for bitcoind.

How to use

Via docker-compose

version: "3"
services:
  btc-rpc-proxy:
    container_name: btc-rpc-proxy
    build: .
    ports:
      - 8331:8331
    volumes:
      - /path/to/config/btc_rpc_proxy.toml:/etc/btc_rpc_proxy.toml

About

This is a proxy made specifically for bitcoind to allow finer-grained control of permissions. It enables you to specify several users and for each user the list of RPC calls they are allowed to make and optionally the name of the wallet they will operate on. When run against a prunded node, the proxy will perform on-demand block fetching and verification, enabling features of a non-pruned node while still using a pruned node.

Fine-grained permission management

This is useful because bitcoind allows every application with password to make possibly harmful calls like stopping the daemon or spending from wallet (if enabled). If you have several applications, you can provide the less trusted ones a different password and permissions than the others using this project.

There's another interesting advantage: since this is written in Rust, it might serve as a filter for some malformed requests which might be exploits. But I don't recommend relying on it!

Overriding wallet

For each user you can set a specific wallet name to be used by setting override_wallet = "wallet_name_here". When this is set the wallet sent in request is ignored and the specified wallet is used instead. Aside from obvious security benefits this can help workaround applications that are incapable of accessing specific wallet (e.g. btc-rpc-explorer at the time of writing).

On-demand block fetching

By connecting to your pruned Bitcoin node through Bitcoin Proxy, your node will now behave as though it is not pruned. If a user or application requires a block that is not retained by your pruned node, Bitcoin Proxy will dynamically fetch the block over the P2P network, then verify its hash against your node to ensure validity.

This means that you can run multiple services against your pruned Bitcoin node — such as Lightning and BTCPay — without them fighting for control over the pruning. Both are happy because both believe they are dealing with an unpruned node.

A tradeoff to the proxy is speed and bandwidth. Every time the proxy needs to fetch a block not retained by your pruned node, it must reach out over the P2P network, consuming both Internet bandwidth and time.

Usage

For security and performance reasons this application is written in Rust. Thus, you need a recent Rust compiler to compile it.

You need to configure the proxy using config files. You can specify their paths using --conf /path/to/file.toml or --conf-dir /path/to/config/dir. Make sure to set their permissions to 600 before you write the passwords to them! If --conf-dir is used, all files in that directory will be loaded and merged. You can use --conf multiple times. This is useful to organize your configuration (e.g. put sensitive information into a separate file).

An example configuration file is provided in this repository, hopefuly it's understandable. After configuring, you only need to run the compiled binary (e.g. using cargo run --release -- --conf btc_rpc_proxy.toml)

A man page can be generated using cfg_me and --help option is provided.

Systemd integration

Using socket activation enables you to delay the start of btc-rpc-proxy until it's actually needed or start it in parallel with its clients leading to faster boot times.

Systemd socket activation is configured using bind_systemd_socket_name option. Setting it to a valid socket name will cause btc-rpc-proxy to use systemd socket activation using the socket with the specified socket name.

This feature is only available for Linux and only if the systemd feature is enabled. (Enabled by default.) Disabling it can decrease compile time and binary size but please keep it enabled if you intend to distribute the binary so that the users can benefit from it. Especially in case of packaged software.

Limitations

• It uses serde_json, which allocates during deserialization (Value). Expect a bit lower performance than without proxy.
• Logging can't be configured yet.
• No support for changing UID.
• No support for Unix sockets.
• Redirect instead of blocking might be a useful feaure, which is now lacking.

Credits

Would like to extend the gratitude to the following individuals and organizations for their valuable contributions to this project:

• Kixunil/btc-rpc-proxy and Start9Labs/btc-rpc-proxy Contributed to finer-grained permission management for bitcoind.
• dobtc/btc-rpc-proxy: Updated dependencies and added Docker-related features.

License

MITNFA