working on a g-counter example

examples/g-counter/g_counter.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"encoding/json"
+	"sort"
+)
+
+type gcounter struct {
+	id     int
+	counts map[int]int
+}
+
+func (c gcounter) incr() { c.counts[c.id]++ }
+
+func (c gcounter) total() int {
+	var n int
+	for _, count := range c.counts {
+		n += count
+	}
+	return n
+}
+
+func (c gcounter) merge(other gcounter) {
+	for id, count := range other.counts {
+		if c.[id] < count {
+			c.[id] = count
+		}
+	}
+}
+
+type pair [2]int
+
+func (c gcounter) MarshalJSON() ([]byte, error) {
+	pairs := make([]pair, 0, len(c.counts))
+	for id, count := range c.counts {
+		pairs = append(pairs, pair{id, count})
+	}
+	sort.Slice(pairs, func(i, j int) bool { return pairs[i][0] < pairs[j][0] })
+	return json.Marshal(pairs)
+}
+
+func (c *gcounter) UnmarshalJSON(b []byte) error {
+	pairs := make([]pair, 0, len(c.counts))
+	if err := json.Unmarshal(b, &pairs); err != nil {
+		return err
+	}
+}

examples/g-counter/g_counter_test.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestGCounterJSON(t *testing.T) {
+	t.Run("marshal", func(t *testing.T) {
+		type test struct {
+			counter gcounter
+			expect  string
+		}
+
+		tests := []test{
+			{
+				gcounter{1, map[int]int{1: 5, 3: 8}},
+				`[[1,5],[3,8]]`,
+			},
+			{
+				gcounter{8, map[int]int{3: 10, 7: 16, 12: 9, 2: 37}},
+				`[[2,37],[3,10],[7,16],[12,9]]`,
+			},
+		}
+
+		for _, test := range tests {
+			b, err := json.Marshal(test.counter)
+			if err != nil {
+				t.Errorf("marshal failed: %s", err)
+				continue
+			}
+			s := string(b)
+			if s != test.expect {
+				t.Errorf("expected json: %s received: %s", test.expect, s)
+			}
+		}
+	})
+
+	t.Run("unmarshal", func(t *testing.T) {
+		type test struct {
+			in     string
+			expect gcounter
+		}
+
+		tests := []test{
+			{
+				`[[1,5],[3,8]]`,
+				gcounter{1, map[int]int{1: 5, 3: 8}},
+			},
+			{
+				`[[2,37],[3,10],[7,16],[12,9]]`,
+				gcounter{8, map[int]int{3: 10, 7: 16, 12: 9, 2: 37}},
+			},
+		}
+
+		for _, test := range tests {
+			var c gcounter
+			if err := json.Unmarshal(test.in, &c); err != nil {
+				t.Errorf("unmarshal failed: %s", err)
+				continue
+			}
+
+			for id, count := range c.counts {
+				n := test.expect.counts[id]
+				if n != count {
+					t.Errorf("mismatched counts for id %d: expected %d, saw %d", id, count, n)
+				}
+			}
+		}
+	})
+}

examples/g-counter/main.go

@@ -0,0 +1 @@
+package main

examples/g-counter/server.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"sync"
+)
+
+type response struct {
+	OK   bool `json:"ok"`
+	Hits int  `json:"hits"`
+}
+
+// server implements a clustered http hit-counter server. Each path is given a
+// g-counter, and every node in the cluster acts as a read-write replica.
+type server struct {
+	sync.Mutex
+
+	// my own id
+	id int
+
+	// a mapping of peer servers id -> addr
+	peers map[int]string
+
+	// distributed counts
+	counters map[string]gcounter
+}
+
+func (s *server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	switch r.URL.Path {
+	case "/join":
+		s.join(w, r)
+	case "/sync":
+		s.sync(w, r)
+	default:
+		s.countHit(w, r)
+	}
+}
+
+func (s *server) countHit(w http.ResponseWriter, r *http.Request) {
+	hits := s.hit(r.URL.Path)
+
+	fmt.Printf("% 8d %s\n", hits, r.URL.Path)
+
+	w.Header().Add("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response{OK: true, Hits: hits})
+}
+
+func (s *server) join(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		Addr string `json:"addr"`
+	}
+}
+
+func (s *server) sync(w http.ResponseWriter, r *http.Request) {
+}
+
+func (s *server) hit(path string) int {
+	s.Lock()
+	defer s.Unlock()
+
+	if s.counters == nil {
+		s.counters = map[string]gcounter{
+			gcounter{s.id, map[int]int{id: 1}},
+		}
+		return 1
+	}
+
+	c, ok := s.counters[path]
+	if !ok {
+		s.counters[path] = gcounter{s.id, map[int]int{id: 1}}
+		return 1
+	}
+
+	c.incr()
+	return c.total()
+}

