check to return exit err if net/rpc call errors

solverrpc/rpc.go

@@ -80,6 +80,15 @@ func startSolver() {
 	}()
 }
 
+func checkExit() error {
+	select {
+	case <-cmdDone:
+		return ErrSolverProcessExited
+	default:
+		return nil
+	}
+}
+
 // StartSolver starts the solver's background process.  This can be used to
 // detect errors starting the solver process before the first call to Roots.
 func StartSolver() error {
@@ -95,8 +104,8 @@ func RootFactors(a []*big.Int, F *big.Int) ([]*big.Int, []int, error) {
 		return nil, nil, err
 	}
 
-	if _, ok := <-cmdDone; ok {
-		return nil, nil, ErrSolverProcessExited
+	if err := checkExit(); err != nil {
+		return nil, nil, err
 	}
 
 	var args struct {
@@ -111,6 +120,9 @@ func RootFactors(a []*big.Int, F *big.Int) ([]*big.Int, []int, error) {
 	}
 	err := client.Call("Solver.RootFactors", args, &result)
 	if err != nil {
+		if exitErr := checkExit(); exitErr != nil {
+			err = exitErr
+		}
 		return nil, nil, err
 	}
 	return result.Roots, result.Exponents, nil
@@ -128,8 +140,8 @@ func Roots(a []*big.Int, F *big.Int) ([]*big.Int, error) {
 		return nil, err
 	}
 
-	if _, ok := <-cmdDone; ok {
-		return nil, ErrSolverProcessExited
+	if err := checkExit(); err != nil {
+		return nil, err
 	}
 
 	var args struct {
@@ -144,6 +156,9 @@ func Roots(a []*big.Int, F *big.Int) ([]*big.Int, error) {
 	}
 	err := client.Call("Solver.Roots", args, &result)
 	if err != nil {
+		if exitErr := checkExit(); exitErr != nil {
+			err = exitErr
+		}
 		return nil, err
 	}
 	if result.RepeatedRoot != nil {