mahonia 默认没有支持GB2312编码, 但是支持GBK, 由于GBK编码完全兼容GB2312, 自己在GBK的代码里面注册一个GB2312就可以完美支持了. https://code.google.com/p/mahonia

mahonia-gbk.diff

 ~GOPATH/src/code.google.com/p/mahonia hg diff 
diff -r 420ce60cb671 gbk.go
--- a/gbk.go	Fri Jul 19 13:15:30 2013 -0700
+++ b/gbk.go	Mon Dec 09 22:27:42 2013 +0800
@@ -12,6 +12,15 @@
 			return encodeGBKRune
 		},
 	})
+	RegisterCharset(&Charset{
+		Name: "GB2312",
+		NewDecoder: func() Decoder {
+			return decodeGBKRune
+		},
+		NewEncoder: func() Encoder {
+			return encodeGBKRune
+		},
+	})
 }
 
 func decodeGBKRune(p []byte) (r rune, size int, status Status) {