Increase file descriptor limit at startup.

limit/limit.go

@@ -0,0 +1,7 @@
+// +build windows plan9
+
+package limit
+
+func Nofile(desired uint64) (uint64, error) {
+	return desired, nil
+}

limit/limit_unix.go

@@ -0,0 +1,44 @@
+// +build !windows
+// +build !plan9
+
+package limit
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+func Nofile(desired uint64) (uint64, error) {
+	var old unix.Rlimit
+
+	err := unix.Getrlimit(unix.RLIMIT_NOFILE, &old)
+	if err != nil {
+		return 0, err
+	}
+
+	if old.Cur >= desired {
+		return old.Cur, nil
+	}
+
+	if old.Max < desired {
+		limit := unix.Rlimit{
+			Cur: desired,
+			Max: desired,
+		}
+		err := unix.Setrlimit(unix.RLIMIT_NOFILE, &limit)
+		if err == nil {
+			return limit.Cur, nil
+		}
+
+		desired = old.Max
+	}
+
+	limit := unix.Rlimit{
+		Cur: desired,
+		Max: old.Max,
+	}
+	err = unix.Setrlimit(unix.RLIMIT_NOFILE, &limit)
+	if err != nil {
+		return old.Cur, err
+	}
+	return limit.Cur, nil
+}