feat: add option to allow setting CURLOPT_INTERFACE

google/cloud/internal/curl_impl.cc

@@ -23,6 +23,7 @@
 #include "google/cloud/internal/rest_options.h"
 #include "google/cloud/internal/user_agent_prefix.h"
 #include "google/cloud/log.h"
+#include "google/cloud/rest_options.h"
 #include "absl/strings/match.h"
 #include "absl/strings/strip.h"
 #include <algorithm>
@@ -196,6 +197,8 @@ CurlImpl::CurlImpl(CurlHandle handle,
   proxy_ = CurlOptProxy(options);
   proxy_username_ = CurlOptProxyUsername(options);
   proxy_password_ = CurlOptProxyPassword(options);
+
+  interface_ = CurlOptInterface(options);
 }
 
 CurlImpl::~CurlImpl() {
@@ -319,6 +322,10 @@ Status CurlImpl::MakeRequest(HttpMethod method, RestContext& context,
     status = handle_.SetOption(CURLOPT_PROXYPASSWORD, proxy_password_->c_str());
     if (!status.ok()) return OnTransferError(context, std::move(status));
   }
+  if (interface_) {
+    status = handle_.SetOption(CURLOPT_INTERFACE, interface_->c_str());
+    if (!status.ok()) return OnTransferError(context, std::move(status));
+  }
 
   if (method == HttpMethod::kGet) {
     status = handle_.SetOption(CURLOPT_NOPROGRESS, 1L);
@@ -786,6 +793,12 @@ absl::optional<std::string> CurlOptProxyPassword(Options const& options) {
   return cfg.password();
 }
 
+absl::optional<std::string> CurlOptInterface(Options const& options) {
+  auto const& cfg = options.get<Interface>();
+  if (cfg.empty()) return absl::nullopt;
+  return cfg;
+}
+
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace rest_internal
 }  // namespace cloud

google/cloud/internal/curl_impl.h

@@ -143,6 +143,8 @@ class CurlImpl {
   absl::optional<std::string> proxy_username_;
   absl::optional<std::string> proxy_password_;
 
+  absl::optional<std::string> interface_;
+
   CurlReceivedHeaders received_headers_;
   std::string url_;
   HttpStatusCode http_code_;
@@ -192,6 +194,9 @@ absl::optional<std::string> CurlOptProxyUsername(Options const& options);
 /// Compute the CURLOPT_PROXYPASSWORD setting from @p options.
 absl::optional<std::string> CurlOptProxyPassword(Options const& options);
 
+/// Compute the CURLOPT_INTERFACE setting from @p options.
+absl::optional<std::string> CurlOptInterface(Options const& options);
+
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace rest_internal
 }  // namespace cloud

google/cloud/internal/curl_impl_test.cc

@@ -14,6 +14,7 @@
 
 #include "google/cloud/internal/curl_impl.h"
 #include "google/cloud/common_options.h"
+#include "google/cloud/rest_options.h"
 #include "google/cloud/testing_util/status_matchers.h"
 #include <gmock/gmock.h>
 #include <vector>
@@ -182,6 +183,12 @@ TEST_F(CurlImplTest, CurlOptProxyPassword) {
       absl::make_optional(std::string("password")));
 }
 
+TEST_F(CurlImplTest, CurlOptInterface) {
+  EXPECT_EQ(CurlOptInterface(Options{}), absl::nullopt);
+  EXPECT_EQ(CurlOptInterface(Options{}.set<Interface>("interface")),
+            absl::make_optional(std::string("interface")));
+}
+
 }  // namespace
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace rest_internal

google/cloud/rest_options.h

@@ -45,10 +45,24 @@ struct RestTracingOptionsOption {
   using Type = TracingOptions;
 };
 
+/**
+ * Sets the interface name to use as outgoing network interface. The
+ * name can be an interface name, IP address, or hostname. To
+ * utilize one of these use the following special prefixes:
+ *
+ * if!<name> for interface name, host!<name for IP address or hostname,
+ * ifhost!<interface>!<host> for interface name and IP address or hostname.
+ *
+ * The default is to use whatever the TCP stack finds suitable.
+ */
+struct Interface {
+  using Type = std::string;
+};
+
 /// The complete list of options accepted by `CurlRestClient`
 using RestOptionList =
     ::google::cloud::OptionList<QuotaUserOption, RestTracingOptionsOption,
-                                ServerTimeoutOption, UserIpOption>;
+                                ServerTimeoutOption, UserIpOption, Interface>;
 
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace cloud