contextjson: Add context marshaler/unmarshaler

common/json/context.go

@@ -3,6 +3,8 @@
 package json
 
 import (
+	"context"
+
 	"github.com/sagernet/sing/common/json/internal/contextjson"
 )
 
@@ -21,3 +23,11 @@ type (
 	SyntaxError = json.SyntaxError
 	RawMessage  = json.RawMessage
 )
+
+type ContextMarshaler interface {
+	MarshalJSONContext(ctx context.Context) ([]byte, error)
+}
+
+type ContextUnmarshaler interface {
+	UnmarshalJSONContext(ctx context.Context, content []byte) error
+}

common/json/internal/contextjson/context.go

@@ -0,0 +1,11 @@
+package json
+
+import "context"
+
+type ContextMarshaler interface {
+	MarshalJSONContext(ctx context.Context) ([]byte, error)
+}
+
+type ContextUnmarshaler interface {
+	UnmarshalJSONContext(ctx context.Context, content []byte) error
+}

common/json/internal/contextjson/context_test.go

@@ -0,0 +1,43 @@
+package json_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/sagernet/sing/common/json/internal/contextjson"
+
+	"github.com/stretchr/testify/require"
+)
+
+type myStruct struct {
+	value string
+}
+
+func (m *myStruct) MarshalJSONContext(ctx context.Context) ([]byte, error) {
+	return json.Marshal(ctx.Value("key").(string))
+}
+
+func (m *myStruct) UnmarshalJSONContext(ctx context.Context, content []byte) error {
+	m.value = ctx.Value("key").(string)
+	return nil
+}
+
+//nolint:staticcheck
+func TestMarshalContext(t *testing.T) {
+	t.Parallel()
+	ctx := context.WithValue(context.Background(), "key", "value")
+	var s myStruct
+	b, err := json.MarshalContext(ctx, &s)
+	require.NoError(t, err)
+	require.Equal(t, []byte(`"value"`), b)
+}
+
+//nolint:staticcheck
+func TestUnmarshalContext(t *testing.T) {
+	t.Parallel()
+	ctx := context.WithValue(context.Background(), "key", "value")
+	var s myStruct
+	err := json.UnmarshalContext(ctx, []byte(`{}`), &s)
+	require.NoError(t, err)
+	require.Equal(t, "value", s.value)
+}

common/json/internal/contextjson/decode.go

@@ -8,6 +8,7 @@
 package json
 
 import (
+	"context"
 	"encoding"
 	"encoding/base64"
 	"fmt"
@@ -95,10 +96,15 @@ import (
 // Instead, they are replaced by the Unicode replacement
 // character U+FFFD.
 func Unmarshal(data []byte, v any) error {
+	return UnmarshalContext(context.Background(), data, v)
+}
+
+func UnmarshalContext(ctx context.Context, data []byte, v any) error {
 	// Check for well-formedness.
 	// Avoids filling out half a data structure
 	// before discovering a JSON syntax error.
 	var d decodeState
+	d.ctx = ctx
 	err := checkValid(data, &d.scan)
 	if err != nil {
 		return err
@@ -209,6 +215,7 @@ type errorContext struct {
 
 // decodeState represents the state while decoding a JSON value.
 type decodeState struct {
+	ctx                   context.Context
 	data                  []byte
 	off                   int // next read offset in data
 	opcode                int // last read result
@@ -428,7 +435,7 @@ func (d *decodeState) valueQuoted() any {
 // If it encounters an Unmarshaler, indirect stops and returns that.
 // If decodingNull is true, indirect stops at the first settable pointer so it
 // can be set to nil.
-func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, encoding.TextUnmarshaler, reflect.Value) {
+func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, ContextUnmarshaler, encoding.TextUnmarshaler, reflect.Value) {
 	// Issue #24153 indicates that it is generally not a guaranteed property
 	// that you may round-trip a reflect.Value by calling Value.Addr().Elem()
 	// and expect the value to still be settable for values derived from
@@ -482,11 +489,14 @@ func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, encoding.TextUnm
 		}
 		if v.Type().NumMethod() > 0 && v.CanInterface() {
 			if u, ok := v.Interface().(Unmarshaler); ok {
-				return u, nil, reflect.Value{}
+				return u, nil, nil, reflect.Value{}
+			}
+			if cu, ok := v.Interface().(ContextUnmarshaler); ok {
+				return nil, cu, nil, reflect.Value{}
 			}
 			if !decodingNull {
 				if u, ok := v.Interface().(encoding.TextUnmarshaler); ok {
-					return nil, u, reflect.Value{}
+					return nil, nil, u, reflect.Value{}
 				}
 			}
 		}
@@ -498,14 +508,14 @@ func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, encoding.TextUnm
 			v = v.Elem()
 		}
 	}
-	return nil, nil, v
+	return nil, nil, nil, v
 }
 
