Remove error state from ClientConn (#27)

Currently method errors are stored in ClientConn.lastError and requires callers
of ClientConn.readResponse to check this field after each call. This is error
prone as it hides the fact that readResponse can fail.

This change removes the ClientConn.lastError field and instead make
ClientConn.readResponse return an error along with the segment. Calling code is
updated accordingly.

internal/vici/clientConn.go

@@ -2,7 +2,6 @@ package vici
 
 import (
 	"fmt"
-	"io"
 	"net"
 	"time"
 )
@@ -17,7 +16,6 @@ type ClientConn struct {
 	conn          net.Conn
 	responseChan  chan segment
 	eventHandlers map[string]func(response map[string]interface{})
-	lastError     error
 
 	// ReadTimeout specifies a time limit for requests made
 	// by this client.
@@ -26,7 +24,6 @@ type ClientConn struct {
 
 func (c *ClientConn) Close() error {
 	close(c.responseChan)
-	c.lastError = io.ErrClosedPipe
 	return c.conn.Close()
 }
 
@@ -79,25 +76,22 @@ func (c *ClientConn) Request(apiname string, concretePayload interface{}) (map[s
 		return nil, fmt.Errorf("writing segment: %w", err)
 	}
 
-	outMsg := c.readResponse()
-	if c.lastError != nil {
-		return nil, fmt.Errorf("read response: %w", c.lastError)
+	outMsg, err := c.readResponse()
+	if err != nil {
+		return nil, fmt.Errorf("read response: %w", err)
 	}
 	if outMsg.typ != stCMD_RESPONSE {
 		return nil, fmt.Errorf("[%s] response error %d", apiname, outMsg.typ)
 	}
 	return outMsg.msg, nil
 }
 
-func (c *ClientConn) readResponse() segment {
+func (c *ClientConn) readResponse() (segment, error) {
 	select {
 	case outMsg := <-c.responseChan:
-		return outMsg
+		return outMsg, nil
 	case <-time.After(c.ReadTimeout):
-		if c.lastError == nil {
-			c.lastError = fmt.Errorf("timeout waiting for message response")
-		}
-		return segment{}
+		return segment{}, fmt.Errorf("timeout waiting for message response")
 	}
 }
 
@@ -114,10 +108,10 @@ func (c *ClientConn) RegisterEvent(name string, handler func(response map[string
 		delete(c.eventHandlers, name)
 		return fmt.Errorf("write segment: %w", err)
 	}
-	outMsg := c.readResponse()
-	if c.lastError != nil {
+	outMsg, err := c.readResponse()
+	if err != nil {
 		delete(c.eventHandlers, name)
-		return fmt.Errorf("read response: %w", c.lastError)
+		return fmt.Errorf("read response: %w", err)
 	}
 
 	if outMsg.typ != stEVENT_CONFIRM {
@@ -135,9 +129,9 @@ func (c *ClientConn) UnregisterEvent(name string) error {
 	if err != nil {
 		return fmt.Errorf("write segment: %w", err)
 	}
-	outMsg := c.readResponse()
-	if c.lastError != nil {
-		return fmt.Errorf("read response: %w", c.lastError)
+	outMsg, err := c.readResponse()
+	if err != nil {
+		return fmt.Errorf("read response: %w", err)
 	}
 
 	if outMsg.typ != stEVENT_CONFIRM {