whisper: polish the messages, fix some bugs, tests

Bugs fixed:
  - Use randomly generated flags as the spec required.
  - During envelope opening check the first bit only for signature.

whisper/message.go

@@ -1,7 +1,11 @@
+// Contains the Whisper protocol Message element. For formal details please see
+// the specs at https://github.com/ethereum/wiki/wiki/Whisper-PoC-1-Protocol-Spec#messages.
+
 package whisper
 
 import (
 	"crypto/ecdsa"
+	"math/rand"
 	"time"
 
 	"github.com/ethereum/go-ethereum/crypto"
@@ -9,8 +13,11 @@ import (
 	"github.com/ethereum/go-ethereum/logger/glog"
 )
 
+// Message represents an end-user data packet to trasmit through the Whisper
+// protocol. These are wrapped into Envelopes that need not be understood by
+// intermediate nodes, just forwarded.
 type Message struct {
-	Flags     byte
+	Flags     byte // First bit it signature presence, rest reserved and should be random
 	Signature []byte
 	Payload   []byte
 	Sent      int64
@@ -18,71 +25,95 @@ type Message struct {
 	To *ecdsa.PublicKey
 }
 
+// Options specifies the exact way a message should be wrapped into an Envelope.
+type Options struct {
+	From   *ecdsa.PrivateKey
+	To     *ecdsa.PublicKey
+	TTL    time.Duration
+	Topics [][]byte
+}
+
+// NewMessage creates and initializes a non-signed, non-encrypted Whisper message.
 func NewMessage(payload []byte) *Message {
-	return &Message{Flags: 0, Payload: payload, Sent: time.Now().Unix()}
+	// Construct an initial flag set: bit #1 = 0 (no signature), rest random
+	flags := byte(rand.Intn(128))
+
+	// Assemble and return the message
+	return &Message{
+		Flags:   flags,
+		Payload: payload,
+		Sent:    time.Now().Unix(),
+	}
 }
 
-func (self *Message) hash() []byte {
-	return crypto.Sha3(append([]byte{self.Flags}, self.Payload...))
+// Wrap bundles the message into an Envelope to transmit over the network.
+//
+// Pov (Proof Of Work) controls how much time to spend on hashing the message,
+// inherently controlling its priority through the network (smaller hash, bigger
+// priority).
+//
+// The user can control the amount of identity, privacy and encryption through
+// the options parameter as follows:
+//   - options.From == nil && options.To == nil: anonymous broadcast
+//   - options.From != nil && options.To == nil: signed broadcast (known sender)
+//   - options.From == nil && options.To != nil: encrypted anonymous message
+//   - options.From != nil && options.To != nil: encrypted signed message
+func (self *Message) Wrap(pow time.Duration, options Options) (*Envelope, error) {
+	// Use the default TTL if non was specified
+	if options.TTL == 0 {
+		options.TTL = DefaultTimeToLive
+	}
+	// Sign and encrypt the message if requested
+	if options.From != nil {
+		if err := self.sign(options.From); err != nil {
+			return nil, err
+		}
+	}
+	if options.To != nil {
+		if err := self.encrypt(options.To); err != nil {
+			return nil, err
+		}
+	}
+	// Wrap the processed message, seal it and return
+	envelope := NewEnvelope(options.TTL, options.Topics, self)
+	envelope.Seal(pow)
+
+	return envelope, nil
 }
 
+// Sign calculates and sets the cryptographic signature for the message , also
+// setting the sign flag.
 func (self *Message) sign(key *ecdsa.PrivateKey) (err error) {
-	self.Flags = 1
+	self.Flags |= 1 << 7
 	self.Signature, err = crypto.Sign(self.hash(), key)
 	return
 }
 
+// Recover retrieves the public key of the message signer.
 func (self *Message) Recover() *ecdsa.PublicKey {
-	defer func() { recover() }() // in case of invalid sig
+	defer func() { recover() }() // in case of invalid signature
+
 	pub, err := crypto.SigToPub(self.hash(), self.Signature)
 	if err != nil {
-		glog.V(logger.Error).Infof("Could not get pubkey from signature: ", err)
+		glog.V(logger.Error).Infof("Could not get public key from signature: %v", err)
 		return nil
 	}
 	return pub
 }
 
-func (self *Message) Encrypt(to *ecdsa.PublicKey) (err error) {
+// Encrypt encrypts a message payload with a public key.
+func (self *Message) encrypt(to *ecdsa.PublicKey) (err error) {
 	self.Payload, err = crypto.Encrypt(to, self.Payload)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return
 }
 
-func (self *Message) Bytes() []byte {
+// Hash calculates the SHA3 checksum of the message flags and payload.
+func (self *Message) hash() []byte {
+	return crypto.Sha3(append([]byte{self.Flags}, self.Payload...))
+}
+
+// Bytes flattens the message contents (flags, signature and payload) into a
+// single binary blob.
+func (self *Message) bytes() []byte {
 	return append([]byte{self.Flags}, append(self.Signature, self.Payload...)...)
 }
-
-type Opts struct {
-	From   *ecdsa.PrivateKey
-	To     *ecdsa.PublicKey
-	Ttl    time.Duration
-	Topics [][]byte
-}
-
-func (self *Message) Seal(pow time.Duration, opts Opts) (*Envelope, error) {
-	if opts.From != nil {
-		err := self.sign(opts.From)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	if opts.To != nil {
-		err := self.Encrypt(opts.To)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	if opts.Ttl == 0 {
-		opts.Ttl = DefaultTtl
-	}
-
-	envelope := NewEnvelope(opts.Ttl, opts.Topics, self)
-	envelope.Seal(pow)
-
-	return envelope, nil
-}