aboutsummaryrefslogtreecommitdiff
path: root/vendor/golang.org/x/net/context
diff options
context:
space:
mode:
authorVidhu Kant Sharma <bokuwakanojogahoshii@yahoo.com>2020-10-19 11:05:36 +0530
committerVidhu Kant Sharma <bokuwakanojogahoshii@yahoo.com>2020-10-19 11:05:36 +0530
commit9c2ad91230d72fe6d661450cc78300ea223ae2bc (patch)
tree17bd774b3f972359dfbb46248f085bbf1c6dae98 /vendor/golang.org/x/net/context
make it better
Diffstat (limited to 'vendor/golang.org/x/net/context')
-rw-r--r--vendor/golang.org/x/net/context/context.go447
1 files changed, 447 insertions, 0 deletions
diff --git a/vendor/golang.org/x/net/context/context.go b/vendor/golang.org/x/net/context/context.go
new file mode 100644
index 0000000..e7ee376
--- /dev/null
+++ b/vendor/golang.org/x/net/context/context.go
@@ -0,0 +1,447 @@
+// Copyright 2014 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 context defines the Context type, which carries deadlines,
+// cancelation signals, and other request-scoped values across API boundaries
+// and between processes.
+//
+// Incoming requests to a server should create a Context, and outgoing calls to
+// servers should accept a Context. The chain of function calls between must
+// propagate the Context, optionally replacing it with a modified copy created
+// using WithDeadline, WithTimeout, WithCancel, or WithValue.
+//
+// Programs that use Contexts should follow these rules to keep interfaces
+// consistent across packages and enable static analysis tools to check context
+// propagation:
+//
+// Do not store Contexts inside a struct type; instead, pass a Context
+// explicitly to each function that needs it. The Context should be the first
+// parameter, typically named ctx:
+//
+// func DoSomething(ctx context.Context, arg Arg) error {
+// // ... use ctx ...
+// }
+//
+// Do not pass a nil Context, even if a function permits it. Pass context.TODO
+// if you are unsure about which Context to use.
+//
+// Use context Values only for request-scoped data that transits processes and
+// APIs, not for passing optional parameters to functions.
+//
+// The same Context may be passed to functions running in different goroutines;
+// Contexts are safe for simultaneous use by multiple goroutines.
+//
+// See http://blog.golang.org/context for example code for a server that uses
+// Contexts.
+package context // import "golang.org/x/net/context"
+
+import (
+ "errors"
+ "fmt"
+ "sync"
+ "time"
+)
+
+// A Context carries a deadline, a cancelation signal, and other values across
+// API boundaries.
+//
+// Context's methods may be called by multiple goroutines simultaneously.
+type Context interface {
+ // Deadline returns the time when work done on behalf of this context
+ // should be canceled. Deadline returns ok==false when no deadline is
+ // set. Successive calls to Deadline return the same results.
+ Deadline() (deadline time.Time, ok bool)
+
+ // Done returns a channel that's closed when work done on behalf of this
+ // context should be canceled. Done may return nil if this context can
+ // never be canceled. Successive calls to Done return the same value.
+ //
+ // WithCancel arranges for Done to be closed when cancel is called;
+ // WithDeadline arranges for Done to be closed when the deadline
+ // expires; WithTimeout arranges for Done to be closed when the timeout
+ // elapses.
+ //
+ // Done is provided for use in select statements:
+ //
+ // // Stream generates values with DoSomething and sends them to out
+ // // until DoSomething returns an error or ctx.Done is closed.
+ // func Stream(ctx context.Context, out <-chan Value) error {
+ // for {
+ // v, err := DoSomething(ctx)
+ // if err != nil {
+ // return err
+ // }
+ // select {
+ // case <-ctx.Done():
+ // return ctx.Err()
+ // case out <- v:
+ // }
+ // }
+ // }
+ //
+ // See http://blog.golang.org/pipelines for more examples of how to use
+ // a Done channel for cancelation.
+ Done() <-chan struct{}
+
+ // Err returns a non-nil error value after Done is closed. Err returns
+ // Canceled if the context was canceled or DeadlineExceeded if the
+ // context's deadline passed. No other values for Err are defined.
+ // After Done is closed, successive calls to Err return the same value.
+ Err() error
+
+ // Value returns the value associated with this context for key, or nil
+ // if no value is associated with key. Successive calls to Value with
+ // the same key returns the same result.
+ //
+ // Use context values only for request-scoped data that transits
+ // processes and API boundaries, not for passing optional parameters to
+ // functions.
+ //
+ // A key identifies a specific value in a Context. Functions that wish
+ // to store values in Context typically allocate a key in a global
+ // variable then use that key as the argument to context.WithValue and
+ // Context.Value. A key can be any type that supports equality;
+ // packages should define keys as an unexported type to avoid
+ // collisions.
+ //
+ // Packages that define a Context key should provide type-safe accessors
+ // for the values stores using that key:
+ //
+ // // Package user defines a User type that's stored in Contexts.
