initial implementation

Author: advdv

README.md

@@ -1,2 +1,11 @@
 # brahms
-Byzantine Resilient Gossip Protocol
+This is an experimental implementation of [Brahms: Byzantine resilient random membership sampling](https://www.cs.technion.ac.il/~gabik/publications/Brahms-COMNET.pdf). It describes a byzantine resilient protocol that creates a well-connected overlay network with each member only needing to knowing at most `O(∛n)` other peers.
+
+## TODO
+- [ ] decide, use and test an actual network transport
+- [ ] instead of Node ids, work with ip addresses and ports
+- [ ] fix the myriad of race conditions on shared memory variables
+- [ ] implement validation of the sample by probing
+- [ ] implement a limited push with a small proof of work
+- [ ] adjust l1 and l2 as the network grobs using an esimate as described [here](https://research.neustar.biz/2012/07/09/sketch-of-the-day-k-minimum-values/)
+- [ ] fix send on closed channel bug with update calls with too short a context

brahms.go

@@ -0,0 +1,76 @@
+package brahms
+
+import (
+	"context"
+	"math/rand"
+	"time"
+)
+
+// Brahms implements the gossip protocol and takes an old view 'v' and returns a
+// new view.
+func Brahms(self NID, rnd *rand.Rand, p P, to time.Duration, s *Sampler, tr Transport, pushes <-chan NID, v View) View {
+
+	// reset push/pull views (line 21)
+	push, pull := View{}, View{}
+
+	// perform sends and write results to these channels
+	cpull := make(chan View, p.βl1())
+	func() {
+		ctx, cancel := context.WithTimeout(context.Background(), to)
+		defer cancel()
+
+		// push our own id to peers picked from the current view (line 22)
+		for id := range v.Pick(rnd, p.αl1()) {
+			go tr.Push(ctx, self, id)
+		}
+
+		// send pull requests to peers picked from the current view (line 25)
+		for id := range v.Pick(rnd, p.βl1()) {
+			go tr.Pull(ctx, cpull, id)
+		}
+
+		// wait for time unit to be done, cancels any open pushes/pulls (line 27)
+		<-ctx.Done()
+		close(cpull)
+	}()
+
+	// drain the buffer of all ids pushed to us (line 28)
+DRAIN:
+	for {
+		select {
+		case id := <-pushes:
+			push[id] = struct{}{}
+		default:
+			break DRAIN
+		}
+	}
+
+	// add all peers that we received as replies from our pull requests (line 32)
+	for pv := range cpull {
+		for id := range pv {
+
+			//NOTE: we divert from the paper by ignoring any pulls
+			if id == self {
+				continue
+			}
+
+			pull[id] = struct{}{}
+		}
+	}
+
+	// only update our view if the nr of pushed ids was not too high (line 35)
+	// NOTE: we divert from the paper here. We're happy to update if either pull
+	// or push yielded us some nodes not necessarily both.
+	if len(push) <= p.αl1() && (len(push) > 0 || len(pull) > 0) {
+
+		// construct our new view from what we've seen this round (line 36)
+		v = push.Pick(rnd, p.αl1()).
+			Concat(pull.Pick(rnd, p.βl1())).
+			Concat(s.Sample().Pick(rnd, p.γl1()))
+	}
+
+	// update the sampler with resuling push/pull (line 37)
+	s.Update(push.Concat(pull))
+
+	return v
+}

