FAB-1045 Gossip pull refactoring: uint64->string

Currently the gossip pull mechanism can only handle items
uint64 as keys (for digests).
I refactored this to be string, because a string can hold
both ints, hashes and can also be used as a key in a map.

This is needed for disseminating entities such as certificates
of peers.

Change-Id: I06be757275dccd4e78f055bb703aeadd52787c33
Signed-off-by: Yacov Manevich <yacovm@il.ibm.com>

gossip/gossip/algo/pull.go

@@ -26,7 +26,7 @@ import (
 )
 
 /* PullEngine is an object that performs pull-based gossip, and maintains an internal state of items
-   identified by uint64 numbers.
+   identified by string numbers.
    The protocol is as follows:
    1) The Initiator sends a Hello message with a specific NONCE to a set of remote peers.
    2) Each remote peer responds with a digest of its messages and returns that NONCE.
@@ -82,14 +82,14 @@ type PullAdapter interface {
 
 	// SendDigest sends a digest to a remote PullEngine.
 	// The context parameter specifies the remote engine to send to.
-	SendDigest(digest []uint64, nonce uint64, context interface{})
+	SendDigest(digest []string, nonce uint64, context interface{})
 
 	// SendReq sends an array of items to a certain remote PullEngine identified
 	// by a string
-	SendReq(dest string, items []uint64, nonce uint64)
+	SendReq(dest string, items []string, nonce uint64)
 
 	// SendRes sends an array of items to a remote PullEngine identified by a context.
-	SendRes(items []uint64, context interface{}, nonce uint64)
+	SendRes(items []string, context interface{}, nonce uint64)
 }
 
 // PullEngine is the component that actually invokes the pull algorithm
@@ -98,7 +98,7 @@ type PullEngine struct {
 	PullAdapter
 	stopFlag           int32
 	state              *util.Set
-	item2owners        map[uint64][]string
+	item2owners        map[string][]string
 	peers2nonces       map[string]uint64
 	nonces2peers       map[uint64]string
 	acceptingDigests   int32
@@ -115,7 +115,7 @@ func NewPullEngine(participant PullAdapter, sleepTime time.Duration) *PullEngine
 		PullAdapter:        participant,
 		stopFlag:           int32(0),
 		state:              util.NewSet(),
-		item2owners:        make(map[uint64][]string),
+		item2owners:        make(map[string][]string),
 		peers2nonces:       make(map[string]uint64),
 		nonces2peers:       make(map[uint64]string),
 		acceptingDigests:   int32(0),
@@ -190,12 +190,12 @@ func (engine *PullEngine) processIncomingDigests() {
 	engine.lock.Lock()
 	defer engine.lock.Unlock()
 
-	requestMapping := make(map[string][]uint64)
+	requestMapping := make(map[string][]string)
 	for n, sources := range engine.item2owners {
 		// select a random source
 		source := sources[rand.Intn(len(sources))]
 		if _, exists := requestMapping[source]; !exists {
-			requestMapping[source] = make([]uint64, 0)
+			requestMapping[source] = make([]string, 0)
 		}
 		// append the number to that source
 		requestMapping[source] = append(requestMapping[source], n)
@@ -218,13 +218,13 @@ func (engine *PullEngine) endPull() {
 	atomic.StoreInt32(&(engine.acceptingResponses), int32(0))
 	engine.outgoingNONCES.Clear()
 
-	engine.item2owners = make(map[uint64][]string)
+	engine.item2owners = make(map[string][]string)
 	engine.peers2nonces = make(map[string]uint64)
 	engine.nonces2peers = make(map[uint64]string)
 }
 
 // OnDigest notifies the engine that a digest has arrived
-func (engine *PullEngine) OnDigest(digest []uint64, nonce uint64, context interface{}) {
+func (engine *PullEngine) OnDigest(digest []string, nonce uint64, context interface{}) {
 	if !engine.isAcceptingDigests() || !engine.outgoingNONCES.Exists(nonce) {
 		return
 	}
@@ -246,14 +246,14 @@ func (engine *PullEngine) OnDigest(digest []uint64, nonce uint64, context interf
 }
 
 // Add adds items to the state
-func (engine *PullEngine) Add(seqs ...uint64) {
+func (engine *PullEngine) Add(seqs ...string) {
 	for _, seq := range seqs {
 		engine.state.Add(seq)
 	}
 }
 
 // Remove removes items from the state
-func (engine *PullEngine) Remove(seqs ...uint64) {
+func (engine *PullEngine) Remove(seqs ...string) {
 	for _, seq := range seqs {
 		engine.state.Remove(seq)
 	}
@@ -267,21 +267,21 @@ func (engine *PullEngine) OnHello(nonce uint64, context interface{}) {
 	})
 
 	a := engine.state.ToArray()
-	digest := make([]uint64, len(a))
+	digest := make([]string, len(a))
 	for i, item := range a {
-		digest[i] = item.(uint64)
+		digest[i] = item.(string)
 	}
 	engine.SendDigest(digest, nonce, context)
 }
 
 // OnReq notifies the engine a request has arrived
-func (engine *PullEngine) OnReq(items []uint64, nonce uint64, context interface{}) {
+func (engine *PullEngine) OnReq(items []string, nonce uint64, context interface{}) {
 	if !engine.incomingNONCES.Exists(nonce) {
 		return
 	}
 	engine.lock.Lock()
 
-	var items2Send []uint64
+	var items2Send []string
 	for _, item := range items {
 		if engine.state.Exists(item) {
 			items2Send = append(items2Send, item)
@@ -294,7 +294,7 @@ func (engine *PullEngine) OnReq(items []uint64, nonce uint64, context interface{
 }
 
 // OnRes notifies the engine a response has arrived
-func (engine *PullEngine) OnRes(items []uint64, nonce uint64) {
+func (engine *PullEngine) OnRes(items []string, nonce uint64) {
 	if !engine.outgoingNONCES.Exists(nonce) || !engine.isAcceptingResponses() {
 		return
 	}