core/types, core/vm: improve docs, add JSON marshaling methods

In this commit, core/types's types learn how to encode and decode
themselves as JSON. The encoding is very similar to what the RPC API
uses. The RPC API is missing some output fields (e.g. transaction
signature values) which will be added to the API in a later commit. Some
fields that the API generates are ignored by the decoder methods here.

core/vm/log.go

@@ -18,6 +18,7 @@ package vm
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 
@@ -25,18 +26,33 @@ import (
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
-type Log struct {
-	// Consensus fields
-	Address common.Address
-	Topics  []common.Hash
-	Data    []byte
+var errMissingLogFields = errors.New("missing required JSON log fields")
 
-	// Derived fields (don't reorder!)
-	BlockNumber uint64
-	TxHash      common.Hash
-	TxIndex     uint
-	BlockHash   common.Hash
-	Index       uint
+// Log represents a contract log event. These events are generated by the LOG
+// opcode and stored/indexed by the node.
+type Log struct {
+	// Consensus fields.
+	Address common.Address // address of the contract that generated the event
+	Topics  []common.Hash  // list of topics provided by the contract.
+	Data    []byte         // supplied by the contract, usually ABI-encoded
+
+	// Derived fields (don't reorder!).
+	BlockNumber uint64      // block in which the transaction was included
+	TxHash      common.Hash // hash of the transaction
+	TxIndex     uint        // index of the transaction in the block
+	BlockHash   common.Hash // hash of the block in which the transaction was included
+	Index       uint        // index of the log in the receipt
+}
+
+type jsonLog struct {
+	Address     *common.Address `json:"address"`
+	Topics      *[]common.Hash  `json:"topics"`
+	Data        string          `json:"data"`
+	BlockNumber string          `json:"blockNumber"`
+	TxIndex     string          `json:"transactionIndex"`
+	TxHash      *common.Hash    `json:"transactionHash"`
+	BlockHash   *common.Hash    `json:"blockHash"`
+	Index       string          `json:"logIndex"`
 }
 
 func NewLog(address common.Address, topics []common.Hash, data []byte, number uint64) *Log {
@@ -64,19 +80,50 @@ func (l *Log) String() string {
 	return fmt.Sprintf(`log: %x %x %x %x %d %x %d`, l.Address, l.Topics, l.Data, l.TxHash, l.TxIndex, l.BlockHash, l.Index)
 }
 
+// MarshalJSON implements json.Marshaler.
 func (r *Log) MarshalJSON() ([]byte, error) {
-	fields := map[string]interface{}{
-		"address":          r.Address,
-		"data":             fmt.Sprintf("%#x", r.Data),
-		"blockNumber":      fmt.Sprintf("%#x", r.BlockNumber),
-		"logIndex":         fmt.Sprintf("%#x", r.Index),
-		"blockHash":        r.BlockHash,
-		"transactionHash":  r.TxHash,
-		"transactionIndex": fmt.Sprintf("%#x", r.TxIndex),
-		"topics":           r.Topics,
-	}
+	return json.Marshal(&jsonLog{
+		Address:     &r.Address,
+		Topics:      &r.Topics,
+		Data:        fmt.Sprintf("0x%x", r.Data),
+		BlockNumber: fmt.Sprintf("0x%x", r.BlockNumber),
+		TxIndex:     fmt.Sprintf("0x%x", r.TxIndex),
+		TxHash:      &r.TxHash,
+		BlockHash:   &r.BlockHash,
+		Index:       fmt.Sprintf("0x%x", r.Index),
+	})
+}
 
-	return json.Marshal(fields)
+// UnmarshalJSON implements json.Umarshaler.
+func (r *Log) UnmarshalJSON(input []byte) error {
+	var dec jsonLog
+	if err := json.Unmarshal(input, &dec); err != nil {
+		return err
+	}
+	if dec.Address == nil || dec.Topics == nil || dec.Data == "" || dec.BlockNumber == "" ||
+		dec.TxIndex == "" || dec.TxHash == nil || dec.BlockHash == nil || dec.Index == "" {
+		return errMissingLogFields
+	}
+	declog := Log{
+		Address:   *dec.Address,
+		Topics:    *dec.Topics,
+		TxHash:    *dec.TxHash,
+		BlockHash: *dec.BlockHash,
+	}
+	if _, err := fmt.Sscanf(dec.Data, "0x%x", &declog.Data); err != nil {
+		return fmt.Errorf("invalid hex log data")
+	}
+	if _, err := fmt.Sscanf(dec.BlockNumber, "0x%x", &declog.BlockNumber); err != nil {
+		return fmt.Errorf("invalid hex log block number")
+	}
+	if _, err := fmt.Sscanf(dec.TxIndex, "0x%x", &declog.TxIndex); err != nil {
+		return fmt.Errorf("invalid hex log tx index")
+	}
+	if _, err := fmt.Sscanf(dec.Index, "0x%x", &declog.Index); err != nil {
+		return fmt.Errorf("invalid hex log index")
+	}
+	*r = declog
+	return nil
 }
 
 type Logs []*Log