rpc: use correct stringer-method for serializing BlockNumberOrHash (#28358)

The String() version of BlockNumberOrHash uses decimal for all block numbers, including negative ones used to indicate labels. Switch to using BlockNumber.String() which encodes it correctly for use in the JSON-RPC API.

rpc/types.go

@@ -21,7 +21,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"math"
-	"strconv"
 	"strings"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -221,7 +220,7 @@ func (bnh *BlockNumberOrHash) Number() (BlockNumber, bool) {
 
 func (bnh *BlockNumberOrHash) String() string {
 	if bnh.BlockNumber != nil {
-		return strconv.Itoa(int(*bnh.BlockNumber))
+		return bnh.BlockNumber.String()
 	}
 	if bnh.BlockHash != nil {
 		return bnh.BlockHash.String()

rpc/types_test.go

@@ -153,3 +153,24 @@ func TestBlockNumberOrHash_WithNumber_MarshalAndUnmarshal(t *testing.T) {
 		})
 	}
 }
+
+func TestBlockNumberOrHash_StringAndUnmarshal(t *testing.T) {
+	tests := []BlockNumberOrHash{
+		BlockNumberOrHashWithNumber(math.MaxInt64),
+		BlockNumberOrHashWithNumber(PendingBlockNumber),
+		BlockNumberOrHashWithNumber(LatestBlockNumber),
+		BlockNumberOrHashWithNumber(EarliestBlockNumber),
+		BlockNumberOrHashWithNumber(32),
+		BlockNumberOrHashWithHash(common.Hash{0xaa}, false),
+	}
+	for _, want := range tests {
+		marshalled, _ := json.Marshal(want.String())
+		var have BlockNumberOrHash
+		if err := json.Unmarshal(marshalled, &have); err != nil {
+			t.Fatalf("cannot unmarshal (%v): %v", string(marshalled), err)
+		}
+		if !reflect.DeepEqual(want, have) {
+			t.Fatalf("wrong result: have %v, want %v", have, want)
+		}
+	}
+}