internal/json: replace segmentio/encoding with encoding/json/v2

.github/workflows/test.yml

@@ -40,7 +40,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: ["1.25", "1.26"]
+        go: ["1.26", "1.27"]
     steps:
       - name: Check out code
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1

go.mod

@@ -1,20 +1,15 @@
 module github.com/modelcontextprotocol/go-sdk
 
-go 1.25.0
+go 1.26
 
 require (
+	github.com/go-json-experiment/json v0.0.0-20260820222146-c27c302e5fc3
 	github.com/golang-jwt/jwt/v5 v5.3.1
 	github.com/google/go-cmp v0.7.0
 	github.com/google/jsonschema-go v0.4.3
-	github.com/segmentio/encoding v0.5.4
 	github.com/yosida95/uritemplate/v3 v3.0.2
 	golang.org/x/oauth2 v0.35.0
+	golang.org/x/sync v0.20.0
 	golang.org/x/time v0.15.0
 	golang.org/x/tools v0.42.0
 )
-
-require (
-	github.com/segmentio/asm v1.1.3 // indirect
-	golang.org/x/sync v0.20.0 // indirect
-	golang.org/x/sys v0.41.0 // indirect
-)

go.sum

@@ -1,21 +1,17 @@
+github.com/go-json-experiment/json v0.0.0-20260820222146-c27c302e5fc3 h1:UADEEmDKgfXbtnGJZ97beY5XLo9ZechG1nlU4KnRrkE=
+github.com/go-json-experiment/json v0.0.0-20260820222146-c27c302e5fc3/go.mod h1:tphK2c80bpPhMOI4v6bIc2xWywPfbqi1Z06+RcrMkDg=
 github.com/golang-jwt/jwt/v5 v5.3.1 h1:kYf81DTWFe7t+1VvL7eS+jKFVWaUnK9cB1qbwn63YCY=
 github.com/golang-jwt/jwt/v5 v5.3.1/go.mod h1:fxCRLWMO43lRc8nhHWY6LGqRcf+1gQWArsqaEUEa5bE=
 github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
 github.com/google/jsonschema-go v0.4.3 h1:/DBOLZTfDow7pe2GmaJNhltueGTtDKICi8V8p+DQPd0=
 github.com/google/jsonschema-go v0.4.3/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
-github.com/segmentio/asm v1.1.3 h1:WM03sfUOENvvKexOLp+pCqgb/WDjsi7EK8gIsICtzhc=
-github.com/segmentio/asm v1.1.3/go.mod h1:Ld3L4ZXGNcSLRg4JBsZ3//1+f/TjYl0Mzen/DQy1EJg=
-github.com/segmentio/encoding v0.5.4 h1:OW1VRern8Nw6ITAtwSZ7Idrl3MXCFwXHPgqESYfvNt0=
-github.com/segmentio/encoding v0.5.4/go.mod h1:HS1ZKa3kSN32ZHVZ7ZLPLXWvOVIiZtyJnO1gPH1sKt0=
 github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
 github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
 golang.org/x/oauth2 v0.35.0 h1:Mv2mzuHuZuY2+bkyWXIHMfhNdJAdwW3FuWeCPYN5GVQ=
 golang.org/x/oauth2 v0.35.0/go.mod h1:lzm5WQJQwKZ3nwavOZ3IS5Aulzxi68dUSgRHujetwEA=
 golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
 golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
-golang.org/x/sys v0.41.0 h1:Ivj+2Cp/ylzLiEU89QhWblYnOE9zerudt9Ftecq2C6k=
-golang.org/x/sys v0.41.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
 golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=
 golang.org/x/tools v0.42.0 h1:uNgphsn75Tdz5Ji2q36v/nsFSfR/9BRFvqhGBaJGd5k=

internal/json/json.go

@@ -8,10 +8,15 @@ package json
 
 import (
 	"bytes"
+	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
+	"reflect"
 
-	"github.com/segmentio/encoding/json"
+	jsonv2 "github.com/go-json-experiment/json"
+	"github.com/go-json-experiment/json/jsontext"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 )
 
 // defaultMaxDepth is the maximum JSON nesting depth accepted by [Unmarshal].
@@ -23,18 +28,42 @@ const defaultMaxDepth = 1000
 // errMaxDepthExceeded is returned by [Unmarshal] when the input nests deeper than [defaultMaxDepth].
 var errMaxDepthExceeded = fmt.Errorf("json: exceeded maximum nesting depth of %d", defaultMaxDepth)
 
+var caseSensitiveV1 = jsonv2.JoinOptions(
+	jsonv1.DefaultOptionsV1(),
+	jsonv2.MatchCaseInsensitiveNames(false),
+)
+
+// caseSensitiveV1UseNumber adds UseNumber, which v2 has no option for: a JSON
+// number decoded into an any becomes a json.Number, so large IDs stay exact.
+var caseSensitiveV1UseNumber = jsonv2.JoinOptions(
+	caseSensitiveV1,
+	jsonv2.WithUnmarshalers(jsonv2.UnmarshalFromFunc(func(dec *jsontext.Decoder, v *any) error {
+		if dec.PeekKind() != '0' {
+			return errors.ErrUnsupported
+		}
+		if p := reflect.ValueOf(*v); p.Kind() == reflect.Pointer && !p.IsNil() {
+			return errors.ErrUnsupported
+		}
+		val, err := dec.ReadValue()
+		if err != nil {
+			return err
+		}
+		*v = json.Number(string(val))
+		return nil
+	})),
+)
+
 type Decoder struct {
-	dec *json.Decoder
+	dec  *jsontext.Decoder
+	opts jsonv2.Options
 }
 
 func NewDecoder(r io.Reader) *Decoder {
-	dec := json.NewDecoder(r)
-	dec.DontMatchCaseInsensitiveStructFields()
-	return &Decoder{dec: dec}
+	return &Decoder{dec: jsontext.NewDecoder(r), opts: caseSensitiveV1}
 }
 
 func (d *Decoder) Decode(v any) error {
-	return d.dec.Decode(v)
+	return jsonv2.UnmarshalDecode(d.dec, v, d.opts)
 }
 
 func Unmarshal(data []byte, v any) error {
@@ -44,12 +73,14 @@ func Unmarshal(data []byte, v any) error {
 	return NewDecoder(bytes.NewReader(data)).Decode(v)
 }
 
+func (d *Decoder) UseNumber() { d.opts = caseSensitiveV1UseNumber }
+
 func UnmarshalUseNumber(data []byte, v any) error {
 	if err := checkMaxDepth(data, defaultMaxDepth); err != nil {
 		return err
 	}
 	dec := NewDecoder(bytes.NewReader(data))
-	dec.dec.UseNumber()
+	dec.UseNumber()
 	return dec.Decode(v)
 }