Add object compression support (#6292)

Add support for streaming (golang/LZ77/snappy) compression.

vendor/github.com/golang/snappy/encode.go

@@ -138,7 +138,7 @@ func NewBufferedWriter(w io.Writer) *Writer {
 	}
 }
 
-// Writer is an io.Writer than can write Snappy-compressed bytes.
+// Writer is an io.Writer that can write Snappy-compressed bytes.
 type Writer struct {
 	w   io.Writer
 	err error

vendor/github.com/golang/snappy/encode_amd64.go

@@ -26,4 +26,4 @@ func extendMatch(src []byte, i, j int) int
 // encodeBlock has the same semantics as in encode_other.go.
 //
 //go:noescape
-func encodeBlock(dst, src []byte) (d int)
+func encodeBlock(dst, src []byte) (d int)

vendor/github.com/golang/snappy/snappy.go

@@ -2,10 +2,21 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package snappy implements the snappy block-based compression format.
-// It aims for very high speeds and reasonable compression.
+// Package snappy implements the Snappy compression format. It aims for very
+// high speeds and reasonable compression.
 //
-// The C++ snappy implementation is at https://github.com/google/snappy
+// There are actually two Snappy formats: block and stream. They are related,
+// but different: trying to decompress block-compressed data as a Snappy stream
+// will fail, and vice versa. The block format is the Decode and Encode
+// functions and the stream format is the Reader and Writer types.
+//
+// The block format, the more common case, is used when the complete size (the
+// number of bytes) of the original data is known upfront, at the time
+// compression starts. The stream format, also known as the framing format, is
+// for when that isn't always true.
+//
+// The canonical, C++ implementation is at https://github.com/google/snappy and
+// it only implements the block format.
 package snappy // import "github.com/golang/snappy"
 
 import (

vendor/vendor.json

@@ -359,10 +359,10 @@
 			"revisionTime": "2018-04-30T18:52:41Z"
 		},
 		{
-			"checksumSHA1": "W+E/2xXcE1GmJ0Qb784ald0Fn6I=",
+			"checksumSHA1": "h1d2lPZf6j2dW/mIqVnd1RdykDo=",
 			"path": "github.com/golang/snappy",
-			"revision": "d9eb7a3d35ec988b8585d4a0068e462c27d28380",
-			"revisionTime": "2016-05-29T05:00:41Z"
+			"revision": "2e65f85255dbc3072edf28d6b5b8efc472979f5a",
+			"revisionTime": "2018-05-18T05:39:59Z"
 		},
 		{
 			"checksumSHA1": "0x0CoHbgoWngucjKSDPFodeL8ek=",