[management,proxy,client] Add L4 capabilities (TLS/TCP/UDP) (#5530)

proxy/internal/netutil/errors.go

@@ -0,0 +1,40 @@
+package netutil
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"net"
+	"syscall"
+)
+
+// ValidatePort converts an int32 proto port to uint16, returning an error
+// if the value is out of the valid 1–65535 range.
+func ValidatePort(port int32) (uint16, error) {
+	if port <= 0 || port > math.MaxUint16 {
+		return 0, fmt.Errorf("invalid port %d: must be 1–65535", port)
+	}
+	return uint16(port), nil
+}
+
+// IsExpectedError returns true for errors that are normal during
+// connection teardown and should not be logged as warnings.
+func IsExpectedError(err error) bool {
+	return errors.Is(err, net.ErrClosed) ||
+		errors.Is(err, context.Canceled) ||
+		errors.Is(err, io.EOF) ||
+		errors.Is(err, syscall.ECONNRESET) ||
+		errors.Is(err, syscall.EPIPE) ||
+		errors.Is(err, syscall.ECONNABORTED)
+}
+
+// IsTimeout checks whether the error is a network timeout.
+func IsTimeout(err error) bool {
+	var netErr net.Error
+	if errors.As(err, &netErr) {
+		return netErr.Timeout()
+	}
+	return false
+}