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Horizon Development Guide

Horizon Development Guide

This document describes how to build Horizon from source, so that you can test and edit the code locally to develop bug fixes and new features.

If you are just starting with Horizon and want to try it out, consider the Quickstart Guide instead. For information about administrating a Horizon instance in production, check out the Administration Guide.

Building Horizon

Building Horizon requires the following developer tools:

  • A Unix-like operating system with the common core commands (cp, tar, mkdir, bash, etc.)
  • Go (this repository is officially supported on the last two releases of Go)
  • git (to check out Horizon's source code)
  • mercurial (needed for go-dep)
  1. Set your GOPATH environment variable, if you haven't already. The default GOPATH is $HOME/go. When building any Go package or application the binaries will be installed by default to $GOPATH/bin.
  2. Clone the code into any directory you prefer: 
    git clone https://github.com/stellar/go
    Or if you prefer to develop inside GOPATH check it out to $GOPATH/src/github.com/stellar/go: 
    git clone https://github.com/stellar/go $GOPATH/src/github.com/stellar/go
    If developing inside GOPATH set the GO111MODULE=on environment variable to turn on Modules for managing dependencies. See the repository README for more information.
  3. Change to the directory where the repository is checked out. e.g. cd go, or if developing inside the GOPATH, cd $GOPATH/src/github.com/stellar/go.
  4. Compile the Horizon binary: go install ./services/horizon. You should see the resulting horizon executable in $GOPATH/bin.
  5. Add Go binaries to your PATH in your bashrc or equivalent, for easy access: export PATH=${GOPATH//://bin:}/bin:$PATH

Open a new terminal. Confirm everything worked by running horizon --help successfully. You should see an informative message listing the command line options supported by Horizon.

Set up Horizon's database

Horizon uses a Postgres database backend to store test fixtures and record information ingested from an associated Stellar Core. To set this up:

  1. Install PostgreSQL.
  2. Run createdb horizon_dev to initialise an empty database for Horizon's use.
  3. Run horizon db init --db-url postgres://localhost/horizon_dev to install Horizon's database schema.

Database problems?

  1. Depending on your installation's defaults, you may need to configure a Postgres DB user with appropriate permissions for Horizon to access the database you created. Refer to the Postgres documentation for details. Note: Remember to restart the Postgres server after making any changes to pg_hba.conf (the Postgres configuration file), or your changes won't take effect!
  2. Make sure you pass the appropriate database name and user (and port, if using something non-standard) to Horizon using --db-url. One way is to use a Postgres URI with the following form: postgres://USERNAME:PASSWORD@localhost:PORT/DB_NAME.
  3. If you get the error connect failed: pq: SSL is not enabled on the server, add ?sslmode=disable to the end of the Postgres URI to allow connecting without SSL. If you get the error zsh: no matches found: postgres://localhost/horizon_dev?sslmode=disable, wrap the url with single quotes horizon db init --db-url 'postgres://localhost/horizon_dev?sslmode=disable'
  4. If your server is responding strangely, and you've exhausted all other options, reboot the machine. On some systems service postgresql restart or equivalent may not fully reset the state of the server.

Run tests

At this point you should be able to run Horizon's unit tests:

cd $GOPATH/src/github.com/stellar/go/services/horizon
go test ./...

Set up Stellar Core

Horizon provides an API to the Stellar network. It does this by ingesting data from an associated stellar-core instance. Thus, to run a full Horizon instance requires a stellar-core instance to be configured, up to date with the network state, and accessible to Horizon. Horizon accesses stellar-core through both an HTTP endpoint and by connecting directly to the stellar-core Postgres database.

The simplest way to set up Stellar Core is using the Stellar Quickstart Docker Image. This is a Docker container that provides both stellar-core and horizon, pre-configured for testing.

  1. Install Docker.
  2. Verify your Docker installation works: docker run hello-world
  3. Create a local directory that the container can use to record state. This is helpful because it can take a few minutes to sync a new stellar-core with enough data for testing, and because it allows you to inspect and modify the configuration if needed. Here, we create a directory called stellar to use as the persistent volume: cd $HOME; mkdir stellar
  4. Download and run the Stellar Quickstart container:
docker run --rm -it -p "8000:8000" -p "11626:11626" -p "11625:11625" -p"8002:5432" -v $HOME/stellar:/opt/stellar --name stellar stellar/quickstart --testnet

In this example we run the container in interactive mode. We map the container's Horizon HTTP port (8000), the stellar-core HTTP port (11626), and the stellar-core peer node port (11625) from the container to the corresponding ports on localhost. Importantly, we map the container's postgresql port (5432) to a custom port (8002) on localhost, so that it doesn't clash with our local Postgres install. The -v option mounts the stellar directory for use by the container. See the Quickstart Image documentation for a detailed explanation of these options.

  1. The container is running both a stellar-core and a horizon instance. Log in to the container and stop Horizon:
docker exec -it stellar /bin/bash
supervisorctl
stop horizon

Check Stellar Core status

Stellar Core takes some time to synchronise with the rest of the network. The default configuration will pull roughly a couple of day's worth of ledgers, and may take 15 - 30 minutes to catch up. Logs are stored in the container at /var/log/supervisor. You can check the progress by monitoring logs with supervisorctl:

docker exec -it stellar /bin/bash
supervisorctl tail -f stellar-core

You can also check status by looking at the HTTP endpoint, e.g. by visiting http://localhost:11626 in your browser.

Connect Horizon to Stellar Core

You can connect Horizon to stellar-core at any time, but Horizon will not begin ingesting data until stellar-core has completed its catch-up process.

Now run your development version of Horizon (which is outside of the container), pointing it at the stellar-core running inside the container:

horizon --db-url="postgres://localhost/horizon_dev" --stellar-core-db-url="postgres://stellar:postgres@localhost:8002/core" --stellar-core-url="http://localhost:11626" --port 8001 --network-passphrase "Test SDF Network ; September 2015" --ingest

If all is well, you should see ingest logs written to standard out. You can test your Horizon instance with a query like: http://localhost:8001/transactions?limit=10&order=asc. Use the Stellar Laboratory to craft other queries to try out, and read about the available endpoints and see examples in the Horizon API reference.

The development cycle

Congratulations! You can now run the full development cycle to build and test your code.

  1. Write code + tests
  2. Run tests
  3. Compile Horizon: go install github.com/stellar/go/services/horizon
  4. Run Horizon (pointing at your running stellar-core)
  5. Try Horizon queries

Check out the Stellar Contributing Guide to see how to contribute your work to the Stellar repositories. Once you've got something that works, open a pull request, linking to the issue that you are resolving with your contribution. We'll get back to you as quickly as we can.