303 lines
7.2 KiB
Go
303 lines
7.2 KiB
Go
package main
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import (
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"bytes"
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"crypto/ed25519"
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"crypto/sha256"
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"encoding/base64"
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"fmt"
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"io"
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"log"
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"math/rand"
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"net/http"
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"sort"
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"strconv"
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"strings"
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"sync"
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"time"
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)
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var myHash string
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var myPos int
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var hashToDomain map[string]string
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var peerHashes []string
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var kvstore map[string][]byte
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// Get the sha256sum of string as a URL-safe unpadded base64 string
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func sha256sum(s string) string {
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b := sha256.Sum256([]byte(s))
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return base64.RawURLEncoding.EncodeToString(b[:])
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}
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// Try to peer with another server
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func addPeer(peer string) error {
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peerHash := sha256sum(peer)
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// Check if already peered
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mu.Lock()
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_, ok := hashToDomain[peerHash]
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mu.Unlock()
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if ok {
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return nil
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}
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mu.Lock()
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hashToDomain[peerHash] = peer
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mu.Unlock()
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// Try request to peer
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log.Printf("%s trying to peer with %s", me, peer)
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resp, err := http.Get(peer + "/peer?peer=" + me)
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if err != nil {
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// Request failed, delete peer
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mu.Lock()
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delete(hashToDomain, peerHash)
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mu.Unlock()
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return err
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}
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log.Printf("%s successfully peered with %s", me, peer)
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mu.Lock()
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i := sort.SearchStrings(peerHashes, peerHash)
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peerHashes = append(peerHashes, "")
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copy(peerHashes[i+1:], peerHashes[i:])
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peerHashes[i] = peerHash
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myPos = sort.SearchStrings(peerHashes, me)
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// Distribute keys to new server
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for id, user := range users {
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phase := time.Now().Unix() / 600
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if keyPos(id + "\n" + fmt.Sprint(phase))-myPos < 5 {
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go http.Post(peer+"/dht/"+id+"?phase="+fmt.Sprint(phase)+"&direct=true", "application/octet-stream", bytes.NewBuffer(user.dhtVal))
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}
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if keyPos(id + "\n" + fmt.Sprint(phase+1))-myPos < 5 {
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go http.Post(peer+"/dht/"+id+"?phase="+fmt.Sprint(phase+1)+"&direct=true", "application/octet-stream", bytes.NewBuffer(user.dhtVal))
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}
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}
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mu.Unlock()
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// Read response body
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body, err := io.ReadAll(resp.Body)
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if err != nil {
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return err
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}
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// Try adding all peers of this peer
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newPeers := strings.Split(string(body), "\n")
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for _, newPeer := range newPeers[:len(newPeers)-1] {
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go addPeer(newPeer)
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}
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return nil
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}
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// Handle incoming peer requests
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func peerHandler(w http.ResponseWriter, r *http.Request) {
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r.ParseForm()
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peer := r.Form.Get("peer")
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if peer == "" {
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w.WriteHeader(http.StatusBadRequest)
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return
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}
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for _, p := range hashToDomain {
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fmt.Fprintf(w, "%s\n", p)
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}
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go addPeer(peer)
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}
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// Find the position of a key in the DHT
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func keyPos(key string) int {
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keyPos := sort.SearchStrings(peerHashes, sha256sum(key))
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if keyPos < myPos {
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keyPos += len(peerHashes)
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}
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return keyPos
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}
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// Get the timestamp of this val
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func timestamp(val []byte) int {
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if len(val) < ed25519.SignatureSize {
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return 0
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}
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message := string(val[:len(val)-ed25519.SignatureSize])
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timestamp, err := strconv.Atoi(strings.Split(message, "\n")[0])
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if err != nil {
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return 0
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}
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return timestamp
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}
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// Get the value for a key from the DHT
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func dhtGet(key, direct string) []byte {
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phase := fmt.Sprint(time.Now().Unix() / 600)
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keyPos := keyPos(key + "\n" + phase)
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if direct != "" && keyPos-myPos < 5 {
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// Directly read from kvstore
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mu.Lock()
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val, ok := kvstore[key+"\n"+phase]
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mu.Unlock()
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if !ok || verify(key, val) != nil {
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return nil
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}
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return val
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}
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// Contact 5 servers that store this key-value pair
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var mu sync.Mutex
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var wg sync.WaitGroup
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var latest []byte
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for i := 0; i < 5 && i < len(peerHashes); i++ {
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wg.Add(1)
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j := hashToDomain[peerHashes[(keyPos+i)%len(peerHashes)]]
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go func() {
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defer wg.Done()
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resp, err := http.Get(j + "/dht/" + key + "?direct")
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if err != nil {
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return
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}
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val, err := io.ReadAll(resp.Body)
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if err != nil {
