make it better

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)
+}