httputil : wrap handlers for additional context (#413)

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

internal/httputil/handlers.go

@@ -1,6 +1,8 @@
 package httputil // import "github.com/pomerium/pomerium/internal/httputil"
 
 import (
+	"errors"
+	"fmt"
 	"net/http"
 )
 
@@ -14,7 +16,7 @@ func HealthCheck(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "text/plain")
 	w.WriteHeader(http.StatusOK)
 	if r.Method == http.MethodGet {
-		w.Write([]byte(http.StatusText(http.StatusOK)))
+		fmt.Fprintln(w, http.StatusText(http.StatusOK))
 	}
 }
 
@@ -24,3 +26,22 @@ func Redirect(w http.ResponseWriter, r *http.Request, url string, code int) {
 	w.Header().Set(HeaderPomeriumResponse, "true")
 	http.Redirect(w, r, url, code)
 }
+
+// The HandlerFunc type is an adapter to allow the use of
+// ordinary functions as HTTP handlers. If f is a function
+// with the appropriate signature, HandlerFunc(f) is a
+// Handler that calls f.
+//
+// adapted from std library to suppport error wrapping
+type HandlerFunc func(http.ResponseWriter, *http.Request) error
+
+// ServeHTTP calls f(w, r) error.
+func (f HandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if err := f(w, r); err != nil {
+		var e *HTTPError
+		if !errors.As(err, &e) {
+			e = &HTTPError{http.StatusInternalServerError, err}
+		}
+		e.ErrorResponse(w, r)
+	}
+}