Various improvements.

cmd/triplex-example/main.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"errors"
+	"fmt"
+
+	"git.hoiting.org/micha/triplex/serial"
+)
+
+func alreadyUsedByClient(idx uint32) bool {
+	return idx%2 == 0
+}
+
+func myRandomIndex(max uint32) (uint32, error) {
+	if max == 0 {
+		return 0, fmt.Errorf("max must be > 0")
+	}
+
+	var buf [4]byte
+	if _, err := rand.Read(buf[:]); err != nil {
+		return 0, err
+	}
+
+	return binary.LittleEndian.Uint32(buf[:]) % max, nil
+}
+
+func main() {
+	opts := serial.RandomCodeOptions{
+		MaxAttempts: 500,
+		IsInUse: func(idx uint32) bool {
+			return alreadyUsedByClient(idx)
+		},
+		RandomIndex: func(max uint32) (uint32, error) {
+			return myRandomIndex(max)
+		},
+	}
+
+	code, idx, err := serial.RandomCodeWithOptions(opts)
+	if err != nil {
+		if errors.Is(err, serial.ErrRandomSourceFailed) {
+			fmt.Println("random source failed")
+			return
+		}
+		if errors.Is(err, serial.ErrNoAvailableIndex) {
+			fmt.Println("no available index found")
+			return
+		}
+		fmt.Println("unexpected error:", err)
+		return
+	}
+
+	fmt.Println("code:", code)
+	fmt.Println("idx:", idx)
+}