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Merged
drlucaa merged 1 commit into from
Nov 24, 2025
Merged

feat: add Metadata() method to export error context #3

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27 changes: 26 additions & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,31 @@ if zerrErr, ok := err.(*zerr.Error); ok {
}
```

### Accessing Metadata

You can access the structured metadata attached to errors using the `Metadata()` method:

```go
// Create an error with metadata
err := zerr.New("database error")
err = zerr.With(err, "table", "users")
err = zerr.With(err, "operation", "insert")
err = zerr.With(err, "user_id", 12345)

// Access metadata (requires type assertion to *zerr.Error)
if zerrErr, ok := err.(*zerr.Error); ok {
metadata := zerrErr.Metadata()
// metadata is map[string]any{"table": "users", "operation": "insert", "user_id": 12345}

// Access individual values
if table, exists := metadata["table"]; exists {
fmt.Printf("Table: %v\n", table)
}
}
```

The `Metadata()` method returns a copy of the error's metadata as a `map[string]any`. It returns an empty map if there is no metadata attached to the error. The returned map is a copy, ensuring that modifications to it do not affect the internal state of the error.

### Stack Traces

Capture stack traces easily using the global `Stack` helper.
Expand Down Expand Up @@ -136,4 +161,4 @@ paths.

## License

MIT
MIT
14 changes: 14 additions & 0 deletions zerr.go
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Expand Up @@ -133,6 +133,20 @@ func (e *Error) WithStack() *Error {
}
}

// Metadata returns a copy of the error's metadata as a map.
// Returns an empty map if there is no metadata attached to the error.
func (e *Error) Metadata() map[string]any {
if len(e.metadata) == 0 {
return make(map[string]any)
}

result := make(map[string]any, len(e.metadata))
for _, meta := range e.metadata {
result[meta.key.Value()] = meta.value
}
return result
}

// Error implements the error interface.
func (e *Error) Error() string {
if e.cause == nil {
Expand Down
74 changes: 73 additions & 1 deletion zerr_test.go
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Expand Up @@ -75,7 +75,7 @@ func TestWithMultipleMetadata(t *testing.T) {
t.Errorf("Expected 3 metadata items, got %d", len(withErr.metadata))
}

expected := map[string]interface{}{
expected := map[string]any{
"key1": "value1",
"key2": 42,
"key3": true,
Expand Down Expand Up @@ -760,3 +760,75 @@ func ExampleWith() {
fmt.Println(err.Error())
// Output: database error
}

func TestMetadata(t *testing.T) {
// Test with no metadata
testErr := New("test")
err, ok := testErr.(*Error)
if !ok {
t.Fatalf("Expected *Error type, got %T", testErr)
}

metadata := err.Metadata()
if metadata == nil {
t.Error("Metadata should not return nil")
}
if len(metadata) != 0 {
t.Errorf("Expected empty metadata, got %d items", len(metadata))
}

// Test with single metadata
withErr := err.With("key", "value")
metadata = withErr.Metadata()
if len(metadata) != 1 {
t.Errorf("Expected 1 metadata item, got %d", len(metadata))
}
if metadata["key"] != "value" {
t.Errorf("Expected metadata[key] = 'value', got %v", metadata["key"])
}

// Test with multiple metadata
multiErr := err.With("key1", "value1").With("key2", 42).With("key3", true)
metadata = multiErr.Metadata()
if len(metadata) != 3 {
t.Errorf("Expected 3 metadata items, got %d", len(metadata))
}

expected := map[string]any{
"key1": "value1",
"key2": 42,
"key3": true,
}

for key, expectedValue := range expected {
if value, exists := metadata[key]; !exists {
t.Errorf("Missing metadata key: %s", key)
} else if value != expectedValue {
t.Errorf("For key %s, expected %v, got %v", key, expectedValue, value)
}
}
}

func TestMetadataImmutability(t *testing.T) {
testErr := New("test")
err, ok := testErr.(*Error)
if !ok {
t.Fatalf("Expected *Error type, got %T", testErr)
}

withErr := err.With("key", "value")
metadata := withErr.Metadata()

// Modify the returned map
metadata["new_key"] = "new_value"
metadata["key"] = "modified_value"

// Get metadata again - should be unchanged
metadata2 := withErr.Metadata()
if metadata2["key"] != "value" {
t.Error("Metadata should be immutable - modifying returned map should not affect original")
}
if _, exists := metadata2["new_key"]; exists {
t.Error("Metadata should be immutable - adding keys to returned map should not affect original")
}
}
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