Fulcrum

A fast & nimble SPV server for Bitcoin Cash, Bitcoin BTC, and Litecoin.

For more information, visit The Official Fulcrum Website™️.

Copyright

(C) 2019-2024 Calin Culianu calin.culianu@gmail.com

License:

GPLv3. See the included LICENSE.txt file or visit gnu.org and read the license.

Highlights:

• Fast: Written in 100% modern C++17 using multi-threaded and asynchronous programming techniques.
• A drop-in replacement for ElectronX/ElectrumX: Fulcrum is 100% protocol-level compatible with the Electrum Cash 1.5.1 protocol. Existing server admins should feel right at home with this software since installation and management of it is nearly identical to ElectronX/ElectrumX server.
• Cross-platform: While this codebase was mainly developed and tested on MacOS, Windows and Linux, it should theoretically work on any modern OS (such as *BSD) that has Qt5 Core and Qt5 Networking available.
• NEW! Triple-coin: Supports BCH, BTC and LTC.

Requirements

• For running:
  • A supported bitcoin full node with its JSON-RPC service enabled, preferably running on the same machine.
    • For BCH: Bitcoin Cash Node, Bitcoin Unlimited Cash, Flowee, and bchd have all been tested extensively and are known to work well with this software.
    • For BTC: Bitcoin Core v0.17.0 or later. No other full nodes are supported by this software for BTC.
    • For LTC: Litecoin Core v0.17.0 or later. No other full nodes are supported by this software for LTC.
      • If using Litcoin Core v0.21.2 or above, your daemon is serializing data using mweb extensions. While Fulcrum understands this serialization format, your Electrum-LTC clients may not. You can run litecoind with -rpcserialversion=1 to have your daemon return transactions in pre-mweb format which is understood by most Electrum-LTC clients.
    • The node must have txindex enabled e.g. txindex=1.
    • The node must not be a pruning node.
    • Optional: For best results, enable zmq for the "hasblock" topic using e.g. zmqpubhashblock=tcp://0.0.0.0:8433 in your bitcoin.conf file (zmq is only available on: Core, BCHN, BU 1.9.1+, or Litecoin Core).
  • Recommended hardware: Minimum 1GB RAM, 64-bit CPU, ~40GB disk space for mainnet BCH, 133GB for BTC (as of Aug 2023). For best results, use an SSD rather than an HDD.
• For compiling:
  • Qt Core & Qt Networking libraries 5.12.5 or above (I use 5.15.2 myself). Qt 5.12.4 (or earlier) is not supported.
  • Optional but recommended: libzmq 4.x development headers and library (also known as libzmq3-dev on Debian/Ubuntu and zeromq-devel on Fedora). Fulcrum will run just fine without linking against libzmq, but it will run better if you do link against libzmq and also turn on zmqpubhashblock notifications in bitcoind (zmq is only available on: Core, BCHN, or BU 1.9.1+).
  • A modern, 64-bit C++17 compiler. clang is recommended but G++ also works. MSVC on Windows is not supported (please use MinGW G++ instead, which ships with Qt Open Source Edition for Windows).

Quickstart

1. Download a pre-built static binary.
2. Verify that the binary runs on your system by executing the binary with ./Fulcrum -h to see the CLI options.
3. Setup a configuration file and to point Fulcrum to your bitcoind JSON-RPC server, specify listening ports, TLS certificates, etc. See: doc/fulcrum-example-config.conf and/or doc/fulcrum-quick-config.conf
4. Also see this section below on Running Fulcrum.

How To Compile

Compiling is for those users that do not wish to use the pre-built static binaries provided here, or for users on platforms for which the static binaries are not provided (such as FreeBSD or macOS). To compile, it's recommended you use the Qt Creator IDE.

1. Get the latest version of Qt Open Source Edition for your platform.
2. Point the Qt Creator IDE at the Fulcrum.pro file.
3. Set the build configuration to "Release". Hit Build. It should "just work".

You may also build from the CLI (on Linux and MacOS):

1. Make sure you have qmake in your path and all the requisite Qt5 dev libs installed.
2. qmake (to generate the Makefile)
3. make -j8 (replace 8 here with the number of cores on your machine)

A note for Linux users: You may have to install the Qt5 networking package separately such as libqt5network5 (depending on your distribution). You also need libbz2-dev otherwise compilation will fail. If you are having trouble finding the required Qt versions, you can try this link: https://launchpad.net/~beineri (for Ubuntu/Debian ppas). For best results, you may wish to also ensure you have pkg-config and libzmq installed (aka libzmq3-dev on Debian/Ubuntu, zeromq-devel on Fedora).

A note for Windows users: Qt 5.13.2 (or above) with MinGW G++ 7.x.x is the compiler/Qt kit you should be using. MSVC is not supported by this codebase at the present time.

