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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The exvar package provides a standardized interface to public variables,
// such as operation counters in servers. It exposes these variables via
// HTTP at /debug/vars in JSON format.
package exvar
import (
"bytes";
"fmt";
"http";
"io";
"log";
"strconv";
"sync";
)
// Var is an abstract type for all exported variables.
type Var interface {
String() string;
}
// Int is a 64-bit integer variable, and satisfies the Var interface.
type Int struct {
i int64;
mu sync.Mutex;
}
func (v *Int) String() string {
return strconv.Itoa64(v.i)
}
func (v *Int) Add(delta int64) {
v.mu.Lock();
defer v.mu.Unlock();
v.i += delta;
}
// Map is a string-to-Var map variable, and satisfies the Var interface.
type Map struct {
m map[string] Var;
mu sync.Mutex;
}
// KeyValue represents a single entry in a Map.
type KeyValue struct {
Key string;
Value Var;
}
func (v *Map) String() string {
v.mu.Lock();
defer v.mu.Unlock();
b := new(bytes.Buffer);
fmt.Fprintf(b, "{");
first := true;
for key, val := range v.m {
if !first {
fmt.Fprintf(b, ", ");
}
fmt.Fprintf(b, "\"%s\": %v", key, val.String());
first = false;
}
fmt.Fprintf(b, "}");
return string(b.Data())
}
func (v *Map) Init() *Map {
v.m = make(map[string] Var);
return v
}
func (v *Map) Get(key string) Var {
v.mu.Lock();
defer v.mu.Unlock();
if av, ok := v.m[key]; ok {
return av
}
return nil
}
func (v *Map) Set(key string, av Var) {
v.mu.Lock();
defer v.mu.Unlock();
v.m[key] = av;
}
func (v *Map) Add(key string, delta int64) {
v.mu.Lock();
defer v.mu.Unlock();
av, ok := v.m[key];
if !ok {
av = new(Int);
v.m[key] = av;
}
// Add to Int; ignore otherwise.
if iv, ok := av.(*Int); ok {
iv.Add(delta);
}
}
// TODO(rsc): Make sure map access in separate thread is safe.
func (v *Map) iterate(c chan<- KeyValue) {
for k, v := range v.m {
c <- KeyValue{ k, v };
}
close(c);
}
func (v *Map) Iter() <-chan KeyValue {
c := make(chan KeyValue);
go v.iterate(c);
return c
}
// String is a string variable, and satisfies the Var interface.
type String struct {
s string;
}
func (v *String) String() string {
return strconv.Quote(v.s)
}
func (v *String) Set(value string) {
v.s = value;
}
// IntFunc wraps a func() int64 to create a value that satisfies the Var interface.
// The function will be called each time the Var is evaluated.
type IntFunc func() int64;
func (v IntFunc) String() string {
return strconv.Itoa64(v())
}
// All published variables.
var vars map[string] Var = make(map[string] Var);
var mutex sync.Mutex;
// Publish declares an named exported variable. This should be called from a
// package's init function when it creates its Vars. If the name is already
// registered then this will log.Crash.
func Publish(name string, v Var) {
mutex.Lock();
defer mutex.Unlock();
if _, existing := vars[name]; existing {
log.Crash("Reuse of exported var name:", name);
}
vars[name] = v;
}
// Get retrieves a named exported variable.
func Get(name string) Var {
if v, ok := vars[name]; ok {
return v
}
return nil
}
// RemoveAll removes all exported variables.
// This is for tests; don't call this on a real server.
func RemoveAll() {
mutex.Lock();
defer mutex.Unlock();
vars = make(map[string] Var);
}
// Convenience functions for creating new exported variables.
func NewInt(name string) *Int {
v := new(Int);
Publish(name, v);
return v
}
func NewMap(name string) *Map {
v := new(Map).Init();
Publish(name, v);
return v
}
func NewString(name string) *String {
v := new(String);
Publish(name, v);
return v
}
// TODO(rsc): Make sure map access in separate thread is safe.
func iterate(c chan<- KeyValue) {
for k, v := range vars {
c <- KeyValue{ k, v };
}
close(c);
}
func Iter() <-chan KeyValue {
c := make(chan KeyValue);
go iterate(c);
return c
}
func exvarHandler(c *http.Conn, req *http.Request) {
c.SetHeader("content-type", "application/json; charset=utf-8");
fmt.Fprintf(c, "{\n");
first := true;
for name, value := range vars {
if !first {
fmt.Fprintf(c, ",\n");
}
first = false;
fmt.Fprintf(c, " %q: %s", name, value);
}
fmt.Fprintf(c, "\n}\n");
}
func init() {
http.Handle("/debug/vars", http.HandlerFunc(exvarHandler));
}
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