From 844927ff1f4a692412031309fa58c04fd9f65208 Mon Sep 17 00:00:00 2001
From: kortschak <dan.kortschak@adelaide.edu.au>
Date: Fri, 8 Aug 2014 21:27:17 +0930
Subject: [PATCH] Make decompressor conditional on reader interface

---
 cayley.go      | 13 ++++++-------
 cayley_test.go | 37 +++++++++++++++++++++++++++----------
 2 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/cayley.go b/cayley.go
index fa0558e..0c2efda 100644
--- a/cayley.go
+++ b/cayley.go
@@ -217,14 +217,13 @@ const (
 	b2zipMagic = "BZh"
 )
 
-type readAtReader interface {
-	io.Reader
-	io.ReaderAt
-}
-
-func decompressor(r readAtReader) (io.Reader, error) {
+func decompressor(r io.Reader) (io.Reader, error) {
+	ra, ok := r.(io.ReaderAt)
+	if !ok {
+		return r, nil
+	}
 	var buf [3]byte
-	_, err := r.ReadAt(buf[:], 0)
+	_, err := ra.ReadAt(buf[:], 0)
 	if err != nil {
 		return nil, err
 	}
diff --git a/cayley_test.go b/cayley_test.go
index eba0720..ce382b2 100644
--- a/cayley_test.go
+++ b/cayley_test.go
@@ -18,6 +18,8 @@ import (
 	"bytes"
 	"compress/bzip2"
 	"compress/gzip"
+	"io"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -419,62 +421,77 @@ func BenchmarkKeanuBullockOther(b *testing.B) {
 	runBench(8, b)
 }
 
+// reader is a test helper to filter non-io.Reader methods from the contained io.Reader.
+type reader struct {
+	r io.Reader
+}
+
+func (r reader) Read(p []byte) (int, error) {
+	return r.r.Read(p)
+}
+
 var testDecompressor = []struct {
 	message string
-	input   []byte
+	input   io.Reader
 	expect  []byte
 	err     error
 	readErr error
 }{
 	{
 		message: "text input",
-		input:   []byte("cayley data\n"),
+		input:   strings.NewReader("cayley data\n"),
 		err:     nil,
 		expect:  []byte("cayley data\n"),
 		readErr: nil,
 	},
 	{
 		message: "gzip input",
-		input: []byte{
+		input: bytes.NewReader([]byte{
 			0x1f, 0x8b, 0x08, 0x00, 0x5c, 0xbc, 0xcd, 0x53, 0x00, 0x03, 0x4b, 0x4e, 0xac, 0xcc, 0x49, 0xad,
 			0x54, 0x48, 0x49, 0x2c, 0x49, 0xe4, 0x02, 0x00, 0x03, 0xe1, 0xfc, 0xc3, 0x0c, 0x00, 0x00, 0x00,
-		},
+		}),
 		err:     nil,
 		expect:  []byte("cayley data\n"),
 		readErr: nil,
 	},
 	{
 		message: "bzip2 input",
-		input: []byte{
+		input: bytes.NewReader([]byte{
 			0x42, 0x5a, 0x68, 0x39, 0x31, 0x41, 0x59, 0x26, 0x53, 0x59, 0xb5, 0x4b, 0xe3, 0xc4, 0x00, 0x00,
 			0x02, 0xd1, 0x80, 0x00, 0x10, 0x40, 0x00, 0x2e, 0x04, 0x04, 0x20, 0x20, 0x00, 0x31, 0x06, 0x4c,
 			0x41, 0x4c, 0x1e, 0xa7, 0xa9, 0x2a, 0x18, 0x26, 0xb1, 0xc2, 0xee, 0x48, 0xa7, 0x0a, 0x12, 0x16,
 			0xa9, 0x7c, 0x78, 0x80,
-		},
+		}),
 		err:     nil,
 		expect:  []byte("cayley data\n"),
 		readErr: nil,
 	},
 	{
 		message: "bad gzip input",
-		input:   []byte{0x1f, 0x8b, 'c', 'a', 'y', 'l', 'e', 'y', ' ', 'd', 'a', 't', 'a', '\n'},
+		input:   strings.NewReader("\x1f\x8bcayley data\n"),
 		err:     gzip.ErrHeader,
 		expect:  nil,
 		readErr: nil,
 	},
 	{
 		message: "bad bzip2 input",
-		input:   []byte{0x42, 0x5a, 0x68, 'c', 'a', 'y', 'l', 'e', 'y', ' ', 'd', 'a', 't', 'a', '\n'},
+		input:   strings.NewReader("\x42\x5a\x68cayley data\n"),
 		err:     nil,
 		expect:  nil,
 		readErr: bzip2.StructuralError("invalid compression level"),
 	},
+	{
+		message: "gzip input without ReadAt",
+		input:   reader{strings.NewReader("\x1f\x8bcayley data\n")},
+		err:     nil,
+		expect:  []byte("\x1f\x8bcayley data\n"),
+		readErr: nil,
+	},
 }
 
 func TestDecompressor(t *testing.T) {
 	for _, test := range testDecompressor {
-		buf := bytes.NewReader(test.input)
-		r, err := decompressor(buf)
+		r, err := decompressor(test.input)
 		if err != test.err {
 			t.Fatalf("Unexpected error for %s, got:%v expect:%v", test.message, err, test.err)
 		}