Merge pull request #13 from mittwald/feat/catch-validation-errors

feat: catch validation errors explicitly, and expose their response body

Author: martin-helmich

README.md

@@ -30,6 +30,8 @@ import "github.com/mittwald/api-client-go/mittwaldv2"
 
 ## Usage
 
+### Initialization and authentication
+
 Use the `mittwaldv2.New` function to instantiate a new client:
 
 ```go
@@ -59,6 +61,26 @@ Other options include:
 Have a look at our [API introduction][api-getting-started] for more information
 on how to obtain an API token and how to get started with the API.
 
+### Error handling
+
+Each API call returns a response object and an error. The response object contains the HTTP status code and the response body, which can be used to check for errors.
+
+Some error conditions are also mapped to specific Go error types that you can check for:
+
+- `httperr.ErrValidation` for validation errors
+- `httperr.ErrBadRequest` for 400 errors (except for validation errors)
+- `httperr.ErrNotFound` for 404 errors
+- `httperr.ErrPermissionDenied` for 403 errors
+
+Use `errors.As` to check for these errors:
+
+```go
+projects, res, err := client.Projects().ListProjects(ctx, req)
+if validationError := new(httperr.ErrValidation); errors.As(err, &validationError) {
+	// ...
+}
+```
+
 ## Example
 
 ```go

pkg/httperr/bad_request_error.go

@@ -0,0 +1,18 @@
+package httperr
+
+import (
+	"fmt"
+	"net/http"
+)
+
+// ErrBadRequest represents the error of an invalid request to the server.
+type ErrBadRequest struct {
+	Response *http.Response
+}
+
+func (e *ErrBadRequest) Error() string {
+	if e == nil || e.Response == nil {
+		return "bad request: <nil>"
+	}
+	return fmt.Sprintf("bad request: %s", e.Response.Request.URL)
+}

pkg/httperr/from_response.go

@@ -1,6 +1,8 @@
 package httperr
 
-import "net/http"
+import (
+	"net/http"
+)
 
 // ErrFromResponse maps an HTTP response (with an error status code) to a (more
 // or less) specific error type.
@@ -10,6 +12,11 @@ func ErrFromResponse(res *http.Response) error {
 		return &ErrNotFound{Response: res}
 	case http.StatusForbidden:
 		return &ErrPermissionDenied{Response: res}
+	case http.StatusBadRequest:
+		if validationError, isValidationError := IsValidationErrorResponse(res); isValidationError {
+			return &ErrValidation{Response: res, ValidationError: validationError}
+		}
+		return &ErrBadRequest{Response: res}
 	default:
 		return &ErrUnexpectedResponse{Response: res}
 	}

pkg/httperr/validation_error.go

@@ -0,0 +1,35 @@
+package httperr
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/mittwald/api-client-go/mittwaldv2/generated/schemas/commonsv2"
+	"net/http"
+)
+
+func IsValidationErrorResponse(res *http.Response) (*commonsv2.ValidationErrors, bool) {
+	target := commonsv2.ValidationErrors{}
+
+	if err := json.NewDecoder(res.Body).Decode(&target); err != nil {
+		return nil, false
+	}
+
+	if target.Type != commonsv2.ValidationErrorsTypeValidationError {
+		return nil, false
+	}
+
+	return &target, true
+}
+
+// ErrValidation represents a validation error response from the server.
+type ErrValidation struct {
+	Response        *http.Response
+	ValidationError *commonsv2.ValidationErrors
+}
+
+func (e *ErrValidation) Error() string {
+	if e.ValidationError != nil && e.ValidationError.Message != nil {
+		return fmt.Sprintf("invalid request: %s", *e.ValidationError.Message)
+	}
+	return "invalid request: <nil>"
+}