feat: add IsCaseInsensitive

context.go

@@ -0,0 +1,17 @@
+package query
+
+import "context"
+
+var caseInsensitiveKey = struct{}{}
+
+func withCaseInsensitive(ctx context.Context, b bool) context.Context {
+	return context.WithValue(ctx, caseInsensitiveKey, b)
+}
+
+// IsCaseInsensitive reports whether case-insensitive querying is enabled or not.
+func IsCaseInsensitive(ctx context.Context) bool {
+	if b, ok := ctx.Value(caseInsensitiveKey).(bool); ok {
+		return b
+	}
+	return false
+}

key.go

@@ -1,6 +1,7 @@
 package query
 
 import (
+	"context"
 	"reflect"
 	"strings"
 )
@@ -13,6 +14,14 @@ type KeyExtractor interface {
 	ExtractByKey(key string) (interface{}, bool)
 }
 
+// KeyExtractorContext is the interface that wraps the ExtractByKey method.
+//
+// ExtractByKey extracts the value by key.
+// It reports whether the key is found and returns the found value.
+type KeyExtractorContext interface {
+	ExtractByKey(ctx context.Context, key string) (any, bool)
+}
+
 // Key represents an extractor to access the value by key.
 type Key struct {
 	key             string
@@ -28,6 +37,11 @@ type Key struct {
 // If v implements the KeyExtractor interface, this method extracts by calling v.ExtractByKey.
 func (e *Key) Extract(v reflect.Value) (reflect.Value, bool) {
 	if v.IsValid() {
+		if i, ok := v.Interface().(KeyExtractorContext); ok {
+			ctx := withCaseInsensitive(context.Background(), e.caseInsensitive)
+			x, ok := i.ExtractByKey(ctx, e.key)
+			return reflect.ValueOf(x), ok
+		}
 		if i, ok := v.Interface().(KeyExtractor); ok {
 			x, ok := i.ExtractByKey(e.key)
 			return reflect.ValueOf(x), ok

key_test.go

@@ -1,8 +1,10 @@
 package query
 
 import (
+	"context"
 	"net/http"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -19,6 +21,27 @@ func (f *keyExtractor) ExtractByKey(_ string) (interface{}, bool) {
 	return nil, false
 }
 
+type keyExtractorContext struct {
+	v map[string]any
+}
+
+func (f *keyExtractorContext) ExtractByKey(ctx context.Context, name string) (interface{}, bool) {
+	if f.v != nil {
+		if v, ok := f.v[name]; ok {
+			return v, true
+		}
+		if IsCaseInsensitive(ctx) {
+			name = strings.ToLower(name)
+			for k, v := range f.v {
+				if strings.ToLower(k) == name {
+					return v, true
+				}
+			}
+		}
+	}
+	return nil, false
+}
+
 type testTags struct {
 	FooBar string `json:"foo_bar" yaml:"fooBar,omitempty"`
 	AnonymousField
@@ -160,6 +183,16 @@ func TestKey_Extract(t *testing.T) {
 				v:      &keyExtractor{v: "value"},
 				expect: "value",
 			},
+			"key extractor context": {
+				key:             "key",
+				caseInsensitive: true,
+				v: &keyExtractorContext{
+					v: map[string]any{
+						"KEY": "value",
+					},
+				},
+				expect: "value",
+			},
 		}
 		for name, test := range tests {
 			test := test
@@ -249,6 +282,14 @@ func TestKey_Extract(t *testing.T) {
 					},
 				},
 			},
+			"key extractor context (case sensitive)": {
+				key: "key",
+				v: &keyExtractorContext{
+					v: map[string]any{
+						"KEY": "value",
+					},
+				},
+			},
 		}
 		for name, test := range tests {
 			test := test