cache: Rewrite to cache only on download (#7575)

This will allow cache to consistently work for
server and gateways. Range GET requests will
be cached in the background after the request
is served from the backend.

Fixes: #7458, #7573, #6265, #6630

cmd/disk-cache-utils.go

@@ -0,0 +1,146 @@
+/*
+ * MinIO Cloud Storage, (C) 2019 MinIO, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/minio/minio/cmd/crypto"
+)
+
+type cacheControl struct {
+	exclude  bool
+	expiry   time.Time
+	maxAge   int
+	sMaxAge  int
+	minFresh int
+}
+
+// cache exclude directives in cache-control header
+var cacheExcludeDirectives = []string{
+	"no-cache",
+	"no-store",
+	"must-revalidate",
+}
+
+// returns true if cache exclude directives are set.
+func isCacheExcludeDirective(s string) bool {
+	for _, directive := range cacheExcludeDirectives {
+		if s == directive {
+			return true
+		}
+	}
+	return false
+}
+
+// returns struct with cache-control settings from user metadata.
+func getCacheControlOpts(m map[string]string) (c cacheControl, err error) {
+	var headerVal string
+	for k, v := range m {
+		if k == "cache-control" {
+			headerVal = v
+		}
+		if k == "expires" {
+			if e, err := http.ParseTime(v); err == nil {
+				c.expiry = e
+			}
+		}
+	}
+	if headerVal == "" {
+		return
+	}
+	headerVal = strings.ToLower(headerVal)
+	headerVal = strings.TrimSpace(headerVal)
+
+	vals := strings.Split(headerVal, ",")
+	for _, val := range vals {
+		val = strings.TrimSpace(val)
+		p := strings.Split(val, "=")
+		if isCacheExcludeDirective(p[0]) {
+			c.exclude = true
+			continue
+		}
+
+		if len(p) != 2 {
+			continue
+		}
+		if p[0] == "max-age" ||
+			p[0] == "s-maxage" ||
+			p[0] == "min-fresh" {
+			i, err := strconv.Atoi(p[1])
+			if err != nil {
+				return c, err
+			}
+			if p[0] == "max-age" {
+				c.maxAge = i
+			}
+			if p[0] == "s-maxage" {
+				c.sMaxAge = i
+			}
+			if p[0] == "min-fresh" {
+				c.minFresh = i
+			}
+		}
+	}
+	return c, nil
+}
+
+// return true if metadata has a cache-control header
+// directive to exclude object from cache.
+func filterFromCache(m map[string]string) bool {
+	c, err := getCacheControlOpts(m)
+	if err != nil {
+		return false
+	}
+	return c.exclude
+}
+
+// returns true if cache expiry conditions met in cache-control/expiry metadata.
+func isStaleCache(objInfo ObjectInfo) bool {
+	c, err := getCacheControlOpts(objInfo.UserDefined)
+	if err != nil {
+		return false
+	}
+	now := time.Now()
+	if c.sMaxAge > 0 && c.sMaxAge > int(now.Sub(objInfo.ModTime).Seconds()) {
+		return true
+	}
+	if c.maxAge > 0 && c.maxAge > int(now.Sub(objInfo.ModTime).Seconds()) {
+		return true
+	}
+	if !c.expiry.Equal(time.Time{}) && c.expiry.Before(time.Now()) {
+		return true
+	}
+	if c.minFresh > 0 && c.minFresh <= int(now.Sub(objInfo.ModTime).Seconds()) {
+		return true
+	}
+	return false
+}
+
+// backendDownError returns true if err is due to backend failure or faulty disk if in server mode
+func backendDownError(err error) bool {
+	_, backendDown := err.(BackendDown)
+	return backendDown || IsErr(err, baseErrs...)
+}
+
+// IsCacheable returns if the object should be saved in the cache.
+func (o ObjectInfo) IsCacheable() bool {
+	return !crypto.IsEncrypted(o.UserDefined)
+}