Remove string checking in API error handling

Use strongly typed errors to set HTTP status codes.
Error interfaces are defined in the api/errors package and errors
returned from controllers are checked against these interfaces.

Errors can be wraeped in a pkg/errors.Causer, as long as somewhere in the
line of causes one of the interfaces is implemented. The special error
interfaces take precedence over Causer, meaning if both Causer and one
of the new error interfaces are implemented, the Causer is not
traversed.

Signed-off-by: Brian Goff <[email protected]>

api/errdefs/defs.go

@@ -0,0 +1,54 @@
+package errdefs
+
+// ErrNotFound signals that the requested object doesn't exist
+type ErrNotFound interface {
+	NotFound()
+}
+
+// ErrInvalidParameter signals that the user input is invalid
+type ErrInvalidParameter interface {
+	InvalidParameter()
+}
+
+// ErrConflict signals that some internal state conflicts with the requested action and can't be performed.
+// A change in state should be able to clear this error.
+type ErrConflict interface {
+	Conflict()
+}
+
+// ErrUnauthorized is used to signify that the user is not authorized to perform a specific action
+type ErrUnauthorized interface {
+	Unauthorized()
+}
+
+// ErrUnavailable signals that the requested action/subsystem is not available.
+type ErrUnavailable interface {
+	Unavailable()
+}
+
+// ErrForbidden signals that the requested action cannot be performed under any circumstances.
+// When a ErrForbidden is returned, the caller should never retry the action.
+type ErrForbidden interface {
+	Forbidden()
+}
+
+// ErrSystem signals that some internal error occurred.
+// An example of this would be a failed mount request.
+type ErrSystem interface {
+	ErrSystem()
+}
+
+// ErrNotModified signals that an action can't be performed because it's already in the desired state
+type ErrNotModified interface {
+	NotModified()
+}
+
+// ErrNotImplemented signals that the requested action/feature is not implemented on the system as configured.
+type ErrNotImplemented interface {
+	NotImplemented()
+}
+
+// ErrUnknown signals that the kind of error that occurred is not known.
+type ErrUnknown interface {
+	Unknown()
+}

api/errdefs/doc.go

@@ -0,0 +1,8 @@
+// Package errdefs defines a set of error interfaces that packages should use for communicating classes of errors.
+// Errors that cross the package boundary should implement one (and only one) of these interfaces.
+//
+// Packages should not reference these interfaces directly, only implement them.
+// To check if a particular error implements one of these interfaces, there are helper
+// functions provided (e.g. `Is<SomeError>`) which can be used rather than asserting the interfaces directly.
+// If you must assert on these interfaces, be sure to check the causal chain (`err.Cause()`).
+package errdefs

api/errdefs/is.go

@@ -0,0 +1,86 @@
+package errdefs
+
+type causer interface {
+	Cause() error
+}
+
+func getImplementer(err error) error {
+	switch e := err.(type) {
+	case
+		ErrNotFound,
+		ErrInvalidParameter,
+		ErrConflict,
+		ErrUnauthorized,
+		ErrUnavailable,
+		ErrForbidden,
+		ErrSystem,
+		ErrNotModified,
+		ErrNotImplemented,
+		ErrUnknown:
+		return e
+	case causer:
+		return getImplementer(e.Cause())
+	default:
+		return err
+	}
+}
+
+// IsNotFound returns if the passed in error is a ErrNotFound
+func IsNotFound(err error) bool {
+	_, ok := getImplementer(err).(ErrNotFound)
+	return ok
+}
+
+// IsInvalidParameter returns if the passed in error is an ErrInvalidParameter
+func IsInvalidParameter(err error) bool {
+	_, ok := getImplementer(err).(ErrInvalidParameter)
+	return ok
+}
+
+// IsConflict returns if the passed in error is a ErrConflict
+func IsConflict(err error) bool {
+	_, ok := getImplementer(err).(ErrConflict)
+	return ok
+}
+
+// IsUnauthorized returns if the the passed in error is an ErrUnauthorized
+func IsUnauthorized(err error) bool {
+	_, ok := getImplementer(err).(ErrUnauthorized)
+	return ok
+}
+
+// IsUnavailable returns if the passed in error is an ErrUnavailable
+func IsUnavailable(err error) bool {
+	_, ok := getImplementer(err).(ErrUnavailable)
+	return ok
+}
+
+// IsForbidden returns if the passed in error is a ErrForbidden
+func IsForbidden(err error) bool {
+	_, ok := getImplementer(err).(ErrForbidden)
+	return ok
+}
+
+// IsSystem returns if the passed in error is a ErrSystem
+func IsSystem(err error) bool {
+	_, ok := getImplementer(err).(ErrSystem)
+	return ok
+}
+
+// IsNotModified returns if the passed in error is a NotModified error
+func IsNotModified(err error) bool {
+	_, ok := getImplementer(err).(ErrNotModified)
+	return ok
+}
+
+// IsNotImplemented returns if the passed in error is a ErrNotImplemented
+func IsNotImplemented(err error) bool {
+	_, ok := getImplementer(err).(ErrNotImplemented)
+	return ok
+}
+
+// IsUnknown returns if the passed in error is an ErrUnknown
+func IsUnknown(err error) bool {
+	_, ok := getImplementer(err).(ErrUnknown)
+	return ok
+}

api/server/httputils/errors.go

@@ -1,9 +1,10 @@
 package httputils
 
 import (
+	"fmt"
 	"net/http"
-	"strings"
 
