Improve Zip File Scanning on Mac

third_party/zlib/google/zip_reader.h

Index: third_party/zlib/google/zip_reader.h
diff --git a/third_party/zlib/google/zip_reader.h b/third_party/zlib/google/zip_reader.h
index c1b6fb3364abeba3c34231e9dd1fea500540029e..49b81ee2da19861a3f61bf7711e8b2e6cb7332a8 100644
--- a/third_party/zlib/google/zip_reader.h
+++ b/third_party/zlib/google/zip_reader.h
@@ -159,9 +159,16 @@ class ZipReader {
   // success. On failure, current_entry_info() becomes NULL.
   bool LocateAndOpenEntry(const base::FilePath& path_in_zip);
 
-  // Extracts the current entry in chunks to |delegate|.
+  // Extracts entirety of the current entry in chunks to |delegate|.

[satorux1, 2017/07/21 05:27:02]

While you are at it, could you add documentation about the return value?

[mortonm, 2017/07/21 16:29:56]

Done. Didn't add an explanation here, but there are a variety of cases that
could cause this function to return false, including not being able to read the
current entry, not being able to write to the delegate, etc

   bool ExtractCurrentEntry(WriterDelegate* delegate) const;
 
+  // Extracts |num_bytes_to_extract| bytes of the current entry to |delegate|,
+  // starting from the beginning of the entry. A negative value for
+  // |num_bytes_to_extract| means the entire current entry will be extracted.
+  // Returns false if |num_bytes_to_extract| is greater than file length.
+  bool ExtractFromBeginningOfCurrentEntry(WriterDelegate* delegate,
+                                          int64_t num_bytes_to_extract) const;
+
   // Extracts the current entry to the given output file path. If the
   // current file is a directory, just creates a directory
   // instead. Returns true on success. OpenCurrentEntryInZip() must be
@@ -202,21 +209,30 @@ class ZipReader {
   // Does not close the file. Returns true on success.
   bool ExtractCurrentEntryToFile(base::File* file) const;
 
-  // Extracts the current entry into memory. If the current entry is a directory
-  // the |output| parameter is set to the empty string. If the current entry is
-  // a file, the |output| parameter is filled with its contents. Returns true on
-  // success. OpenCurrentEntryInZip() must be called beforehand.
-  // Note: the |output| parameter can be filled with a big amount of data, avoid
-  // passing it around by value, but by reference or pointer.
-  // Note: the value returned by EntryInfo::original_size() cannot be
-  // trusted, so the real size of the uncompressed contents can be different.
-  // Use max_read_bytes to limit the ammount of memory used to carry the entry.
-  // If the real size of the uncompressed data is bigger than max_read_bytes
-  // then false is returned. |max_read_bytes| must be non-zero.
+  // Extracts the current entry into memory. If the current entry is a
+  // directory, the |output| parameter is set to the empty string. If the
+  // current entry is a file, the |output| parameter is filled with its
+  // contents. Returns true on success. OpenCurrentEntryInZip() must be called
+  // beforehand. Note: the |output| parameter can be filled with a big amount of
+  // data, avoid passing it around by value, but by reference or pointer. Note:
+  // the value returned by EntryInfo::original_size() cannot be trusted, so the
+  // real size of the uncompressed contents can be different. Use
+  // |max_read_bytes| to limit the ammount of memory used to carry the entry. If
+  // the real size of the uncompressed data is bigger than |max_read_bytes| then
+  // false is returned. |max_read_bytes| must be non-zero.
   bool ExtractCurrentEntryToString(
       size_t max_read_bytes,
       std::string* output) const;
 
+  // Same as ExtractCurrentEntryToString(), except specifies the number of bytes
+  // to read into the string so that it is possible to only read a partial
+  // amount of the entry into a string. If
+  // |read_entire_file|, returns true only if |num_bytes_to_extract| is at least
+  // the size of entire file.
+  bool ExtractFromBeginningOfCurrentEntryToString(size_t num_bytes_to_extract,
+                                                  bool read_entire_file,
+                                                  std::string* output) const;
+
   // Returns the current entry info. Returns NULL if the current entry is
   // not yet opened. OpenCurrentEntryInZip() must be called beforehand.
   EntryInfo* current_entry_info() const {