Function clientSideDigestExample

example/digest-optimistic-locking/main.go:200–244

clientSideDigestExample demonstrates calculating digests without fetching from Redis

(ctx context.Context, rdb *redis.Client)

// clientSideDigestExample demonstrates calculating digests without fetching from Redis
func clientSideDigestExample(ctx context.Context, rdb *redis.Client) {
	key := "product:1001:price"

	// Scenario: We know the expected current value
	expectedCurrentValue := "29.99"
	newValue := "24.99"

	// Set initial value
	rdb.Set(ctx, key, expectedCurrentValue, 0)
	fmt.Printf("Current price: $%s\n", expectedCurrentValue)

	// Calculate digest client-side (no need to fetch from Redis!)
	expectedDigest := helper.DigestString(expectedCurrentValue)
	fmt.Printf("Expected digest (calculated client-side): 0x%016x\n", expectedDigest)

	// Update price only if it matches our expectation
	result := rdb.SetIFDEQ(ctx, key, newValue, expectedDigest, 0)

	if result.Err() == redis.Nil {
		fmt.Println("✗ Price was already changed by someone else")
		actualValue := rdb.Get(ctx, key).Val()
		fmt.Printf("  Actual current price: $%s\n", actualValue)
	} else if result.Err() != nil {
		fmt.Printf("✗ Error: %v\n", result.Err())
	} else {
		fmt.Printf("✓ Price updated successfully to $%s\n", newValue)
	}

	// Demonstrate with binary data
	fmt.Println("\nBinary data example:")
	binaryKey := "image:thumbnail"
	binaryData := []byte{0xFF, 0xD8, 0xFF, 0xE0} // JPEG header

	rdb.Set(ctx, binaryKey, binaryData, 0)

	// Calculate digest for binary data
	binaryDigest := helper.DigestBytes(binaryData)
	fmt.Printf("Binary data digest: 0x%016x\n", binaryDigest)

	// Verify it matches Redis
	redisDigest := rdb.Digest(ctx, binaryKey).Val()
	if binaryDigest == redisDigest {
		fmt.Println("✓ Binary digest matches!")
	}
}