[reliable-chat] / server / server.go

/*  reliable-chat - multipath chat
 *  Copyright (C) 2012  Scott Worley <sworley@chkno.net>
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as
 *  published by the Free Software Foundation, version 3.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package main

import "container/list"
import "encoding/json"
import "expvar"
import "flag"
import "log"
import "net/http"
import "strconv"
import "time"

var port = flag.Int("port", 21059, "Port to listen on")
var localaddress = flag.String("localaddress", "", "Local address to bind to")
var max_messages = flag.Int("maxmessages", 1000, "Maximum number of messages to retain")

var start_time = expvar.NewInt("start_time")
var speak_count = expvar.NewInt("speak_count")
var fetch_count = expvar.NewInt("fetch_count")
var fetch_wait_count = expvar.NewInt("fetch_wait_count")
var fetch_wake_count = expvar.NewInt("fetch_wake_count")
var drop_due_to_limit_count = expvar.NewInt("drop_due_to_limit_count")

type Message struct {
        Time time.Time
        ID   string
        Text string
}

type StoreRequest struct {
        StartTime time.Time
        Messages  chan<- []Message
}

type Store struct {
        Add chan *Message
        Get chan *StoreRequest
}

var monotonic_clock chan chan time.Time

const minimum_clock_increment = time.Millisecond

func start_clock() {
        internal_monotonic_clock := make(chan chan time.Time, 1)
        go func() {
                last_time := time.Now()
        main:
                for {
                        select {
                        case request, ok := <-internal_monotonic_clock:
                                if !ok {
                                        break main
                                }
                                earliest_acceptable_time := last_time.Add(minimum_clock_increment)
                                current_time := time.Now()
                                if current_time.Before(earliest_acceptable_time) {
                                        current_time = earliest_acceptable_time
                                }
                                request <- current_time
                                last_time = current_time
                        }
                }
        }()
        monotonic_clock = internal_monotonic_clock
}

func now() time.Time {
        c := make(chan time.Time, 0)
        monotonic_clock <- c
        return <-c
}

func manage_store(store Store) {
        messages := list.New()
        message_count := 0
        waiting := list.New()
main:
        for {
                select {
                case new_message, ok := <-store.Add:
                        if !ok {
                                break main
                        }
                        speak_count.Add(1)
                        for waiter := waiting.Front(); waiter != nil; waiter = waiter.Next() {
                                waiter.Value.(*StoreRequest).Messages <- []Message{*new_message}
                                close(waiter.Value.(*StoreRequest).Messages)
                                fetch_wake_count.Add(1)
                        }
                        waiting.Init()
                        messages.PushBack(new_message)
                        if message_count < *max_messages {
                                message_count++
                        } else {
                                messages.Remove(messages.Front())
                                drop_due_to_limit_count.Add(1)
                        }
                case request, ok := <-store.Get:
                        if !ok {
                                break main
                        }
                        fetch_count.Add(1)
                        if messages.Back() == nil || !request.StartTime.Before(messages.Back().Value.(*Message).Time) {
                                waiting.PushBack(request)
                                fetch_wait_count.Add(1)
                        } else {
                                start := messages.Back()
                                response_size := 1
                                if messages.Front().Value.(*Message).Time.After(request.StartTime) {
                                        start = messages.Front()
                                        response_size = message_count
                                } else {
                                        for start.Prev().Value.(*Message).Time.After(request.StartTime) {
                                                start = start.Prev()
                                                response_size++
                                        }
                                }
                                response_messages := make([]Message, 0, response_size)
                                for m := start; m != nil; m = m.Next() {
                                        response_messages = append(response_messages, *m.Value.(*Message))
                                }
                                request.Messages <- response_messages
                        }
                }
        }
}

func start_store() Store {
        store := Store{make(chan *Message, 20), make(chan *StoreRequest, 20)}
        go manage_store(store)
        return store
}

const robots_txt = `User-agent: *
Disallow: /
`

func start_server(store Store) {
        http.HandleFunc("/fetch", func(w http.ResponseWriter, r *http.Request) {
                var since time.Time
                url_since := r.FormValue("since")
                if url_since != "" {
                        err := json.Unmarshal([]byte(url_since), &since)
                        if err != nil {
                                log.Print("fetch: parse since: ", err)
                                w.WriteHeader(http.StatusBadRequest)
                                w.Write([]byte("Could not parse since as date"))
                                return
                        }
                }
                messages_from_store := make(chan []Message, 1)
                store.Get <- &StoreRequest{since, messages_from_store}

                json_encoded, err := json.Marshal(<-messages_from_store)
                if err != nil {
                        log.Print("json encode: ", err)
                        w.WriteHeader(http.StatusInternalServerError)
                        return
                }
                w.Header().Add("Content-Type", "application/json")
                w.Header().Add("Access-Control-Allow-Origin", "*")
                w.Write(json_encoded)
        })

        http.HandleFunc("/speak", func(w http.ResponseWriter, r *http.Request) {
                store.Add <- &Message{
                        now(),
                        r.FormValue("id"),
                        r.FormValue("text")}
                w.Header().Add("Access-Control-Allow-Origin", "*")
        })

        http.HandleFunc("/robots.txt", func(w http.ResponseWriter, r *http.Request) {
                w.Write([]byte(robots_txt))
        })

        log.Fatal(http.ListenAndServe(*localaddress+":"+strconv.Itoa(*port), nil))
}

func main() {
        flag.Parse()
        start_clock()
        start_time.Set(now().UnixNano())
        store := start_store()
        start_server(store)
}