tailscale/envknob/envknob.go

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// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package envknob provides access to environment-variable tweakable
// debug settings.
//
// These are primarily knobs used by Tailscale developers during
// development or by users when instructed to by Tailscale developers
// when debugging something. They are not a stable interface and may
// be removed or any time.
//
// A related package, control/controlknobs, are knobs that can be
// changed at runtime by the control plane. Sometimes both are used:
// an envknob for the default/explicit value, else falling back
// to the controlknob value.
package envknob
import (
"log"
"os"
"strconv"
"sync"
"tailscale.com/types/opt"
)
var (
mu sync.Mutex
set = map[string]string{}
list []string
)
func noteEnv(k, v string) {
if v == "" {
return
}
mu.Lock()
defer mu.Unlock()
if _, ok := set[k]; !ok {
list = append(list, k)
}
set[k] = v
}
// logf is logger.Logf, but logger depends on envknob, so for circular
// dependency reasons, make a type alias (so it's still assignable,
// but has nice docs here).
type logf = func(format string, args ...any)
// LogCurrent logs the currently set environment knobs.
func LogCurrent(logf logf) {
mu.Lock()
defer mu.Unlock()
for _, k := range list {
logf("envknob: %s=%q", k, set[k])
}
}
// String returns the named environment variable, using os.Getenv.
//
// If the variable is non-empty, it's also tracked & logged as being
// an in-use knob.
func String(envVar string) string {
v := os.Getenv(envVar)
noteEnv(envVar, v)
return v
}
// Bool returns the boolean value of the named environment variable.
// If the variable is not set, it returns false.
// An invalid value exits the binary with a failure.
func Bool(envVar string) bool {
return boolOr(envVar, false)
}
// BoolDefaultTrue is like Bool, but returns true by default if the
// environment variable isn't present.
func BoolDefaultTrue(envVar string) bool {
return boolOr(envVar, true)
}
func boolOr(envVar string, implicitValue bool) bool {
val := os.Getenv(envVar)
if val == "" {
return implicitValue
}
b, err := strconv.ParseBool(val)
if err == nil {
noteEnv(envVar, strconv.FormatBool(b)) // canonicalize
return b
}
log.Fatalf("invalid boolean environment variable %s value %q", envVar, val)
panic("unreachable")
}
// LookupBool returns the boolean value of the named environment value.
// The ok result is whether a value was set.
// If the value isn't a valid int, it exits the program with a failure.
func LookupBool(envVar string) (v bool, ok bool) {
val := os.Getenv(envVar)
if val == "" {
return false, false
}
b, err := strconv.ParseBool(val)
if err == nil {
return b, true
}
log.Fatalf("invalid boolean environment variable %s value %q", envVar, val)
panic("unreachable")
}
// OptBool is like Bool, but returns an opt.Bool, so the caller can
// distinguish between implicitly and explicitly false.
func OptBool(envVar string) opt.Bool {
b, ok := LookupBool(envVar)
if !ok {
return ""
}
var ret opt.Bool
ret.Set(b)
return ret
}
// LookupInt returns the integer value of the named environment value.
// The ok result is whether a value was set.
// If the value isn't a valid int, it exits the program with a failure.
func LookupInt(envVar string) (v int, ok bool) {
val := os.Getenv(envVar)
if val == "" {
return 0, false
}
v, err := strconv.Atoi(val)
if err == nil {
noteEnv(envVar, val)
return v, true
}
log.Fatalf("invalid integer environment variable %s: %v", envVar, val)
panic("unreachable")
}
// UseWIPCode is whether TAILSCALE_USE_WIP_CODE is set to permit use
// of Work-In-Progress code.
func UseWIPCode() bool { return Bool("TAILSCALE_USE_WIP_CODE") }
// CanSSHD is whether the Tailscale SSH server is allowed to run.
//
// If disabled, the SSH server won't start (won't intercept port 22)
// if already enabled and any attempt to re-enable it will result in
// an error.
func CanSSHD() bool { return !Bool("TS_DISABLE_SSH_SERVER") }
// SSHPolicyFile returns the path, if any, to the SSHPolicy JSON file for development.
func SSHPolicyFile() string { return String("TS_DEBUG_SSH_POLICY_FILE") }
// SSHIgnoreTailnetPolicy is whether to ignore the Tailnet SSH policy for development.
func SSHIgnoreTailnetPolicy() bool { return Bool("TS_DEBUG_SSH_IGNORE_TAILNET_POLICY") }