Merge pull request #33 from syncthing/negcache

Set Retry-After header

cmd/discosrv/main.go

@@ -14,6 +14,12 @@ import (
 	"github.com/thejerf/suture"
 )
 
+const (
+	minNegCache  = 60        // seconds
+	maxNegCache  = 3600      // seconds
+	maxDeviceAge = 7 * 86400 // one week, in seconds
+)
+
 var (
 	lruSize     = 10240
 	limitAvg    = 5

cmd/discosrv/psql.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"database/sql"
+	"fmt"
 
 	_ "github.com/lib/pq"
 )
@@ -100,7 +101,7 @@ func postgresCompile(db *sql.DB) (map[string]*sql.Stmt, error) {
 	stmts := map[string]string{
 		"cleanAddress":  "DELETE FROM Addresses WHERE Seen < now() - '2 hour'::INTERVAL",
 		"cleanRelay":    "DELETE FROM Relays WHERE Seen < now() - '2 hour'::INTERVAL",
-		"cleanDevice":   "DELETE FROM Devices WHERE Seen < now() - '24 hour'::INTERVAL",
+		"cleanDevice":   fmt.Sprintf("DELETE FROM Devices WHERE Seen < now() - '%d hour'::INTERVAL", maxDeviceAge/3600),
 		"countAddress":  "SELECT count(*) FROM Addresses",
 		"countDevice":   "SELECT count(*) FROM Devices",
 		"countRelay":    "SELECT count(*) FROM Relays",
@@ -109,6 +110,7 @@ func postgresCompile(db *sql.DB) (map[string]*sql.Stmt, error) {
 		"insertDevice":  "INSERT INTO Devices (DeviceID, Seen) VALUES ($1, now())",
 		"selectAddress": "SELECT Address FROM Addresses WHERE DeviceID=$1 AND Seen > now() - '1 hour'::INTERVAL ORDER BY random() LIMIT 16",
 		"selectRelay":   "SELECT Address, Latency FROM Relays WHERE DeviceID=$1 AND Seen > now() - '1 hour'::INTERVAL ORDER BY random() LIMIT 16",
+		"selectDevice":  "SELECT Seen FROM Devices WHERE DeviceID=$1",
 		"updateAddress": "UPDATE Addresses SET Seen=now() WHERE DeviceID=$1 AND Address=$2",
 		"updateDevice":  "UPDATE Devices SET Seen=now() WHERE DeviceID=$1",
 		"deleteRelay":   "DELETE FROM Relays WHERE DeviceID=$1",

cmd/discosrv/ql.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"database/sql"
+	"fmt"
 	"log"
 
 	"github.com/cznic/ql"
@@ -71,7 +72,7 @@ func qlCompile(db *sql.DB) (map[string]*sql.Stmt, error) {
 	stmts := map[string]string{
 		"cleanAddress":  `DELETE FROM Addresses WHERE Seen < now() - duration("2h")`,
 		"cleanRelay":    `DELETE FROM Relays WHERE Seen < now() - duration("2h")`,
-		"cleanDevice":   `DELETE FROM Devices WHERE Seen < now() - duration("24h")`,
+		"cleanDevice":   fmt.Sprintf(`DELETE FROM Devices WHERE Seen < now() - duration("%dh")`, maxDeviceAge/3600),
 		"countAddress":  "SELECT count(*) FROM Addresses",
 		"countDevice":   "SELECT count(*) FROM Devices",
 		"countRelay":    "SELECT count(*) FROM Relays",
@@ -80,6 +81,7 @@ func qlCompile(db *sql.DB) (map[string]*sql.Stmt, error) {
 		"insertDevice":  "INSERT INTO Devices (DeviceID, Seen) VALUES ($1, now())",
 		"selectAddress": `SELECT Address from Addresses WHERE DeviceID==$1 AND Seen > now() - duration("1h") LIMIT 16`,
 		"selectRelay":   `SELECT Address, Latency from Relays WHERE DeviceID==$1 AND Seen > now() - duration("1h") LIMIT 16`,
+		"selectDevice":  "SELECT Seen FROM Devices WHERE DeviceID==$1",
 		"updateAddress": "UPDATE Addresses Seen=now() WHERE DeviceID==$1 AND Address==$2",
 		"updateDevice":  "UPDATE Devices Seen=now() WHERE DeviceID==$1",
 		"deleteRelay":   "DELETE FROM Relays WHERE DeviceID==$1",

cmd/discosrv/querysrv.go

@@ -12,6 +12,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"strconv"
 	"sync"
 	"time"
 
@@ -30,6 +31,7 @@ type querysrv struct {
 }
 
 type announcement struct {
+	Seen   time.Time
 	Direct []string   `json:"direct"`
 	Relays []annRelay `json:"relays"`
 }
@@ -57,6 +59,22 @@ func (s *safeCache) Add(key string, val interface{}) {
 	s.mut.Unlock()
 }
 
+func negCacheFor(lastSeen time.Time) int {
+	since := time.Since(lastSeen).Seconds()
+	if since >= maxDeviceAge {
+		return maxNegCache
+	}
+	if since < 0 {
+		// That's weird
+		return minNegCache
+	}
+
+	// Return a value linearly scaled from minNegCache (at zero seconds ago)
+	// to maxNegCache (at maxDeviceAge seconds ago).
+	r := since / maxDeviceAge
+	return int(minNegCache + r*(maxNegCache-minNegCache))
+}
+
 func (s *querysrv) Serve() {
 	s.limiter = &safeCache{
 		Cache: lru.New(lruSize),
@@ -158,6 +176,18 @@ func (s *querysrv) handleGET(w http.ResponseWriter, req *http.Request) {
 
 	var ann announcement
 
+	ann.Seen, err = s.getDeviceSeen(deviceID)
+	negCache := strconv.Itoa(negCacheFor(ann.Seen))
+	w.Header().Set("Retry-After", negCache)
+	w.Header().Set("Cache-Control", "public, max-age="+negCache)
+
+	if err != nil {
+		// The device is not in the database.
+		globalStats.Query()
+		http.Error(w, "Not Found", http.StatusNotFound)
+		return
+	}
+
 	ann.Direct, err = s.getAddresses(deviceID)
 	if err != nil {
 		log.Println("getAddresses:", err)
@@ -385,6 +415,15 @@ func (s *querysrv) getAddresses(device protocol.DeviceID) ([]string, error) {
 	return res, nil
 }
 
+func (s *querysrv) getDeviceSeen(device protocol.DeviceID) (time.Time, error) {
+	row := s.prep["selectDevice"].QueryRow(device.String())
+	var seen time.Time
+	if err := row.Scan(&seen); err != nil {
+		return time.Time{}, err
+	}
+	return seen, nil
+}
+
 func (s *querysrv) getRelays(device protocol.DeviceID) ([]annRelay, error) {
 	rows, err := s.prep["selectRelay"].Query(device.String())
 	if err != nil {