Minimize the number of range requests made by PDFium

pdf/document_loader.h

Index: pdf/document_loader.h
diff --git a/pdf/document_loader.h b/pdf/document_loader.h
index 4e734a0663a4fab82964544eb3f6ae61668b7c81..7e175debdcf878a9511d10a6ebbb2e6e2523ba1d 100644
--- a/pdf/document_loader.h
+++ b/pdf/document_loader.h
@@ -7,6 +7,7 @@
 
 #include <list>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
@@ -14,8 +15,6 @@
 #include "ppapi/cpp/url_loader.h"
 #include "ppapi/utility/completion_callback_factory.h"
 
-#define kDefaultRequestSize 32768u
-
 namespace chrome_pdf {
 
 class DocumentLoader {
@@ -81,12 +80,24 @@ class DocumentLoader {
   void LoadFullDocument();
   // Download pending requests.
   void DownloadPendingRequests();
+  // Remove completed ranges.
+  void RemoveCompletedRanges();
+  // Returns true if we are already in progress satisfying the request, or just
+  // about ready to start. This helps us avoid expensive jumping around, and
+  // even worse leaving tiny gaps in the byte stream that might have to be
+  // filled later.
+  bool SatisfyingRequest(size_t pos, size_t size) const;
   // Called when we complete server request and read all data from it.
   void ReadComplete();
   // Creates request to download size byte of data data starting from position.
   pp::URLRequestInfo GetRequest(uint32_t position, uint32_t size) const;
-  // Returns current request size in bytes.
-  uint32_t GetRequestSize() const;
+  // Updates the rendering by the Client.
+  void UpdateRendering();
+
+  // Document below size will be downloaded in one chunk.
+  static const uint32_t kMinFileSize = 64 * 1024;
+  // Number was chosen in crbug.com/78264#c8
+  enum { kDefaultRequestSize = 65536 };
 
   Client* client_;
   std::string url_;
@@ -97,6 +108,15 @@ class DocumentLoader {
   bool request_pending_;
   typedef std::list<std::pair<size_t, size_t> > PendingRequests;
   PendingRequests pending_requests_;
+  // The starting position of the HTTP request currently being processed.
+  size_t current_request_offset_;
+  // The size of the byte range the current HTTP request must download before
+  // being cancelled.
+  size_t current_request_size_;
+  // The actual byte range size of the current HTTP request. This may be larger
+  // than |current_request_size_| and the request may be cancelled before
+  // reaching |current_request_offset_| + |current_request_extended_size_|.
+  size_t current_request_extended_size_;
   char buffer_[kDefaultRequestSize];
   uint32_t current_pos_;
   uint32_t current_chunk_size_;