Add RegexpCompileFunc to override regexp.Compile

mux.go

@@ -19,6 +19,10 @@ var (
 	ErrMethodMismatch = errors.New("method is not allowed")
 	// ErrNotFound is returned when no route match is found.
 	ErrNotFound = errors.New("no matching route was found")
+	// RegexpCompileFunc aliases regexp.Compile and enables overriding it.
+	// Do not run this function from `init()` in importable packages.
+	// Changing this value is not safe for concurrent use.
+	RegexpCompileFunc = regexp.Compile
 )
 
 // NewRouter returns a new router instance.
@@ -524,7 +528,7 @@ func mapFromPairsToRegex(pairs ...string) (map[string]*regexp.Regexp, error) {
 	}
 	m := make(map[string]*regexp.Regexp, length/2)
 	for i := 0; i < length; i += 2 {
-		regex, err := regexp.Compile(pairs[i+1])
+		regex, err := RegexpCompileFunc(pairs[i+1])
 		if err != nil {
 			return nil, err
 		}

regexp.go

@@ -93,7 +93,7 @@ func newRouteRegexp(tpl string, typ regexpType, options routeRegexpOptions) (*ro
 
 		// Append variable name and compiled pattern.
 		varsN[i/2] = name
-		varsR[i/2], err = regexp.Compile(fmt.Sprintf("^%s$", patt))
+		varsR[i/2], err = RegexpCompileFunc(fmt.Sprintf("^%s$", patt))
 		if err != nil {
 			return nil, err
 		}
@@ -125,7 +125,7 @@ func newRouteRegexp(tpl string, typ regexpType, options routeRegexpOptions) (*ro
 		reverse.WriteByte('/')
 	}
 	// Compile full regexp.
-	reg, errCompile := regexp.Compile(pattern.String())
+	reg, errCompile := RegexpCompileFunc(pattern.String())
 	if errCompile != nil {
 		return nil, errCompile
 	}

route_test.go

@@ -0,0 +1,66 @@
+package mux
+
+import (
+	"net/http"
+	"regexp"
+	"sync"
+	"testing"
+)
+
+var testNewRouterMu sync.Mutex
+var testHandler = http.NotFoundHandler()
+
+func BenchmarkNewRouter(b *testing.B) {
+	testNewRouterMu.Lock()
+	defer testNewRouterMu.Unlock()
+
+	// Set the RegexpCompileFunc to the default regexp.Compile.
+	RegexpCompileFunc = regexp.Compile
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		testNewRouter(b, testHandler)
+	}
+}
+
+func BenchmarkNewRouterRegexpFunc(b *testing.B) {
+	testNewRouterMu.Lock()
+	defer testNewRouterMu.Unlock()
+
+	// We preallocate the size to 8.
+	cache := make(map[string]*regexp.Regexp, 8)
+
+	// Override the RegexpCompileFunc to reuse compiled expressions
+	// from the `cache` map. Real world caches should have eviction
+	// policies or some sort of approach to limit memory use.
+	RegexpCompileFunc = func(expr string) (*regexp.Regexp, error) {
+		if regex, ok := cache[expr]; ok {
+			return regex, nil
+		}
+
+		regex, err := regexp.Compile(expr)
+		if err != nil {
+			return nil, err
+		}
+
+		cache[expr] = regex
+		return regex, nil
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		testNewRouter(b, testHandler)
+	}
+}
+
+func testNewRouter(_ testing.TB, handler http.Handler) {
+	r := NewRouter()
+	// A route with a route variable:
+	r.Handle("/metrics/{type}", handler)
+	r.Queries("orgID", "{orgID:[0-9]*?}")
+	r.Host("{subdomain}.domain.com")
+}