compress/zlib: actually use provided dictionary.

R=rsc, bradfitz, bradfitzgoog
CC=golang-dev
https://golang.org/cl/4518056

src/pkg/compress/zlib/writer.go

@@ -89,7 +89,7 @@ func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, os.Error) {
 		}
 	}
 	z.w = w
-	z.compressor = flate.NewWriter(w, level)
+	z.compressor = flate.NewWriterDict(w, level, dict)
 	z.digest = adler32.New()
 	return z, nil
 }

src/pkg/compress/zlib/writer_test.go

@@ -5,6 +5,7 @@
 package zlib
 
 import (
+	"bytes"
 	"io"
 	"io/ioutil"
 	"os"
@@ -121,3 +122,20 @@ func TestWriterDict(t *testing.T) {
 		}
 	}
 }
+
+func TestWriterDictIsUsed(t *testing.T) {
+	var input = []byte("Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.")
+	buf := bytes.NewBuffer(nil)
+	compressor, err := NewWriterDict(buf, BestCompression, input)
+	if err != nil {
+		t.Errorf("error in NewWriterDict: %s", err)
+		return
+	}
+	compressor.Write(input)
+	compressor.Close()
+	const expectedMaxSize = 25
+	output := buf.Bytes()
+	if len(output) > expectedMaxSize {
+		t.Errorf("result too large (got %d, want <= %d bytes). Is the dictionary being used?", len(output), expectedMaxSize)
+	}
+}