Struct Client exposes sensitive data (#784) (#786)

(cherry picked from commit ecd5ee1)

Co-authored-by: Sergio Mena <sergio@informal.systems>

rpc/jsonrpc/client/http_json_client.go

@@ -139,6 +139,8 @@ var _ HTTPClient = (*Client)(nil)
 var _ Caller = (*Client)(nil)
 var _ Caller = (*RequestBatch)(nil)
 
+var _ fmt.Stringer = (*Client)(nil)
+
 // New returns a Client pointed at the given address.
 // An error is returned on invalid remote. The function panics when remote is nil.
 func New(remote string) (*Client, error) {
@@ -232,6 +234,10 @@ func getHTTPRespErrPrefix(resp *http.Response) string {
 	return fmt.Sprintf("error in json rpc client, with http response metadata: (Status: %s, Protocol %s)", resp.Status, resp.Proto)
 }
 
+func (c *Client) String() string {
+	return fmt.Sprintf("&Client{user=%v, addr=%v, client=%v, nextReqID=%v}", c.username, c.address, c.client, c.nextReqID)
+}
+
 // NewRequestBatch starts a batch of requests for this client.
 func (c *Client) NewRequestBatch() *RequestBatch {
 	return &RequestBatch{