Refactor config and split them in packages (#8351)

This change is related to larger config migration PR
change, this is a first stage change to move our
configs to `cmd/config/` - divided into its subsystems

cmd/config/cache/lookup.go

@@ -0,0 +1,79 @@
+/*
+ * 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 cache
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/minio/minio/cmd/config"
+	"github.com/minio/minio/pkg/env"
+)
+
+// Cache ENVs
+const (
+	EnvCacheDrives              = "MINIO_CACHE_DRIVES"
+	EnvCacheExclude             = "MINIO_CACHE_EXCLUDE"
+	EnvCacheExpiry              = "MINIO_CACHE_EXPIRY"
+	EnvCacheMaxUse              = "MINIO_CACHE_MAXUSE"
+	EnvCacheEncryptionMasterKey = "MINIO_CACHE_ENCRYPTION_MASTER_KEY"
+)
+
+const (
+	cacheEnvDelimiter = ";"
+)
+
+// LookupConfig - extracts cache configuration provided by environment
+// variables and merge them with provided CacheConfiguration.
+func LookupConfig(cfg Config) (Config, error) {
+	if drives := env.Get(EnvCacheDrives, strings.Join(cfg.Drives, ",")); drives != "" {
+		driveList, err := parseCacheDrives(strings.Split(drives, cacheEnvDelimiter))
+		if err != nil {
+			return cfg, err
+		}
+		cfg.Drives = driveList
+	}
+
+	if excludes := env.Get(EnvCacheExclude, strings.Join(cfg.Exclude, ",")); excludes != "" {
+		excludeList, err := parseCacheExcludes(strings.Split(excludes, cacheEnvDelimiter))
+		if err != nil {
+			return cfg, err
+		}
+		cfg.Exclude = excludeList
+	}
+
+	if expiryStr := env.Get(EnvCacheExpiry, strconv.Itoa(cfg.Expiry)); expiryStr != "" {
+		expiry, err := strconv.Atoi(expiryStr)
+		if err != nil {
+			return cfg, config.ErrInvalidCacheExpiryValue(err)
+		}
+		cfg.Expiry = expiry
+	}
+
+	if maxUseStr := env.Get(EnvCacheMaxUse, strconv.Itoa(cfg.MaxUse)); maxUseStr != "" {
+		maxUse, err := strconv.Atoi(maxUseStr)
+		if err != nil {
+			return cfg, config.ErrInvalidCacheMaxUse(err)
+		}
+		// maxUse should be a valid percentage.
+		if maxUse > 0 && maxUse <= 100 {
+			cfg.MaxUse = maxUse
+		}
+	}
+
+	return cfg, nil
+}