fix: restjson error deserialization when no body is present

Author: lucix-aws

CHANGELOG_PENDING.md

@@ -3,3 +3,5 @@
 ### SDK Enhancements
 
 ### SDK Bugs
+* `restjson`: Correct failure to deserialize errors.
+  * Deserialize generic error information when no response body is present.

private/protocol/restjson/unmarshal_error.go

@@ -2,6 +2,7 @@ package restjson
 
 import (
 	"bytes"
+	"encoding/json"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -40,54 +41,30 @@ func (u *UnmarshalTypedError) UnmarshalError(
 	resp *http.Response,
 	respMeta protocol.ResponseMetadata,
 ) (error, error) {
-
-	code := resp.Header.Get(errorTypeHeader)
-	msg := resp.Header.Get(errorMessageHeader)
-
-	body := resp.Body
-	if len(code) == 0 || len(msg) == 0 {
-		// If unable to get code from HTTP headers have to parse JSON message
-		// to determine what kind of exception this will be.
-		var buf bytes.Buffer
-		var jsonErr jsonErrorResponse
-		teeReader := io.TeeReader(resp.Body, &buf)
-		err := jsonutil.UnmarshalJSONError(&jsonErr, teeReader)
-		if err != nil {
-			return nil, err
-		}
-
-		body = ioutil.NopCloser(&buf)
-		if len(code) == 0 {
-			code = jsonErr.Code
-		}
-		msg = jsonErr.Message
+	code, msg, err := unmarshalErrorInfo(resp)
+	if err != nil {
+		return nil, err
 	}
 
-	// If code has colon separators remove them so can compare against modeled
-	// exception names.
-	code = strings.SplitN(code, ":", 2)[0]
-
-	if fn, ok := u.exceptions[code]; ok {
-		// If exception code is know, use associated constructor to get a value
-		// for the exception that the JSON body can be unmarshaled into.
-		v := fn(respMeta)
-		if err := jsonutil.UnmarshalJSONCaseInsensitive(v, body); err != nil {
-			return nil, err
-		}
+	fn, ok := u.exceptions[code]
+	if !ok {
+		return awserr.NewRequestFailure(
+			awserr.New(code, msg, nil),
+			respMeta.StatusCode,
+			respMeta.RequestID,
+		), nil
+	}
 
-		if err := rest.UnmarshalResponse(resp, v, true); err != nil {
-			return nil, err
-		}
+	v := fn(respMeta)
+	if err := jsonutil.UnmarshalJSONCaseInsensitive(v, resp.Body); err != nil {
+		return nil, err
+	}
 
-		return v, nil
+	if err := rest.UnmarshalResponse(resp, v, true); err != nil {
+		return nil, err
 	}
 
-	// fallback to unmodeled generic exceptions
-	return awserr.NewRequestFailure(
-		awserr.New(code, msg, nil),
-		respMeta.StatusCode,
-		respMeta.RequestID,
-	), nil
+	return v, nil
 }
 
 // UnmarshalErrorHandler is a named request handler for unmarshaling restjson
@@ -101,36 +78,80 @@ var UnmarshalErrorHandler = request.NamedHandler{
 func UnmarshalError(r *request.Request) {
 	defer r.HTTPResponse.Body.Close()
 
-	var jsonErr jsonErrorResponse
-	err := jsonutil.UnmarshalJSONError(&jsonErr, r.HTTPResponse.Body)
+	code, msg, err := unmarshalErrorInfo(r.HTTPResponse)
 	if err != nil {
 		r.Error = awserr.NewRequestFailure(
-			awserr.New(request.ErrCodeSerialization,
-				"failed to unmarshal response error", err),
+			awserr.New(request.ErrCodeSerialization, "failed to unmarshal response error", err),
 			r.HTTPResponse.StatusCode,
 			r.RequestID,
 		)
 		return
 	}
 
-	code := r.HTTPResponse.Header.Get(errorTypeHeader)
-	if code == "" {
-		code = jsonErr.Code
-	}
-	msg := r.HTTPResponse.Header.Get(errorMessageHeader)
-	if msg == "" {
-		msg = jsonErr.Message
-	}
-
-	code = strings.SplitN(code, ":", 2)[0]
 	r.Error = awserr.NewRequestFailure(
-		awserr.New(code, jsonErr.Message, nil),
+		awserr.New(code, msg, nil),
 		r.HTTPResponse.StatusCode,
 		r.RequestID,
 	)
 }
 
 type jsonErrorResponse struct {
+	Type    string `json:"__type"`
 	Code    string `json:"code"`
 	Message string `json:"message"`
 }
+
+func (j *jsonErrorResponse) SanitizedCode() string {
+	code := j.Code
+	if len(j.Type) > 0 {
+		code = j.Type
+	}
+	return sanitizeCode(code)
+}
+
+// Remove superfluous components from a restJson error code.
+//   - If a : character is present, then take only the contents before the
+//     first : character in the value.
+//   - If a # character is present, then take only the contents after the first
+//     # character in the value.
+//
+// All of the following error values resolve to FooError:
+//   - FooError
+//   - FooError:http://internal.amazon.com/coral/com.amazon.coral.validate/
+//   - aws.protocoltests.restjson#FooError
+//   - aws.protocoltests.restjson#FooError:http://internal.amazon.com/coral/com.amazon.coral.validate/
+func sanitizeCode(code string) string {
+	noColon := strings.SplitN(code, ":", 2)[0]
+	hashSplit := strings.SplitN(noColon, "#", 2)
+	return hashSplit[len(hashSplit)-1]
+}
+
+// attempt to garner error details from the response, preferring header values
+// when present
+func unmarshalErrorInfo(resp *http.Response) (code string, msg string, err error) {
+	code = sanitizeCode(resp.Header.Get(errorTypeHeader))
+	msg = resp.Header.Get(errorMessageHeader)
+	if len(code) > 0 && len(msg) > 0 {
+		return
+	}
+
+	// a modeled error will have to be re-deserialized later, so the body must
+	// be preserved
+	var buf bytes.Buffer
+	tee := io.TeeReader(resp.Body, &buf)
+	defer func() { resp.Body = ioutil.NopCloser(&buf) }()
+
+	var jsonErr jsonErrorResponse
+	if decodeErr := json.NewDecoder(tee).Decode(&jsonErr); decodeErr != nil && decodeErr != io.EOF {
+		err = awserr.NewUnmarshalError(decodeErr, "failed to decode response body", buf.Bytes())
+		return
+	}
+
+	if len(code) == 0 {
+		code = jsonErr.SanitizedCode()
+	}
+	if len(msg) == 0 {
+		msg = jsonErr.Message
+	}
+	return
+}