merge upstream net/http: 2024-01-30(e8b5bc)

internal/godebug/godebug.go

@@ -2,33 +2,244 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package godebug parses the GODEBUG environment variable.
+// 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.
 package godebug
 
-import "os"
+// Note: Be careful about new imports here. Any package
+// that internal/godebug imports cannot itself import internal/godebug,
+// meaning it cannot introduce a GODEBUG setting of its own.
+// We keep imports to the absolute bare minimum.
+import (
+	"sync"
+	"sync/atomic"
+	_ "unsafe" // go:linkname
 
-// Get returns the value for the provided GODEBUG key.
-func Get(key string) string {
-	return get(os.Getenv("GODEBUG"), key)
+	"github.com/imroc/req/v3/internal/bisect"
+	"github.com/imroc/req/v3/internal/godebugs"
+)
+
+// A Setting is a single setting in the $GODEBUG environment variable.
+type Setting struct {
+	name string
+	once sync.Once
+	*setting
+}
+
+type setting struct {
+	value          atomic.Pointer[value]
+	nonDefaultOnce sync.Once
+	nonDefault     atomic.Uint64
+	info           *godebugs.Info
+}
+
+type value struct {
+	text   string
+	bisect *bisect.Matcher
+}
+
+// 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 New(name string) *Setting {
+	return &Setting{name: name}
+}
+
+// Name returns the name of the setting.
+func (s *Setting) Name() string {
+	if s.name != "" && s.name[0] == '#' {
+		return s.name[1:]
+	}
+	return s.name
 }
 
-// get returns the value part of key=value in s (a GODEBUG value).
-func get(s, key string) string {
-	for i := 0; i < len(s)-len(key)-1; i++ {
-		if i > 0 && s[i-1] != ',' {
-			continue
+// Undocumented reports whether this is an undocumented setting.
+func (s *Setting) Undocumented() bool {
+	return s.name != "" && s.name[0] == '#'
+}
+
+// String returns a printable form for the setting: name=value.
+func (s *Setting) String() string {
+	return s.Name() + "=" + s.Value()
+}
+
+// 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 (s *Setting) IncNonDefault() {
+	s.nonDefaultOnce.Do(s.register)
+	s.nonDefault.Add(1)
+}
+
+func (s *Setting) register() {
+	if s.info == nil || s.info.Opaque {
+		panic("godebug: unexpected IncNonDefault of " + s.name)
+	}
+}
+
+// cache is a cache of all the GODEBUG settings,
+// a locked map[string]*atomic.Pointer[string].
+//
+// All Settings with the same name share a single
+// *atomic.Pointer[string], so that when GODEBUG
+// changes only that single atomic string pointer
+// needs to be updated.
+//
+// A name appears in the values map either if it is the
+// name of a Setting for which Value has been called
+// at least once, or if the name has ever appeared in
+// a name=value pair in the $GODEBUG environment variable.
+// Once entered into the map, the name is never removed.
+var cache sync.Map // name string -> value *atomic.Pointer[string]
+
+var empty value
+
+// 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.
+func (s *Setting) Value() string {
+	s.once.Do(func() {
+		s.setting = lookup(s.Name())
+		if s.info == nil && !s.Undocumented() {
+			panic("godebug: Value of name not listed in godebugs.All: " + s.name)
 		}
-		afterKey := s[i+len(key):]
-		if afterKey[0] != '=' || s[i:i+len(key)] != key {
-			continue
+	})
+	v := *s.value.Load()
+	if v.bisect != nil && !v.bisect.Stack(&stderr) {
+		return ""
+	}
+	return v.text
+}
+
+// lookup returns the unique *setting value for the given name.
+func lookup(name string) *setting {
+	if v, ok := cache.Load(name); ok {
+		return v.(*setting)
+	}
+	s := new(setting)
+	s.info = godebugs.Lookup(name)
+	s.value.Store(&empty)
+	if v, loaded := cache.LoadOrStore(name, s); loaded {
+		// Lost race: someone else created it. Use theirs.
+		return v.(*setting)
+	}
+
+	return s
+}
+
+func newIncNonDefault(name string) func() {
+	s := New(name)
+	s.Value()
+	return s.IncNonDefault
+}
+
+var updateMu sync.Mutex
+
+// update records an updated GODEBUG setting.
+// def is the default GODEBUG setting for the running binary,
+// and env is the current value of the $GODEBUG environment variable.
+func update(def, env string) {
+	updateMu.Lock()
+	defer updateMu.Unlock()
+
+	// Update all the cached values, creating new ones as needed.
+	// We parse the environment variable first, so that any settings it has
+	// are already locked in place (did[name] = true) before we consider
+	// the defaults.
+	did := make(map[string]bool)
+	parse(did, env)
+	parse(did, def)
+
+	// Clear any cached values that are no longer present.
+	cache.Range(func(name, s any) bool {
+		if !did[name.(string)] {
+			s.(*setting).value.Store(&empty)
 		}
-		val := afterKey[1:]
-		for i, b := range val {
-			if b == ',' {
-				return val[:i]
+		return true
+	})
+}
+
+// parse parses the GODEBUG setting string s,
+// which has the form k=v,k2=v2,k3=v3.
+// Later settings override earlier ones.
+// Parse only updates settings k=v for which did[k] = false.
+// It also sets did[k] = true for settings that it updates.
+// Each value v can also have the form v#pattern,
+// in which case the GODEBUG is only enabled for call stacks
+// matching pattern, for use with golang.org/x/tools/cmd/bisect.
+func parse(did map[string]bool, s string) {
+	// Scan the string backward so that later settings are used
+	// and earlier settings are ignored.
+	// Note that a forward scan would cause cached values
+	// to temporarily use the ignored value before being
+	// updated to the "correct" one.
+	end := len(s)
+	eq := -1
+	for i := end - 1; i >= -1; i-- {
+		if i == -1 || s[i] == ',' {
+			if eq >= 0 {
+				name, arg := s[i+1:eq], s[eq+1:end]
+				if !did[name] {
+					did[name] = true
+					v := &value{text: arg}
+					for j := 0; j < len(arg); j++ {
+						if arg[j] == '#' {
+							v.text = arg[:j]
+							v.bisect, _ = bisect.New(arg[j+1:])
+							break
+						}
+					}
+					lookup(name).value.Store(v)
+				}
 			}
+			eq = -1
+			end = i
+		} else if s[i] == '=' {
+			eq = i
 		}
-		return val
 	}
-	return ""
+}
+
+type runtimeStderr struct{}
+
+var stderr runtimeStderr
+
+func (*runtimeStderr) Write(b []byte) (int, error) {
+	return len(b), nil
 }

