mats/go-redis-inventory
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Mats Törnberg
2025-11-10 20:38:51 +01:00
commit 19d7ad0de6
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0
README.md Normal file
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go.mod Normal file
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module git.tornberg.me/mats/go-redis-inventory
go 1.25.1
require github.com/redis/go-redis/v9 v9.16.0
require (
github.com/cespare/xxhash/v2 v2.3.0 // indirect
github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f // indirect
)

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go.sum Normal file
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github.com/bsm/ginkgo/v2 v2.12.0 h1:Ny8MWAHyOepLGlLKYmXG4IEkioBysk6GpaRTLC8zwWs=
github.com/bsm/ginkgo/v2 v2.12.0/go.mod h1:SwYbGRRDovPVboqFv0tPTcG1sN61LM1Z4ARdbAV9g4c=
github.com/bsm/gomega v1.27.10 h1:yeMWxP2pV2fG3FgAODIY8EiRE3dy0aeFYt4l7wh6yKA=
github.com/bsm/gomega v1.27.10/go.mod h1:JyEr/xRbxbtgWNi8tIEVPUYZ5Dzef52k01W3YH0H+O0=
github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f h1:lO4WD4F/rVNCu3HqELle0jiPLLBs70cWOduZpkS1E78=
github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f/go.mod h1:cuUVRXasLTGF7a8hSLbxyZXjz+1KgoB3wDUb6vlszIc=
github.com/redis/go-redis/v9 v9.16.0 h1:OotgqgLSRCmzfqChbQyG1PHC3tLNR89DG4jdOERSEP4=
github.com/redis/go-redis/v9 v9.16.0/go.mod h1:u410H11HMLoB+TP67dz8rL9s6QW2j76l0//kSOd3370=

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pkg/inventory/listener.go Normal file
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package inventory
import (
"context"
"encoding/json"
"fmt"
"log"
"strings"
"github.com/redis/go-redis/v9"
)
type InventoryChange struct {
SKU string `json:"sku"`
StockLocationID string `json:"stock_location_id"`
Value int64 `json:"value"`
}
type InventoryChangeHandler func(changes []InventoryChange)
type InventoryChangeListener struct {
client *redis.Client
ctx context.Context
handler InventoryChangeHandler
ready chan struct{}
}
func NewInventoryChangeListener(client *redis.Client, ctx context.Context, handler InventoryChangeHandler) *InventoryChangeListener {
return &InventoryChangeListener{
client: client,
ctx: ctx,
handler: handler,
ready: make(chan struct{}),
}
}
func (l *InventoryChangeListener) WaitReady() {
<-l.ready
}
func (l *InventoryChangeListener) Start() error {
pubsub := l.client.Subscribe(l.ctx, "inventory_changed")
defer pubsub.Close()
// Signal that we're ready to receive messages
close(l.ready)
ch := pubsub.Channel()
for msg := range ch {
var payload map[string]int64
if err := json.Unmarshal([]byte(msg.Payload), &payload); err != nil {
log.Printf("Failed to unmarshal inventory change message: %v", err)
continue
}
changes := make([]InventoryChange, 0, len(payload))
for key, newValue := range payload {
// Parse key: "inventory:sku:location"
parts := strings.Split(key, ":")
if len(parts) != 3 || parts[0] != "inventory" {
log.Printf("Invalid inventory key format: %s", key)
continue
}
sku := parts[1]
locationID := parts[2]
changes = append(changes, InventoryChange{
SKU: sku,
StockLocationID: locationID,
Value: newValue,
})
}
if l.handler != nil {
l.handler(changes)
} else {
// Default logging
for _, change := range changes {
fmt.Printf("Inventory changed: SKU %s at location %s -> %d\n", change.SKU, change.StockLocationID, change.Value)
}
}
}
return nil
}

