Improves ParseError response when server response is an unknown json

CHANGELOG.md

@@ -48,6 +48,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Fixes wrong response parsing for security get requests ([#572](https://github.com/opensearch-project/opensearch-go/pull/572))
 - Fixes opensearchtransport ignores request context cancellation when `retryBackoff` is configured ([#540](https://github.com/opensearch-project/opensearch-go/pull/540))
 - Fixes opensearchtransport sleeps unexpectedly after the last retry ([#540](https://github.com/opensearch-project/opensearch-go/pull/540))
+- Improves ParseError response when server response is an unknown json ([#592](https://github.com/opensearch-project/opensearch-go/pull/592))
 
 ### Security
 

UPGRADING.md

@@ -11,6 +11,46 @@
 
 # Upgrading Opensearch GO Client
 
+## Upgrading to >= 5.0.0
+Version 5.0.0 returns `*opensearch.StringError` error type instead of `*fmt.wrapError` when response received from the server is an unknown JSON. For example, consider delete document API which returns an unknown JSON body when document is not found.
+
+Before 5.0.0:
+```go
+docDelResp, err = client.Document.Delete(ctx, opensearchapi.DocumentDeleteReq{Index: "movies", DocumentID: "3"})
+if err != nil {
+	fmt.Println(err)
+
+	if !errors.Is(err, opensearch.ErrJSONUnmarshalBody) && docDelResp != nil {
+		resp := docDelResp.Inspect().Response
+		// get http status
+		fmt.Println(resp.StatusCode)
+		body := strings.TrimPrefix(err.Error(), "opensearch error response could not be parsed as error: ")
+		errResp := opensearchapi.DocumentDeleteResp{}
+		json.Unmarshal([]byte(body), &errResp) 
+		// extract result field from the body 
+		fmt.Println(errResp.Result)
+	}
+}
+```
+
+After 5.0.0:
+```go
+docDelResp, err = client.Document.Delete(ctx, opensearchapi.DocumentDeleteReq{Index: "movies", DocumentID: "3"})
+if err != nil {
+	// parse into *opensearch.StringError
+	var myStringErr *opensearch.StringError
+	if errors.As(err, &myStringErr) {
+		// get http status
+		fmt.Println(myStringErr.Status)
+		errResp := opensearchapi.DocumentDeleteResp{}
+		json.Unmarshal([]byte(myStringErr.Err), &errResp)
+		// extract result field from the body
+		fmt.Println(errResp.Result)
+	}
+}
+```
+
+
 ## Upgrading to >= 4.0.0
 
 Version 4.0.0 moved the error types, added with 3.0.0, from opensearchapi to opensearch, renamed them and added new error types.

error.go

@@ -175,7 +175,7 @@ func ParseError(resp *Response) error {
 		return parseError(body, &apiError)
 	}
 
-	return fmt.Errorf("%w: %s", ErrUnknownOpensearchError, string(body))
+	return &StringError{Status: resp.StatusCode, Err: string(body)}
 }
 
 func parseError(body []byte, errStruct error) error {

error_test.go

@@ -120,6 +120,22 @@ func TestError(t *testing.T) {
 		_ = fmt.Sprintf("%s", testError)
 	})
 
+	t.Run("StringErrorUnknownJSON", func(t *testing.T) {
+		resp := &opensearch.Response{
+			StatusCode: http.StatusNotFound,
+			Body: io.NopCloser(
+				strings.NewReader(`{"_index":"index","_id":"2","matched":false}`),
+			),
+		}
+		assert.True(t, resp.IsError())
+		err := opensearch.ParseError(resp)
+		var testError *opensearch.StringError
+		require.True(t, errors.As(err, &testError))
+		assert.Equal(t, http.StatusNotFound, testError.Status)
+		assert.Contains(t, testError.Err, "{\"_index\":\"index\",\"_id\":\"2\",\"matched\":false}")
+		_ = fmt.Sprintf("%s", testError)
+	})
+
 	t.Run("Error", func(t *testing.T) {
 		resp := &opensearch.Response{
 			StatusCode: http.StatusBadRequest,
@@ -189,14 +205,6 @@ func TestError(t *testing.T) {
 				},
 				WantedErrors: []error{opensearch.ErrJSONUnmarshalBody, opensearch.ErrUnknownOpensearchError},
 			},
-			{
-				Name: "unknown json",
-				Resp: &opensearch.Response{
-					StatusCode: http.StatusNotFound,
-					Body:       io.NopCloser(strings.NewReader(`{"_index":"index","_id":"2","matched":false}`)),
-				},
-				WantedErrors: []error{opensearch.ErrUnknownOpensearchError},
-			},
 			{
 				Name: "io read error",
 				Resp: &opensearch.Response{