 // array consumes an array from d.data[d.off-1:], decoding into v.
 // The first byte of the array ('[') has been read already.
 func (d *decodeState) array(v reflect.Value) error {
 	// Check for unmarshaler.
-	u, ut, pv := indirect(v, false)
+	u, cu, ut, pv := indirect(v, false)
 	if u != nil {
 		start := d.readIndex()
 		d.skip()
@@ -515,6 +525,15 @@ func (d *decodeState) array(v reflect.Value) error {
 		}
 		return nil
 	}
+	if cu != nil {
+		start := d.readIndex()
+		d.skip()
+		err := cu.UnmarshalJSONContext(d.ctx, d.data[start:d.off])
+		if err != nil {
+			d.saveError(err)
+		}
+		return nil
+	}
 	if ut != nil {
 		d.saveError(&UnmarshalTypeError{Value: "array", Type: v.Type(), Offset: int64(d.off)})
 		d.skip()
@@ -612,7 +631,7 @@ var (
 // The first byte ('{') of the object has been read already.
 func (d *decodeState) object(v reflect.Value) error {
 	// Check for unmarshaler.
-	u, ut, pv := indirect(v, false)
+	u, cu, ut, pv := indirect(v, false)
 	if u != nil {
 		start := d.readIndex()
 		d.skip()
@@ -622,6 +641,15 @@ func (d *decodeState) object(v reflect.Value) error {
 		}
 		return nil
 	}
+	if cu != nil {
+		start := d.readIndex()
+		d.skip()
+		err := cu.UnmarshalJSONContext(d.ctx, d.data[start:d.off])
+		if err != nil {
+			d.saveError(err)
+		}
+		return nil
+	}
 	if ut != nil {
 		d.saveError(&UnmarshalTypeError{Value: "object", Type: v.Type(), Offset: int64(d.off)})
 		d.skip()
@@ -870,14 +898,21 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		return nil
 	}
 	isNull := item[0] == 'n' // null
-	u, ut, pv := indirect(v, isNull)
+	u, cu, ut, pv := indirect(v, isNull)
 	if u != nil {
 		err := u.UnmarshalJSON(item)
 		if err != nil {
 			d.saveError(err)
 		}
 		return nil
 	}
+	if cu != nil {
+		err := cu.UnmarshalJSONContext(d.ctx, item)
+		if err != nil {
+			d.saveError(err)
+		}
+		return nil
+	}
 	if ut != nil {
 		if item[0] != '"' {
 			if fromQuoted {

common/json/internal/contextjson/encode.go

@@ -12,6 +12,7 @@ package json
 
 import (
 	"bytes"
+	"context"
 	"encoding"
 	"encoding/base64"
 	"fmt"
@@ -156,7 +157,11 @@ import (
 // handle them. Passing cyclic structures to Marshal will result in
 // an error.
 func Marshal(v any) ([]byte, error) {
-	e := newEncodeState()
+	return MarshalContext(context.Background(), v)
+}
+
+func MarshalContext(ctx context.Context, v any) ([]byte, error) {
+	e := newEncodeState(ctx)
 	defer encodeStatePool.Put(e)
 
 	err := e.marshal(v, encOpts{escapeHTML: true})
@@ -251,6 +256,7 @@ var hex = "0123456789abcdef"
 type encodeState struct {
 	bytes.Buffer // accumulated output
 
+	ctx context.Context
 	// Keep track of what pointers we've seen in the current recursive call
 	// path, to avoid cycles that could lead to a stack overflow. Only do
 	// the relatively expensive map operations if ptrLevel is larger than
@@ -264,7 +270,7 @@ const startDetectingCyclesAfter = 1000
 
 var encodeStatePool sync.Pool
 
-func newEncodeState() *encodeState {
+func newEncodeState(ctx context.Context) *encodeState {
 	if v := encodeStatePool.Get(); v != nil {
 		e := v.(*encodeState)
 		e.Reset()
@@ -274,7 +280,7 @@ func newEncodeState() *encodeState {
 		e.ptrLevel = 0
 		return e
 	}
-	return &encodeState{ptrSeen: make(map[any]struct{})}
+	return &encodeState{ctx: ctx, ptrSeen: make(map[any]struct{})}
 }
 
 // jsonError is an error wrapper type for internal use only.
@@ -371,8 +377,9 @@ func typeEncoder(t reflect.Type) encoderFunc {
 }
 
 var (
-	marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
-	textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
+	marshalerType        = reflect.TypeOf((*Marshaler)(nil)).Elem()
+	contextMarshalerType = reflect.TypeOf((*ContextMarshaler)(nil)).Elem()
+	textMarshalerType    = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
 )
 
