|
| 1 | +// This example demonstrates kfake, a fake in-memory Kafka cluster for |
| 2 | +// testing without a real broker. kfake provides control functions that let |
| 3 | +// you intercept, observe, modify, or delay any Kafka protocol request. |
| 4 | +// |
| 5 | +// Three modes show different control function patterns: |
| 6 | +// |
| 7 | +// - inject-error: one-shot ControlKey to inject a produce error; kgo retries |
| 8 | +// and succeeds because the control is consumed after one interception |
| 9 | +// - observe: KeepControl to persistently count every request type flowing |
| 10 | +// through the cluster during a produce-and-consume cycle |
| 11 | +// - sleep: SleepControl with SleepOutOfOrder to coordinate between requests, |
| 12 | +// delaying a fetch response until a produce arrives |
| 13 | +// |
| 14 | +// Unlike other examples in this directory, this one does not require a running |
| 15 | +// Kafka cluster - everything runs in-process. |
| 16 | +package main |
| 17 | + |
| 18 | +import ( |
| 19 | + "context" |
| 20 | + "flag" |
| 21 | + "fmt" |
| 22 | + "os" |
| 23 | + "sort" |
| 24 | + "sync" |
| 25 | + "sync/atomic" |
| 26 | + "time" |
| 27 | + |
| 28 | + "github.com/twmb/franz-go/pkg/kerr" |
| 29 | + "github.com/twmb/franz-go/pkg/kfake" |
| 30 | + "github.com/twmb/franz-go/pkg/kgo" |
| 31 | + "github.com/twmb/franz-go/pkg/kmsg" |
| 32 | +) |
| 33 | + |
| 34 | +var mode = flag.String("mode", "inject-error", "demo mode: inject-error, observe, sleep") |
| 35 | + |
| 36 | +func die(msg string, args ...any) { |
| 37 | + fmt.Fprintf(os.Stderr, msg+"\n", args...) |
| 38 | + os.Exit(1) |
| 39 | +} |
| 40 | + |
| 41 | +func main() { |
| 42 | + flag.Parse() |
| 43 | + switch *mode { |
| 44 | + case "inject-error": |
| 45 | + demoInjectError() |
| 46 | + case "observe": |
| 47 | + demoObserve() |
| 48 | + case "sleep": |
| 49 | + demoSleep() |
| 50 | + default: |
| 51 | + die("unknown mode %q; use inject-error, observe, or sleep", *mode) |
| 52 | + } |
| 53 | +} |
| 54 | + |
| 55 | +// demoInjectError uses a one-shot ControlKey to inject a retriable error on |
| 56 | +// the first produce request. Because KeepControl is NOT called, the control |
| 57 | +// is removed after handling one request. The client retries and the second |
| 58 | +// produce goes through normally. |
| 59 | +func demoInjectError() { |
| 60 | + c, err := kfake.NewCluster( |
| 61 | + kfake.NumBrokers(1), |
| 62 | + kfake.SeedTopics(1, "test-topic"), |
| 63 | + ) |
| 64 | + if err != nil { |
| 65 | + die("NewCluster: %v", err) |
| 66 | + } |
| 67 | + defer c.Close() |
| 68 | + |
| 69 | + // One-shot control: return NOT_LEADER_FOR_PARTITION on the first produce. |
| 70 | + // The control handles exactly one request and is then removed. |
| 71 | + var intercepted atomic.Bool |
| 72 | + c.ControlKey(int16(kmsg.Produce), func(kreq kmsg.Request) (kmsg.Response, error, bool) { |
| 73 | + intercepted.Store(true) |
| 74 | + fmt.Println(" [control] intercepted produce, returning NOT_LEADER_FOR_PARTITION") |
| 75 | + |
| 76 | + req := kreq.(*kmsg.ProduceRequest) |
| 77 | + resp := req.ResponseKind().(*kmsg.ProduceResponse) |
| 78 | + for _, rt := range req.Topics { |
| 79 | + st := kmsg.NewProduceResponseTopic() |
| 80 | + st.Topic = rt.Topic |
| 81 | + for _, rp := range rt.Partitions { |
| 82 | + sp := kmsg.NewProduceResponseTopicPartition() |
| 83 | + sp.Partition = rp.Partition |
| 84 | + sp.ErrorCode = kerr.NotLeaderForPartition.Code |
| 85 | + st.Partitions = append(st.Partitions, sp) |
| 86 | + } |
| 87 | + resp.Topics = append(resp.Topics, st) |
| 88 | + } |
| 89 | + return resp, nil, true |
| 90 | + }) |
| 91 | + |
| 92 | + cl, err := kgo.NewClient( |
| 93 | + kgo.SeedBrokers(c.ListenAddrs()...), |
| 94 | + kgo.DefaultProduceTopic("test-topic"), |
| 95 | + ) |