+	"github.com/docker/docker/api/errdefs"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/versions"
 	"github.com/gorilla/mux"
@@ -20,13 +21,8 @@ type httpStatusError interface {
 	HTTPErrorStatusCode() int
 }
 
-// inputValidationError is an interface
-// that errors generated by invalid
-// inputs can implement to tell the
-// api layer to set a 400 status code
-// in the response.
-type inputValidationError interface {
-	IsValidationError() bool
+type causer interface {
+	Cause() error
 }
 
 // GetHTTPErrorStatusCode retrieves status code from error message.
@@ -37,49 +33,44 @@ func GetHTTPErrorStatusCode(err error) int {
 	}
 
 	var statusCode int
-	errMsg := err.Error()
 
-	switch e := err.(type) {
-	case httpStatusError:
-		statusCode = e.HTTPErrorStatusCode()
-	case inputValidationError:
+	// Stop right there
+	// Are you sure you should be adding a new error class here? Do one of the existing ones work?
+
+	// Note that the below functions are already checking the error causal chain for matches.
+	switch {
+	case errdefs.IsNotFound(err):
+		statusCode = http.StatusNotFound
+	case errdefs.IsInvalidParameter(err):
 		statusCode = http.StatusBadRequest
+	case errdefs.IsConflict(err):
+		statusCode = http.StatusConflict
+	case errdefs.IsUnauthorized(err):
+		statusCode = http.StatusUnauthorized
+	case errdefs.IsUnavailable(err):
+		statusCode = http.StatusServiceUnavailable
+	case errdefs.IsForbidden(err):
+		statusCode = http.StatusForbidden
+	case errdefs.IsNotModified(err):
+		statusCode = http.StatusNotModified
+	case errdefs.IsNotImplemented(err):
+		statusCode = http.StatusNotImplemented
+	case errdefs.IsSystem(err) || errdefs.IsUnknown(err):
+		statusCode = http.StatusInternalServerError
 	default:
 		statusCode = statusCodeFromGRPCError(err)
 		if statusCode != http.StatusInternalServerError {
 			return statusCode
 		}
 
-		// FIXME: this is brittle and should not be necessary, but we still need to identify if
-		// there are errors falling back into this logic.
-		// If we need to differentiate between different possible error types,
-		// we should create appropriate error types that implement the httpStatusError interface.
-		errStr := strings.ToLower(errMsg)
-
-		for _, status := range []struct {
-			keyword string
-			code    int
-		}{
-			{"not found", http.StatusNotFound},
-			{"cannot find", http.StatusNotFound},
-			{"no such", http.StatusNotFound},
-			{"bad parameter", http.StatusBadRequest},
-			{"no command", http.StatusBadRequest},
-			{"conflict", http.StatusConflict},
-			{"impossible", http.StatusNotAcceptable},
-			{"wrong login/password", http.StatusUnauthorized},
-			{"unauthorized", http.StatusUnauthorized},
-			{"hasn't been activated", http.StatusForbidden},
-			{"this node", http.StatusServiceUnavailable},
-			{"needs to be unlocked", http.StatusServiceUnavailable},
-			{"certificates have expired", http.StatusServiceUnavailable},
-			{"repository does not exist", http.StatusNotFound},
-		} {
-			if strings.Contains(errStr, status.keyword) {
-				statusCode = status.code
-				break
-			}
+		if e, ok := err.(causer); ok {
+			return GetHTTPErrorStatusCode(e.Cause())
 		}
+
+		logrus.WithFields(logrus.Fields{
+			"module":     "api",
+			"error_type": fmt.Sprintf("%T", err),
+		}).Debugf("FIXME: Got an API for which error does not match any expected type!!!: %+v", err)
 	}
 
 	if statusCode == 0 {
@@ -133,6 +124,9 @@ func statusCodeFromGRPCError(err error) int {
 	case codes.Unavailable: // code 14
 		return http.StatusServiceUnavailable
 	default:
+		if e, ok := err.(causer); ok {
+			return statusCodeFromGRPCError(e.Cause())
+		}
 		// codes.Canceled(1)
 		// codes.Unknown(2)
 		// codes.DeadlineExceeded(4)