| 1 | package docs |
| 2 | |
| 3 | import ( |
| 4 | "sync" |
| 5 | "testing" |
| 6 | "time" |
| 7 | ) |
| 8 | |
| 9 | // recv waits briefly for a seq on ch. The wait exists because a |
| 10 | // broadcast and its delivery are not the same instant; it is not a |
| 11 | // synchronisation mechanism the code under test relies on, only a |
| 12 | // bound on how long a test is willing to be wrong. |
| 13 | func recv(t *testing.T, ch <-chan int64) (int64, bool) { |
| 14 | t.Helper() |
| 15 | select { |
| 16 | case seq := <-ch: |
| 17 | return seq, true |
| 18 | case <-time.After(time.Second): |
| 19 | return 0, false |
| 20 | } |
| 21 | } |
| 22 | |
| 23 | // quiet asserts nothing arrives. Shorter than recv's timeout because |
| 24 | // a false negative here costs a slow test and a false positive costs |
| 25 | // a wrong belief about isolation. |
| 26 | func quiet(t *testing.T, ch <-chan int64) bool { |
| 27 | t.Helper() |
| 28 | select { |
| 29 | case seq := <-ch: |
| 30 | t.Errorf("received seq %d on a channel that should have been quiet", seq) |
| 31 | return false |
| 32 | case <-time.After(50 * time.Millisecond): |
| 33 | return true |
| 34 | } |
| 35 | } |
| 36 | |
| 37 | func TestHubDeliversToItsOwnDocumentOnly(t *testing.T) { |
| 38 | h := newHub() |
| 39 | |
| 40 | mine, stop := h.subscribe(1) |
| 41 | defer stop() |
| 42 | theirs, stopTheirs := h.subscribe(2) |
| 43 | defer stopTheirs() |
| 44 | |
| 45 | h.broadcast(1, 7) |
| 46 | |
| 47 | if seq, ok := recv(t, mine); !ok || seq != 7 { |
| 48 | t.Errorf("subscriber to document 1 got (%d, %v), want (7, true)", seq, ok) |
| 49 | } |
| 50 | quiet(t, theirs) |
| 51 | } |
| 52 | |
| 53 | // A broadcast with nobody listening is not an error and not a leak. |
| 54 | func TestHubBroadcastWithNoSubscribers(t *testing.T) { |
| 55 | h := newHub() |
| 56 | h.broadcast(42, 1) // must not panic or block |
| 57 | |
| 58 | ch, stop := h.subscribe(42) |
| 59 | defer stop() |
| 60 | quiet(t, ch) // and must not have been queued up for a later arrival |
| 61 | } |
| 62 | |
| 63 | // Unsubscribing stops delivery, and doing it twice is safe: the SSE |
| 64 | // handler defers its stop and may also stop early on a write failure. |
| 65 | func TestHubUnsubscribeStopsDeliveryAndIsIdempotent(t *testing.T) { |
| 66 | h := newHub() |
| 67 | ch, stop := h.subscribe(1) |
| 68 | |
| 69 | stop() |
| 70 | stop() |
| 71 | |
| 72 | h.broadcast(1, 3) |
| 73 | quiet(t, ch) |
| 74 | } |
| 75 | |
| 76 | // TestHubSlowSubscriberNeverBlocksABroadcaster is the property the |
| 77 | // whole design rests on: broadcast runs on the HTTP request goroutine |
| 78 | // that just accepted an update, so a subscriber that is not reading — |
| 79 | // a browser tab on a wedged connection, a handler between select |
| 80 | // turns — must never be able to hold that request open. The slot is |
| 81 | // one deep and sends are non-blocking, which is safe precisely |
| 82 | // because the seq is advisory: a client that misses a notification |
| 83 | // still fetches ?since=cursor and gets everything. |
| 84 | func TestHubSlowSubscriberNeverBlocksABroadcaster(t *testing.T) { |
| 85 | h := newHub() |
| 86 | ch, stop := h.subscribe(1) |
| 87 | defer stop() |
| 88 | |
| 89 | done := make(chan struct{}) |
| 90 | go func() { |
| 91 | defer close(done) |
| 92 | for seq := int64(1); seq <= 100; seq++ { |
| 93 | h.broadcast(1, seq) |
| 94 | } |
| 95 | }() |
| 96 | |
| 97 | select { |
| 98 | case <-done: |
| 99 | case <-time.After(time.Second): |
| 100 | t.Fatal("broadcast blocked on a subscriber that was not reading") |
| 101 | } |
| 102 | |
| 103 | // The subscriber missed most of them, which is fine and is the |
| 104 | // point — but it must still be told that something happened, or |
| 105 | // it would never fetch. |
| 106 | if _, ok := recv(t, ch); !ok { |
| 107 | t.Error("a subscriber that fell behind was left with no pending notification at all") |
| 108 | } |
| 109 | } |
| 110 | |
| 111 | // The map must not grow forever: a document with no subscribers left |
| 112 | // holds no entry. |
| 113 | func TestHubForgetsDocumentsWithNoSubscribers(t *testing.T) { |
| 114 | h := newHub() |
| 115 | |
| 116 | _, stopA := h.subscribe(1) |
| 117 | _, stopB := h.subscribe(1) |
| 118 | |
| 119 | stopA() |
| 120 | if got := h.documentCount(); got != 1 { |
| 121 | t.Errorf("after one of two subscribers left, hub tracks %d documents, want 1", got) |
| 122 | } |
| 123 | stopB() |
| 124 | if got := h.documentCount(); got != 0 { |
| 125 | t.Errorf("after the last subscriber left, hub tracks %d documents, want 0", got) |
| 126 | } |
| 127 | } |
| 128 | |
| 129 | // Run with -race, this is the test that catches a missing lock. |
| 130 | func TestHubUnderConcurrentUse(t *testing.T) { |
| 131 | h := newHub() |
| 132 | |
| 133 | var wg sync.WaitGroup |
| 134 | for i := 0; i < 8; i++ { |
| 135 | wg.Add(1) |
| 136 | go func(n int) { |
| 137 | defer wg.Done() |
| 138 | for j := 0; j < 50; j++ { |
| 139 | ch, stop := h.subscribe(int64(n % 3)) |
| 140 | h.broadcast(int64(n%3), int64(j)) |
| 141 | select { |
| 142 | case <-ch: |
| 143 | default: |
| 144 | } |
| 145 | stop() |
| 146 | } |
| 147 | }(i) |
| 148 | } |
| 149 | wg.Wait() |
| 150 | |
| 151 | if got := h.documentCount(); got != 0 { |
| 152 | t.Errorf("hub tracks %d documents after every subscriber left, want 0", got) |
| 153 | } |
| 154 | } |
| 155 | |
amadan