Download resumption - Preliminary

content/browser/renderer_host/resource_dispatcher_host_impl.cc

Index: content/browser/renderer_host/resource_dispatcher_host_impl.cc
diff --git a/content/browser/renderer_host/resource_dispatcher_host_impl.cc b/content/browser/renderer_host/resource_dispatcher_host_impl.cc
index 111edc5a9fdabf7eed215daf838f2d97c91f399b..c2d4552ca0567270123d30922a38542dac47d998 100644
--- a/content/browser/renderer_host/resource_dispatcher_host_impl.cc
+++ b/content/browser/renderer_host/resource_dispatcher_host_impl.cc
@@ -49,6 +49,7 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/download_manager.h"
+#include "content/public/browser/download_save_info.h"
 #include "content/public/browser/global_request_id.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/resource_dispatcher_host_delegate.h"
@@ -498,6 +499,9 @@ net::Error ResourceDispatcherHostImpl::BeginDownload(
     int route_id,
     bool prefer_cache,
     scoped_ptr<DownloadSaveInfo> save_info,
+    const std::string& last_modified,
+    const std::string& etag,
+    content::DownloadId download_id,
     const DownloadStartedCallback& started_callback) {
   if (is_shutdown_)
     return CallbackAndReturn(started_callback, net::ERR_INSUFFICIENT_RESOURCES);
@@ -536,6 +540,27 @@ net::Error ResourceDispatcherHostImpl::BeginDownload(
   request_id_--;
 
   const net::URLRequestContext* request_context = context->GetRequestContext();
+
+  // If we're not at the beginning of the file, retrieve only the remaining
+  // portion.
+  if (save_info->offset > 0) {
+    request->SetExtraRequestHeaderByName(
+        "Range",
+        StringPrintf("bytes=%" PRId64 "-", save_info->offset),
+        true);
+  }
+
+  // If it's the second (or later) request for this file, make sure it
+  // hasn't been modified.
+  if (!last_modified.empty()) {
+    request->SetExtraRequestHeaderByName("If-Unmodified-Since",
+                                         last_modified,
+                                         true);
+  }
+  if (!etag.empty()) {
+    // Set requested ETAG.
+    request->SetExtraRequestHeaderByName("If-Match", etag, true);
+  }
   if (!request_context->job_factory()->IsHandledURL(url)) {
     VLOG(1) << "Download request for unsupported protocol: "
             << url.possibly_invalid_spec();