internal/godebugs/table.go

@@ -0,0 +1,78 @@
+// Copyright 2023 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.
+
+// Package godebugs provides a table of known GODEBUG settings,
+// for use by a variety of other packages, including internal/godebug,
+// runtime, runtime/metrics, and cmd/go/internal/load.
+package godebugs
+
+// An Info describes a single known GODEBUG setting.
+type Info struct {
+	Name    string // name of the setting ("panicnil")
+	Package string // package that uses the setting ("runtime")
+	Changed int    // minor version when default changed, if any; 21 means Go 1.21
+	Old     string // value that restores behavior prior to Changed
+	Opaque  bool   // setting does not export information to runtime/metrics using [internal/godebug.Setting.IncNonDefault]
+}
+
+// All is the table of known settings, sorted by Name.
+//
+// Note: After adding entries to this table, run 'go generate runtime/metrics'
+// to update the runtime/metrics doc comment.
+// (Otherwise the runtime/metrics test will fail.)
+//
+// Note: After adding entries to this table, update the list in doc/godebug.md as well.
+// (Otherwise the test in this package will fail.)
+var All = []Info{
+	{Name: "execerrdot", Package: "os/exec"},
+	{Name: "gocachehash", Package: "cmd/go"},
+	{Name: "gocachetest", Package: "cmd/go"},
+	{Name: "gocacheverify", Package: "cmd/go"},
+	{Name: "gotypesalias", Package: "go/types"},
+	{Name: "http2client", Package: "net/http"},
+	{Name: "http2debug", Package: "net/http", Opaque: true},
+	{Name: "http2server", Package: "net/http"},
+	{Name: "httplaxcontentlength", Package: "net/http", Changed: 22, Old: "1"},
+	{Name: "httpmuxgo121", Package: "net/http", Changed: 22, Old: "1"},
+	{Name: "installgoroot", Package: "go/build"},
+	{Name: "jstmpllitinterp", Package: "html/template"},
+	//{Name: "multipartfiles", Package: "mime/multipart"},
+	{Name: "multipartmaxheaders", Package: "mime/multipart"},
+	{Name: "multipartmaxparts", Package: "mime/multipart"},
+	{Name: "multipathtcp", Package: "net"},
+	{Name: "netdns", Package: "net", Opaque: true},
+	{Name: "panicnil", Package: "runtime", Changed: 21, Old: "1"},
+	{Name: "randautoseed", Package: "math/rand"},
+	{Name: "tarinsecurepath", Package: "archive/tar"},
+	{Name: "tls10server", Package: "crypto/tls", Changed: 22, Old: "1"},
+	{Name: "tlsmaxrsasize", Package: "crypto/tls"},
+	{Name: "tlsrsakex", Package: "crypto/tls", Changed: 22, Old: "1"},
+	{Name: "tlsunsafeekm", Package: "crypto/tls", Changed: 22, Old: "1"},
+	{Name: "winreadlinkvolume", Package: "os", Changed: 22, Old: "0"},
+	{Name: "winsymlink", Package: "os", Changed: 22, Old: "0"},
+	{Name: "x509sha1", Package: "crypto/x509"},
+	{Name: "x509usefallbackroots", Package: "crypto/x509"},
+	{Name: "x509usepolicies", Package: "crypto/x509"},
+	{Name: "zipinsecurepath", Package: "archive/zip"},
+}
+
+// Lookup returns the Info with the given name.
+func Lookup(name string) *Info {
+	// binary search, avoiding import of sort.
+	lo := 0
+	hi := len(All)
+	for lo < hi {
+		m := int(uint(lo+hi) >> 1)
+		mid := All[m].Name
+		if name == mid {
+			return &All[m]
+		}
+		if name < mid {
+			hi = m
+		} else {
+			lo = m + 1
+		}
+	}
+	return nil
+}