 // newTypeEncoder constructs an encoderFunc for a type.
@@ -385,9 +392,15 @@ func newTypeEncoder(t reflect.Type, allowAddr bool) encoderFunc {
 	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(marshalerType) {
 		return newCondAddrEncoder(addrMarshalerEncoder, newTypeEncoder(t, false))
 	}
+	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(contextMarshalerType) {
+		return newCondAddrEncoder(addrContextMarshalerEncoder, newTypeEncoder(t, false))
+	}
 	if t.Implements(marshalerType) {
 		return marshalerEncoder
 	}
+	if t.Implements(contextMarshalerType) {
+		return contextMarshalerEncoder
+	}
 	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(textMarshalerType) {
 		return newCondAddrEncoder(addrTextMarshalerEncoder, newTypeEncoder(t, false))
 	}
@@ -470,6 +483,47 @@ func addrMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	}
 }
 
+func contextMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
+	if v.Kind() == reflect.Pointer && v.IsNil() {
+		e.WriteString("null")
+		return
+	}
+	m, ok := v.Interface().(ContextMarshaler)
+	if !ok {
+		e.WriteString("null")
+		return
+	}
+	b, err := m.MarshalJSONContext(e.ctx)
+	if err == nil {
+		e.Grow(len(b))
+		out := availableBuffer(&e.Buffer)
+		out, err = appendCompact(out, b, opts.escapeHTML)
+		e.Buffer.Write(out)
+	}
+	if err != nil {
+		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})
+	}
+}
+
+func addrContextMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
+	va := v.Addr()
+	if va.IsNil() {
+		e.WriteString("null")
+		return
+	}
+	m := va.Interface().(ContextMarshaler)
+	b, err := m.MarshalJSONContext(e.ctx)
+	if err == nil {
+		e.Grow(len(b))
+		out := availableBuffer(&e.Buffer)
+		out, err = appendCompact(out, b, opts.escapeHTML)
+		e.Buffer.Write(out)
+	}
+	if err != nil {
+		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})
+	}
+}
+
 func textMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	if v.Kind() == reflect.Pointer && v.IsNil() {
 		e.WriteString("null")
@@ -827,7 +881,7 @@ func newSliceEncoder(t reflect.Type) encoderFunc {
 	// Byte slices get special treatment; arrays don't.
 	if t.Elem().Kind() == reflect.Uint8 {
 		p := reflect.PointerTo(t.Elem())
-		if !p.Implements(marshalerType) && !p.Implements(textMarshalerType) {
+		if !p.Implements(marshalerType) && !p.Implements(contextMarshalerType) && !p.Implements(textMarshalerType) {
 			return encodeByteSlice
 		}
 	}

common/json/internal/contextjson/stream.go

@@ -6,6 +6,7 @@ package json
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"io"
 )
@@ -29,7 +30,11 @@ type Decoder struct {
 // The decoder introduces its own buffering and may
 // read data from r beyond the JSON values requested.
 func NewDecoder(r io.Reader) *Decoder {
-	return &Decoder{r: r}
+	return NewDecoderContext(context.Background(), r)
+}
+
+func NewDecoderContext(ctx context.Context, r io.Reader) *Decoder {
+	return &Decoder{r: r, d: decodeState{ctx: ctx}}
 }
 
 // UseNumber causes the Decoder to unmarshal a number into an interface{} as a
@@ -183,6 +188,7 @@ func nonSpace(b []byte) bool {
 
 // An Encoder writes JSON values to an output stream.
 type Encoder struct {
+	ctx        context.Context
 	w          io.Writer
 	err        error
 	escapeHTML bool
@@ -194,7 +200,11 @@ type Encoder struct {
 
 // NewEncoder returns a new encoder that writes to w.
 func NewEncoder(w io.Writer) *Encoder {
-	return &Encoder{w: w, escapeHTML: true}
+	return NewEncoderContext(context.Background(), w)
+}
+
+func NewEncoderContext(ctx context.Context, w io.Writer) *Encoder {
+	return &Encoder{ctx: ctx, w: w, escapeHTML: true}
 }
 
 // Encode writes the JSON encoding of v to the stream,
@@ -207,7 +217,7 @@ func (enc *Encoder) Encode(v any) error {
 		return enc.err
 	}
 
-	e := newEncodeState()
+	e := newEncodeState(enc.ctx)
 	defer encodeStatePool.Put(e)
 
 	err := e.marshal(v, encOpts{escapeHTML: enc.escapeHTML})