ab_testing

A/B Testing Plugin

This plugin implements A/B testing by routing a percentage of users to a v2 endpoint based on a deterministic hash of their user ID. It rewrites the request path from /v1/ to /v2/ for eligible users, allowing gradual rollout of new features or versions. Use this plugin when you need to split traffic between two versions of an API or service based on user identity. It operates during the request headers processing phase.

How It Works

1. The proxy receives an HTTP request and invokes the plugin's on_http_request_headers callback.
2. The plugin extracts the :path header and checks if it starts with /v1/.
3. If the path contains a user query parameter, the plugin computes a deterministic hash of the user ID and reduces it to a value between 0 and 99.
4. If the hash value is less than or equal to the configured percentile (50), the plugin rewrites the path by replacing /v1/ with /v2/, preserving the rest of the path and all query parameters.
5. The plugin returns Action::Continue, forwarding the (potentially modified) request to the upstream server.

Implementation Notes

• Path extraction: The plugin reads the :path header and handles query parameters.
• Specific libraries used for URLs: C++ uses boost::urls, Go relies on the standard net/url, and Rust builds a full URL and uses the url crate.
• Hashing: Device type detection / user identity routing depends on a deterministic hash of the extracted user ID. Rust implements a custom hash function to match C++ test expectations.
• Threshold: The 50% threshold for routing to the v2 endpoint is hardcoded as a constant.

Configuration

No configuration required. The percentile threshold and path prefixes are hardcoded as constants:

• a_path / A_PATH: /v1/
• b_path / B_PATH: /v2/
• percentile / PERCENTILE: 50

Build

Build the plugin for any supported language from the plugins/ directory:

# Rust
bazelisk build //samples/ab_testing:plugin_rust.wasm

# C++
bazelisk build //samples/ab_testing:plugin_cpp.wasm

# Go
bazelisk build //samples/ab_testing:plugin_go.wasm

Test

Run the unit tests defined in tests.textpb:

# Using Docker (recommended)
docker run -it -v $(pwd):/mnt \
    us-docker.pkg.dev/service-extensions-samples/plugins/wasm-tester:main \
    --proto /mnt/samples/ab_testing/tests.textpb \
    --plugin /mnt/bazel-bin/samples/ab_testing/plugin_rust.wasm

# Using Bazel (all languages)
bazelisk test --test_output=all //samples/ab_testing:tests

Expected Behavior

Derived from tests.textpb:

Available Languages

• Rust
• C++
• Go