impl(rest): set ReadFunctionAbort via RAII (#14617)

google/cloud/internal/curl_impl.cc

@@ -487,6 +487,22 @@ std::size_t CurlImpl::HeaderCallback(absl::Span<char> response) {
                               response.size());
 }
 
+class CurlImpl::ReadFunctionAbortGuard {
+ public:
+  explicit ReadFunctionAbortGuard(CurlImpl& impl) : impl_(impl) {}
+  ~ReadFunctionAbortGuard() {
+    // If curl_closed_ is true, then the handle has already been recycled and
+    // attempting to set an option on it will error.
+    if (!impl_.curl_closed_) {
+      impl_.handle_.SetOptionUnchecked(CURLOPT_READFUNCTION,
+                                       &ReadFunctionAbort);
+    }
+  }
+
+ private:
+  CurlImpl& impl_;
+};
+
 Status CurlImpl::MakeRequestImpl(RestContext& context) {
   TRACE_STATE() << ", url_=" << url_;
 
@@ -509,6 +525,11 @@ Status CurlImpl::MakeRequestImpl(RestContext& context) {
   handle_.SetOptionUnchecked(CURLOPT_HTTP_VERSION,
                              VersionToCurlCode(http_version_));
 
+  // All data in the WriteVector should be written after ReadImpl returns unless
+  // an error, typically a timeout, has occurred. Use ReadFunctionAbortGuard to
+  // leverage RAII to instruct curl to not attempt to send anymore data on this
+  // handle regardless if an error or exception is encountered.
+  ReadFunctionAbortGuard guard(*this);
   auto error = curl_multi_add_handle(multi_.get(), handle_.handle_.get());
 
   // This indicates that we are using the API incorrectly. The application
@@ -524,18 +545,7 @@ Status CurlImpl::MakeRequestImpl(RestContext& context) {
   // thus make available the status_code and headers. Any response data
   // should be put into the spill buffer, which makes them available for
   // subsequent calls to Read() after the headers have been extracted.
-  auto read_status = ReadImpl(context, {}).status();
-
-  // All data in the WriteVector should have been written by now, unless an
-  // error, typically a timeout, has occurred. Instruct curl to not attempt to
-  // send anymore data on this handle. If curl_closed_ is true, then the handle
-  // has already been recycled and attempting to set an option on it will error.
-  if (!curl_closed_) {
-    status = handle_.SetOption(CURLOPT_READFUNCTION, &ReadFunctionAbort);
-    if (!status.ok()) return OnTransferError(context, std::move(status));
-  }
-
-  return read_status;
+  return ReadImpl(context, {}).status();
 }
 
 StatusOr<std::size_t> CurlImpl::ReadImpl(RestContext& context,

google/cloud/internal/curl_impl.h

@@ -107,6 +107,7 @@ class CurlImpl {
   std::size_t HeaderCallback(absl::Span<char> response);
 
  private:
+  class ReadFunctionAbortGuard;
   Status MakeRequestImpl(RestContext& context);
   StatusOr<std::size_t> ReadImpl(RestContext& context, absl::Span<char> output);