+ // package user
+ //
+ // import "golang.org/x/net/context"
+ //
+ // // User is the type of value stored in the Contexts.
+ // type User struct {...}
+ //
+ // // key is an unexported type for keys defined in this package.
+ // // This prevents collisions with keys defined in other packages.
+ // type key int
+ //
+ // // userKey is the key for user.User values in Contexts. It is
+ // // unexported; clients use user.NewContext and user.FromContext
+ // // instead of using this key directly.
+ // var userKey key = 0
+ //
+ // // NewContext returns a new Context that carries value u.
+ // func NewContext(ctx context.Context, u *User) context.Context {
+ // return context.WithValue(ctx, userKey, u)
+ // }
+ //
+ // // FromContext returns the User value stored in ctx, if any.
+ // func FromContext(ctx context.Context) (*User, bool) {
+ // u, ok := ctx.Value(userKey).(*User)
+ // return u, ok
+ // }
+ Value(key interface{}) interface{}
+}
+
+// Canceled is the error returned by Context.Err when the context is canceled.
+var Canceled = errors.New("context canceled")
+
+// DeadlineExceeded is the error returned by Context.Err when the context's
+// deadline passes.
+var DeadlineExceeded = errors.New("context deadline exceeded")
+
+// An emptyCtx is never canceled, has no values, and has no deadline. It is not
+// struct{}, since vars of this type must have distinct addresses.
+type emptyCtx int
+
+func (*emptyCtx) Deadline() (deadline time.Time, ok bool) {
+ return
+}
+
+func (*emptyCtx) Done() <-chan struct{} {
+ return nil
+}
+
+func (*emptyCtx) Err() error {
+ return nil
+}
+
+func (*emptyCtx) Value(key interface{}) interface{} {
+ return nil
+}
+
+func (e *emptyCtx) String() string {
+ switch e {
+ case background:
+ return "context.Background"
+ case todo:
+ return "context.TODO"
+ }
+ return "unknown empty Context"
+}
+
+var (
+ background = new(emptyCtx)
+ todo = new(emptyCtx)
+)
+
+// Background returns a non-nil, empty Context. It is never canceled, has no
+// values, and has no deadline. It is typically used by the main function,
+// initialization, and tests, and as the top-level Context for incoming
+// requests.
+func Background() Context {
+ return background
+}
+
+// TODO returns a non-nil, empty Context. Code should use context.TODO when
+// it's unclear which Context to use or it's is not yet available (because the
+// surrounding function has not yet been extended to accept a Context
+// parameter). TODO is recognized by static analysis tools that determine
+// whether Contexts are propagated correctly in a program.
+func TODO() Context {
+ return todo
+}
+
+// A CancelFunc tells an operation to abandon its work.
+// A CancelFunc does not wait for the work to stop.
+// After the first call, subsequent calls to a CancelFunc do nothing.
+type CancelFunc func()
+
+// WithCancel returns a copy of parent with a new Done channel. The returned
+// context's Done channel is closed when the returned cancel function is called
+// or when the parent context's Done channel is closed, whichever happens first.
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this Context complete.
+func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
+ c := newCancelCtx(parent)
+ propagateCancel(parent, &c)
+ return &c, func() { c.cancel(true, Canceled) }
+}
+
+// newCancelCtx returns an initialized cancelCtx.
+func newCancelCtx(parent Context) cancelCtx {
+ return cancelCtx{
+ Context: parent,
+ done: make(chan struct{}),
+ }
+}
+
+// propagateCancel arranges for child to be canceled when parent is.
+func propagateCancel(parent Context, child canceler) {
+ if parent.Done() == nil {
+ return // parent is never canceled
+ }
+ if p, ok := parentCancelCtx(parent); ok {
+ p.mu.Lock()
+ if p.err != nil {
+ // parent has already been canceled
+ child.cancel(false, p.err)
+ } else {
+ if p.children == nil {
+ p.children = make(map[canceler]bool)
+ }
+ p.children[child] = true
+ }
+ p.mu.Unlock()
+ } else {
+ go func() {
+ select {
+ case <-parent.Done():
+ child.cancel(false, parent.Err())
+ case <-child.Done():
+ }
+ }()
+ }
+}
+
+// parentCancelCtx follows a chain of parent references until it finds a
+// *cancelCtx. This function understands how each of the concrete types in this
+// package represents its parent.
+func parentCancelCtx(parent Context) (*cancelCtx, bool) {
+ for {
+ switch c := parent.(type) {
+ case *cancelCtx:
+ return c, true
+ case *timerCtx:
+ return &c.cancelCtx, true
+ case *valueCtx:
+ parent = c.Context
+ default:
+ return nil, false
+ }
+ }
+}
+
+// removeChild removes a context from its parent.
+func removeChild(parent Context, child canceler) {
+ p, ok := parentCancelCtx(parent)
+ if !ok {
+ return
+ }
+ p.mu.Lock()
+ if p.children != nil {
+ delete(p.children, child)
+ }
+ p.mu.Unlock()
+}
+
+// A canceler is a context type that can be canceled directly. The
+// implementations are *cancelCtx and *timerCtx.
