OOPIFs: Transitioning MHTML generation from view-oriented to frame-oriented.

content/common/frame_messages.h

Index: content/common/frame_messages.h
diff --git a/content/common/frame_messages.h b/content/common/frame_messages.h
index f4fc8b5b1e3bbe4eca185a760961e2e0d1bd0e88..b70017e2e1e381f3084c4533394d31fa61beb3f5 100644
--- a/content/common/frame_messages.h
+++ b/content/common/frame_messages.h
@@ -29,6 +29,7 @@
 #include "content/public/common/three_d_api_types.h"
 #include "content/public/common/transition_element.h"
 #include "ipc/ipc_message_macros.h"
+#include "ipc/ipc_platform_file.h"
 #include "third_party/WebKit/public/web/WebFrameOwnerProperties.h"
 #include "third_party/WebKit/public/web/WebTreeScopeType.h"
 #include "ui/gfx/ipc/gfx_param_traits.h"
@@ -717,6 +718,31 @@ IPC_MESSAGE_ROUTED3(FrameMsg_GetSerializedHtmlWithLocalLinks,
                     std::vector<base::FilePath> /* paths of local copy */,
                     base::FilePath /* local directory path */)
 
+// Serialize target frame and its resources into MHTML and write it into the
+// provided destination file handle.
+//
+// When starting generation of a new MHTML document, one needs to start by
+// sending FrameMsg_SerializeAsMHTML for the *main* frame (when handling the
+// main frame, the renderer generates MHTML header + mhtml boundary marker).
+//
+// When serializing the first, main frame of an MHTML document,
+// |mhtml_boundary_marker| should be an empty string.  Otherwise it needs to be
+// the marker generated and reported back by the previous
+// FrameHostMsg_SerializeAsMHTMLResponse.

[ncarter (slow), 2015/12/04 22:54:47]

It seems like the back-and-forth for boundary-marker passing is a little more
complicated than we might actually need: from the code it looks like we just
need to use a consistent boundary marker across all frames, right?

Would it be better to generate the boundary marker (or ten bytes from
base::RandBytes() that could be turned into a boundary marker) in the browser
process MHTMLGenerationManager, and pass it to all frames? Or is that more
trouble than it's worth?

[Łukasz Anforowicz, 2015/12/05 00:18:39]

Thanks for bringing that up.  I am not quite happy with what I have here now. 
Initially I was simply hesitant to break-up the boundary generation code from
the rest of MHTML serialization/generation code in MHTMLArchive, but after
reading the specs I see that this is supposed to be a generic mime multipart
boundary and I don't see a problem with having such generic code in the browser,
far away from the MHTMLArchive code.

For now I'll have an ad-hoc code for generating the boundary inside
MHTMLGenerationManager.  I'll try to add a shared/generic utility function later
into net/base/mime_util.h.

Interestingly there is a restricted set of characters that can go here (guid
characters seem ok) - there is BNF in section "7.2.1 Multipart: The common
syntax" of rfc1341.  And I probably want to preserve some properties of what
MHTMLParser does (i.e. leading "----" substring) although this is silly CYA
approach that I am a bit ashamed of... (otoh, I don't entirely disagree with not
changing "it" if it ain't broken...).

[ncarter (slow), 2015/12/07 18:39:57]

Yeah, my instinct is also to apply the "if it ain't broken" logic here.

+//
+// For more details about frame to content id map please see
+// WebPageSerializer::generateMHTMLParts method.
+//
+// |is_last_frame| controls whether the serializer in the renderer will
+// emit the MHTML footer.
+using FrameRoutingIdToContentIdMap = std::map<int, std::string>;
+IPC_MESSAGE_ROUTED5(FrameMsg_SerializeAsMHTML,
+                    int /* job_id (used to match responses to requests) */,
+                    IPC::PlatformFileForTransit /* destination file handle */,
+                    std::string /* mhtml boundary marker */,
+                    FrameRoutingIdToContentIdMap,
+                    bool /* is last frame */)
+
 IPC_MESSAGE_ROUTED1(FrameMsg_SetFrameOwnerProperties,
                     blink::WebFrameOwnerProperties /* frame_owner_properties */)
 
@@ -1246,6 +1272,12 @@ IPC_MESSAGE_ROUTED2(FrameHostMsg_SerializedHtmlWithLocalLinksResponse,
                     std::string /* data buffer */,
                     bool /* end of data? */)
 
+// Response to FrameMsg_SerializeAsMHTML.
+IPC_MESSAGE_ROUTED3(FrameHostMsg_SerializeAsMHTMLResponse,
+                    int /* job_id (used to match responses to requests) */,
+                    bool /* true if success, false if error */,
+                    std::string /* mhtml boundary marker that was used */)
+
 // Sent when the renderer updates hint for importance of a tab.
 IPC_MESSAGE_ROUTED1(FrameHostMsg_UpdatePageImportanceSignals,
                     content::PageImportanceSignals)