URL Matching Nuance with mux Router in Go

When building web applications in Go with the mux router, it’s essential to understand how route matching works, especially when dealing with URLs that have query parameters. One common issue developers face is with trailing slashes in the URL paths, which can break route matching unexpectedly.

Table of Contents

• Problem: Trailing Slash on Route Matching
• Solution
• Conclusion

Problem: Trailing Slash on Route Matching

Consider the following two endpoints in a Go application:

// Broken

// http://localhost:8080/org/send
r.HandleFunc("/org/send/", Send).Methods("POST")

// http://localhost:8080/org/retrieve/?param=val
r.HandleFunc("/org/{id}/retrieve", Retrieve).Methods("GET")

Trailing Slash Issues with Static and Dynamic Endpoints

In mux, static paths like /org/send do not match if a trailing slash is added (e.g., /org/send/), resulting in a 404 page not found error.

On the other hand, dynamic paths like /org/{id}/retrieve/?param=val require a trailing slash to match correctly (e.g., /org/{id}/retrieve/); without it, a 404 error will occur.

This happens because mux treats paths strictly.

Solution

To fix this, register route paths consistently:

• Static paths (e.g., /org/send) should not include a trailing slash.
• Dynamic paths (e.g., /org/{id}/retrieve/) should include a trailing slash in the matcher.

Example:

// Fixed
r.HandleFunc("/org/send", Send).Methods("POST")  // No trailing slash
r.HandleFunc("/org/{id}/retrieve/", Retrieve).Methods("GET")  // Trailing slash needed

Alternatively, you can add additional matchers to handle static routes with and without slashes and error-correcting middleware to match dynamic routes with missing slashes.

Conclusion

Understanding how mux handles trailing slashes and how it matches paths is key to ensuring that your routes work as expected. Be mindful of static vs. dynamic path matching, and ensure consistency in how you define your routes.

Back to Top