examples/hit-counter/server_test.go

@@ -8,9 +8,6 @@ import (
 	"github.com/jordanorelli/tea"
 )
 
-// testStartServer is a test that checks that the server can start. If this
-// test passes, we retain a reference to the server for future tests to
-// utilize.
 type testStartServer struct {
 	Server *httptest.Server `tea:"save"`
 }
@@ -26,16 +23,14 @@ func (test *testStartServer) After(t *testing.T) {
 	test.Server.Close()
 }
 
-// testHits sends a request to a hitcount server created in a previous test,
-// checking that the number of hits returned matches what we expect.
-type testHits struct {
+type testRequest struct {
 	Server *httptest.Server `tea:"load"`
 
 	path   string
-	hits int
+	expect int
 }
 
-func (test *testHits) Run(t *testing.T) {
+func (test *testRequest) Run(t *testing.T) {
 	client := test.Server.Client()
 
 	res, err := client.Get(test.Server.URL + test.path)
@@ -49,39 +44,50 @@ func (test *testHits) Run(t *testing.T) {
 		t.Fatalf("response at %s was not json: %v", test.path, err)
 	}
 
-	if body.Hits != test.hits {
-		t.Errorf("expected a count of %d hits but saw %d instead", test.hits, body.Hits)
+	if body.Hits != test.expect {
+		t.Errorf("expected a count of %d but saw %d", test.expect, body.Hits)
 	}
 }
 
 func TestServer(t *testing.T) {
-	// start with a root node that creates our test server
-	root := tea.New(&testStartServer{})
-
-	// add a child node: this test is run if the root test passes. If the root
-	// test is failed, this test and all of its descendents are logged as
-	// skipped.
-	one := root.Child(&testHits{path: "/alice", hits: 1})
+	type list []testRequest
 
-	// the effects of the first test create the initial state for the second test.
-	two := one.Child(&testHits{path: "/alice", hits: 2})
-
-	// since we have never visited /bob, we know that bob should only have one hit.
-	two.Child(&testHits{path: "/bob", hits: 1})
+	runSeries := func(node *tea.Tree, tests list) *tea.Tree {
+		for i := 0; i < len(tests); i++ {
+			node = node.Child(&tests[i])
+		}
+		return node
+	}
 
-	// but we could also run the exact same test off of the root, like so:
-	root.Child(&testHits{path: "/bob", hits: 1})
+	runSiblings := func(node *tea.Tree, tests list) {
+		for i := 0; i < len(tests); i++ {
+			node.Child(&tests[i])
+		}
+	}
 
-	// since tests are values in tea, we can re-use the exact same test from
-	// different initial states by saving the test as a variable.
-	bob := &testHits{path: "/bob", hits: 1}
+	root := tea.New(&testStartServer{})
 
-	// these two executions of the same test value are operating on different
-	// program states. Since they are not in the same sequence, they have no
-	// effect on one another, even though they're utilizing the same test
-	// value.
-	two.Child(bob)
-	root.Child(bob)
+	runSeries(root, list{
+		{path: "/users/alice", expect: 1},
+		{path: "/users/alice", expect: 2},
+		{path: "/users/alice", expect: 3},
+		{path: "/users/alice", expect: 4},
+	})
+
+	runSeries(root, list{
+		{path: "/users/bob", expect: 1},
+		{path: "/users/alice", expect: 1},
+		{path: "/users/alice", expect: 2},
+		{path: "/users/alice", expect: 3},
+		{path: "/users/bob", expect: 2},
+	})
+
+	runSiblings(root, list{
+		{path: "/users/alice", expect: 1},
+		{path: "/users/alice", expect: 1},
+		{path: "/users/alice", expect: 1},
+		{path: "/users/alice", expect: 1},
+	})
 
 	tea.Run(t, root)
 }