rpc: refactor subscriptions and filters

rpc/utils.go

@@ -17,17 +17,26 @@
 package rpc
 
 import (
-	"crypto/rand"
+	"bufio"
+	crand "crypto/rand"
+	"encoding/binary"
 	"encoding/hex"
-	"errors"
 	"math/big"
+	"math/rand"
 	"reflect"
+	"sync"
+	"time"
 	"unicode"
 	"unicode/utf8"
 
 	"golang.org/x/net/context"
 )
 
+var (
+	subscriptionIDGenMu sync.Mutex
+	subscriptionIDGen   = idGenerator()
+)
+
 // Is this an exported - upper case - name?
 func isExported(name string) bool {
 	rune, _ := utf8.DecodeRuneInString(name)
@@ -218,11 +227,28 @@ METHODS:
 	return callbacks, subscriptions
 }
 
-func newSubscriptionID() (string, error) {
-	var subid [16]byte
-	n, _ := rand.Read(subid[:])
-	if n != 16 {
-		return "", errors.New("Unable to generate subscription id")
+// idGenerator helper utility that generates a (pseudo) random sequence of
+// bytes that are used to generate identifiers.
+func idGenerator() *rand.Rand {
+	if seed, err := binary.ReadVarint(bufio.NewReader(crand.Reader)); err == nil {
+		return rand.New(rand.NewSource(seed))
 	}
-	return "0x" + hex.EncodeToString(subid[:]), nil
+	return rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
+}
+
+// NewID generates a identifier that can be used as an identifier in the RPC interface.
+// e.g. filter and subscription identifier.
+func NewID() ID {
+	subscriptionIDGenMu.Lock()
+	defer subscriptionIDGenMu.Unlock()
+
+	id := make([]byte, 16)
+	for i := 0; i < len(id); i += 7 {
+		val := subscriptionIDGen.Int63()
+		for j := 0; i+j < len(id) && j < 7; j++ {
+			id[i+j] = byte(val)
+			val >>= 8
+		}
+	}
+	return ID("0x" + hex.EncodeToString(id))
 }