// Copyright 2016 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 http

import (
	"io"
	"strconv"
	"strings"
	"time"
	"unicode/utf8"

	"golang.org/x/net/http/httpguts"
)

// maxInt64 is the effective "infinite" value for the Server and
// Transport's byte-limiting readers.
const maxInt64 = 1<<63 - 1

// aLongTimeAgo is a non-zero time, far in the past, used for
// immediate cancellation of network operations.
var aLongTimeAgo = time.Unix(1, 0)

// TODO(bradfitz): move common stuff here. The other files have accumulated
// generic http stuff in random places.

// contextKey is a value for use with context.WithValue. It's used as
// a pointer so it fits in an interface{} without allocation.
type contextKey struct {
	name string
}

func (k *contextKey) String() string { return "net/http context value " + k.name }

// Given a string of the form "host", "host:port", or "[ipv6::address]:port",
// return true if the string includes a port.
func hasPort(s string) bool { return strings.LastIndex(s, ":") > strings.LastIndex(s, "]") }

// removeEmptyPort strips the empty port in ":port" to ""
// as mandated by RFC 3986 Section 6.2.3.
func removeEmptyPort(host string) string {
	if hasPort(host) {
		return strings.TrimSuffix(host, ":")
	}
	return host
}

func isNotToken(r rune) bool {
	return !httpguts.IsTokenRune(r)
}

func isASCII(s string) bool {
	for i := 0; i < len(s); i++ {
		if s[i] >= utf8.RuneSelf {
			return false
		}
	}
	return true
}

// stringContainsCTLByte reports whether s contains any ASCII control character.
func stringContainsCTLByte(s string) bool {
	for i := 0; i < len(s); i++ {
		b := s[i]
		if b < ' ' || b == 0x7f {
			return true
		}
	}
	return false
}

func hexEscapeNonASCII(s string) string {
	newLen := 0
	for i := 0; i < len(s); i++ {
		if s[i] >= utf8.RuneSelf {
			newLen += 3
		} else {
			newLen++
		}
	}
	if newLen == len(s) {
		return s
	}
	b := make([]byte, 0, newLen)
	for i := 0; i < len(s); i++ {
		if s[i] >= utf8.RuneSelf {
			b = append(b, '%')
			b = strconv.AppendInt(b, int64(s[i]), 16)
		} else {
			b = append(b, s[i])
		}
	}
	return string(b)
}

// NoBody is an io.ReadCloser with no bytes. Read always returns EOF
// and Close always returns nil. It can be used in an outgoing client
// request to explicitly signal that a request has zero bytes.
// An alternative, however, is to simply set Request.Body to nil.
var NoBody = noBody{}

type noBody struct{}

func (noBody) Read([]byte) (int, error)         { return 0, io.EOF }
func (noBody) Close() error                     { return nil }
func (noBody) WriteTo(io.Writer) (int64, error) { return 0, nil }

var (
	// verify that an io.Copy from NoBody won't require a buffer:
	_ io.WriterTo   = NoBody
	_ io.ReadCloser = NoBody
)

// PushOptions describes options for Pusher.Push.
type PushOptions struct {
	// Method specifies the HTTP method for the promised request.
	// If set, it must be "GET" or "HEAD". Empty means "GET".
	Method string

	// Header specifies additional promised request headers. This cannot
	// include HTTP/2 pseudo header fields like ":path" and ":scheme",
	// which will be added automatically.
	Header Header
}

// Pusher is the interface implemented by ResponseWriters that support
// HTTP/2 server push. For more background, see
// https://tools.ietf.org/html/rfc7540#section-8.2.
type Pusher interface {
	// Push initiates an HTTP/2 server push. This constructs a synthetic
	// request using the given target and options, serializes that request
	// into a PUSH_PROMISE frame, then dispatches that request using the
	// server's request handler. If opts is nil, default options are used.
	//
	// The target must either be an absolute path (like "/path") or an absolute
	// URL that contains a valid host and the same scheme as the parent request.
	// If the target is a path, it will inherit the scheme and host of the
	// parent request.
	//
	// The HTTP/2 spec disallows recursive pushes and cross-authority pushes.
	// Push may or may not detect these invalid pushes; however, invalid
	// pushes will be detected and canceled by conforming clients.
	//
	// Handlers that wish to push URL X should call Push before sending any
	// data that may trigger a request for URL X. This avoids a race where the
	// client issues requests for X before receiving the PUSH_PROMISE for X.
	//
	// Push will run in a separate goroutine making the order of arrival
	// non-deterministic. Any required synchronization needs to be implemented
	// by the caller.
	//
	// Push returns ErrNotSupported if the client has disabled push or if push
	// is not supported on the underlying connection.
	Push(target string, opts *PushOptions) error
}