// 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.
// See https://code.google.com/p/go/source/browse/CONTRIBUTORS
// Licensed under the same terms as Go itself:
// https://code.google.com/p/go/source/browse/LICENSE

// Package http2 implements the HTTP/2 protocol.
//
// This is a work in progress. This package is low-level and intended
// to be used directly by very few people. Most users will use it
// indirectly through integration with the net/http package. See
// ConfigureServer. That ConfigureServer call will likely be automatic
// or available via an empty import in the future.
//
// This package currently targets draft-14. See http://http2.github.io/
package http2

import (
	"net/http"
	"strconv"
)

var VerboseLogs = false

const (
	// ClientPreface is the string that must be sent by new
	// connections from clients.
	ClientPreface = "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"

	// SETTINGS_MAX_FRAME_SIZE default
	// http://http2.github.io/http2-spec/#rfc.section.6.5.2
	initialMaxFrameSize = 16384

	npnProto = "h2-14"

	// http://http2.github.io/http2-spec/#SettingValues
	initialHeaderTableSize = 4096

	initialWindowSize = 65535 // 6.9.2 Initial Flow Control Window Size
)

var (
	clientPreface = []byte(ClientPreface)
)

type streamState int

const (
	stateIdle streamState = iota
	stateOpen
	stateHalfClosedLocal
	stateHalfClosedRemote
	stateResvLocal
	stateResvRemote
	stateClosed
)

var stateName = [...]string{
	stateIdle:             "Idle",
	stateOpen:             "Open",
	stateHalfClosedLocal:  "HalfClosedLocal",
	stateHalfClosedRemote: "HalfClosedRemote",
	stateResvLocal:        "ResvLocal",
	stateResvRemote:       "ResvRemote",
	stateClosed:           "Closed",
}

func (st streamState) String() string {
	return stateName[st]
}

func validHeader(v string) bool {
	if len(v) == 0 {
		return false
	}
	for _, r := range v {
		// "Just as in HTTP/1.x, header field names are
		// strings of ASCII characters that are compared in a
		// case-insensitive fashion. However, header field
		// names MUST be converted to lowercase prior to their
		// encoding in HTTP/2. "
		if r >= 127 || ('A' <= r && r <= 'Z') {
			return false
		}
	}
	return true
}

var httpCodeStringCommon = map[int]string{} // n -> strconv.Itoa(n)

func init() {
	for i := 100; i <= 999; i++ {
		if v := http.StatusText(i); v != "" {
			httpCodeStringCommon[i] = strconv.Itoa(i)
		}
	}
}

func httpCodeString(code int) string {
	if s, ok := httpCodeStringCommon[code]; ok {
		return s
	}
	return strconv.Itoa(code)
}

// from pkg io
type stringWriter interface {
	WriteString(s string) (n int, err error)
}

// A gate lets two goroutines coordinate their activities.
type gate chan struct{}

func (g gate) Done() { g <- struct{}{} }
func (g gate) Wait() { <-g }