net/http: Handling Nested Groups

[gavin-iru]

Go version

go 1.24.1

Output of go env in your module/workspace:

GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/hb/1n61v0yj11zc1rnwkbm974tm0000gn/T/go-build1330795007=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/***/go.mod'
GOMODCACHE='/Users/**/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/**/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/**/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.1.darwin-arm64'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/***/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/chin/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.1.darwin-arm64/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

ServeMux Pattern Matching Behavior with Grouped Routes

Problem Description

I'm trying to organize my HTTP routes into logical groups using nested ServeMux, but I'm encountering unexpected behavior with pattern matching.

API Structure

I have the following API endpoints:

GET    /v1/users
POST   /v1/users
GET    /v1/users/attributes
GET    /v1/users/{id}

Implementation Attempt

I'm trying to organize the code by grouping user-related handlers:

func mainHandler() {
    mux := http.NewServeMux()
    userHandler := userHandler(mux)
}

func userHandler(mux *http.ServeMux) {
    userMux := http.NewServeMux()
    
    userMux.Handle("GET /users", getUserLogic())
    userMux.Handle("POST /users", postUserLogic())
    userMux.Handle("GET /users/attributes", getUserAttributesLogic())
    userMux.Handle("GET /users/{id}", getUserByIdLogic())
}

What did you see happen?

Observed Behavior

I've tried three different approaches to register the user routes:

Scenario 1: Without trailing slash

mux.Handle("/v1/users", userMux)

Result: Only matches /v1/users endpoints, returns 404 for /v1/users/attributes and /v1/users/{id}

Scenario 2: With trailing slash

mux.Handle("/v1/users/", userMux)

Result: Only matches /v1/users/attributes and /v1/users/{id}, returns 404 for /v1/users endpoints

Scenario 3: Using StripPrefix

mux.Handle("/v1/users/", http.StripPrefix("/v1/users", userMux))

With modified handlers:

userMux.Handle("GET ", getUserLogic())
userMux.Handle("POST ", postUserLogic())
userMux.Handle("GET /attributes", getUserAttributesLogic())
userMux.Handle("GET /{id}", getUserByIdLogic())

Result: Error - "Pattern matching fails because host/path missing /"

What did you expect to see?

Question

Why does ServeMux exhibit this behavior with grouped routes, and is there a way to achieve the desired routing structure without requiring trailing slashes? The current pattern matching seems to force us to choose between handling root-level routes (/v1/users) OR nested routes (/v1/users/*), but not both simultaneously.

I'd prefer not to add trailing slashes to all my routes. Is this a limitation of ServeMux, or am I missing something in the implementation?

[seankhliao]

You can register both /v1/users and /v1/users/ pointing to the same nested mux.

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