interrupt and resume download with CONTENT_LENGTH_MISMATCH errors

content/browser/download/download_request_core.cc

Index: content/browser/download/download_request_core.cc
diff --git a/content/browser/download/download_request_core.cc b/content/browser/download/download_request_core.cc
index 7e8d102d55c6b7b99df107aa0e86eb7f542ffa76..83cea35d62b266f1aec90dde2c593ba0e058e39b 100644
--- a/content/browser/download/download_request_core.cc
+++ b/content/browser/download/download_request_core.cc
@@ -398,7 +398,8 @@ void DownloadRequestCore::OnResponseCompleted(
             << " status.error() = " << status.error()
             << " response_code = " << response_code;
 
-  DownloadInterruptReason reason = HandleRequestStatus(status);
+  DownloadInterruptReason reason = HandleRequestStatus(
+      status, request()->response_headers()->HasStrongValidators());
 
   if (status.error() == net::ERR_ABORTED) {
     // ERR_ABORTED == something outside of the network
@@ -500,7 +501,7 @@ std::string DownloadRequestCore::DebugString() const {
 
 // static
 DownloadInterruptReason DownloadRequestCore::HandleRequestStatus(
-    const net::URLRequestStatus& status) {
+    const net::URLRequestStatus& status, bool has_strong_validators) {
   net::Error error_code = net::OK;
   if (!status.is_success()) {
     error_code = static_cast<net::Error>(status.error());  // Normal case.
@@ -509,12 +510,23 @@ DownloadInterruptReason DownloadRequestCore::HandleRequestStatus(
       error_code = net::ERR_FAILED;
   }
 
-  // ERR_CONTENT_LENGTH_MISMATCH is allowed since a number of servers in the
-  // wild close the connection too early by mistake. Other browsers - IE9,
-  // Firefox 11.0, and Safari 5.1.4 - treat downloads as complete in both cases,
-  // so we follow their lead.
-  if (error_code == net::ERR_CONTENT_LENGTH_MISMATCH)
+  // ERR_CONTENT_LENGTH_MISMATCH can be caused by 1 of the following reasons:
+  // 1. server close the connection too early.

[asanka, 2017/04/26 21:17:33]

The more common case isn't the server closing the connection, but a middlebox.
Imagine what happens if the UA is connecting through a proxy and the connection
between the proxy and the server breaks. The proxy isn't going to bother
emulating a network error. Instead it'll just close the connection.

Also "Server closes the connection too early." (consistent capitalization,
singular verb).

[qinmin, 2017/04/27 18:20:54]

Done. Thanks for the info.

+  // 2. The content-length header is wrong.
+  // If the download has strong validators, we can interrupt the download
+  // and let it resume automatically. Otherwise, resuming the download will
+  // cause it to restart and the download may never complete if the error was
+  // caused by reason 2. As a result, downloads without strong validators are
+  // treated as completed here.
+  // TODO(qinmin): check the metrics from downloads with strong validators,
+  // and decide whether we should interrupt downloads without strong validators
+  // rather than complete them.
+  if (error_code == net::ERR_CONTENT_LENGTH_MISMATCH &&
+      !has_strong_validators) {
     error_code = net::OK;
+    RecordDownloadCount(COMPLETED_WITH_CONTENT_LENGTH_MISMATCH_COUNT);
+  }
+
   DownloadInterruptReason reason = ConvertNetErrorToInterruptReason(
       error_code, DOWNLOAD_INTERRUPT_FROM_NETWORK);