Move AlwaysErrorRequestImpl to HostResolver

Was just used for MappedHostResolver, but moving to HostResolver to be
more generally available to HostResolver implementations.

Also rename to FailingRequestImpl.

Bug: 1006902
Change-Id: Ifffe9971057d8e93a653593d93a6dc88e053f8f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1828099
Commit-Queue: Eric Orth <ericorth@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701250}

net/dns/host_resolver.cc

@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/no_destructor.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
 #include "net/base/address_list.h"
@@ -23,6 +24,49 @@
 
 namespace net {
 
+namespace {
+
+class FailingRequestImpl : public HostResolver::ResolveHostRequest {
+ public:
+  explicit FailingRequestImpl(int error) : error_(error) {}
+  ~FailingRequestImpl() override = default;
+
+  int Start(CompletionOnceCallback callback) override { return error_; }
+
+  const base::Optional<AddressList>& GetAddressResults() const override {
+    static base::NoDestructor<base::Optional<AddressList>> nullopt_result;
+    return *nullopt_result;
+  }
+
+  const base::Optional<std::vector<std::string>>& GetTextResults()
+      const override {
+    static const base::NoDestructor<base::Optional<std::vector<std::string>>>
+        nullopt_result;
+    return *nullopt_result;
+  }
+
+  const base::Optional<std::vector<HostPortPair>>& GetHostnameResults()
+      const override {
+    static const base::NoDestructor<base::Optional<std::vector<HostPortPair>>>
+        nullopt_result;
+    return *nullopt_result;
+  }
+
+  const base::Optional<HostCache::EntryStaleness>& GetStaleInfo()
+      const override {
+    static const base::NoDestructor<base::Optional<HostCache::EntryStaleness>>
+        nullopt_result;
+    return *nullopt_result;
+  }
+
+ private:
+  const int error_;
+
+  DISALLOW_COPY_AND_ASSIGN(FailingRequestImpl);
+};
+
+}  // namespace
+
 const size_t HostResolver::ManagerOptions::kDefaultRetryAttempts =
     static_cast<size_t>(-1);
 
@@ -171,4 +215,10 @@ HostResolverFlags HostResolver::ParametersToHostResolverFlags(
 
 HostResolver::HostResolver() = default;
 
+// static
+std::unique_ptr<HostResolver::ResolveHostRequest>
+HostResolver::CreateFailingRequest(int error) {
+  return std::make_unique<FailingRequestImpl>(error);
+}
+
 }  // namespace net

net/dns/host_resolver.h

@@ -342,6 +342,10 @@ class NET_EXPORT HostResolver {
  protected:
   HostResolver();
 
+  // Utility to create a request implementation that always fails with |error|
+  // immediately on start.
+  static std::unique_ptr<ResolveHostRequest> CreateFailingRequest(int error);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(HostResolver);
 };

net/dns/mapped_host_resolver.cc

@@ -7,7 +7,6 @@
 #include <string>
 #include <utility>
 
-#include "base/no_destructor.h"
 #include "base/strings/string_util.h"
 #include "base/values.h"
 #include "net/base/host_port_pair.h"
@@ -15,43 +14,6 @@
 
 namespace net {
 
-class MappedHostResolver::AlwaysErrorRequestImpl
-    : public HostResolver::ResolveHostRequest {
- public:
-  explicit AlwaysErrorRequestImpl(int error) : error_(error) {}
-
-  int Start(CompletionOnceCallback callback) override { return error_; }
-
-  const base::Optional<AddressList>& GetAddressResults() const override {
-    static base::NoDestructor<base::Optional<AddressList>> nullopt_result;
-    return *nullopt_result;
-  }
-
-  const base::Optional<std::vector<std::string>>& GetTextResults()
-      const override {
-    static const base::NoDestructor<base::Optional<std::vector<std::string>>>
-        nullopt_result;
-    return *nullopt_result;
-  }
-
-  const base::Optional<std::vector<HostPortPair>>& GetHostnameResults()
-      const override {
-    static const base::NoDestructor<base::Optional<std::vector<HostPortPair>>>
-        nullopt_result;
-    return *nullopt_result;
-  }
-
-  const base::Optional<HostCache::EntryStaleness>& GetStaleInfo()
-      const override {
-    static const base::NoDestructor<base::Optional<HostCache::EntryStaleness>>
-        nullopt_result;
-    return *nullopt_result;
-  }
-
- private:
-  const int error_;
-};
-
 MappedHostResolver::MappedHostResolver(std::unique_ptr<HostResolver> impl)
     : impl_(std::move(impl)) {}
 
@@ -70,7 +32,7 @@ MappedHostResolver::CreateRequest(
   rules_.RewriteHost(&rewritten);
 
   if (rewritten.host() == "~NOTFOUND")
-    return std::make_unique<AlwaysErrorRequestImpl>(ERR_NAME_NOT_RESOLVED);
+    return CreateFailingRequest(ERR_NAME_NOT_RESOLVED);
 
   return impl_->CreateRequest(rewritten, source_net_log, optional_parameters);
 }

net/dns/mapped_host_resolver.h

@@ -61,8 +61,6 @@ class NET_EXPORT MappedHostResolver : public HostResolver {
   HostResolverManager* GetManagerForTesting() override;
 
  private:
-  class AlwaysErrorRequestImpl;
-
   std::unique_ptr<HostResolver> impl_;
 
   HostMappingRules rules_;