fix(message): json version detection

message.go

@@ -23,6 +23,7 @@ import (
 
 	bin "github.com/gagliardetto/binary"
 	"github.com/gagliardetto/treeout"
+	jsoniter "github.com/json-iterator/go"
 
 	"github.com/gagliardetto/solana-go/text"
 )
@@ -195,42 +196,69 @@ func (mx *Message) NumWritableLookups() int {
 func (mx Message) MarshalJSON() ([]byte, error) {
 	if mx.version == MessageVersionLegacy {
 		out := struct {
-			AccountKeys     []string              `json:"accountKeys"`
+			AccountKeys     PublicKeySlice        `json:"accountKeys"`
 			Header          MessageHeader         `json:"header"`
-			RecentBlockhash string                `json:"recentBlockhash"`
+			RecentBlockhash Hash                  `json:"recentBlockhash"`
 			Instructions    []CompiledInstruction `json:"instructions"`
 		}{
-			AccountKeys:     make([]string, len(mx.AccountKeys)),
+			AccountKeys:     mx.AccountKeys,
 			Header:          mx.Header,
-			RecentBlockhash: mx.RecentBlockhash.String(),
+			RecentBlockhash: mx.RecentBlockhash,
 			Instructions:    mx.Instructions,
 		}
-		for i, key := range mx.AccountKeys {
-			out.AccountKeys[i] = key.String()
-		}
 		return json.Marshal(out)
 	}
 	// Versioned message:
+	lookups := mx.AddressTableLookups
+	if lookups == nil {
+		lookups = MessageAddressTableLookupSlice{}
+	}
 	out := struct {
-		AccountKeys         []string                    `json:"accountKeys"`
-		Header              MessageHeader               `json:"header"`
-		RecentBlockhash     string                      `json:"recentBlockhash"`
-		Instructions        []CompiledInstruction       `json:"instructions"`
-		AddressTableLookups []MessageAddressTableLookup `json:"addressTableLookups"`
+		AccountKeys         PublicKeySlice                 `json:"accountKeys"`
+		Header              MessageHeader                  `json:"header"`
+		RecentBlockhash     Hash                           `json:"recentBlockhash"`
+		Instructions        []CompiledInstruction          `json:"instructions"`
+		AddressTableLookups MessageAddressTableLookupSlice `json:"addressTableLookups"`
 	}{
-		AccountKeys:         make([]string, len(mx.AccountKeys)),
+		AccountKeys:         mx.AccountKeys,
 		Header:              mx.Header,
-		RecentBlockhash:     mx.RecentBlockhash.String(),
+		RecentBlockhash:     mx.RecentBlockhash,
 		Instructions:        mx.Instructions,
-		AddressTableLookups: mx.AddressTableLookups,
+		AddressTableLookups: lookups,
 	}
-	for i, key := range mx.AccountKeys {
-		out.AccountKeys[i] = key.String()
+	return json.Marshal(out)
+}
+
+// UnmarshalJSON decodes the message from JSON and determines its version.
+// The Solana RPC emits `addressTableLookups` only for versioned (V0+)
+// messages; its presence in the JSON is what distinguishes V0 from legacy,
+// since the private `version` field has no wire representation.
+func (mx *Message) UnmarshalJSON(data []byte) error {
+	// Decode `addressTableLookups` via a RawMessage pointer so presence of the
+	// key can be detected in a single parse. A non-nil pointer means the key
+	// was present in the JSON (even if its value is `null`), which selects V0.
+	aux := struct {
+		AccountKeys         PublicKeySlice        `json:"accountKeys"`
+		Header              MessageHeader         `json:"header"`
+		RecentBlockhash     Hash                  `json:"recentBlockhash"`
+		Instructions        []CompiledInstruction `json:"instructions"`
+		AddressTableLookups *jsoniter.RawMessage  `json:"addressTableLookups"`
+	}{}
+	if err := json.Unmarshal(data, &aux); err != nil {
+		return err
 	}
-	if out.AddressTableLookups == nil {
-		out.AddressTableLookups = make([]MessageAddressTableLookup, 0)
+	mx.AccountKeys = aux.AccountKeys
+	mx.Header = aux.Header
+	mx.RecentBlockhash = aux.RecentBlockhash
+	mx.Instructions = aux.Instructions
+
+	if aux.AddressTableLookups == nil {
+		mx.version = MessageVersionLegacy
+		mx.AddressTableLookups = nil
+		return nil
 	}
-	return json.Marshal(out)
+	mx.version = MessageVersionV0
+	return json.Unmarshal(*aux.AddressTableLookups, &mx.AddressTableLookups)
 }
 
