From b146a84f7fe1f680441b54399b9b023024d72b40 Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Tue, 28 Sep 2021 15:38:42 +0200
Subject: [PATCH] dnsdist: Better handling of outgoing DoH workers

This commit raises the number of DoH workers to be at least 1, always, unless
told otherwise via setOutgoingDoHWorkerThreads(0).
In that last case it raises an exception if the console is used to declare
a new DoH backend later on.
---
 pdns/dnsdist-lua.cc                 |  7 ++++++-
 pdns/dnsdistdist/dnsdist-nghttp2.cc | 14 ++++++++++----
 pdns/dnsdistdist/dnsdist-nghttp2.hh |  2 +-
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/pdns/dnsdist-lua.cc b/pdns/dnsdist-lua.cc
index c5daacf693..2aaa8d3df9 100644
--- a/pdns/dnsdist-lua.cc
+++ b/pdns/dnsdist-lua.cc
@@ -536,7 +536,12 @@ static void setupLuaConfig(LuaContext& luaCtx, bool client, bool configCheck)
           if (ret->d_tlsCtx) {
             setupDoHClientProtocolNegotiation(ret->d_tlsCtx);
           }
-          if (g_outgoingDoHWorkerThreads == 0) {
+
+          if (g_configurationDone && g_outgoingDoHWorkerThreads && *g_outgoingDoHWorkerThreads == 0) {
+            throw std::runtime_error("Error: setOutgoingDoHWorkerThreads() is set to 0 so no outgoing DoH worker thread is available to serve queries");
+          }
+
+          if (!g_outgoingDoHWorkerThreads || *g_outgoingDoHWorkerThreads == 0) {
             g_outgoingDoHWorkerThreads = 1;
           }
 
diff --git a/pdns/dnsdistdist/dnsdist-nghttp2.cc b/pdns/dnsdistdist/dnsdist-nghttp2.cc
index abebdec1b4..0f1e78d8fa 100644
--- a/pdns/dnsdistdist/dnsdist-nghttp2.cc
+++ b/pdns/dnsdistdist/dnsdist-nghttp2.cc
@@ -40,7 +40,7 @@
 
 std::atomic<uint64_t> g_dohStatesDumpRequested{0};
 std::unique_ptr<DoHClientCollection> g_dohClientThreads{nullptr};
-uint16_t g_outgoingDoHWorkerThreads{0};
+std::optional<uint16_t> g_outgoingDoHWorkerThreads{std::nullopt};
 
 #ifdef HAVE_NGHTTP2
 class DoHConnectionToBackend : public TCPConnectionToBackend
@@ -1229,9 +1229,15 @@ void DoHClientCollection::addThread()
 bool initDoHWorkers()
 {
 #ifdef HAVE_NGHTTP2
-  if (g_outgoingDoHWorkerThreads > 0) {
-    g_dohClientThreads = std::make_unique<DoHClientCollection>(g_outgoingDoHWorkerThreads);
-    for (size_t idx = 0; idx < g_outgoingDoHWorkerThreads; idx++) {
+  if (!g_outgoingDoHWorkerThreads) {
+    /* Unless the value has been set to 0 explicitly, always start at least one outgoing DoH worker thread, in case a DoH backend
+       is added at a later time. */
+    g_outgoingDoHWorkerThreads = 1;
+  }
+
+  if (g_outgoingDoHWorkerThreads && *g_outgoingDoHWorkerThreads > 0) {
+    g_dohClientThreads = std::make_unique<DoHClientCollection>(*g_outgoingDoHWorkerThreads);
+    for (size_t idx = 0; idx < *g_outgoingDoHWorkerThreads; idx++) {
       g_dohClientThreads->addThread();
     }
   }
diff --git a/pdns/dnsdistdist/dnsdist-nghttp2.hh b/pdns/dnsdistdist/dnsdist-nghttp2.hh
index f57e4e46fa..a44930f4ca 100644
--- a/pdns/dnsdistdist/dnsdist-nghttp2.hh
+++ b/pdns/dnsdistdist/dnsdist-nghttp2.hh
@@ -57,7 +57,7 @@ private:
 
 extern std::unique_ptr<DoHClientCollection> g_dohClientThreads;
 extern std::atomic<uint64_t> g_dohStatesDumpRequested;
-extern uint16_t g_outgoingDoHWorkerThreads;
+extern std::optional<uint16_t> g_outgoingDoHWorkerThreads;
 
 class TLSCtx;
 
-- 
2.47.2