From 97313ac873eee4365fc1de253a538335defcfed7 Mon Sep 17 00:00:00 2001
From: Andras Banki-Horvath <bhandras@gmail.com>
Date: Thu, 12 May 2022 22:09:38 +0200
Subject: [PATCH] rpcclient: save the last error when retrying

---
 rpcclient/infrastructure.go | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/rpcclient/infrastructure.go b/rpcclient/infrastructure.go
index b7732bc6..f931b835 100644
--- a/rpcclient/infrastructure.go
+++ b/rpcclient/infrastructure.go
@@ -771,7 +771,7 @@ func (c *Client) handleSendPostMessage(jReq *jsonRequest,
 	url := protocol + "://" + c.config.Host
 
 	var (
-		err          error
+		err, lastErr error
 		backoff      time.Duration
 		httpResponse *http.Response
 	)
@@ -807,6 +807,12 @@ func (c *Client) handleSendPostMessage(jReq *jsonRequest,
 			break
 		}
 
+		// Save the last error for the case where we backoff further,
+		// retry and get an invalid response but no error. If this
+		// happens the saved last error will be used to enrich the error
+		// message that we pass back to the caller.
+		lastErr = err
+
 		// Backoff sleep otherwise.
 		backoff = requestRetryInterval * time.Duration(i+1)
 		if backoff > time.Minute {
@@ -833,7 +839,8 @@ func (c *Client) handleSendPostMessage(jReq *jsonRequest,
 	if httpResponse == nil {
 		jReq.responseChan <- &Response{
 			err: fmt.Errorf("invalid http POST response (nil), "+
-				"method: %s, id: %d", jReq.method, jReq.id),
+				"method: %s, id: %d, last error=%v",
+				jReq.method, jReq.id, lastErr),
 		}
 	}