| 96 | + if err != nil { |
| 97 | + die("NewClient: %v", err) |
| 98 | + } |
| 99 | + defer cl.Close() |
| 100 | + |
| 101 | + fmt.Println("inject-error: producing a record (first attempt will fail)...") |
| 102 | + ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) |
| 103 | + defer cancel() |
| 104 | + |
| 105 | + r := &kgo.Record{Value: []byte("hello")} |
| 106 | + if err := cl.ProduceSync(ctx, r).FirstErr(); err != nil { |
| 107 | + die("produce failed: %v", err) |
| 108 | + } |
| 109 | + |
| 110 | + fmt.Printf(" produced to partition %d offset %d\n", r.Partition, r.Offset) |
| 111 | + fmt.Printf(" control intercepted first attempt: %v\n", intercepted.Load()) |
| 112 | + fmt.Println(" kgo retried automatically and succeeded") |
| 113 | +} |
| 114 | + |
| 115 | +// demoObserve uses KeepControl to persistently observe every request without |
| 116 | +// intercepting. The control function returns (nil, nil, false) - "not handled" |
| 117 | +// - so all requests are processed normally by the cluster. |
| 118 | +func demoObserve() { |
| 119 | + c, err := kfake.NewCluster( |
| 120 | + kfake.NumBrokers(1), |
| 121 | + kfake.SeedTopics(3, "test-topic"), |
| 122 | + ) |
| 123 | + if err != nil { |
| 124 | + die("NewCluster: %v", err) |
| 125 | + } |
| 126 | + defer c.Close() |
| 127 | + |
| 128 | + // Persistent observer using Control (matches all request keys). |
| 129 | + // KeepControl prevents the control from being removed after use. |
| 130 | + var mu sync.Mutex |
| 131 | + counts := make(map[string]int) |
| 132 | + c.Control(func(kreq kmsg.Request) (kmsg.Response, error, bool) { |
| 133 | + c.KeepControl() |
| 134 | + mu.Lock() |
| 135 | + counts[kmsg.NameForKey(kreq.Key())]++ |
| 136 | + mu.Unlock() |
| 137 | + return nil, nil, false |
| 138 | + }) |
| 139 | + |
| 140 | + cl, err := kgo.NewClient( |
| 141 | + kgo.SeedBrokers(c.ListenAddrs()...), |
| 142 | + kgo.DefaultProduceTopic("test-topic"), |
| 143 | + kgo.ConsumeTopics("test-topic"), |
| 144 | + ) |
| 145 | + if err != nil { |
| 146 | + die("NewClient: %v", err) |
| 147 | + } |
| 148 | + |
| 149 | + fmt.Println("observe: producing 10 records...") |
| 150 | + ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) |
| 151 | + defer cancel() |
| 152 | + |
| 153 | + for i := range 10 { |
| 154 | + r := &kgo.Record{Value: []byte(fmt.Sprintf("record-%d", i))} |
| 155 | + if err := cl.ProduceSync(ctx, r).FirstErr(); err != nil { |
| 156 | + die("produce: %v", err) |
| 157 | + } |
| 158 | + } |
| 159 | + |
| 160 | + fmt.Println("observe: consuming records...") |
| 161 | + fetches := cl.PollFetches(ctx) |
| 162 | + fmt.Printf(" consumed %d records\n", fetches.NumRecords()) |
| 163 | + |
| 164 | + cl.Close() |
| 165 | + |
| 166 | + fmt.Println("\n request type counts:") |
| 167 | + mu.Lock() |
| 168 | + keys := make([]string, 0, len(counts)) |
| 169 | + for k := range counts { |
| 170 | + keys = append(keys, k) |
| 171 | + } |
| 172 | + sort.Strings(keys) |
| 173 | + for _, k := range keys { |
| 174 | + fmt.Printf(" %-30s %d\n", k, counts[k]) |
| 175 | + } |
| 176 | + mu.Unlock() |
| 177 | +} |
| 178 | + |
| 179 | +// demoSleep uses SleepControl with SleepOutOfOrder to coordinate between |
| 180 | +// requests on different connections. A fetch control function sleeps until a |
| 181 | +// produce request arrives, guaranteeing the fetch returns data rather than |
| 182 | +// timing out empty. |
| 183 | +// |
| 184 | +// franz-go uses separate connections for produce and fetch requests, so |
| 185 | +// SleepOutOfOrder allows the produce to be processed while the fetch sleeps. |
| 186 | +func demoSleep() { |
| 187 | + c, err := kfake.NewCluster( |
| 188 | + kfake.NumBrokers(1), |
| 189 | + kfake.SeedTopics(1, "test-topic"), |
| 190 | + // SleepOutOfOrder allows requests on other connections to |
