log_query

Log Query Plugin

This plugin demonstrates how to parse URL query parameters from HTTP requests and log specific values. It extracts the token query parameter from the request path, handles URL decoding, and logs the value (or "<missing>" if not present). Use this plugin when you need to extract and log query parameters for debugging, implement parameter-based logic, or learn URL parsing in Proxy-WASM. It operates during the request headers processing phase.

How It Works

1. The proxy receives an HTTP request from a client and invokes the plugin's on_http_request_headers callback.

2. The plugin reads the :path pseudo-header, which contains the request path including query parameters (e.g., /foo?bar=baz&token=value&a=b).

3. URL parsing: The plugin parses the path as a URL:

   • C++ uses Boost.URL's parse_uri_reference() to parse the path as a relative URL reference.
   • Go uses url.Parse() from the standard library.
   • Rust uses the url crate with a dummy base URL (http://example.com) to parse relative paths.

4. Parameter extraction: The plugin searches for the token query parameter:

   • If found, the value is extracted and URL-decoded (e.g., so%20special becomes so special).
   • If not found, the string "<missing>" is used.

5. Logging: The plugin logs the token value using the appropriate logging mechanism:

   • C++: LOG_INFO("token: " + token)
   • Go: proxywasm.LogInfof("token: %s", token)
   • Rust: info!("token: {}", token)

6. The plugin returns Continue / ActionContinue, allowing the request to proceed normally to the upstream server.

Implementation Notes

• Path retrieval: Extracts the raw HTTP path string via the :path pseudo-header.
• URL parsing: Leverages standard URL libraries across languages (Boost.URL in C++, net/url in Go, url crate in Rust) to safely decode and parse query parameters.
• Fallback behaviors: Gracefully handles missing token parameters by emitting a <missing> string rather than triggering errors.

Configuration

No configuration required.

Build

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

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

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

# Go
bazelisk build //samples/log_query: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/log_query/tests.textpb \
    --plugin /mnt/bazel-bin/samples/log_query/plugin_rust.wasm

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

Expected Behavior

Derived from tests.textpb:

Scenario	Description
NoPath	Does not log anything when the :path pseudo-header is completely missing.
NoToken	Logs a missing status when the expected token parameter is not present in the URL.
LogToken	Correctly parses, URL-decodes, and logs the value of the provided token.

Available Languages

• Rust
• C++
• Go

Use Cases

• Debugging: Log specific query parameters for troubleshooting.
• Parameter extraction: Extract tokens, API keys, or other parameters for processing.
• Conditional logic: Make routing or authentication decisions based on query parameters.
• Analytics: Track usage of specific parameter values.
• Learning tool: Understand URL parsing APIs in Proxy-WASM environments.