brahms_test.go

@@ -0,0 +1,84 @@
+package brahms
+
+import (
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/advanderveer/go-test"
+)
+
+func TestBrahmsNoReply(t *testing.T) {
+	p, _ := NewParams(0.1, 0.7, 0.2, 10, 2)
+	r := rand.New(rand.NewSource(1))
+	s := NewSampler(r, p.l2())
+	self := NID{0x01}
+
+	p0 := make(chan NID)
+	v0 := NewView(NID{0x01})
+	tr0 := NewMockTransport()
+
+	v1 := Brahms(self, r, p, time.Millisecond*10, s, tr0, p0, v0)
+
+	//view should be unchanged transport returned nothing
+	test.Equals(t, v0, v1)
+
+	//should have pushed our own nid
+	test.Equals(t, true, tr0.DidPush(self))
+
+	//sample should be empty
+	test.Equals(t, View{}, s.Sample())
+}
+
+func TestBrahmsWithJustPushes(t *testing.T) {
+	p, _ := NewParams(0.1, 0.7, 0.2, 10, 2)
+	r := rand.New(rand.NewSource(1))
+	s := NewSampler(r, p.l2())
+	self := NID{0x01}
+
+	id1 := NID{0x01, 0x02}
+	p0 := make(chan NID, 10)
+	p0 <- id1
+	v0 := NewView(NID{0x01})
+	tr0 := NewMockTransport()
+
+	// with just a pull response we update the view with just that info
+	v1 := Brahms(self, r, p, time.Millisecond*10, s, tr0, p0, v0)
+	test.Equals(t, 0, len(p0))
+	test.Equals(t, NewView(id1), v1)
+
+	// but the pushed id should have been added to the sample
+	test.Equals(t, NewView(id1), s.Sample())
+
+	t.Run("with too many pushes", func(t *testing.T) {
+		p1 := make(chan NID, 10)
+		p1 <- NID{0xaa, 0xaa}
+		p1 <- NID{0xbb, 0xbb} //with the given params this is too much push
+
+		v2 := Brahms(NID{0xff, 0xff}, r, p, time.Millisecond*10, s, tr0, p1, v0)
+
+		//with too many pushes the view shouldn't have changed
+		test.Equals(t, v2, v0)
+	})
+}
+
+func TestBrahmsWithPullsAndPushes(t *testing.T) {
+	p, _ := NewParams(0.1, 0.7, 0.2, 10, 2)
+	r := rand.New(rand.NewSource(1))
+	s := NewSampler(r, p.l2())
+	self := NID{0x01}
+	other := NID{0x02}
+
+	v0 := NewView(other)
+	pull1 := NID{0x01, 0x02}
+	push1 := NID{0x02, 0x02}
+	p0 := make(chan NID, 10)
+	p0 <- push1
+	tr0 := NewMockTransport()
+	tr0.SetPull(other, NewView(pull1, pull1))
+
+	//with both pushes and pulls the view should get updated
+	v1 := Brahms(self, r, p, time.Millisecond*10, s, tr0, p0, v0)
+	test.Equals(t, NewView(pull1, push1), v1)
+	test.Equals(t, NewView(pull1, push1), s.Sample())
+}

core.go

@@ -0,0 +1,57 @@
+package brahms
+
+import (
+	"math/rand"
+	"time"
+)
+
+// Core implements the core algorithm
+type Core struct {
+	rnd     *rand.Rand
+	self    NID
+	view    View
+	pushes  chan NID
+	params  P
+	sampler *Sampler
+	tr      Transport
+}
+
+// NewCore initializes the core
+func NewCore(rnd *rand.Rand, self NID, v0 View, p P, tr Transport) (a *Core) {
+	a = &Core{
+		self:    self,
+		view:    v0,
+		pushes:  make(chan NID, 100),
+		params:  p,
+		sampler: NewSampler(rnd, p.l2()),
+		tr:      tr,
+		rnd:     rnd,
+	}
+
+	//initialize the sampler with our initial view
+	a.sampler.Update(v0)
+	return
+}
+
+// @TODO probe for sample validation
+
+// ID returns this core's id
+func (h *Core) ID() NID { return h.self }
+
+// UpdateView runs the algorithm to update the view
+func (h *Core) UpdateView(to time.Duration) {
+	h.view = Brahms(h.self, h.rnd, h.params, to, h.sampler, h.tr, h.pushes, h.view)
+}
+
+// HandlePull responds to pulls by returning a copy of our view
+func (h *Core) HandlePull() View {
+	return h.view.Copy()
+}
+
+// HandlePush handles incoming ids
+func (h *Core) HandlePush(id NID) {
+	select {
+	case h.pushes <- id:
+	default: //push buffer is full, discard
+	}
+}

