package standard library
go1.22.5 Latest Latest

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Published: Jul 2, 2024 License: BSD-3-Clause Imports: 5 Imported by: 0



Package godebug makes the settings in the $GODEBUG environment variable available to other packages. These settings are often used for compatibility tweaks, when we need to change a default behavior but want to let users opt back in to the original. For example GODEBUG=http2server=0 disables HTTP/2 support in the net/http server.

In typical usage, code should declare a Setting as a global and then call Value each time the current setting value is needed:

var http2server = godebug.New("http2server")

func ServeConn(c net.Conn) {
	if http2server.Value() == "0" {
		disallow HTTP/2

Each time a non-default setting causes a change in program behavior, code should call Setting.IncNonDefault to increment a counter that can be reported by runtime/metrics.Read. Note that counters used with IncNonDefault must be added to various tables in other packages. See the Setting.IncNonDefault documentation for details.



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type Setting added in go1.20

type Setting struct {
	// contains filtered or unexported fields

A Setting is a single setting in the $GODEBUG environment variable.

func New added in go1.20

func New(name string) *Setting

New returns a new Setting for the $GODEBUG setting with the given name.

GODEBUGs meant for use by end users must be listed in ../godebugs/table.go, which is used for generating and checking various documentation. If the name is not listed in that table, New will succeed but calling Value on the returned Setting will panic. To disable that panic for access to an undocumented setting, prefix the name with a #, as in godebug.New("#gofsystrace"). The # is a signal to New but not part of the key used in $GODEBUG.

func (*Setting) IncNonDefault added in go1.21.0

func (s *Setting) IncNonDefault()

IncNonDefault increments the non-default behavior counter associated with the given setting. This counter is exposed in the runtime/metrics value /godebug/non-default-behavior/<name>:events.

Note that Value must be called at least once before IncNonDefault.

func (*Setting) Name added in go1.20

func (s *Setting) Name() string

Name returns the name of the setting.

func (*Setting) String added in go1.20

func (s *Setting) String() string

String returns a printable form for the setting: name=value.

func (*Setting) Undocumented added in go1.21.0

func (s *Setting) Undocumented() bool

Undocumented reports whether this is an undocumented setting.

func (*Setting) Value added in go1.20

func (s *Setting) Value() string

Value returns the current value for the GODEBUG setting s.

Value maintains an internal cache that is synchronized with changes to the $GODEBUG environment variable, making Value efficient to call as frequently as needed. Clients should therefore typically not attempt their own caching of Value's result.

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