From 2e5c7586b75669ff15f244b020b0e01dc300d7dd Mon Sep 17 00:00:00 2001
From: Otto Moerbeek <otto.moerbeek@open-xchange.com>
Date: Wed, 26 Jun 2024 10:06:25 +0200
Subject: [PATCH] Tidy AXFRRetriever::timeoutReadn

Including a fix to timeout potentially underflowing.
Coverity complains about n (now called bytesRead) overflowing, but that's a false positive, as numread is bounded.
---
 pdns/axfr-retriever.cc | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/pdns/axfr-retriever.cc b/pdns/axfr-retriever.cc
index f2630c9aeb..9b2a4bf92e 100644
--- a/pdns/axfr-retriever.cc
+++ b/pdns/axfr-retriever.cc
@@ -171,23 +171,31 @@ int AXFRRetriever::getChunk(Resolver::res_t &res, vector<DNSRecord>* records, ui
 
 void AXFRRetriever::timeoutReadn(uint16_t bytes, uint16_t timeoutsec)
 {
-  time_t start=time(nullptr);
-  int n=0;
-  int numread;
-  while(n<bytes) {
+  const time_t start = time(nullptr);
+  uint16_t bytesRead = 0;
+
+  while (bytesRead < bytes) {
     // coverity[store_truncates_time_t]
-    int res=waitForData(d_sock, static_cast<int>(timeoutsec - (time(nullptr) - start)));
-    if(res<0)
-      throw ResolverException("Reading data from remote nameserver over TCP: "+stringerror());
-    if(!res)
+    auto elapsed = time(nullptr) - start;
+    if (elapsed > timeoutsec) {
       throw ResolverException("Timeout while reading data from remote nameserver over TCP");
+    }
+    auto res = waitForData(d_sock, static_cast<int>(timeoutsec - elapsed));
+    if (res < 0) {
+      throw ResolverException("Reading data from remote nameserver over TCP: " + stringerror());
+    }
+    if (res == 0) {
+      throw ResolverException("Timeout while reading data from remote nameserver over TCP");
+    }
 
-    numread=recv(d_sock, &d_buf.at(n), bytes-n, 0);
-    if(numread<0)
-      throw ResolverException("Reading data from remote nameserver over TCP: "+stringerror());
-    if(numread==0)
+    auto received = recv(d_sock, &d_buf.at(bytesRead), bytes - bytesRead, 0);
+    if (received < 0) {
+      throw ResolverException("Reading data from remote nameserver over TCP: " + stringerror());
+    }
+    if (received == 0) {
       throw ResolverException("Remote nameserver closed TCP connection");
-    n+=numread;
+    }
+    bytesRead += static_cast<uint16_t>(received);
   }
 }
 
-- 
2.47.2