NaCl: enable meta-based validation for shared libraries.

ppapi/native_client/src/trusted/plugin/file_downloader.cc

Index: ppapi/native_client/src/trusted/plugin/file_downloader.cc
diff --git a/ppapi/native_client/src/trusted/plugin/file_downloader.cc b/ppapi/native_client/src/trusted/plugin/file_downloader.cc
index ce7fe30b2046f58b4348926d3560e0e40673ccfd..4cdd1948404735b429a816a54c57726da586f7b3 100644
--- a/ppapi/native_client/src/trusted/plugin/file_downloader.cc
+++ b/ppapi/native_client/src/trusted/plugin/file_downloader.cc
@@ -5,6 +5,7 @@
 #include "native_client/src/trusted/plugin/file_downloader.h"
 
 #include <stdio.h>
+#include <string.h>
 #include <string>
 
 #include "native_client/src/include/portability_io.h"
@@ -145,7 +146,8 @@ bool FileDownloader::Open(
 }
 
 void FileDownloader::OpenFast(const nacl::string& url,
-                              PP_FileHandle file_handle) {
+                              PP_FileHandle file_handle,
+                              uint64_t nonce) {
   PLUGIN_PRINTF(("FileDownloader::OpenFast (url=%s)\n", url.c_str()));
   CHECK(instance_ != NULL);
   open_time_ = NaClGetTimeOfDayMicroseconds();
@@ -154,9 +156,13 @@ void FileDownloader::OpenFast(const nacl::string& url,
   url_ = url;
   mode_ = DOWNLOAD_NONE;
   file_handle_ = file_handle;
+  nonce_ = nonce;
 }
 
-int32_t FileDownloader::GetPOSIXFileDescriptor() {
+struct NaClFileInfo FileDownloader::GetFileInfo() {
+  struct NaClFileInfo info;
+  memset(&info, 0, sizeof(info));
+  info.desc = -1;
   int32_t file_desc = NACL_NO_FILE_DESC;
   if (not_streaming() && file_handle_ != PP_kInvalidFileHandle) {
 #if NACL_WINDOWS
@@ -165,13 +171,14 @@ int32_t FileDownloader::GetPOSIXFileDescriptor() {
 #else
     file_desc = file_handle_;
 #endif
+    info.nonce = nonce_;
   } else {
     if (!streaming_to_file()) {
-      return NACL_NO_FILE_DESC;
+      return info;

[dmichael (off chromium), 2013/05/15 18:37:53]

I find these error returns less obvious now. Not sure of a nicer way to do it.
You could maybe do:
return { NACL_NO_FILE_DESC, nonce };
? That has the downside that NaClFileInfo can only change by appending, though.

[Nick Bray (chromium), 2013/05/16 16:38:17]

The file info structure is defined in the NaCl repo, so I want to avoid any
assumptions about the layout.  I get what you're saying and considered it
myself, but didn't see a better way.

[dmichael (off chromium), 2013/05/16 17:08:35]

How about a simple little helper function in the unnamed namespace, and do:
MakeNaClFileInfo(NACL_NO_FILE_DESC, nonce);
here.
MakeNaClFileInfo would do the memset and assign those fields without making
assumptions about layout.

Or if you have any better ideas, I'm open. I would just like it to be super
obvious that these branches are error conditions somehow.

[Nick Bray (chromium), 2013/05/16 17:44:15]

Didn't think of that one.  Good idea.  Done.

     }
     // Use the trusted interface to get the file descriptor.
     if (file_io_trusted_interface_ == NULL) {
-      return NACL_NO_FILE_DESC;
+      return info;
     }
     file_desc = file_io_trusted_interface_->GetOSFileDescriptor(
         file_reader_.pp_resource());
@@ -183,12 +190,13 @@ int32_t FileDownloader::GetPOSIXFileDescriptor() {
   if (posix_desc == -1) {
     // Close the Windows HANDLE if it can't be converted.
     CloseHandle(reinterpret_cast<HANDLE>(file_desc));
-    return NACL_NO_FILE_DESC;
+    return info;
   }
   file_desc = posix_desc;
 #endif
 
-  return file_desc;
+  info.desc = file_desc;
+  return info;
 }
 
 int64_t FileDownloader::TimeSinceOpenMilliseconds() const {