Fix tcp::resolver data race in the asio backend and be defensive agai…

…nst empty results (#1339)

* Move TCP resolver to asio_context rather than asio_client, as that type is not safe to touch from multiple threads.

* Defend against empty responses from async_resolve.

Co-authored-by: Jinming Hu [email protected]

Release/src/http/client/http_client_asio.cpp

@@ -474,7 +474,6 @@ class asio_client final : public _http_client_communicator
 public:
  asio_client(http::uri&& address, http_client_config&& client_config)
  : _http_client_communicator(std::move(address), std::move(client_config))
- , m_resolver(crossplat::threadpool::shared_instance().service())
  , m_pool(std::make_shared<asio_connection_pool>())
  {
  }
@@ -502,8 +501,6 @@ class asio_client final : public _http_client_communicator
 
  virtual pplx::task<http_response> propagate(http_request request) override;
 
- tcp::resolver m_resolver;
-
 private:
  const std::shared_ptr<asio_connection_pool> m_pool;
 };
@@ -520,6 +517,7 @@ class asio_context final : public request_context, public std::enable_shared_fro
  , m_content_length(0)
  , m_needChunked(false)
  , m_timer(client->client_config().timeout<std::chrono::microseconds>())
+ , m_resolver(crossplat::threadpool::shared_instance().service())
  , m_connection(connection)
 #ifdef CPPREST_PLATFORM_ASIO_CERT_VERIFICATION_AVAILABLE
  , m_openssl_failed(false)
@@ -585,11 +583,11 @@ class asio_context final : public request_context, public std::enable_shared_fro
  tcp::resolver::query query(utility::conversions::to_utf8string(proxy_host), to_string(proxy_port));
 
  auto client = std::static_pointer_cast<asio_client>(m_context->m_http_client);
- client->m_resolver.async_resolve(query,
- boost::bind(&ssl_proxy_tunnel::handle_resolve,
- shared_from_this(),
- boost::asio::placeholders::error,
- boost::asio::placeholders::iterator));
+ m_context->m_resolver.async_resolve(query,
+  boost::bind(&ssl_proxy_tunnel::handle_resolve,
+  shared_from_this(),
+  boost::asio::placeholders::error,
+  boost::asio::placeholders::iterator));
  }
 
  private:
@@ -887,12 +885,11 @@ class asio_context final : public request_context, public std::enable_shared_fro
  auto tcp_port = proxy_type == http_proxy_type::http ? proxy_port : port;
 
  tcp::resolver::query query(tcp_host, to_string(tcp_port));
- auto client = std::static_pointer_cast<asio_client>(ctx->m_http_client);
- client->m_resolver.async_resolve(query,
- boost::bind(&asio_context::handle_resolve,
- ctx,
- boost::asio::placeholders::error,
- boost::asio::placeholders::iterator));
+ ctx->m_resolver.async_resolve(query,
+ boost::bind(&asio_context::handle_resolve,
+ ctx,
+ boost::asio::placeholders::error,
+ boost::asio::placeholders::iterator));
  }
 
  // Register for notification on cancellation to abort this request.
@@ -1053,6 +1050,10 @@ class asio_context final : public request_context, public std::enable_shared_fro
  {
  report_error("Error resolving address", ec, httpclient_errorcode_context::connect);
  }
+ else if (endpoints == tcp::resolver::iterator())
+ {
+ report_error("Failed to resolve address", ec, httpclient_errorcode_context::connect);
+ }
  else
  {
  m_timer.reset();
@@ -1452,8 +1453,8 @@ class asio_context final : public request_context, public std::enable_shared_fro
  }
  }
 
- m_content_length = (std::numeric_limits<size_t>::max)(); // Without Content-Length header, size should be same as
- // TCP stream - set it size_t max.
+ m_content_length = (std::numeric_limits<size_t>::max)(); // Without Content-Length header, size should be same
+ // as TCP stream - set it size_t max.
  m_response.headers().match(header_names::content_length, m_content_length);
 
  if (!this->handle_compression())
@@ -1936,6 +1937,7 @@ class asio_context final : public request_context, public std::enable_shared_fro
  uint64_t m_content_length;
  bool m_needChunked;
  timeout_timer m_timer;
+ tcp::resolver m_resolver;
  boost::asio::streambuf m_body_buf;
  std::shared_ptr<asio_connection> m_connection;