package godebug

Import Path
	internal/godebug (on go.dev)

Dependency Relation
	imports 5 packages, and imported by 20 packages


Involved Source Files

	
		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 must call [Setting.IncNonDefault] to increment a counter that can
		be reported by [runtime/metrics.Read]. The call must only happen when
		the program executes a non-default behavior, not just when the setting
		is set to a non-default value. This is occasionally (but very rarely)
		infeasible, in which case the internal/godebugs table entry must set
		Opaque: true, and the documentation in doc/godebug.md should
		mention that metrics are unavailable.
		
		Conventionally, the global variable representing a godebug is named
		for the godebug itself, with no case changes:
		
			var gotypesalias = godebug.New("gotypesalias") // this
			var goTypesAlias = godebug.New("gotypesalias") // NOT THIS
		
		The test in internal/godebugs that checks for use of IncNonDefault
		requires the use of this convention.
		
		Note that counters used with IncNonDefault must be added to
		various tables in other packages. See the [Setting.IncNonDefault]
		documentation for details.


Package-Level Type Names (only one)


	/* sort by:  |  */
	
		A Setting is a single setting in the $GODEBUG environment variable.

		
			
				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.

			
				Name returns the name of the setting.

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

			
				Undocumented reports whether this is an undocumented setting.

			
				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.

		
			*Setting : expvar.Var
			*Setting : fmt.Stringer
		
			func New(name string) *Setting




Package-Level Functions (only one)


	
		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.
		
		Note that almost all settings should arrange to call [IncNonDefault] precisely
		when program behavior is changing from the default due to the setting
		(not just when the setting is different, but when program behavior changes).
		See the [internal/godebug] package comment for more.