 func (mx *Message) EncodeToTree(txTree treeout.Branches) {

message_test.go

@@ -1233,6 +1233,72 @@ func TestHasDuplicates_Loaded(t *testing.T) {
 	})
 }
 
+// Regression test for https://github.com/solana-foundation/solana-go/issues/339:
+// when decoding an RPC response with `encoding: json`, the Message version was
+// always left as Legacy because the private `version` field has no JSON tag.
+// The presence of `addressTableLookups` in the raw JSON now selects V0.
+func TestMessageJSONVersionDetection(t *testing.T) {
+	legacyJSON := []byte(`{
+		"accountKeys": ["11111111111111111111111111111111"],
+		"header": {"numRequiredSignatures":1,"numReadonlySignedAccounts":0,"numReadonlyUnsignedAccounts":0},
+		"recentBlockhash": "11111111111111111111111111111111",
+		"instructions": []
+	}`)
+	v0JSON := []byte(`{
+		"accountKeys": ["11111111111111111111111111111111"],
+		"header": {"numRequiredSignatures":1,"numReadonlySignedAccounts":0,"numReadonlyUnsignedAccounts":0},
+		"recentBlockhash": "11111111111111111111111111111111",
+		"instructions": [],
+		"addressTableLookups": []
+	}`)
+
+	var legacy Message
+	require.NoError(t, json.Unmarshal(legacyJSON, &legacy))
+	assert.Equal(t, MessageVersionLegacy, legacy.GetVersion())
+	assert.False(t, legacy.IsVersioned())
+
+	var versioned Message
+	require.NoError(t, json.Unmarshal(v0JSON, &versioned))
+	assert.Equal(t, MessageVersionV0, versioned.GetVersion())
+	assert.True(t, versioned.IsVersioned())
+}
+
+// TestMessageJSONVersionRoundtrip ensures MarshalJSON/UnmarshalJSON preserve
+// the message version across the round-trip.
+func TestMessageJSONVersionRoundtrip(t *testing.T) {
+	blockhash := Hash{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
+		17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32}
+
+	for _, tc := range []struct {
+		name    string
+		version MessageVersion
+		lookups MessageAddressTableLookupSlice
+	}{
+		{"legacy", MessageVersionLegacy, nil},
+		{"v0_no_lookups", MessageVersionV0, nil},
+		{"v0_with_lookups", MessageVersionV0, MessageAddressTableLookupSlice{
+			{AccountKey: newUniqueKey(), WritableIndexes: []uint8{0, 1}, ReadonlyIndexes: []uint8{2}},
+		}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			original := Message{
+				version:             tc.version,
+				Header:              MessageHeader{NumRequiredSignatures: 1},
+				AccountKeys:         PublicKeySlice{newUniqueKey()},
+				RecentBlockhash:     blockhash,
+				Instructions:        []CompiledInstruction{},
+				AddressTableLookups: tc.lookups,
+			}
+			data, err := json.Marshal(original)
+			require.NoError(t, err)
+
+			var decoded Message
+			require.NoError(t, json.Unmarshal(data, &decoded))
+			assert.Equal(t, tc.version, decoded.GetVersion())
+		})
+	}
+}
+
 // hasDuplicates is a test helper matching Rust's has_duplicates check.
 func hasDuplicates(keys PublicKeySlice) bool {
 	seen := make(map[PublicKey]struct{}, len(keys))

transaction.go

@@ -453,17 +453,17 @@ func NewTransaction(instructions []Instruction, recentBlockHash Hash, opts ...Tr
 	}
 
 	var idx uint16
-	accountKeyIndex := make(map[string]uint16, len(message.AccountKeys)+len(lookupsWritableKeys)+len(lookupsReadOnlyKeys))
+	accountKeyIndex := make(map[PublicKey]uint16, len(message.AccountKeys)+len(lookupsWritableKeys)+len(lookupsReadOnlyKeys))
 	for _, acc := range message.AccountKeys {
-		accountKeyIndex[acc.String()] = idx
+		accountKeyIndex[acc] = idx
 		idx++
 	}
 	for _, acc := range lookupsWritableKeys {
-		accountKeyIndex[acc.String()] = idx
+		accountKeyIndex[acc] = idx
 		idx++
 	}
 	for _, acc := range lookupsReadOnlyKeys {
-		accountKeyIndex[acc.String()] = idx
+		accountKeyIndex[acc] = idx
 		idx++
 	}
 
@@ -479,14 +479,14 @@ func NewTransaction(instructions []Instruction, recentBlockHash Hash, opts ...Tr
 		accounts = instruction.Accounts()
 		accountIndex := make([]uint16, len(accounts))
 		for idx, acc := range accounts {
-			accountIndex[idx] = accountKeyIndex[acc.PublicKey.String()]
+			accountIndex[idx] = accountKeyIndex[acc.PublicKey]
 		}
 		data, err := instruction.Data()
 		if err != nil {
 			return nil, fmt.Errorf("unable to encode instructions [%d]: %w", txIdx, err)
 		}
 		message.Instructions = append(message.Instructions, CompiledInstruction{
-			ProgramIDIndex: accountKeyIndex[instruction.ProgramID().String()],
+			ProgramIDIndex: accountKeyIndex[instruction.ProgramID()],
 			Accounts:       accountIndex,
 			Data:           data,
 		})