package cleanhttp

import (
	"net/http"
	"strings"
	"unicode"
)

// HandlerInput provides input options to cleanhttp's handlers
type HandlerInput struct {
	ErrStatus int
}

// PrintablePathCheckHandler is a middleware that ensures the request path
// contains only printable runes.
func PrintablePathCheckHandler(next http.Handler, input *HandlerInput) http.Handler {
	// Nil-check on input to make it optional
	if input == nil {
		input = &HandlerInput{
			ErrStatus: http.StatusBadRequest,
		}
	}

	// Default to http.StatusBadRequest on error
	if input.ErrStatus == 0 {
		input.ErrStatus = http.StatusBadRequest
	}

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r != nil {
			// Check URL path for non-printable characters
			idx := strings.IndexFunc(r.URL.Path, func(c rune) bool {
				return !unicode.IsPrint(c)
			})

			if idx != -1 {
				w.WriteHeader(input.ErrStatus)
				return
			}

			if next != nil {
				next.ServeHTTP(w, r)
			}
		}

		return
	})
}

package cleanhttp

import (
	"net/http"
	"strings"
	"unicode"
)

// HandlerInput provides input options to cleanhttp's handlers
type HandlerInput struct {
	ErrStatus int
}

// PrintablePathCheckHandler is a middleware that ensures the request path
// contains only printable runes.
func PrintablePathCheckHandler(next http.Handler, input *HandlerInput) http.Handler {
	// Nil-check on input to make it optional
	if input == nil {
		input = &HandlerInput{
			ErrStatus: http.StatusBadRequest,
		}
	}

	// Default to http.StatusBadRequest on error
	if input.ErrStatus == 0 {
		input.ErrStatus = http.StatusBadRequest
	}

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Check URL path for non-printable characters
		idx := strings.IndexFunc(r.URL.Path, func(c rune) bool {
			return !unicode.IsPrint(c)
		})

		if idx != -1 {
			w.WriteHeader(input.ErrStatus)
			return
		}

		next.ServeHTTP(w, r)
		return
	})
}

--- 
+++ 
@@ -27,17 +27,22 @@
 	}
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		// Check URL path for non-printable characters
-		idx := strings.IndexFunc(r.URL.Path, func(c rune) bool {
-			return !unicode.IsPrint(c)
-		})
+		if r != nil {
+			// Check URL path for non-printable characters
+			idx := strings.IndexFunc(r.URL.Path, func(c rune) bool {
+				return !unicode.IsPrint(c)
+			})
 
-		if idx != -1 {
-			w.WriteHeader(input.ErrStatus)
-			return
+			if idx != -1 {
+				w.WriteHeader(input.ErrStatus)
+				return
+			}
+
+			if next != nil {
+				next.ServeHTTP(w, r)
+			}
 		}
 
-		next.ServeHTTP(w, r)
 		return
 	})
 }
Fix a panic if the request passed in is nil
