fs/rc: add more infrastructure to help writing rc functions

- Fs cache for rc commands
- Helper functions for parsing the input
- Reshape command for manipulating JSON blobs
- Background Job starting, control, query and expiry

fs/rc/cache.go

@@ -0,0 +1,60 @@
+// This implements the Fs cache
+
+package rc
+
+import (
+	"sync"
+
+	"github.com/ncw/rclone/fs"
+)
+
+var (
+	fsCacheMu sync.Mutex
+	fsCache   = map[string]fs.Fs{}
+	fsNewFs   = fs.NewFs // for tests
+)
+
+// GetFsNamed gets a fs.Fs named fsName either from the cache or creates it afresh
+func GetFsNamed(in Params, fsName string) (f fs.Fs, err error) {
+	fsCacheMu.Lock()
+	defer fsCacheMu.Unlock()
+
+	fsString, err := in.GetString(fsName)
+	if err != nil {
+		return nil, err
+	}
+
+	f = fsCache[fsString]
+	if f == nil {
+		f, err = fsNewFs(fsString)
+		if err == nil {
+			fsCache[fsString] = f
+		}
+	}
+	return f, err
+}
+
+// GetFs gets a fs.Fs named "fs" either from the cache or creates it afresh
+func GetFs(in Params) (f fs.Fs, err error) {
+	return GetFsNamed(in, "fs")
+}
+
+// GetFsAndRemoteNamed gets the fsName parameter from in, makes a
+// remote or fetches it from the cache then gets the remoteName
+// parameter from in too.
+func GetFsAndRemoteNamed(in Params, fsName, remoteName string) (f fs.Fs, remote string, err error) {
+	remote, err = in.GetString(remoteName)
+	if err != nil {
+		return
+	}
+	f, err = GetFsNamed(in, fsName)
+	return
+
+}
+
+// GetFsAndRemote gets the `fs` parameter from in, makes a remote or
+// fetches it from the cache then gets the `remote` parameter from in
+// too.
+func GetFsAndRemote(in Params) (f fs.Fs, remote string, err error) {
+	return GetFsAndRemoteNamed(in, "fs", "remote")
+}