useragent.go

// -*- Mode: Go; indent-tabs-mode: t -*-

/*
 * Copyright (C) 2016-2020 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package snapdenv

import (
	"fmt"
	"strings"

	"github.com/snapcore/snapd/arch"
	"github.com/snapcore/snapd/osutil"
	"github.com/snapcore/snapd/release"
)

// UserAgent to send
var userAgent = "unset"

// SetUserAgentFromVersion sets up a user-agent string.
func SetUserAgentFromVersion(version string, probeForceDevMode func() bool, extraProds ...string) (restore func()) {
	extras := make([]string, 1, 3)
	extras[0] = "series " + release.Series
	if release.OnClassic {
		extras = append(extras, "classic")
	}
	if probeForceDevMode != nil && probeForceDevMode() {
		extras = append(extras, "devmode")
	}
	if release.OnWSL {
		extras = append(extras, "wsl")
	}
	if Testing() {
		extras = append(extras, "testing")
	}
	extraProdStr := ""
	if len(extraProds) != 0 {
		extraProdStr = " " + strings.Join(extraProds, " ")
	}
	origUserAgent := userAgent

	// xxx this assumes ReleaseInfo's ID and VersionID don't have weird characters
	// (see rfc 7231 for values of weird)
	// assumption checks out in practice, q.v. https://github.com/zyga/os-release-zoo
	userAgent = fmt.Sprintf("snapd/%v (%s)%s %s/%s (%s) linux/%s", version,
		strings.Join(extras, "; "), extraProdStr, release.ReleaseInfo.ID,
		release.ReleaseInfo.VersionID, string(arch.DpkgArchitecture()),
		sanitizeKernelVersion(osutil.KernelVersion()))
	return func() {
		userAgent = origUserAgent
	}
}

func sanitizeKernelVersion(in string) string {
	out := stripUnsafeRunes(in)
	// Arbitrary choice, limit kernel version to 25 characters
	if len(out) > 25 {
		out = out[:25]
	}
	return out
}

func safeRuneMapper(r rune) rune {
	if r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' || r == '-' || r == '_' || r == '.' {
		return r
	}
	return -1
}

func stripUnsafeRunes(in string) string {
	return strings.Map(safeRuneMapper, in)
}

// UserAgent returns the user-agent string setup through SetUserAgentFromVersion.
func UserAgent() string {
	return userAgent
}