| 191 | + // proceed while a control function is sleeping. |
| 192 | + kfake.SleepOutOfOrder(), |
| 193 | + ) |
| 194 | + if err != nil { |
| 195 | + die("NewCluster: %v", err) |
| 196 | + } |
| 197 | + defer c.Close() |
| 198 | + |
| 199 | + // Signal channel: produce observer notifies when data has been written. |
| 200 | + produced := make(chan struct{}, 1) |
| 201 | + |
| 202 | + // Observe produces: signal when one arrives. KeepControl keeps this |
| 203 | + // observer active for the entire test. |
| 204 | + c.ControlKey(int16(kmsg.Produce), func(kmsg.Request) (kmsg.Response, error, bool) { |
| 205 | + c.KeepControl() |
| 206 | + select { |
| 207 | + case produced <- struct{}{}: |
| 208 | + default: |
| 209 | + } |
| 210 | + return nil, nil, false |
| 211 | + }) |
| 212 | + |
| 213 | + // Sleep the first fetch until a produce is observed. SleepControl |
| 214 | + // yields so that the produce request (on a different connection) can |
| 215 | + // be processed while this fetch waits. DropControl removes this |
| 216 | + // control after it fires, so subsequent fetches run normally. |
| 217 | + c.ControlKey(int16(kmsg.Fetch), func(kmsg.Request) (kmsg.Response, error, bool) { |
| 218 | + fmt.Println(" [control] fetch arrived, sleeping until produce completes...") |
| 219 | + c.SleepControl(func() { |
| 220 | + <-produced |
| 221 | + }) |
| 222 | + fmt.Println(" [control] produce observed, waking fetch") |
| 223 | + // DropControl removes this control even though we return |
| 224 | + // handled=false. Without it, the control would fire again |
| 225 | + // on the next fetch because unhandled controls are kept. |
| 226 | + c.DropControl() |
| 227 | + return nil, nil, false |
| 228 | + }) |
| 229 | + |
| 230 | + // Start a consumer - its first fetch will sleep in the control. |
| 231 | + consumer, err := kgo.NewClient( |
| 232 | + kgo.SeedBrokers(c.ListenAddrs()...), |
| 233 | + kgo.ConsumeTopics("test-topic"), |
| 234 | + ) |
| 235 | + if err != nil { |
| 236 | + die("NewClient consumer: %v", err) |
| 237 | + } |
| 238 | + defer consumer.Close() |
| 239 | + |
| 240 | + ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) |
| 241 | + defer cancel() |
| 242 | + |
| 243 | + // Poll in the background - the fetch will sleep until produce arrives. |
| 244 | + type result struct { |
| 245 | + n int |
| 246 | + err error |
| 247 | + } |
| 248 | + done := make(chan result, 1) |
| 249 | + go func() { |
| 250 | + f := consumer.PollFetches(ctx) |
| 251 | + var fetchErr error |
| 252 | + f.EachError(func(_ string, _ int32, err error) { |
| 253 | + fetchErr = err |
| 254 | + }) |
| 255 | + done <- result{f.NumRecords(), fetchErr} |
| 256 | + }() |
| 257 | + |
| 258 | + // Brief pause to let the consumer connect and issue its fetch. |
| 259 | + time.Sleep(100 * time.Millisecond) |
| 260 | + |
| 261 | + // Produce a record - this wakes the sleeping fetch control. |
| 262 | + producer, err := kgo.NewClient( |
| 263 | + kgo.SeedBrokers(c.ListenAddrs()...), |
| 264 | + kgo.DefaultProduceTopic("test-topic"), |
| 265 | + ) |
| 266 | + if err != nil { |
| 267 | + die("NewClient producer: %v", err) |
| 268 | + } |
| 269 | + defer producer.Close() |
| 270 | + |
| 271 | + fmt.Println("sleep: producing a record (will wake the sleeping fetch)...") |
| 272 | + r := &kgo.Record{Value: []byte("coordinated")} |
| 273 | + if err := producer.ProduceSync(ctx, r).FirstErr(); err != nil { |
| 274 | + die("produce: %v", err) |
| 275 | + } |
| 276 | + fmt.Printf(" produced to partition %d offset %d\n", r.Partition, r.Offset) |
| 277 | + |
| 278 | + res := <-done |
| 279 | + if res.err != nil { |
| 280 | + die("consume: %v", res.err) |
| 281 | + } |
| 282 | + fmt.Printf(" consumer fetched %d record(s) after being woken\n", res.n) |
| 283 | +} |
0 commit comments