cmd/syncthing, lib/api: Separate api/gui into own package (ref #4085) (#5529)

* cmd/syncthing, lib/gui: Separate gui into own package (ref #4085)

* fix tests

* Don't use main as interface name (make old go happy)

* gui->api

* don't leak state via locations and use in-tree config

* let api (un-)subscribe to config

* interface naming and exporting

* lib/ur

* fix tests and lib/foldersummary

* shorter URVersion and ur debug fix

* review

* model.JsonCompletion(FolderCompletion) -> FolderCompletion.Map()

* rename debug facility https -> api

* folder summaries in model

* disassociate unrelated constants

* fix merge fail

* missing id assignement

lib/ur/memsize_linux.go

@@ -0,0 +1,39 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package ur
+
+import (
+	"bufio"
+	"errors"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func memorySize() (int64, error) {
+	f, err := os.Open("/proc/meminfo")
+	if err != nil {
+		return 0, err
+	}
+
+	s := bufio.NewScanner(f)
+	if !s.Scan() {
+		return 0, errors.New("/proc/meminfo parse error 1")
+	}
+
+	l := s.Text()
+	fs := strings.Fields(l)
+	if len(fs) != 3 || fs[2] != "kB" {
+		return 0, errors.New("/proc/meminfo parse error 2")
+	}
+
+	kb, err := strconv.ParseInt(fs[1], 10, 64)
+	if err != nil {
+		return 0, err
+	}
+	return kb * 1024, nil
+}