aws: add de/serialization typed error to the SDK (aws#514)

* Adds HTTP based de/serialization typed error
* This PR doesn't replace the old usages of Err codes for de/serialization error.
* The serialization/ deserialization error types are generic, and not transport specific. This conforms with layered error design discussed.

aws/request.go

@@ -24,6 +24,33 @@ const (
 	ErrCodeRead = "ReadError"
 )
 
+// SerializationError provides a generic request serialization error
+type SerializationError struct {
+	Err error // original error
+}
+
+// Error returns a formatted error for SerializationError
+func (e *SerializationError) Error() string {
+	return fmt.Sprintf("serialization failed: %v", e.Err)
+}
+
+// Unwrap returns the underlying Error in DeserializationError
+func (e *SerializationError) Unwrap() error { return e.Err }
+
+// DeserializationError provides a HTTP transport specific
+// request deserialization error
+type DeserializationError struct {
+	Err error //  original error
+}
+
+// Error returns a formatted error for DeserializationError
+func (e *DeserializationError) Error() string {
+	return fmt.Sprintf("deserialization failed, %v", e.Err)
+}
+
+// Unwrap returns the underlying Error in DeserializationError
+func (e *DeserializationError) Unwrap() error { return e.Err }
+
 // RequestSendError provides a generic request transport error.
 type RequestSendError struct {
 	Response interface{}

aws/typed_error_test.go

@@ -0,0 +1,112 @@
+package aws_test
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/internal/sdkio"
+	"github.com/aws/aws-sdk-go-v2/private/protocol/json/jsonutil"
+)
+
+type mockOP struct {
+	Message *string `locationName:"message" type:"string"`
+}
+
+type mockUnmarshaler struct {
+	output *mockOP
+}
+
+const correctResponse = `{"message": "Hello"}`
+const responseWithMissingDelimiter = `"message": "Hello"}`
+const invalidResponse = `{"message": true}`
+
+func TestHTTPDeserializationError(t *testing.T) {
+	cases := map[string]struct {
+		responseBody   string
+		responseStatus int
+		requestID      string
+		errorIsSet     bool
+	}{
+		"No error": {
+			responseBody:   correctResponse,
+			requestID:      "mockReqID",
+			responseStatus: 200,
+		},
+		"Missing delimiter": {
+			responseBody:   responseWithMissingDelimiter,
+			errorIsSet:     true,
+			requestID:      "mockReqID",
+			responseStatus: 200,
+		},
+		"Invalid response": {
+			responseBody:   invalidResponse,
+			errorIsSet:     true,
+			requestID:      "mockReqID",
+			responseStatus: 200,
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			r := &aws.Request{
+				HTTPResponse: &http.Response{
+					StatusCode: 200,
+					Body:       ioutil.NopCloser(bytes.NewReader([]byte(c.responseBody))),
+				},
+				RequestID: "mockReqID",
+			}
+
+			u := mockUnmarshaler{
+				output: &mockOP{},
+			}
+			// unmarshal request response
+			u.unmarshalOperation(r)
+
+			if c.errorIsSet {
+				if r.Error == nil {
+					t.Fatal("Expected error, got none")
+				}
+				if r.Error == nil {
+					t.Fatal("Expected error, got none")
+				}
+				var e *aws.DeserializationError
+				if errors.As(r.Error, &e) {
+					if e, a := c.responseBody, e.Unwrap().Error(); !strings.Contains(a, e) {
+						t.Fatalf("Expected response body to contain %v, got %v", e, a)
+					}
+				} else {
+					t.Fatalf("Expected error to be of type %T, got %T", e, r.Error)
+				}
+			} else {
+				if r.Error != nil {
+					t.Fatalf("Expected no error, got %v", r.Error)
+				}
+			}
+		})
+	}
+}
+
+// unmarshal operation unmarshal's request response
+func (u *mockUnmarshaler) unmarshalOperation(r *aws.Request) {
+	b := make([]byte, 1024)
+	ringbuffer := sdkio.NewRingBuffer(b)
+	// wraps ring buffer around the response body
+	body := io.TeeReader(r.HTTPResponse.Body, ringbuffer)
+
+	// If unmarshaling function returns an error, it is a deserialization error
+	if err := jsonutil.UnmarshalJSON(u.output, body); err != nil {
+		snapshot := make([]byte, 1024)
+		ringbuffer.Read(snapshot)
+		r.Error = &aws.DeserializationError{
+			Err: fmt.Errorf("unable to deserialize Json payload: %w.\n"+
+				"Here's a snapshot of response being deserialized: %s", err, snapshot),
+		}
+	}
+}