What to do if compiling fails

If you have problems compiling, the most likely culprit would be your compiler not being C++17 compliant (please use a recent version of GCC or clang on Linux, Apple's Xcode on Mac, or MinGW G++ 7.x on Windows).

The other likely culprit is the fact that at the present time I have included a statically-built librocksdb in the codebase. There are versions of this library for Windows, Mac, and Linux included right in the source tree, and Fulcrum.pro looks for them and links to them. Instructions are included within the Fulcrum.pro project file about how to build your own static librocksdb if the bundled one does not work on your system.

If you are still having trouble, file an issue here in this github.

Linking against the system librocksdb.so (experimental)

You may optionally build against the system rocksdb (Linux only) if your distribution offers rocksdb version 6.6.4 or newer.

1. qmake LIBS=-lrocksdb (to generate the Makefile without linking to the included static lib)
2. make clean && make -j8 (replace 8 here with the number of cores on your machine)

Note: Some Linux distributions have been known to package librocksdb.so incorrectly. See here for an example, so until I can be confident most distributions do it right, I am considering using the system librocksdb.so an experimental feature for the time being (in principle it should work ok if the library is compiled correctly).

Making sure libzmq is detected and used (optional but recommended)

Ensure that libzmq3 (Debian/Ubuntu) and/or zeromq-devel (Fedora/Redhat) is installed, and that pkg-config is also installed. If on Unix (macOS, Linux, or Windows MinGW), then ideally the qmake step will find libzmq on your system and automatically use it. If that is not the case, you may try passing flags to qmake such as LIBS+="-L/path/to/libdir_containting_libzmq -lzmq" and INCLUDEPATH+="/path/to/dir_containing_zmq_h" as arguments when you invoke qmake. Using libzmq is optional but highly recommended. If you have trouble getting Fulcrum to compile against your libzmq, open a new issue and maybe I can help.

Building the Windows static Fulcrum.exe

New! I recently added a mechanism using Docker to build a statically-linked Windows .exe. This build is 100% compatible with any stock 64-bit Windows 7 or above system -- you don't have to install anything -- it just works. You can download the pre-built .exe yourself here from the releases page.

If you want to build it yourself though, you can do so, but it requires Docker on either a MacOS or a Linux host system (it may work on Windows too with Linux tools for Windows -- but I haven't tried it myself). It builds all dependencies, including a static Qt and static rocksdb. As such, it may take a while so be patient.

1. Make sure Docker is installed such that you don't need to use sudo. This is the default on MacOS, but on Linux you may need to follow these instructions here.

2. Run the build script:

   $ contrib/build/build.sh windows master

The first argument to the script is the platform to build (in this case windows). The second argument to the script is a git branch or tag to build. Two .exe files will be generated, Fulcrum.exe and FulcrumAdmin.exe, which will appear in dist/win after the build process completes.

• Note: You can point the build script to any repository, not just this one, by giving it a GIT_REPO environment variable:

  $ GIT_REPO=https://github.com/myusername/MyFulcrumFork contrib/build/build.sh windows master

  $ GIT_REPO=$(pwd) contrib/build/build.sh windows master

Building a static executable for Linux

New! I recently added a mechanism using Docker to build a statically-linked Linux executable. This build is 100% compatible with most stock 64-bit Linux systems with a new enough glibc and libstdc++. So on a relatively modern Linux system, you don't have to install anything -- it just works. You can download the pre-built binary yourself here from the releases page.

If you want to build it yourself though, you can do so, but it requires Docker on either a MacOS or a Linux host system. It builds a static Qt and static rocksdb.

1. Make sure Docker is installed such that you don't need to use sudo. This is the default on MacOS, but on Linux you may need to follow these instructions here.

2. Run the build script:

   $ contrib/build/build.sh linux master

The first argument to the script is the platform to build (in this case linux). You may also specify oldlinux as the first argument if you wish to build for an older system (in which case the Docker container will use Ubuntu 16.04 to compile, instead of the Ubuntu "latest" tag). The second argument to the script is a git branch or tag to build.

• Note: You can point the build script to any repository, not just this one, by giving it a GIT_REPO environment variable:

  $ GIT_REPO=https://github.com/myusername/MyFulcrumFork contrib/build/build.sh linux master

  $ GIT_REPO=$(pwd) contrib/build/build.sh linux master

---

Running Fulcrum

Execute the binary, with -h to see the built-in help, e.g. ./Fulcrum -h. You can set most options from the CLI, but you can also specify a config file as an argument. See:

• doc/fulcrum-example-config.conf in the source tree. This sample config file is very well documented with comments.
• doc/fulcrum-quick-config.conf in the source tree. This is a more abbreviated config file you can use as a starting point as well.

