Instrustment handlers for logging/error handling

This refactors a bit of the http handler code.
Moves error handling for handler functions to a generic handler.
This also has a side-effect of being able to propagate errors from the
provider to send the correct status code, provided the error type
matches a pre-defined interface.

vendor/github.com/cpuguy83/strongerrors/status/http.go

@@ -0,0 +1,37 @@
+package status
+
+import (
+	"net/http"
+
+	"github.com/cpuguy83/strongerrors"
+)
+
+// HTTPCode takes an error and returns the HTTP status code for the given error
+// If a match is found then the second return argument will be true, otherwise it will be false.
+// nolint: gocyclo
+func HTTPCode(err error) (int, bool) {
+	switch {
+	case strongerrors.IsNotFound(err):
+		return http.StatusNotFound, true
+	case strongerrors.IsInvalidArgument(err):
+		return http.StatusBadRequest, true
+	case strongerrors.IsConflict(err):
+		return http.StatusConflict, true
+	case strongerrors.IsUnauthenticated(err), strongerrors.IsForbidden(err):
+		return http.StatusForbidden, true
+	case strongerrors.IsUnauthorized(err):
+		return http.StatusUnauthorized, true
+	case strongerrors.IsUnavailable(err):
+		return http.StatusServiceUnavailable, true
+	case strongerrors.IsForbidden(err):
+		return http.StatusForbidden, true
+	case strongerrors.IsAlreadyExists(err), strongerrors.IsNotModified(err):
+		return http.StatusNotModified, true
+	case strongerrors.IsNotImplemented(err):
+		return http.StatusNotImplemented, true
+	case strongerrors.IsSystem(err) || strongerrors.IsUnknown(err) || strongerrors.IsDataLoss(err) || strongerrors.IsExhausted(err):
+		return http.StatusInternalServerError, true
+	default:
+		return http.StatusInternalServerError, false
+	}
+}