go-create-cache

Generate cache files for Go backend using Redis.

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Install skill "go-create-cache" with this command: npx skills add cristiano-pacheco/ai-rules/cristiano-pacheco-ai-rules-go-create-cache

Go Create Cache

Generate cache files for Go backend using Redis.

Two-File Pattern

Every cache requires two files:

  • Port interface: internal/modules/<module>/ports/<cache_name>_cache.go

  • Cache implementation: internal/modules/<module>/cache/<cache_name>_cache.go

Port File Layout Order

  • Interface definition (XxxCache — no suffix)

Cache File Layout Order

  • Constants (cache key prefix, TTL)

  • Implementation struct (XxxCache )

  • Compile-time interface assertion

  • Constructor (NewXxxCache )

  • Methods (Set , Get , Delete , etc.)

  • Helper methods (buildKey , etc.)

Port Interface Structure

Location: internal/modules/<module>/ports/<cache_name>_cache.go

package ports

type UserActivatedCache interface { Set(userID uint64) error Get(userID uint64) (bool, error) Delete(userID uint64) error }

Cache Implementation Structure

Location: internal/modules/<module>/cache/<cache_name>_cache.go

package cache

import ( "context" "errors" "fmt" "time"

"github.com/cristiano-pacheco/bricks/pkg/redis"
"github.com/cristiano-pacheco/pingo/internal/modules/&#x3C;module>/ports"

)

const ( cacheKeyPrefix = "entity_name:" cacheTTLMin = 23 * time.Hour cacheTTLMax = 25 * time.Hour )

type EntityCache struct { redisClient redis.UniversalClient }

var _ ports.EntityCache = (*EntityCache)(nil)

func NewEntityCache(redisClient redis.UniversalClient) *EntityCache { return &EntityCache{ redisClient: redisClient, } }

func (c *EntityCache) Set(id uint64) error { key := c.buildKey(id) ctx := context.Background()

ttl := c.calculateTTL()
return c.redisClient.Set(ctx, key, "1", ttl).Err()

}

func (c *EntityCache) calculateTTL() time.Duration { min := cacheTTLMin.Milliseconds() max := cacheTTLMax.Milliseconds() randomMs := min + rand.Int63n(max-min+1) return time.Duration(randomMs) * time.Millisecond }

func (c *EntityCache) Get(id uint64) (bool, error) { key := c.buildKey(id) ctx := context.Background()

result := c.redisClient.Get(ctx, key)
if err := result.Err(); err != nil {
	if errors.Is(err, redisClient.Nil) {
		return false, nil // Key does not exist
	}
	return false, err
}

return true, nil

}

func (c *EntityCache) Delete(id uint64) error { key := c.buildKey(id) ctx := context.Background()

return c.redisClient.Del(ctx, key).Err()

}

func (c *EntityCache) buildKey(id uint64) string { return fmt.Sprintf("%s%d", cacheKeyPrefix, id) }

Cache Variants

Boolean flag cache (Set/Get/Delete)

Use when caching simple existence or state flags.

Port (ports/user_activated_cache.go ):

type UserActivatedCache interface { Set(userID uint64) error Get(userID uint64) (bool, error) Delete(userID uint64) error }

Implementation notes:

  • Store "1" as value for true state

  • Return false, nil when key doesn't exist (not an error)

  • Use errors.Is(err, redisClient.Nil) to detect missing keys

Value cache (Set/Get/Delete with data)

Use when caching structured data or strings.

Port (ports/session_cache.go ):

type SessionCache interface { Set(sessionID string, data SessionData) error Get(sessionID string) (*SessionData, error) Delete(sessionID string) error }

Implementation notes:

  • Serialize data with json.Marshal before storing

  • Deserialize with json.Unmarshal when retrieving

  • Return nil, nil when key doesn't exist (not an error)

  • TTL is internal to the cache implementation with randomized range to prevent cache stampede

Redis Client Usage

The cache uses redis.UniversalClient directly from the Bricks Redis package (github.com/cristiano-pacheco/bricks/pkg/redis ).