core_test.go

@@ -0,0 +1,91 @@
+package brahms
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"math"
+	"math/rand"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/advanderveer/go-test"
+)
+
+func TestMiniNetCore(t *testing.T) {
+	rnd := rand.New(rand.NewSource(1))
+	prm, _ := NewParams(0.45, 0.45, 0.1, 100, 10)
+
+	//create a mini network with three cores
+	tr := NewMemNetTransport()
+	c1 := NewCore(rnd, NID{0x01}, NewView(NID{0x02}), prm, tr)
+	tr.AddCore(c1)
+	c2 := NewCore(rnd, NID{0x02}, NewView(NID{0x03}), prm, tr)
+	tr.AddCore(c2)
+	c3 := NewCore(rnd, NID{0x03}, NewView(), prm, tr)
+	tr.AddCore(c3)
+
+	// after two iterations we should have a connected graph
+	for i := 0; i < 2; i++ {
+		c1.UpdateView(time.Millisecond)
+		c2.UpdateView(time.Millisecond)
+		c3.UpdateView(time.Millisecond)
+	}
+
+	// view and sampler should show a connected graph
+	test.Equals(t, NewView(NID{0x02}, NID{0x03}), c1.view)
+	test.Equals(t, NewView(NID{0x02}, NID{0x03}), c1.sampler.Sample())
+	test.Equals(t, NewView(NID{0x01}, NID{0x03}), c2.view)
+	test.Equals(t, NewView(NID{0x01}, NID{0x03}), c2.sampler.Sample())
+	test.Equals(t, NewView(NID{0x01}, NID{0x02}), c3.view)
+	test.Equals(t, NewView(NID{0x01}, NID{0x02}), c3.sampler.Sample())
+}
+
+func TestLargeNetwork(t *testing.T) {
+	r := rand.New(rand.NewSource(1))
+	n := uint64(100)
+	q := 20
+	m := 2.0
+	l := int(math.Round(m * math.Pow(float64(n), 1.0/3)))
+	p, _ := NewParams(
+		0.45,
+		0.45,
+		0.1,
+		l, l,
+	)
+
+	tr := NewMemNetTransport()
+	cores := make([]*Core, 0, n)
+	for i := uint64(1); i <= n; i++ {
+		id := NID{}
+		other := NID{}
+		binary.LittleEndian.PutUint64(id[:], i)
+		binary.LittleEndian.PutUint64(other[:], i+1)
+		if i == n {
+			other = NID{0x01}
+		}
+
+		c := NewCore(r, id, NewView(other), p, tr)
+		tr.AddCore(c)
+		cores = append(cores, c)
+	}
+
+	for i := 0; i < q; i++ {
+		buf := bytes.NewBuffer(nil)
+		draw(t, buf, cores)
+		drawPNG(t, buf, fmt.Sprintf(filepath.Join("draws", "network_%d.png"), i))
+
+		for _, c := range cores {
+			c.UpdateView(time.Microsecond * 700)
+		}
+	}
+
+	var tot float64
+	for _, c := range cores {
+		tot += float64(len(c.view))
+	}
+
+	fmt.Println("l1/l2:", p.l2(), "avg:", tot/float64(len(cores)))
+
+}

draw_test.go

@@ -0,0 +1,41 @@
+package brahms
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/advanderveer/go-test"
+)
+
+func drawPNG(t *testing.T, buf io.Reader, name string) {
+	f, err := os.Create(name)
+	test.Ok(t, err)
+	defer f.Close()
+
+	cmd := exec.Command("neato", "-Tpng")
+	cmd.Stdin = buf
+	cmd.Stdout = f
+	test.Ok(t, cmd.Run())
+}
+
+func draw(t testing.TB, w io.Writer, cores []*Core) {
+	fmt.Fprintln(w, `digraph {`)
+	fmt.Fprintln(w, `layout=neato;`)
+	fmt.Fprintln(w, `overlap=scalexy;`)
+	fmt.Fprintln(w, `sep="+1";`)
+
+	for _, c := range cores {
+		fmt.Fprintf(w, "\t"+`"%.6x" [style="filled,solid",label="%.6x"`, c.ID(), c.ID())
+		fmt.Fprintf(w, `,fillcolor="#ffffff"`)
+		fmt.Fprintf(w, "]\n")
+
+		for id := range c.view {
+			fmt.Fprintf(w, "\t"+`"%.6x" -> "%.6x";`+"\n", c.ID(), id)
+		}
+	}
+
+	fmt.Fprintln(w, `}`)
+}

draws/.gitignore

@@ -0,0 +1 @@
+*.png

go.mod

@@ -0,0 +1,8 @@
+module github.com/advanderveer/brahms
+
+go 1.12
+
+require (
+	github.com/advanderveer/go-test v1.0.1
+	github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2
+)

go.sum

@@ -0,0 +1,4 @@
+github.com/advanderveer/go-test v1.0.1 h1:FuP/a1WOTT66sx7J6oeY+7ACmNEvBxiJh6ZdR1fc5pQ=
+github.com/advanderveer/go-test v1.0.1/go.mod h1:cTvlXX1T7hQFO4xVUN2FEVnwEkhzUZzapJOi4JCoX1I=
+github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2 h1:tdlZCpZ/P9DhczCTSixgIKmwPv6+wP5DGjqLYw5SUiA=
+github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2/go.mod h1:SqUrOPUnsFjfmXRMNPybcSiG0BgUW2AuFH8PAnS2iTw=