Fix reading zip64 files with max length file comment.

If a zip file has a comment that is 65,535 characters long - which is a
valid length and the maximum allowable length - the initial read of the
archive fails to find the Zip64 End of Central Directory Locator and
therefore cannot read the rest of the file.

This commit fixes this by making sure that we look far enough back into
the file from the end to find this locator, and then use the
information in it to find the Zip64 End of Central Directory Record.

Test added to catch regressions.

Fixes #509.

lib/zip/central_directory.rb

@@ -6,15 +6,16 @@ module Zip
   class CentralDirectory
     extend Forwardable
 
-    END_OF_CDS             = 0x06054b50
+    END_OF_CD_SIG          = 0x06054b50
-    ZIP64_END_OF_CDS       = 0x06064b50
+    ZIP64_END_OF_CD_SIG    = 0x06064b50
-    ZIP64_EOCD_LOCATOR     = 0x07064b50
+    ZIP64_EOCD_LOCATOR_SIG = 0x07064b50
 
     STATIC_EOCD_SIZE       = 22
     ZIP64_STATIC_EOCD_SIZE = 56
     ZIP64_EOCD_LOC_SIZE    = 20
-    MAX_FILE_COMMENT_SIZE  = 1 << 16
+    MAX_FILE_COMMENT_SIZE  = (1 << 16) - 1
-    MAX_END_OF_CDS_SIZE    = MAX_FILE_COMMENT_SIZE + STATIC_EOCD_SIZE
+    MAX_END_OF_CD_SIZE     =
+      MAX_FILE_COMMENT_SIZE + STATIC_EOCD_SIZE + ZIP64_EOCD_LOC_SIZE
 
     attr_accessor :comment
 
@@ -47,7 +48,7 @@ module Zip
 
     def write_e_o_c_d(io, offset, cdir_size) #:nodoc:
       tmp = [
-        END_OF_CDS,
+        END_OF_CD_SIG,
         0, # @numberOfThisDisk
         0, # @numberOfDiskWithStartOfCDir
         @entry_set ? [@entry_set.size, 0xFFFF].min : 0,
@@ -64,7 +65,7 @@ module Zip
 
     def write_64_e_o_c_d(io, offset, cdir_size) #:nodoc:
       tmp = [
-        ZIP64_END_OF_CDS,
+        ZIP64_END_OF_CD_SIG,
         44, # size of zip64 end of central directory record (excludes signature and field itself)
         VERSION_MADE_BY,
         VERSION_NEEDED_TO_EXTRACT_ZIP64,
@@ -82,7 +83,7 @@ module Zip
 
     def write_64_eocd_locator(io, zip64_eocd_offset)
       tmp = [
-        ZIP64_EOCD_LOCATOR,
+        ZIP64_EOCD_LOCATOR_SIG,
         0, # number of disk containing the start of zip64 eocd record
         zip64_eocd_offset, # offset of the start of zip64 eocd record in its disk
         1 # total number of disks
@@ -93,15 +94,7 @@ module Zip
     private :write_64_eocd_locator
 
     def unpack_64_e_o_c_d(buffer) #:nodoc:
-      index = buffer.rindex([ZIP64_END_OF_CDS].pack('V'))
+      _, # ZIP64_END_OF_CD_SIG. We know we have this at this point.
-      raise Error, 'Zip64 end of central directory signature not found' unless index
-
-      l_index = buffer.rindex([ZIP64_EOCD_LOCATOR].pack('V'))
-      raise Error, 'Zip64 end of central directory signature locator not found' unless l_index
-
-      buf = buffer.slice(index..l_index)
-
-      _, # ZIP64_END_OF_CDS signature. We know we have this at this point.
       @size_of_zip64_e_o_c_d,
       @version_made_by,
       @version_needed_for_extract,
@@ -110,7 +103,7 @@ module Zip
       @total_number_of_entries_in_cdir_on_this_disk,
       @size,
       @size_in_bytes,
-      @cdir_offset = buf.unpack('VQ<vvVVQ<Q<Q<Q<')
+      @cdir_offset = buffer.unpack('VQ<vvVVQ<Q<Q<Q<')
 
       zip64_extensible_data_size =
         @size_of_zip64_e_o_c_d - ZIP64_STATIC_EOCD_SIZE + 12
@@ -124,20 +117,22 @@ module Zip
                                end
     end
 