Common operations:

  • Set(ctx, key, value, ttl)

  • Store value with TTL

  • Get(ctx, key)

  • Retrieve value

  • Del(ctx, key)

  • Delete key

  • Exists(ctx, key)

  • Check if key exists

  • Incr(ctx, key)

  • Increment counter

  • Expire(ctx, key, ttl)

  • Set TTL on existing key

Key Building

Always use a helper method to build cache keys consistently:

func (c *EntityCache) buildKey(id uint64) string { return fmt.Sprintf("%s%d", cacheKeyPrefix, id) }

For string IDs:

func (c *EntityCache) buildKey(id string) string { return fmt.Sprintf("%s%s", cacheKeyPrefix, id) }

For composite keys:

func (c *EntityCache) buildKey(userID uint64, resourceID string) string { return fmt.Sprintf("%s%d:%s", cacheKeyPrefix, userID, resourceID) }

TTL Configuration

Define TTL as a range at the package level to prevent cache stampede (multiple entries expiring simultaneously):

const ( cacheKeyPrefix = "entity_name:" cacheTTLMin = 12 * time.Hour // Minimum TTL cacheTTLMax = 24 * time.Hour // Maximum TTL )

Use a helper function to calculate randomized TTL:

import ( "math/rand" "time" )

func (c *EntityCache) calculateTTL() time.Duration { min := cacheTTLMin.Milliseconds() max := cacheTTLMax.Milliseconds() randomMs := min + rand.Int63n(max-min+1) return time.Duration(randomMs) * time.Millisecond }

Common TTL ranges:

  • Short-lived: 4-6 minutes

  • Rate limits, OTP codes

  • Session data: 50-70 minutes

  • User sessions

  • Daily data: 12-25 hours

  • User activation status, daily metrics

  • Weekly data: 6.5-7.5 days

  • Weekly aggregations

Why randomized TTL? When many cache entries are created at the same time (e.g., during traffic spikes), they would all expire simultaneously, causing a "thundering herd" to the database. Randomizing TTL spreads out expirations over time.

Error Handling

Missing Key vs Error

Distinguish between "key not found" (normal) and actual errors:

result := client.Get(ctx, key) if err := result.Err(); err != nil { if errors.Is(err, redisClient.Nil) { return false, nil // Key doesn't exist - not an error } return false, err // Actual error }

Context Usage

Use context.Background() for cache operations unless you have a specific context:

ctx := context.Background()

For operations called from handlers/use cases, accept context as parameter:

func (c *EntityCache) Set(ctx context.Context, id uint64) error { key := c.buildKey(id) // Use provided ctx return c.redisClient.Set(ctx, key, "1", cacheTTL).Err() }

Naming

  • Port interface: XxxCache (in ports package, no suffix)

  • Implementation struct: XxxCache (in cache package, same name — disambiguated by package)

  • Constructor: NewXxxCache , returns a pointer of the struct implementation

  • Constants: cacheKeyPrefix and cacheTTL (lowercase, package-level)

Fx Wiring

Add to internal/modules/<module>/module.go :

fx.Provide( fx.Annotate( cache.NewXxxCache, fx.As(new(ports.XxxCache)), ), ),

Dependencies

Caches depend on:

  • redis.UniversalClient from "github.com/cristiano-pacheco/bricks/pkg/redis" — Redis operations interface

Example 1: Boolean Flag Cache (User Activation)

Port interface (ports/user_activated_cache.go ):

package ports

type UserActivatedCache interface { Set(userID uint64) error Get(userID uint64) (bool, error) Delete(userID uint64) error }

Implementation (cache/user_activated_cache.go ):

package cache

import ( "context" "errors" "fmt" "strconv" "time"

"github.com/cristiano-pacheco/bricks/pkg/redis"
"github.com/cristiano-pacheco/pingo/internal/modules/identity/ports"

)

const ( cacheKeyPrefix = "user_activated:" cacheTTLMin = 23 * time.Hour cacheTTLMax = 25 * time.Hour )

type UserActivatedCache struct { redisClient redis.UniversalClient }

var _ ports.UserActivatedCache = (*UserActivatedCache)(nil)

func NewUserActivatedCache(redisClient redis.UniversalClient) *UserActivatedCache { return &UserActivatedCache{ redisClient: redisClient, } }

func (c *UserActivatedCache) Set(userID uint64) error { key := c.buildKey(userID) ctx := context.Background()

ttl := c.calculateTTL()
return c.redisClient.Set(ctx, key, "1", ttl).Err()

}

func (c *UserActivatedCache) calculateTTL() time.Duration { min := cacheTTLMin.Milliseconds() max := cacheTTLMax.Milliseconds() randomMs := min + rand.Int63n(max-min+1) return time.Duration(randomMs) * time.Millisecond }

func (c *UserActivatedCache) Get(userID uint64) (bool, error) { key := c.buildKey(userID) ctx := context.Background()

result := c.redisClient.Get(ctx, key)
if err := result.Err(); err != nil {
	if errors.Is(err, redisClient.Nil) {
		return false, nil
	}
	return false, err
}

return true, nil

}

func (c *UserActivatedCache) Delete(userID uint64) error { key := c.buildKey(userID) ctx := context.Background()

return c.redisClient.Del(ctx, key).Err()

