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/context.go

@@ -0,0 +1,68 @@
+package http
+
+import (
+	"context"
+	"net"
+	"net/http"
+)
+
+type ctxKey int
+
+const (
+	ctxKeyAuth ctxKey = iota
+	ctxKeyPublicURL
+	ctxKeyUnixSock
+	ctxKeyUser
+)
+
+// NewBaseContext initializes the context for all requests, adding info for use in middleware and handlers
+func NewBaseContext(ctx context.Context, url string) func(l net.Listener) context.Context {
+	return func(l net.Listener) context.Context {
+		if l.Addr().Network() == "unix" {
+			ctx = context.WithValue(ctx, ctxKeyUnixSock, true)
+			return ctx
+		}
+
+		ctx = context.WithValue(ctx, ctxKeyPublicURL, url)
+		return ctx
+	}
+}
+
+// IsAuthenticated checks if this request was authenticated via a middleware
+func IsAuthenticated(r *http.Request) bool {
+	if v := r.Context().Value(ctxKeyAuth); v != nil {
+		return true
+	}
+	if v := r.Context().Value(ctxKeyUser); v != nil {
+		return true
+	}
+	return false
+}
+
+// IsUnixSocket checks if the request was received on a unix socket, used to skip auth & CORS
+func IsUnixSocket(r *http.Request) bool {
+	v, _ := r.Context().Value(ctxKeyUnixSock).(bool)
+	return v
+}
+
+// PublicURL returns the URL defined in NewBaseContext, used for logging & CORS
+func PublicURL(r *http.Request) string {
+	v, _ := r.Context().Value(ctxKeyPublicURL).(string)
+	return v
+}
+
+// CtxGetAuth is a wrapper over the private Auth context key
+func CtxGetAuth(ctx context.Context) interface{} {
+	return ctx.Value(ctxKeyAuth)
+}
+
+// CtxGetUser is a wrapper over the private User context key
+func CtxGetUser(ctx context.Context) (string, bool) {
+	v, ok := ctx.Value(ctxKeyUser).(string)
+	return v, ok
+}
+
+// CtxSetUser is a test helper that injects a User value into context
+func CtxSetUser(ctx context.Context, value string) context.Context {
+	return context.WithValue(ctx, ctxKeyUser, value)
+}