1 files changed, 82 insertions, 3 deletions

diff --git a/lib/rubygems/package/tar_reader/entry.rb b/lib/rubygems/package/tar_reader/entry.rb
index e7b0cd0602..9e7b327431 100644
--- a/lib/rubygems/package/tar_reader/entry.rb
+++ b/lib/rubygems/package/tar_reader/entry.rb
@@ -9,6 +9,20 @@
 
 class Gem::Package::TarReader::Entry
   ##
+  # Creates a new tar entry for +header+ that will be read from +io+
+  # If a block is given, the entry is yielded and then closed.
+
+  def self.open(header, io, &block)
+    entry = new header, io
+    return entry unless block_given?
+    begin
+      yield entry
+    ensure
+      entry.close
+    end
+  end
+
+  ##
   # Header for this tar entry
 
   attr_reader :header
@@ -21,6 +35,7 @@ class Gem::Package::TarReader::Entry
     @header = header
     @io = io
     @orig_pos = @io.pos
+    @end_pos = @orig_pos + @header.size
     @read = 0
   end
 
@@ -39,7 +54,14 @@ class Gem::Package::TarReader::Entry
   # Closes the tar entry
 
   def close
+    return if closed?
+    # Seek to the end of the entry if it wasn't fully read
+    seek(0, IO::SEEK_END)
+    # discard trailing zeros
+    skip = (512 - (@header.size % 512)) % 512
+    @io.read(skip)
     @closed = true
+    nil
   end
 
   ##
@@ -117,6 +139,14 @@ class Gem::Package::TarReader::Entry
     bytes_read
   end
 
+  ##
+  # Seek to the position in the tar entry
+
+  def pos=(new_pos)
+    seek(new_pos, IO::SEEK_SET)
+    new_pos
+  end
+
   def size
     @header.size
   end
@@ -158,12 +188,61 @@ class Gem::Package::TarReader::Entry
   end
 
   ##
+  # Seeks to +offset+ bytes into the tar file entry
+  # +whence+ can be IO::SEEK_SET, IO::SEEK_CUR, or IO::SEEK_END
+
+  def seek(offset, whence = IO::SEEK_SET)
+    check_closed
+
+    new_pos =
+      case whence
+      when IO::SEEK_SET then @orig_pos + offset
+      when IO::SEEK_CUR then @io.pos + offset
+      when IO::SEEK_END then @end_pos + offset
+      else
+        raise ArgumentError, "invalid whence"
+      end
+
+    if new_pos < @orig_pos
+      new_pos = @orig_pos
+    elsif new_pos > @end_pos
+      new_pos = @end_pos
+    end
+
+    pending = new_pos - @io.pos
+
+    if @io.respond_to?(:seek)
+      begin
+        # avoid reading if the @io supports seeking
+        @io.seek new_pos, IO::SEEK_SET
+        pending = 0
+      rescue Errno::EINVAL
+      end
+    end
+
+    # if seeking isn't supported or failed
+    # negative seek requires that we rewind and read
+    if pending < 0
+      @io.rewind
+      pending = new_pos
+    end
+
+    while pending > 0 do
+      size_read = @io.read([pending, 4096].min).size
+      raise UnexpectedEOF if @io.eof?
+      pending -= size_read
+    end
+
+    @read = @io.pos - @orig_pos
+
+    0
+  end
+
+  ##
   # Rewinds to the beginning of the tar file entry
 
   def rewind
     check_closed
-
-    @io.pos = @orig_pos
-    @read = 0
+    seek(0, IO::SEEK_SET)
   end
 end