}

func (c *UserActivatedCache) buildKey(userID uint64) string { return fmt.Sprintf("%s%s", cacheKeyPrefix, strconv.FormatUint(userID, 10)) }

Fx wiring (module.go ):

fx.Provide( fx.Annotate( cache.NewUserActivatedCache, fx.As(new(ports.UserActivatedCache)), ), ),

Example 2: JSON Data Cache (User Session)

DTO (dto/user_session_dto.go ):

package dto

import "time"

type UserSessionData struct { UserID uint64 json:"user_id" Email string json:"email" Name string json:"name" Roles []string json:"roles" LastActivity time.Time json:"last_activity" IPAddress string json:"ip_address" }

Port interface (ports/user_session_cache.go ):

package ports

import ( "time"

"github.com/cristiano-pacheco/pingo/internal/modules/identity/dto"

)

type UserSessionCache interface { Set(sessionID string, data dto.UserSessionData) error Get(sessionID string) (*dto.UserSessionData, error) Delete(sessionID string) error Exists(sessionID string) (bool, error) }

Implementation (cache/user_session_cache.go ):

package cache

import ( "context" "encoding/json" "errors" "fmt" "time"

"github.com/cristiano-pacheco/bricks/pkg/redis"
"github.com/cristiano-pacheco/pingo/internal/modules/identity/dto"
"github.com/cristiano-pacheco/pingo/internal/modules/identity/ports"

)

const ( sessionCacheKeyPrefix = "user_session:" sessionCacheTTLMin = 50 * time.Minute sessionCacheTTLMax = 70 * time.Minute )

type UserSessionCache struct { redisClient redis.UniversalClient }

var _ ports.UserSessionCache = (*UserSessionCache)(nil)

func NewUserSessionCache(redisClient redis.UniversalClient) *UserSessionCache { return &UserSessionCache{ redisClient: redisClient, } }

func (c *UserSessionCache) Set(sessionID string, data dto.UserSessionData) error { key := c.buildKey(sessionID) ctx := context.Background()

jsonData, err := json.Marshal(data)
if err != nil {
	return fmt.Errorf("failed to marshal session data: %w", err)
}

ttl := c.calculateTTL()
return c.redisClient.Set(ctx, key, jsonData, ttl).Err()

}

func (c *UserSessionCache) calculateTTL() time.Duration { min := sessionCacheTTLMin.Milliseconds() max := sessionCacheTTLMax.Milliseconds() randomMs := min + rand.Int63n(max-min+1) return time.Duration(randomMs) * time.Millisecond }

func (c *UserSessionCache) Get(sessionID string) (*dto.UserSessionData, error) { key := c.buildKey(sessionID) ctx := context.Background()

result := c.redisClient.Get(ctx, key)
if err := result.Err(); err != nil {
	if errors.Is(err, redisClient.Nil) {
		return nil, nil
	}
	return nil, err
}

jsonData, err := result.Bytes()
if err != nil {
	return nil, fmt.Errorf("failed to get bytes: %w", err)
}

var data dto.UserSessionData
if err := json.Unmarshal(jsonData, &#x26;data); err != nil {
	return nil, fmt.Errorf("failed to unmarshal session data: %w", err)
}

return &#x26;data, nil

}

func (c *UserSessionCache) Delete(sessionID string) error { key := c.buildKey(sessionID) ctx := context.Background()

return c.redisClient.Del(ctx, key).Err()

}

func (c *UserSessionCache) Exists(sessionID string) (bool, error) { key := c.buildKey(sessionID) ctx := context.Background()

result := c.redisClient.Exists(ctx, key)
if err := result.Err(); err != nil {
	return false, err
}

return result.Val() > 0, nil

}

func (c *UserSessionCache) buildKey(sessionID string) string { return fmt.Sprintf("%s%s", sessionCacheKeyPrefix, sessionID) }

Fx wiring (module.go ):

fx.Provide( fx.Annotate( cache.NewUserSessionCache, fx.As(new(ports.UserSessionCache)), ), ),

Example 3: Protobuf Data Cache (User Profile)

