Refactor cache code, add comments

src/cache.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"image"
+	"log"
+)
+
+type ResultCacheKey struct {
+	UUID    string `json:"uuid"`
+	Type    string `json:"type"`
+	Scale   int    `json:"scale"`
+	Overlay bool   `json:"overlay"`
+}
+
+// GetCacheKey returns the key used in the cache based on the rendering options, calculated as an SHA-256 hash.
+func GetResultCacheKey(uuid, renderType string, opts *QueryParams) (string, error) {
+	rawKey := ResultCacheKey{
+		UUID:    uuid,
+		Type:    renderType,
+		Scale:   opts.Scale,
+		Overlay: opts.Overlay,
+	}
+
+	rawKeyData, err := json.Marshal(rawKey)
+
+	if err != nil {
+		return "", err
+	}
+
+	hash := sha256.Sum256(rawKeyData)
+
+	return fmt.Sprintf("result:%s", hex.EncodeToString(hash[:])), nil
+}
+
+// GetCachedRenderResult returns the render result from Redis cache, or nil if it does not exist or cache is disabled.
+func GetCachedRenderResult(renderType, uuid string, opts *QueryParams) ([]byte, error) {
+	if conf.Cache.RenderCacheDuration == nil {
+		return nil, nil
+	}
+
+	key, err := GetResultCacheKey(uuid, renderType, opts)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return r.GetBytes(key)
+}
+
+// SetCachedRenderResult puts the render result into cache, or does nothing is cache is disabled.
+func SetCachedRenderResult(renderType, uuid string, opts *QueryParams, data []byte) error {
+	if conf.Cache.RenderCacheDuration == nil {
+		return nil
+	}
+
+	key, err := GetResultCacheKey(uuid, renderType, opts)
+
+	if err != nil {
+		return err
+	}
+
+	return r.Set(key, data, *conf.Cache.RenderCacheDuration)
+}
+
+// GetCachedSkin returns the raw skin of a player by UUID from the cache, also returning if the player has a slim player model.
+func GetCachedSkin(uuid string) (*image.NRGBA, bool, error) {
+	cache, ok, err := r.GetNRGBA(fmt.Sprintf("skin:%s", uuid))
+
+	if err != nil {
+		return nil, false, err
+	}
+
+	if ok {
+		slim, err := r.Exists(fmt.Sprintf("slim:%s", uuid))
+
+		if err != nil {
+			return nil, false, err
+		}
+
+		if conf.Environment == "development" {
+			log.Printf("Retrieved player skin from cache (uuid=%s, slim=%v)\n", uuid, slim)
+		}
+
+		return cache, slim, nil
+	}
+
+	return nil, false, nil
+}