cmd/syncthing: Add cli as a subcommand (fixes #6566, fixes #4719) (#7364)

* cmd/syncthing: Add cli as a subcommand (fixes #6566, fixes #4719)

* Hijack help

* Add comment

* Revert go.mod/go.sum

cmd/syncthing/cli/utils.go

@@ -0,0 +1,94 @@
+// Copyright (C) 2019 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 cli
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+
+	"github.com/syncthing/syncthing/lib/config"
+	"github.com/urfave/cli"
+)
+
+func responseToBArray(response *http.Response) ([]byte, error) {
+	bytes, err := ioutil.ReadAll(response.Body)
+	if err != nil {
+		return nil, err
+	}
+	return bytes, response.Body.Close()
+}
+
+func emptyPost(url string) cli.ActionFunc {
+	return func(c *cli.Context) error {
+		client := c.App.Metadata["client"].(*APIClient)
+		_, err := client.Post(url, "")
+		return err
+	}
+}
+
+func dumpOutput(url string) cli.ActionFunc {
+	return func(c *cli.Context) error {
+		client := c.App.Metadata["client"].(*APIClient)
+		response, err := client.Get(url)
+		if err != nil {
+			return err
+		}
+		return prettyPrintResponse(c, response)
+	}
+}
+
+func getConfig(c *APIClient) (config.Configuration, error) {
+	cfg := config.Configuration{}
+	response, err := c.Get("system/config")
+	if err != nil {
+		return cfg, err
+	}
+	bytes, err := responseToBArray(response)
+	if err != nil {
+		return cfg, err
+	}
+	err = json.Unmarshal(bytes, &cfg)
+	if err == nil {
+		return cfg, err
+	}
+	return cfg, nil
+}
+
+func expects(n int, actionFunc cli.ActionFunc) cli.ActionFunc {
+	return func(ctx *cli.Context) error {
+		if ctx.NArg() != n {
+			plural := ""
+			if n != 1 {
+				plural = "s"
+			}
+			return fmt.Errorf("expected %d argument%s, got %d", n, plural, ctx.NArg())
+		}
+		return actionFunc(ctx)
+	}
+}
+
+func prettyPrintJSON(data interface{}) error {
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	return enc.Encode(data)
+}
+
+func prettyPrintResponse(c *cli.Context, response *http.Response) error {
+	bytes, err := responseToBArray(response)
+	if err != nil {
+		return err
+	}
+	var data interface{}
+	if err := json.Unmarshal(bytes, &data); err != nil {
+		return err
+	}
+	// TODO: Check flag for pretty print format
+	return prettyPrintJSON(data)
+}