expvar

Documentation

Overview

Package expvar 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. As of Go 1.22, the /debug/vars request must use GET.

Operations to set or modify these public variables are atomic.

In addition to adding the HTTP handler, this package registers the following variables:

cmdline   os.Args
memstats  runtime.Memstats

The package is sometimes only imported for the side effect of registering its HTTP handler and the above variables. To use it this way, link this package into your program:

import _ "expvar"

Index

• func Do(f func(KeyValue))
• func Handler() http.Handler
• func Publish(name string, v Var)
• type Float
  • func NewFloat(name string) *Float
  • func (v *Float) Add(delta float64)
  • func (v *Float) Set(value float64)
  • func (v *Float) String() string
  • func (v *Float) Value() float64
• type Func
  • func (f Func) String() string
  • func (f Func) Value() any
• type Int
  • func NewInt(name string) *Int
  • func (v *Int) Add(delta int64)
  • func (v *Int) Set(value int64)
  • func (v *Int) String() string
  • func (v *Int) Value() int64
• type KeyValue
• type Map
  • func NewMap(name string) *Map
  • func (v *Map) Add(key string, delta int64)
  • func (v *Map) AddFloat(key string, delta float64)
  • func (v *Map) Delete(key string)
  • func (v *Map) Do(f func(KeyValue))
  • func (v *Map) Get(key string) Var
  • func (v *Map) Init() *Map
  • func (v *Map) Set(key string, av Var)
  • func (v *Map) String() string
• type String
  • func NewString(name string) *String
  • func (v *String) Set(value string)
  • func (v *String) String() string
  • func (v *String) Value() string
• type Var
  • func Get(name string) Var

Functions

func Do

func Do(f func(KeyValue))

Do calls f for each exported variable. The global variable map is locked during the iteration, but existing entries may be concurrently updated.

func Handler

func Handler() http.Handler

Handler returns the expvar HTTP Handler.

This is only needed to install the handler in a non-standard location.

func Publish

func Publish(name string, v Var)

Publish declares a 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.Panic.

Types

type Float

type Float struct {
	// contains filtered or unexported fields
}

Float is a 64-bit float variable that satisfies the Var interface.

func NewFloat

func NewFloat(name string) *Float

func (*Float) Add

func (v *Float) Add(delta float64)

Add adds delta to v.

func (*Float) Set

func (v *Float) Set(value float64)

Set sets v to value.

func (*Float) String

func (v *Float) String() string

func (*Float) Value

func (v *Float) Value() float64

type Func

type Func func() any

Func implements Var by calling the function and formatting the returned value using JSON.

func (Func) String

func (f Func) String() string

func (Func) Value

func (f Func) Value() any

type Int

type Int struct {
	// contains filtered or unexported fields
}

Int is a 64-bit integer variable that satisfies the Var interface.

func NewInt

func NewInt(name string) *Int

func (*Int) Add

func (v *Int) Add(delta int64)

func (*Int) Set

func (v *Int) Set(value int64)

func (*Int) String

func (v *Int) String() string

func (*Int) Value

func (v *Int) Value() int64

type KeyValue

type KeyValue struct {
	Key   string
	Value Var
}

KeyValue represents a single entry in a Map.

type Map

type Map struct {
	// contains filtered or unexported fields
}

Map is a string-to-Var map variable that satisfies the Var interface.

func NewMap

func NewMap(name string) *Map

func (*Map) Add

func (v *Map) Add(key string, delta int64)

Add adds delta to the *Int value stored under the given map key.

func (*Map) AddFloat

func (v *Map) AddFloat(key string, delta float64)

AddFloat adds delta to the *Float value stored under the given map key.

func (*Map) Delete

func (v *Map) Delete(key string)

Delete deletes the given key from the map.

func (*Map) Do

func (v *Map) Do(f func(KeyValue))

Do calls f for each entry in the map. The map is locked during the iteration, but existing entries may be concurrently updated.

func (*Map) Get

func (v *Map) Get(key string) Var

func (*Map) Init

func (v *Map) Init() *Map

Init removes all keys from the map.

func (*Map) Set

func (v *Map) Set(key string, av Var)

func (*Map) String

func (v *Map) String() string

type String

type String struct {
	// contains filtered or unexported fields
}

String is a string variable, and satisfies the Var interface.

func NewString

func NewString(name string) *String

func (*String) Set

func (v *String) Set(value string)

func (*String) String

func (v *String) String() string

String implements the Var interface. To get the unquoted string use String.Value.

func (*String) Value

func (v *String) Value() string

type Var

type Var interface {
	// String returns a valid JSON value for the variable.
	// Types with String methods that do not return valid JSON
	// (such as time.Time) must not be used as a Var.
	String() string
}

Var is an abstract type for all exported variables.

func Get

func Get(name string) Var

Get retrieves a named exported variable. It returns nil if the name has not been registered.