+    def unpack_64_eocd_locator(buffer) #:nodoc:
+      _, # ZIP64_EOCD_LOCATOR_SIG. We know we have this at this point.
+      _, zip64_eocd_offset, = buffer.unpack('VVQ<V')
+
+      zip64_eocd_offset
+    end
+
     def unpack_e_o_c_d(buffer) #:nodoc:
-      index = buffer.rindex([END_OF_CDS].pack('V'))
+      _, # END_OF_CD_SIG. We know we have this at this point.
-      raise Error, 'Zip end of central directory signature not found' unless index
-
-      buf = buffer.slice(index, buffer.size)
-
-      _, # END_OF_CDS signature. We know we have this at this point.
       num_disk,
       num_disk_cdir,
       num_cdir_disk,
       num_entries,
       size_in_bytes,
       cdir_offset,
-      comment_length = buf.unpack('VvvvvVVv')
+      comment_length = buffer.unpack('VvvvvVVv')
 
       @number_of_this_disk = num_disk unless num_disk == 0xFFFF
       @number_of_disk_with_start_of_cdir = num_disk_cdir unless num_disk_cdir == 0xFFFF
@@ -147,7 +142,7 @@ module Zip
       @cdir_offset = cdir_offset unless cdir_offset == 0xFFFFFFFF
 
       @comment = if comment_length.positive?
-                   buf.slice(STATIC_EOCD_SIZE, comment_length)
+                   buffer.slice(STATIC_EOCD_SIZE, comment_length)
                  else
                    ''
                  end
@@ -203,22 +198,45 @@ module Zip
     end
 
     def read_eocds(io) #:nodoc:
-      buf = start_buf(io)
+      base_location, data = eocd_data(io)
-      unpack_64_e_o_c_d(buf) if zip64_file?(buf)
+
-      unpack_e_o_c_d(buf)
+      eocd_location = data.rindex([END_OF_CD_SIG].pack('V'))
+      raise Error, 'Zip end of central directory signature not found' unless eocd_location
+
+      zip64_eocd_locator = data.rindex([ZIP64_EOCD_LOCATOR_SIG].pack('V'))
+
+      if zip64_eocd_locator
+        zip64_eocd_location = data.rindex([ZIP64_END_OF_CD_SIG].pack('V'))
+
+        zip64_eocd_data =
+          if zip64_eocd_location
+            data.slice(zip64_eocd_location..zip64_eocd_locator)
+          else
+            zip64_eocd_location = unpack_64_eocd_locator(
+              data.slice(zip64_eocd_locator..eocd_location)
+            )
+            unless zip64_eocd_location
+              raise Error, 'Zip64 end of central directory signature not found'
             end
 
-    def zip64_file?(buf)
+            io.seek(zip64_eocd_location, IO::SEEK_SET)
-      buf.rindex([ZIP64_END_OF_CDS].pack('V')) && buf.rindex([ZIP64_EOCD_LOCATOR].pack('V'))
+            io.read(base_location + zip64_eocd_locator - zip64_eocd_location)
           end
 
-    def start_buf(io)
+        unpack_64_e_o_c_d(zip64_eocd_data)
+      end
+
+      unpack_e_o_c_d(data.slice(eocd_location..-1))
+    end
+
+    def eocd_data(io)
       begin
-        io.seek(-MAX_END_OF_CDS_SIZE, IO::SEEK_END)
+        io.seek(-MAX_END_OF_CD_SIZE, IO::SEEK_END)
       rescue Errno::EINVAL
         io.seek(0, IO::SEEK_SET)
       end
-      io.read
+
+      [io.tell, io.read]
     end
 
     # Reads the End of Central Directory Record (and the Zip64 equivalent if

test/file_test.rb

@@ -208,6 +208,11 @@ class ZipFileTest < MiniTest::Test
     Zip::File.open('test/data/max_length_file_comment.zip')
   end
 
+  def test_open_zip64_file_with_max_length_comment
+    # Should not raise any errors.
+    Zip::File.open('test/data/zip64_max_length_file_comment.zip')
+  end
+
   def test_count_entries
     [
       ['test/data/osx-archive.zip', 4],