Initial importHEADmain

1 files changed, 62 insertions, 0 deletions

diff --git a/internal/sync/latency.go b/internal/sync/latency.go
new file mode 100644
index 0000000..dd3268b
--- /dev/null
+++ b/internal/sync/latency.go
@@ -0,0 +1,62 @@
+package sync
+
+import (
+	"fmt"
+	"net"
+	"sort"
+	"sync"
+	"time"
+
+	"vpnem/internal/models"
+)
+
+// LatencyResult holds a server's latency measurement.
+type LatencyResult struct {
+	Tag     string `json:"tag"`
+	Region  string `json:"region"`
+	Latency int    `json:"latency_ms"` // -1 means unreachable
+}
+
+// MeasureLatency pings all servers concurrently and returns results sorted by latency.
+func MeasureLatency(servers []models.Server, timeout time.Duration) []LatencyResult {
+	var wg sync.WaitGroup
+	results := make([]LatencyResult, len(servers))
+
+	for i, s := range servers {
+		wg.Add(1)
+		go func(idx int, srv models.Server) {
+			defer wg.Done()
+			ms := tcpPing(srv.Server, srv.ServerPort, timeout)
+			results[idx] = LatencyResult{
+				Tag:     srv.Tag,
+				Region:  srv.Region,
+				Latency: ms,
+			}
+		}(i, s)
+	}
+
+	wg.Wait()
+
+	sort.Slice(results, func(i, j int) bool {
+		if results[i].Latency == -1 {
+			return false
+		}
+		if results[j].Latency == -1 {
+			return true
+		}
+		return results[i].Latency < results[j].Latency
+	})
+
+	return results
+}
+
+func tcpPing(host string, port int, timeout time.Duration) int {
+	addr := fmt.Sprintf("%s:%d", host, port)
+	start := time.Now()
+	conn, err := net.DialTimeout("tcp", addr, timeout)
+	if err != nil {
+		return -1
+	}
+	conn.Close()
+	return int(time.Since(start).Milliseconds())
+}