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pkg/inventory/redis_service.go Normal file
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package inventory
import (
"context"
"errors"
"fmt"
"strconv"
"github.com/redis/go-redis/v9"
)
type RedisInventoryService struct {
client *redis.Client
ctx context.Context
luaScripts map[string]*redis.Script
}
func NewRedisInventoryService(client *redis.Client, ctx context.Context) (*RedisInventoryService, error) {
rdb := client
// Ping Redis to check connection
_, err := rdb.Ping(ctx).Result()
if err != nil {
return nil, err
}
return &RedisInventoryService{
client: rdb,
ctx: ctx,
luaScripts: make(map[string]*redis.Script),
}, nil
}
func (s *RedisInventoryService) LoadLuaScript(key string) error {
// Get the script from Redis
script, err := s.client.Get(s.ctx, key).Result()
if err != nil {
return err
}
// Load the script into the luaScripts cache
s.luaScripts[key] = redis.NewScript(script)
return nil
}
func (s *RedisInventoryService) AddWarehouse(warehouse *Warehouse) error {
// Convert warehouse to Redis-friendly format
data := map[string]interface{}{
"id": string(warehouse.ID),
"name": warehouse.Name,
"inventory": warehouse.Inventory,
}
// Store in Redis with a key pattern like "warehouse:<ID>"
key := "warehouse:" + string(warehouse.ID)
_, err := s.client.HMSet(s.ctx, key, data).Result()
return err
}
func (s *RedisInventoryService) GetInventory(sku SKU, locationID LocationID) (int64, error) {
cmd := s.client.Get(s.ctx, getInventoryKey(sku, locationID))
if err := cmd.Err(); err != nil {
return 0, err
}
i, err := cmd.Int64()
if err != nil {
return 0, err
}
return i, nil
}
func getInventoryKey(sku SKU, locationID LocationID) string {
return fmt.Sprintf("inventory:%s:%s", sku, locationID)
}
func (s *RedisInventoryService) UpdateInventory(rdb redis.Pipeliner, sku SKU, locationID LocationID, quantity int64) error {
key := getInventoryKey(sku, locationID)
cmd := rdb.Set(s.ctx, key, quantity, 0)
return cmd.Err()
}
var (
ErrInsufficientInventory = errors.New("insufficient inventory")
ErrInvalidQuantity = errors.New("invalid quantity")
ErrMissingReservation = errors.New("missing reservation")
)
func makeKeysAndArgs(req ...ReserveRequest) ([]string, []string) {
keys := make([]string, len(req))
args := make([]string, len(req))
for i, r := range req {
if r.Quantity <= 0 {
return nil, nil
}
keys[i] = getInventoryKey(r.SKU, r.LocationID)
args[i] = strconv.Itoa(int(r.Quantity))
}
return keys, args
}
func (s *RedisInventoryService) ReservationCheck(req ...ReserveRequest) (*ReserveRequest, error) {
if len(req) == 0 {
return nil, ErrMissingReservation
}
keys, args := makeKeysAndArgs(req...)
if keys == nil || args == nil {
return nil, ErrInvalidQuantity
}
cmd := reservationCheck.Run(s.ctx, s.client, keys, args)
if err := cmd.Err(); err != nil {
return nil, err
}
val := cmd.Val().(int64)
if val > 0 {
return nil, nil // success
}
// val is negative index of failing request
failingIndex := int(-val) - 1 // 0-based
return &req[failingIndex], ErrInsufficientInventory
}
func (s *RedisInventoryService) ReserveInventory(req ...ReserveRequest) error {
if len(req) == 0 {
return ErrMissingReservation
}
keys, args := makeKeysAndArgs(req...)
if keys == nil || args == nil {
return ErrInvalidQuantity
}
cmd := reserveScript.Run(s.ctx, s.client, keys, args)
if err := cmd.Err(); err != nil {
return err
}
if val, err := cmd.Int(); err != nil {
return err
} else if val != 1 {
return ErrInsufficientInventory
}
return nil
}
var reservationCheck = redis.NewScript(`
-- Get the number of keys passed
local num_keys = #KEYS
-- Ensure the number of keys matches the number of quantities
if num_keys ~= #ARGV then
return {err = "Script requires the same number of keys and quantities."}
end
-- ---
-- CHECK PHASE
-- ---
-- Loop through all keys to check their values first
for i = 1, num_keys do
local key = KEYS[i]
local quantity_to_check = tonumber(ARGV[i])
-- Fail if the quantity is not a valid number
if not quantity_to_check then
return {err = "Invalid quantity provided for key: " .. key}
end
-- Get the current value stored at the key
local current_val = tonumber(redis.call('GET', key))
-- Check the condition
-- Fail if:
-- 1. The key doesn't exist (current_val is nil)
-- 2. The value is not > the required quantity
if not current_val or current_val < quantity_to_check then
-- Return negative index (1-based) to indicate which request failed
return -i
end
end
return 1
`)
var reserveScript = redis.NewScript(`
-- Get the number of keys passed
local num_keys = #KEYS
-- Ensure the number of keys matches the number of quantities
if num_keys ~= #ARGV then
return {err = "Script requires the same number of keys and quantities."}
end
local new_values = {}
local payload = {}
-- ---
-- 1. CHECK PHASE
-- ---
-- Loop through all keys to check their values first
for i = 1, num_keys do
local key = KEYS[i]
local quantity_to_check = tonumber(ARGV[i])
-- Fail if the quantity is not a valid number
if not quantity_to_check then
return {err = "Invalid quantity provided for key: " .. key}
end
-- Get the current value stored at the key
local current_val = tonumber(redis.call('GET', key))
-- Check the condition
-- Fail if:
-- 1. The key doesn't exist (current_val is nil)
-- 2. The value is not > the required quantity
if not current_val or current_val < quantity_to_check then
-- Return 0 to indicate the operation failed and no changes were made
return 0
end
-- If the check passes, store the new value
local new_val = current_val - quantity_to_check
table.insert(new_values, new_val)
-- Add this key and its *new* value to our payload map
payload[key] = new_val
end
-- ---
-- 2. UPDATE PHASE
-- ---
-- If the script reaches this point, all checks passed.
-- Now, loop again and apply all the updates.
for i = 1, num_keys do
local key = KEYS[i]
local new_val = new_values[i]
-- Set the key to its new calculated value
redis.call('SET', key, new_val)
end
local message_payload = cjson.encode(payload)
-- Publish the JSON-encoded message to the specified channel
redis.call('PUBLISH', "inventory_changed", message_payload)
-- Return 1 to indicate the operation was successful
return 1
`)

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pkg/inventory/types.go Normal file
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package inventory
import "time"
type SKU string
type LocationID string
type InventoryItem struct {
SKU SKU
Quantity int
LastUpdate time.Time
}
type Warehouse struct {
ID LocationID
Name string
Inventory []InventoryItem
}
type InventoryService interface {
GetInventory(sku SKU, locationID LocationID) (int64, error)
ReserveInventory(req ...ReserveRequest) error
ReservationCheck(req ...ReserveRequest) (*ReserveRequest, error)
}
type ReserveRequest struct {
SKU SKU
LocationID LocationID
Quantity uint32
}