serve http: support unix sockets and multiple listners

- add support for unix sockets (which skip the auth).
- add support for multiple listeners
- collapse unnecessary internal structure of lib/http so it can all be
  imported together
- moves files in sub directories of lib/http into the main lib/http
  directory and reworks the code that uses them.

See: https://forum.rclone.org/t/wip-rc-rcd-over-unix-socket/33619
Fixes: #6605

lib/http/template.go

@@ -0,0 +1,95 @@
+package http
+
+import (
+	"embed"
+	"html/template"
+	"os"
+	"time"
+
+	"github.com/spf13/pflag"
+
+	"github.com/rclone/rclone/fs/config/flags"
+)
+
+// TemplateHelp describes how to use a custom template
+var TemplateHelp = `
+#### Template
+
+` + "`--template`" + ` allows a user to specify a custom markup template for HTTP
+and WebDAV serve functions.  The server exports the following markup
+to be used within the template to server pages:
+
+| Parameter   | Description |
+| :---------- | :---------- |
+| .Name       | The full path of a file/directory. |
+| .Title      | Directory listing of .Name |
+| .Sort       | The current sort used.  This is changeable via ?sort= parameter |
+|             | Sort Options: namedirfirst,name,size,time (default namedirfirst) |
+| .Order      | The current ordering used.  This is changeable via ?order= parameter |
+|             | Order Options: asc,desc (default asc) |
+| .Query      | Currently unused. |
+| .Breadcrumb | Allows for creating a relative navigation |
+|-- .Link     | The relative to the root link of the Text. |
+|-- .Text     | The Name of the directory. |
+| .Entries    | Information about a specific file/directory. |
+|-- .URL      | The 'url' of an entry.  |
+|-- .Leaf     | Currently same as 'URL' but intended to be 'just' the name. |
+|-- .IsDir    | Boolean for if an entry is a directory or not. |
+|-- .Size     | Size in Bytes of the entry. |
+|-- .ModTime  | The UTC timestamp of an entry. |
+`
+
+// TemplateConfig for the templating functionality
+type TemplateConfig struct {
+	Path string
+}
+
+// AddFlagsPrefix for the templating functionality
+func (cfg *TemplateConfig) AddFlagsPrefix(flagSet *pflag.FlagSet, prefix string) {
+	flags.StringVarP(flagSet, &cfg.Path, prefix+"template", "", cfg.Path, "User-specified template")
+}
+
+// AddTemplateFlagsPrefix for the templating functionality
+func AddTemplateFlagsPrefix(flagSet *pflag.FlagSet, prefix string, cfg *TemplateConfig) {
+	cfg.AddFlagsPrefix(flagSet, prefix)
+}
+
+// DefaultTemplateCfg returns a new config which can be customized by command line flags
+func DefaultTemplateCfg() TemplateConfig {
+	return TemplateConfig{}
+}
+
+// AfterEpoch returns the time since the epoch for the given time
+func AfterEpoch(t time.Time) bool {
+	return t.After(time.Time{})
+}
+
+// Assets holds the embedded filesystem for the default template
+//
+//go:embed templates
+var Assets embed.FS
+
+// GetTemplate returns the HTML template for serving directories via HTTP/WebDAV
+func GetTemplate(tmpl string) (*template.Template, error) {
+	var readFile = os.ReadFile
+	if tmpl == "" {
+		tmpl = "templates/index.html"
+		readFile = Assets.ReadFile
+	}
+
+	data, err := readFile(tmpl)
+	if err != nil {
+		return nil, err
+	}
+
+	funcMap := template.FuncMap{
+		"afterEpoch": AfterEpoch,
+	}
+
+	tpl, err := template.New("index").Funcs(funcMap).Parse(string(data))
+	if err != nil {
+		return nil, err
+	}
+
+	return tpl, nil
+}