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return
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}
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err = verify(key, val)
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if err != nil {
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return
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}
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mu.Lock()
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if latest == nil || timestamp(val) > timestamp(latest) {
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latest = val
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}
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mu.Unlock()
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}()
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}
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// Wait for all to finish or time out
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wg.Wait()
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return latest
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}
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// Post a key-value pair into the DHT
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func dhtPost(key, phase, direct string, val []byte) error {
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err := verify(key, val)
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if err != nil {
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return err
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}
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if phase == "" {
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phase = fmt.Sprint(time.Now().Unix() / 600)
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}
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user, ok := users[key]
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if ok {
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curPhase, err := strconv.Atoi(phase)
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if err != nil {
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return err
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}
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nextPhase := time.Now().Unix()/600 + 1
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if int64(curPhase) < nextPhase && user.phase < nextPhase {
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user.phase = nextPhase
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go dhtPost(key, fmt.Sprint(nextPhase), "", val)
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}
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}
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keyPos := keyPos(key + "\n" + phase)
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if direct != "" && keyPos-myPos < 5 {
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// Directly write to kvstore
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mu.Lock()
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curVal, ok := kvstore[key+"\n"+phase]
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if !ok || timestamp(val) > timestamp(curVal) {
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kvstore[key+"\n"+phase] = val
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}
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mu.Unlock()
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return nil
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}
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// Contact 5 servers that store this key-value pair
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for i := 0; i < 5 && i < len(peerHashes); i++ {
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j := hashToDomain[peerHashes[(keyPos+i)%len(peerHashes)]]
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go http.Post(j+"/dht/"+key+"?phase="+phase+"&direct=true", "application/octet-stream", bytes.NewBuffer(val))
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}
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return nil
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}
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// Handle DHT requests
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func dhtHandler(w http.ResponseWriter, r *http.Request) {
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key := r.URL.Path[5:]
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r.ParseForm()
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if r.Method == "GET" {
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val := dhtGet(key, r.Form.Get("direct"))
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if val == nil {
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w.WriteHeader(http.StatusNotFound)
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return
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}
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w.Write(val)
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} else if r.Method == "POST" {
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val, err := io.ReadAll(r.Body)
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if err != nil || dhtPost(key, r.Form.Get("phase"), r.Form.Get("direct"), val) != nil {
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w.WriteHeader(http.StatusInternalServerError)
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return
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}
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w.WriteHeader(http.StatusOK)
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}
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}
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// Clean out offline peers
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func cleanPeers() {
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for true {
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mu.Lock()
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peer := hashToDomain[peerHashes[rand.Intn(len(peerHashes))]]
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mu.Unlock()
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_, err := http.Get(peer)
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if err != nil {
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// Bad response, so remove peer
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mu.Lock()
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i := sort.SearchStrings(peerHashes, sha256sum(peer))
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peerHashes = append(peerHashes[:i], peerHashes[i+1:]...)
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myPos = sort.SearchStrings(peerHashes, me)
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// Distribute keys on this server to other servers
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if len(peerHashes) >= 5 {
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for id, user := range users {
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phase := time.Now().Unix() / 600
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kpos := keyPos(id + "\n" + fmt.Sprint(phase))
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if kpos-i < 5 {
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server := hashToDomain[peerHashes[(kpos+4)%len(peerHashes)]]
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go http.Post(server+"/dht/"+id+"?phase="+fmt.Sprint(phase)+"&direct=true", "application/octet-stream", bytes.NewBuffer(user.dhtVal))
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}
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kpos = keyPos(id + "\n" + fmt.Sprint(phase+1))
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if kpos-i < 5 {
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server := hashToDomain[peerHashes[(kpos+4)%len(peerHashes)]]
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go http.Post(server+"/dht/"+id+"?phase="+fmt.Sprint(phase+1)+"&direct=true", "application/octet-stream", bytes.NewBuffer(user.dhtVal))
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}
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}
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}
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mu.Unlock()
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}
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time.Sleep(5 * time.Second)
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}
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}
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// Clean out old keys from the KVStore every minute
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func cleanKVStore() {
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for true {
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// This locks the mutex for a while which sucks
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mu.Lock()
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for key := range kvstore {
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timestamp, err := strconv.Atoi(strings.Split(key, "\n")[1])
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if err != nil || int64(timestamp)+1 < time.Now().Unix()/600 {
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delete(kvstore, key)
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}
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}
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mu.Unlock()
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time.Sleep(time.Minute)
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}
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}
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// Redistribute key-value pairs periodically
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func redistributeKeys() {
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for true {
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mu.Lock()
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for id, user := range users {
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nextPhase := time.Now().Unix()/600 + 1
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if user.phase < nextPhase {
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go dhtPost(id, fmt.Sprint(nextPhase), "", user.dhtVal)
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}
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}
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mu.Unlock()
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time.Sleep(time.Duration(rand.Intn(300)) * time.Second)
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}
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}
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