Fulcrum requires a bitcoind instance running either on testnet or mainnet (or regtest for testing), which you must tell it about via the CLI options or via the config file. You also need to tell it what port(s) to listen on and optionally what SSL certificates to use (if using SSL). Note: Electron Cash (and/or Electrum) at this time no longer support connecting to non-SSL servers, so you should probably configure SSL for production use.

It is recommended you specify a data dir (-D via CLI or datadir= via config file) on an SSD drive for best results. Synching against testnet should take you about 10-20 minutes (more on slower machines), and mainnet can take anywhere from 4 hours to 20+ hours, depending on machine and drive speed. I have not tried synching against mainnet on an HDD and it will probably take days if you are lucky.

As long as the server is still synchronizing, all public-facing ports will not yet be bound for listening and as such an attempt to connect to one of the RPC ports will fail with a socket error such as e.g. "Connection refused". Once the server finishes synching it will behave like an ElectronX/ElectrumX server and it can receive requests from Electron Cash (or Electrum if on BTC).

You may also wish to read the Fulcrum manpage.

Admin Script: FulcrumAdmin

Fulcrum comes with an admin script (Python 3.6+ is required on the system to run this script). You may send commands to Fulcrum using this script. The script requires that an admin port (config var admin=, CLI arg -a) be configured for your server. To run the script, execute ./FulcrumAdmin -h and you will see a list of possible subcommands that you can send to Fulcrum. Below you see all available commands (the below assumes the admin port is on port 8000):

$ ./FulcrumAdmin -p 8000 addpeer              Add a peer to the server's list of peers
$ ./FulcrumAdmin -p 8000 ban                  Ban clients by ID and/or IP address
$ ./FulcrumAdmin -p 8000 banpeer              Ban peers by hostname suffix
$ ./FulcrumAdmin -p 8000 bitcoind_throttle    Query or set server bitcoind_throttle setting
$ ./FulcrumAdmin -p 8000 clients (sessions)   Print information on all the currently connected clients
$ ./FulcrumAdmin -p 8000 getinfo              Get server information
$ ./FulcrumAdmin -p 8000 kick                 Kick clients by ID and/or IP address
$ ./FulcrumAdmin -p 8000 listbanned (banlist) Print the list of banned IP addresses and peer hostnames
$ ./FulcrumAdmin -p 8000 loglevel             Set the server's logging verbosity
$ ./FulcrumAdmin -p 8000 maxbuffer            Query or set server max_buffer setting
$ ./FulcrumAdmin -p 8000 peers                Print peering information
$ ./FulcrumAdmin -p 8000 query                Query for balance, UTXO, and history information for one or more addresses
$ ./FulcrumAdmin -p 8000 rmpeer               Remove peers by hostname suffix
$ ./FulcrumAdmin -p 8000 simdjson             Get or set the server's 'simdjson' (JSON parser) setting
$ ./FulcrumAdmin -p 8000 stop (shutdown)      Gracefully shut down the server
$ ./FulcrumAdmin -p 8000 unban                Unban IP addresses
$ ./FulcrumAdmin -p 8000 unbanpeer            Unban peers by hostname suffix

---

Protocol Documentation

Documentation for the Electrum Cash protocol that Fulcrum uses is available here.

---

Platform Notes

Windows

This codebase will not compile correctly (or at all) using MSVC. Please use the MinGW and/or G++ kit in Qt Creator to build this software.

Linux

If you have clang on your system, configure the project to use it as the compiler preferentially over g++. g++ works great too, but clang is preferred.

MacOS

Everything should just work (I use MacOS as my dev machine).

---

F.A.Q.

Q: Why Qt? This isn't a GUI app!

A: Yes, I know. However, Qt is a very robust, cross-platform and fast application framework. You can use its "Core" library for console apps, servers, etc. It has great network support and other basic things a programmer needs to get stuff done.

Q: Why is the compiled binary called Fulcrum (capital F) and not fulcrum (lowercase f) as is customary on Linux/Unix?

A: Because I like capital letters, even on Linux. I also develop (this and other software) for macOS and Windows and over there the Linux/Unix lowecase thing looks a little out-of-place. Perhaps my sensibilities have been affected by my win32 and macOS dev work, or perhaps I'm just unconventional. Embrace the lack of convention here! That being said, if the capital F bothers you, feel free to rename it or represent it as fulcrum wherever you like.

---

Donations

Sure! Send BCH here:

bitcoincash:qphax4s4n9h60jxj2fkrjs35w2tvgd4wzvf52cgtzc

You may also send BTC to the BTC-equivalent of the above address, which is: 1BCHBCH6TXBaXyc5HReLBm1sNytBF2kkPD

---

Sponsors