fs: split overgrown fs.go (#5405)

Nothing is added or removed and no package is renamed by this change.
Just rearrange definitions between source files in the fs directory.

New source files:
- types.go      Filesystem types and interfaces
- features.go   Features and optional interfaces
- registry.go   Filesystem registry and backend options
- newfs.go      NewFs and its helpers
- configmap.go  Getters and Setters for ConfigMap
- pacer.go      Pacer with logging and calculator
The final fs.go contains what is left.

Also rename options.go to open_options.go
to dissociate from registry options.

fs/newfs.go

@@ -0,0 +1,122 @@
+// NewFs and its helpers
+
+package fs
+
+import (
+	"context"
+	"crypto/md5"
+	"encoding/base64"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/rclone/rclone/fs/config/configmap"
+	"github.com/rclone/rclone/fs/fspath"
+)
+
+// NewFs makes a new Fs object from the path
+//
+// The path is of the form remote:path
+//
+// Remotes are looked up in the config file.  If the remote isn't
+// found then NotFoundInConfigFile will be returned.
+//
+// On Windows avoid single character remote names as they can be mixed
+// up with drive letters.
+func NewFs(ctx context.Context, path string) (Fs, error) {
+	Debugf(nil, "Creating backend with remote %q", path)
+	fsInfo, configName, fsPath, config, err := ConfigFs(path)
+	if err != nil {
+		return nil, err
+	}
+	overridden := fsInfo.Options.Overridden(config)
+	if len(overridden) > 0 {
+		extraConfig := overridden.String()
+		//Debugf(nil, "detected overriden config %q", extraConfig)
+		md5sumBinary := md5.Sum([]byte(extraConfig))
+		suffix := base64.RawURLEncoding.EncodeToString(md5sumBinary[:])
+		// 5 characters length is 5*6 = 30 bits of base64
+		const maxLength = 5
+		if len(suffix) > maxLength {
+			suffix = suffix[:maxLength]
+		}
+		suffix = "{" + suffix + "}"
+		Debugf(configName, "detected overridden config - adding %q suffix to name", suffix)
+		// Add the suffix to the config name
+		//
+		// These need to work as filesystem names as the VFS cache will use them
+		configName += suffix
+	}
+	return fsInfo.NewFs(ctx, configName, fsPath, config)
+}
+
+// ConfigFs makes the config for calling NewFs with.
+//
+// It parses the path which is of the form remote:path
+//
+// Remotes are looked up in the config file.  If the remote isn't
+// found then NotFoundInConfigFile will be returned.
+func ConfigFs(path string) (fsInfo *RegInfo, configName, fsPath string, config *configmap.Map, err error) {
+	// Parse the remote path
+	fsInfo, configName, fsPath, connectionStringConfig, err := ParseRemote(path)
+	if err != nil {
+		return
+	}
+	config = ConfigMap(fsInfo, configName, connectionStringConfig)
+	return
+}
+
+// ParseRemote deconstructs a path into configName, fsPath, looking up
+// the fsName in the config file (returning NotFoundInConfigFile if not found)
+func ParseRemote(path string) (fsInfo *RegInfo, configName, fsPath string, connectionStringConfig configmap.Simple, err error) {
+	parsed, err := fspath.Parse(path)
+	if err != nil {
+		return nil, "", "", nil, err
+	}
+	configName, fsPath = parsed.Name, parsed.Path
+	var fsName string
+	var ok bool
+	if configName != "" {
+		if strings.HasPrefix(configName, ":") {
+			fsName = configName[1:]
+		} else {
+			m := ConfigMap(nil, configName, parsed.Config)
+			fsName, ok = m.Get("type")
+			if !ok {
+				return nil, "", "", nil, ErrorNotFoundInConfigFile
+			}
+		}
+	} else {
+		fsName = "local"
+		configName = "local"
+	}
+	fsInfo, err = Find(fsName)
+	return fsInfo, configName, fsPath, parsed.Config, err
+}
+
+// ConfigString returns a canonical version of the config string used
+// to configure the Fs as passed to fs.NewFs
+func ConfigString(f Fs) string {
+	name := f.Name()
+	root := f.Root()
+	if name == "local" && f.Features().IsLocal {
+		return root
+	}
+	return name + ":" + root
+}
+
+// TemporaryLocalFs creates a local FS in the OS's temporary directory.
+//
+// No cleanup is performed, the caller must call Purge on the Fs themselves.
+func TemporaryLocalFs(ctx context.Context) (Fs, error) {
+	path, err := ioutil.TempDir("", "rclone-spool")
+	if err == nil {
+		err = os.Remove(path)
+	}
+	if err != nil {
+		return nil, err
+	}
+	path = filepath.ToSlash(path)
+	return NewFs(ctx, path)
+}