Proto definition (proto/user_profile.proto ):

syntax = "proto3";

package identity;

option go_package = "github.com/cristiano-pacheco/pingo/internal/modules/identity/proto";

message UserProfile { uint64 user_id = 1; string email = 2; string name = 3; repeated string roles = 4; int64 last_login = 5; string avatar_url = 6; }

Port interface (ports/user_profile_cache.go ):

package ports

import ( "time"

"github.com/cristiano-pacheco/pingo/internal/modules/identity/proto"

)

type UserProfileCache interface { Set(userID uint64, profile *proto.UserProfile) error Get(userID uint64) (*proto.UserProfile, error) Delete(userID uint64) error }

Implementation (cache/user_profile_cache.go ):

package cache

import ( "context" "errors" "fmt" "time"

"github.com/cristiano-pacheco/bricks/pkg/redis"
"github.com/cristiano-pacheco/pingo/internal/modules/identity/ports"
"github.com/cristiano-pacheco/pingo/internal/modules/identity/proto"
"google.golang.org/protobuf/proto"

)

const ( profileCacheKeyPrefix = "user_profile:" profileCacheTTLMin = 12 * time.Hour profileCacheTTLMax = 24 * time.Hour )

type UserProfileCache struct { redisClient redis.UniversalClient }

var _ ports.UserProfileCache = (*UserProfileCache)(nil)

func NewUserProfileCache(redisClient redis.UniversalClient) *UserProfileCache { return &UserProfileCache{ redisClient: redisClient, } }

func (c *UserProfileCache) Set(userID uint64, profile *proto.UserProfile) error { key := c.buildKey(userID) ctx := context.Background()

data, err := proto.Marshal(profile)
if err != nil {
	return fmt.Errorf("failed to marshal profile: %w", err)
}

ttl := c.calculateTTL()
return c.redisClient.Set(ctx, key, data, ttl).Err()

}

func (c *UserProfileCache) calculateTTL() time.Duration { min := profileCacheTTLMin.Milliseconds() max := profileCacheTTLMax.Milliseconds() randomMs := min + rand.Int63n(max-min+1) return time.Duration(randomMs) * time.Millisecond }

func (c *UserProfileCache) Get(userID uint64) (*proto.UserProfile, error) { key := c.buildKey(userID) ctx := context.Background()

result := c.redisClient.Get(ctx, key)
if err := result.Err(); err != nil {
	if errors.Is(err, redisClient.Nil) {
		return nil, nil
	}
	return nil, err
}

data, err := result.Bytes()
if err != nil {
	return nil, fmt.Errorf("failed to get bytes: %w", err)
}

var profile proto.UserProfile
if err := proto.Unmarshal(data, &#x26;profile); err != nil {
	return nil, fmt.Errorf("failed to unmarshal profile: %w", err)
}

return &#x26;profile, nil

}

func (c *UserProfileCache) Delete(userID uint64) error { key := c.buildKey(userID) ctx := context.Background()

return c.redisClient.Del(ctx, key).Err()

}

func (c *UserProfileCache) buildKey(userID uint64) string { return fmt.Sprintf("%s%d", profileCacheKeyPrefix, userID) }

Fx wiring (module.go ):

fx.Provide( fx.Annotate( cache.NewUserProfileCache, fx.As(new(ports.UserProfileCache)), ), ),

Critical Rules

  • Two files: Port interface in ports/ , implementation in cache/

  • Interface in ports: Interface lives in ports/<name>_cache.go

  • Interface assertion: Add var _ ports.XxxCache = (*XxxCache)(nil) below the struct

  • Constructor: MUST return pointer *XxxCache

  • Constants: Define cacheKeyPrefix , cacheTTLMin , and cacheTTLMax at package level

  • Randomized TTL: MUST use calculateTTL() helper to prevent cache stampede

  • Key builder: Always use a buildKey() helper method

  • Missing keys: Return zero value + nil error, not an error (use errors.Is(err, redisClient.Nil) )

  • Context: Use context.Background() or accept context.Context parameter

  • No comments: Do not add redundant comments above methods

  • Add detailed comment on interfaces: Provide comprehensive comments on the port interfaces to describe their purpose and usage

  • Redis client type: Use redis.UniversalClient interface

  • No TTL parameters: TTL is internal to cache, never exposed in interface methods

Workflow

  • Create port interface in ports/<name>_cache.go

  • Create cache implementation in cache/<name>_cache.go

  • Add Fx wiring to module's module.go

  • Run make lint to verify

  • Run make nilaway for static analysis

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