Set X-Cache and X-Cache-Lookup headers for cache (#8794)

X-Cache sets cache status of HIT if object is
served from the disk cache, or MISS otherwise.
X-Cache-Lookup is set to HIT if object was found
in the cache even if not served (for e.g. if cache
 entry was invalidated by ETag verification)

cmd/api-headers.go

@@ -91,7 +91,10 @@ func setObjectHeaders(w http.ResponseWriter, objInfo ObjectInfo, rs *HTTPRangeSp
 	if !objInfo.Expires.IsZero() {
 		w.Header().Set(xhttp.Expires, objInfo.Expires.UTC().Format(http.TimeFormat))
 	}
-
+	if globalCacheConfig.Enabled {
+		w.Header().Set(xhttp.XCache, objInfo.CacheStatus.String())
+		w.Header().Set(xhttp.XCacheLookup, objInfo.CacheLookupStatus.String())
+	}
 	// Set all other user defined metadata.
 	for k, v := range objInfo.UserDefined {
 		if HasPrefix(k, ReservedMetadataPrefix) {

cmd/disk-cache-backend.go

@@ -91,6 +91,8 @@ func (m *cacheMeta) ToObjectInfo(bucket, object string) (o ObjectInfo) {
 	o = ObjectInfo{
 		Bucket:            bucket,
 		Name:              object,
+		CacheStatus:       CacheHit,
+		CacheLookupStatus: CacheHit,
 	}
 
 	// We set file info only if its valid.

cmd/disk-cache-utils.go

@@ -28,6 +28,24 @@ import (
 	"github.com/minio/minio/cmd/crypto"
 )
 
+// CacheStatusType - whether the request was served from cache.
+type CacheStatusType string
+
+const (
+	// CacheHit - whether object was served from cache.
+	CacheHit CacheStatusType = "HIT"
+
+	// CacheMiss - object served from backend.
+	CacheMiss CacheStatusType = "MISS"
+)
+
+func (c CacheStatusType) String() string {
+	if c != "" {
+		return string(c)
+	}
+	return string(CacheMiss)
+}
+
 type cacheControl struct {
 	expiry       time.Time
 	maxAge       int

cmd/disk-cache.go

@@ -223,7 +223,10 @@ func (c *cacheObjects) GetObjectNInfo(ctx context.Context, bucket, object string
 		}
 		if cc.noStore {
 			c.cacheStats.incMiss()
-			return c.GetObjectNInfo(ctx, bucket, object, rs, h, lockType, opts)
+			bReader, err := c.GetObjectNInfo(ctx, bucket, object, rs, h, lockType, opts)
+			bReader.ObjInfo.CacheLookupStatus = CacheHit
+			bReader.ObjInfo.CacheStatus = CacheMiss
+			return bReader, err
 		}
 	}
 
@@ -272,8 +275,14 @@ func (c *cacheObjects) GetObjectNInfo(ctx context.Context, bucket, object string
 		default:
 		}
 	}
+
+	bkReader, bkErr := c.GetObjectNInfoFn(ctx, bucket, object, rs, h, lockType, opts)
+	// Record if cache has a hit that was invalidated by ETag verification
+	if cacheErr == nil {
+		bkReader.ObjInfo.CacheLookupStatus = CacheHit
+	}
 	if !dcache.diskAvailable(objInfo.Size) {
-		return c.GetObjectNInfoFn(ctx, bucket, object, rs, h, lockType, opts)
+		return bkReader, bkErr
 	}
 
 	if rs != nil {
@@ -290,12 +299,9 @@ func (c *cacheObjects) GetObjectNInfo(ctx context.Context, bucket, object string
 				c.put(ctx, dcache, bucket, object, bReader, bReader.ObjInfo.Size, rs, ObjectOptions{UserDefined: getMetadata(bReader.ObjInfo)})
 			}
 		}()
-		return c.GetObjectNInfoFn(ctx, bucket, object, rs, h, lockType, opts)
-	}
-	bkReader, bkErr := c.GetObjectNInfoFn(ctx, bucket, object, rs, h, lockType, opts)
-	if bkErr != nil {
-		return nil, bkErr
+		return bkReader, bkErr
 	}
+
 	// Initialize pipe.
 	pipeReader, pipeWriter := io.Pipe()
 	teeReader := io.TeeReader(bkReader, pipeWriter)

cmd/http/headers.go

@@ -40,6 +40,12 @@ const (
 	Action             = "Action"
 )
 
+// Non standard S3 HTTP response constants
+const (
+	XCache       = "X-Cache"
+	XCacheLookup = "X-Cache-Lookup"
+)
+
 // Standard S3 HTTP request constants
 const (
 	IfModifiedSince   = "If-Modified-Since"

cmd/object-api-datatypes.go

@@ -143,6 +143,11 @@ type ObjectInfo struct {
 	// Date and time at which the object is no longer able to be cached
 	Expires time.Time
 
+	// CacheStatus sets status of whether this is a cache hit/miss
+	CacheStatus CacheStatusType
+	// CacheLookupStatus sets whether a cacheable response is present in the cache
+	CacheLookupStatus CacheStatusType
+
 	// Specify object storage class
 	StorageClass string