+type canceler interface {
+ cancel(removeFromParent bool, err error)
+ Done() <-chan struct{}
+}
+
+// A cancelCtx can be canceled. When canceled, it also cancels any children
+// that implement canceler.
+type cancelCtx struct {
+ Context
+
+ done chan struct{} // closed by the first cancel call.
+
+ mu sync.Mutex
+ children map[canceler]bool // set to nil by the first cancel call
+ err error // set to non-nil by the first cancel call
+}
+
+func (c *cancelCtx) Done() <-chan struct{} {
+ return c.done
+}
+
+func (c *cancelCtx) Err() error {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ return c.err
+}
+
+func (c *cancelCtx) String() string {
+ return fmt.Sprintf("%v.WithCancel", c.Context)
+}
+
+// cancel closes c.done, cancels each of c's children, and, if
+// removeFromParent is true, removes c from its parent's children.
+func (c *cancelCtx) cancel(removeFromParent bool, err error) {
+ if err == nil {
+ panic("context: internal error: missing cancel error")
+ }
+ c.mu.Lock()
+ if c.err != nil {
+ c.mu.Unlock()
+ return // already canceled
+ }
+ c.err = err
+ close(c.done)
+ for child := range c.children {
+ // NOTE: acquiring the child's lock while holding parent's lock.
+ child.cancel(false, err)
+ }
+ c.children = nil
+ c.mu.Unlock()
+
+ if removeFromParent {
+ removeChild(c.Context, c)
+ }
+}
+
+// WithDeadline returns a copy of the parent context with the deadline adjusted
+// to be no later than d. If the parent's deadline is already earlier than d,
+// WithDeadline(parent, d) is semantically equivalent to parent. The returned
+// context's Done channel is closed when the deadline expires, when the returned
+// cancel function is called, or when the parent context's Done channel is
+// closed, whichever happens first.
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this Context complete.
+func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc) {
+ if cur, ok := parent.Deadline(); ok && cur.Before(deadline) {
+ // The current deadline is already sooner than the new one.
+ return WithCancel(parent)
+ }
+ c := &timerCtx{
+ cancelCtx: newCancelCtx(parent),
+ deadline: deadline,
+ }
+ propagateCancel(parent, c)
+ d := deadline.Sub(time.Now())
+ if d <= 0 {
+ c.cancel(true, DeadlineExceeded) // deadline has already passed
+ return c, func() { c.cancel(true, Canceled) }
+ }
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ if c.err == nil {
+ c.timer = time.AfterFunc(d, func() {
+ c.cancel(true, DeadlineExceeded)
+ })
+ }
+ return c, func() { c.cancel(true, Canceled) }
+}
+
+// A timerCtx carries a timer and a deadline. It embeds a cancelCtx to
+// implement Done and Err. It implements cancel by stopping its timer then
+// delegating to cancelCtx.cancel.
+type timerCtx struct {
+ cancelCtx
+ timer *time.Timer // Under cancelCtx.mu.
+
+ deadline time.Time
+}
+
+func (c *timerCtx) Deadline() (deadline time.Time, ok bool) {
+ return c.deadline, true
+}
+
+func (c *timerCtx) String() string {
+ return fmt.Sprintf("%v.WithDeadline(%s [%s])", c.cancelCtx.Context, c.deadline, c.deadline.Sub(time.Now()))
+}
+
+func (c *timerCtx) cancel(removeFromParent bool, err error) {
+ c.cancelCtx.cancel(false, err)
+ if removeFromParent {
+ // Remove this timerCtx from its parent cancelCtx's children.
+ removeChild(c.cancelCtx.Context, c)
+ }
+ c.mu.Lock()
+ if c.timer != nil {
+ c.timer.Stop()
+ c.timer = nil
+ }
+ c.mu.Unlock()
+}
+
+// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this Context complete:
+//
+// func slowOperationWithTimeout(ctx context.Context) (Result, error) {
+// ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
+// defer cancel() // releases resources if slowOperation completes before timeout elapses
+// return slowOperation(ctx)
+// }
+func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
+ return WithDeadline(parent, time.Now().Add(timeout))
+}
+
+// WithValue returns a copy of parent in which the value associated with key is
+// val.
+//
+// Use context Values only for request-scoped data that transits processes and
+// APIs, not for passing optional parameters to functions.
+func WithValue(parent Context, key interface{}, val interface{}) Context {
+ return &valueCtx{parent, key, val}
+}
+
+// A valueCtx carries a key-value pair. It implements Value for that key and
+// delegates all other calls to the embedded Context.
+type valueCtx struct {
+ Context
+ key, val interface{}
+}
+
+func (c *valueCtx) String() string {
+ return fmt.Sprintf("%v.WithValue(%#v, %#v)", c.Context, c.key, c.val)
+}
+
+func (c *valueCtx) Value(key interface{}) interface{} {
+ if c.key == key {
+ return c.val
+ }
+ return c.Context.Value(key)
+}