WIP Disclaimer

This template is currently a work-in-progress. Feel free to play around with it and give us feedback. Note also that this template depends on a development version of DuckDB.

Get in contact with fellow extension developers on https://discord.duckdb.org and follow https://duckdb.org/news for more information on official launch.

DuckDB Extension Template

The main goal of this template is to allow users to easily develop, test and distribute their own DuckDB extension.

Getting started

First step to getting started is to create your own repo from this template by clicking Use this template. Then clone your new repository using

git clone --recurse-submodules https://github.com/<you>/<your-new-extension-repo>.git

Note that --recurse-submodules will ensure the correct version of duckdb is pulled allowing you to get started right away.

Building

Dependencies

DuckDB extensions use VCPKG for dependency management. To demonstrate that, the example extension in the template links against OpenSSL. Enabling VCPKG is very simple: follow the installation instructions and export the following variable:

export VCPKG_TOOLCHAIN_PATH=<path_to_your_vcpkg_installation>/scripts/buildsystems/vcpkg.cmake

Note: while using VCPKG for installation is recommended, the build will still work as long as CMake's find_package function is able to locate a compatible openssl version. Alternatively, feel free to remove the OpenSSL dependency completely to build the example extension without dependencies.

Build steps

Now to build the extension, run:

make

The main binaries that will be built are:

./build/release/duckdb
./build/release/test/unittest
./build/release/extension/<extension_name>/<extension_name>.duckdb_extension

• duckdb is the binary for the duckdb shell with the extension code automatically loaded.
• unittest is the test runner of duckdb. Again, the extension is already linked into the binary.
• <extension_name>.duckdb_extension is the loadable binary as it would be distributed.

Running the extension

To run the extension code, simply start the shell with ./build/release/duckdb.

Now we can use the features from the extension directly in DuckDB. The template contains a single scalar function quack() that takes a string arguments and returns a string:

D select quack('Jane') as result;
┌───────────────┐
│    result     │
│    varchar    │
├───────────────┤
│ Quack Jane 🐥 │
└───────────────┘

Running the tests

Different tests can be created for DuckDB extensions. The primary way of testing DuckDB extensions should be the SQL tests in ./test/sql. These SQL tests can be run using:

make test

Getting started with your own extension

After creating a repository from this template, the first step is to name your extension. To rename the extension, run:

python3 ./scripts/set_extension_name.py <extension_name_you_want>

Feel free to delete the script after this step.

Now you're good to go! After a (re)build, you should now be able to use your duckdb extension:

./build/release/duckdb
D select <extension_name_you_chose>('Jane') as result;
┌─────────────────────────────────────┐
│                result               │
│               varchar               │
├─────────────────────────────────────┤
│ <extension_name_you_chose> Jane 🐥  │
└─────────────────────────────────────┘

For inspiration/examples on how to extend DuckDB in a more meaningful way, check out the test extensions, the in-tree extensions, and the out-of-tree extensions.

Distributing your extension

Easy distribution of extensions built with this template is facilitated using a similar process used by DuckDB itself. Binaries are generated for various versions/platforms allowing duckdb to automatically install the correct binary.

This step requires that you pass the following 4 parameters to your GitHub repo as action secrets:

secret name	description
S3_REGION	s3 region holding your bucket
S3_BUCKET	the name of the bucket to deploy to
S3_DEPLOY_ID	the S3 key id
S3_DEPLOY_KEY	the S3 key secret

After setting these variables, all pushes to main will trigger a new (dev) release. Note that your AWS token should have full permissions to the bucket, and you will need to have ACLs enabled.

Installing the deployed binaries

To install your extension binaries from S3, you will need to do two things. Firstly, DuckDB should be launched with the allow_unsigned_extensions option set to true. How to set this will depend on the client you're using. Some examples:

CLI:

duckdb -unsigned

Python:

con = duckdb.connect(':memory:', config={'allow_unsigned_extensions' : 'true'})

NodeJS:

db = new duckdb.Database(':memory:', {"allow_unsigned_extensions": "true"});

Secondly, you will need to set the repository endpoint in DuckDB to the HTTP url of your bucket + version of the extension you want to install. To do this run the following SQL query in DuckDB:

SET custom_extension_repository='bucket.s3.eu-west-1.amazonaws.com/<your_extension_name>/latest';

Note that the /latest path will allow you to install the latest extension version available for your current version of DuckDB. To specify a specific version, you can pass the version instead.

After running these steps, you can install and load your extension using the regular INSTALL/LOAD commands in DuckDB:

INSTALL <your_extension_name>
LOAD <your_extension_name>

Versioning of your extension

Extension binaries will only work for the specific DuckDB version they were built for. Since you may want to support multiple versions of DuckDB for a release of your extension, you can specify which versions to build for in the CI of this template. By default, the CI will build your extension against the version of the DuckDB submodule, which should generally be the most recent version of DuckDB. To build for multiple versions of DuckDB, simply add the version to the matrix variable, e.g.:

strategy:
    matrix:
        duckdb_version: [ '<submodule_version>', 'v0.7.0']

Setting up CLion

Opening project

Configuring CLion with the extension template requires a little work. Firstly, make sure that the DuckDB submodule is available. Then make sure to open ./duckdb/CMakeLists.txt (so not the top level CMakeLists.txt file from this repo) as a project in CLion. Now to fix your project path go to tools->CMake->Change Project Root(docs) to set the project root to the root dir of this repo.

Debugging

To set up debugging in CLion, there are two simple steps required. Firstly, in CLion -> Settings / Preferences -> Build, Execution, Deploy -> CMake you will need to add the desired builds (e.g. Debug, Release, RelDebug, etc). There's different ways to configure this, but the easiest is to leave all empty, except the build path, which needs to be set to ../build/{build type}. Now on a clean repository you will first need to run make {build type} to initialize the CMake build directory. After running make, you will be able to (re)build from CLion by using the build target we just created. If you use the CLion editor, you can create a CLion CMake profiles matching the CMake variables that are described in the makefile, and then you don't need to invoke the Makefile.

The second step is to configure the unittest runner as a run/debug configuration. To do this, go to Run -> Edit Configurations and click + -> Cmake Application. The target and executable should be unittest. This will run all the DuckDB tests. To specify only running the extension specific tests, add --test-dir ../../.. [sql] to the Program Arguments. Note that it is recommended to use the unittest executable for testing/development within CLion. The actual DuckDB CLI currently does not reliably work as a run target in CLion.