1 files changed, 86 insertions, 0 deletions
diff --git a/src/pkg/image/format.go b/src/pkg/image/format.go
new file mode 100644
index 000000000..1d541b094
--- /dev/null
+++ b/src/pkg/image/format.go
@@ -0,0 +1,86 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package image
+
+import (
+	"bufio"
+	"io"
+	"os"
+)
+
+// An UnknownFormatErr indicates that decoding encountered an unknown format.
+var UnknownFormatErr = os.NewError("image: unknown format")
+
+// A format holds an image format's name, magic header and how to decode it.
+type format struct {
+	name, magic  string
+	decode       func(io.Reader) (Image, os.Error)
+	decodeConfig func(io.Reader) (Config, os.Error)
+}
+
+// Formats is the list of registered formats.
+var formats []format
+
+// RegisterFormat registers an image format for use by Decode.
+// Name is the name of the format, like "jpeg" or "png".
+// Magic is the magic prefix that identifies the format's encoding.
+// Decode is the function that decodes the encoded image.
+// DecodeConfig is the function that decodes just its configuration.
+func RegisterFormat(name, magic string, decode func(io.Reader) (Image, os.Error), decodeConfig func(io.Reader) (Config, os.Error)) {
+	formats = append(formats, format{name, magic, decode, decodeConfig})
+}
+
+// A reader is an io.Reader that can also peek ahead.
+type reader interface {
+	io.Reader
+	Peek(int) ([]byte, os.Error)
+}
+
+// AsReader converts an io.Reader to a reader.
+func asReader(r io.Reader) reader {
+	if rr, ok := r.(reader); ok {
+		return rr
+	}
+	return bufio.NewReader(r)
+}
+
+// sniff determines the format of r's data.
+func sniff(r reader) format {
+	for _, f := range formats {
+		s, err := r.Peek(len(f.magic))
+		if err == nil && string(s) == f.magic {
+			return f
+		}
+	}
+	return format{}
+}
+
+// Decode decodes an image that has been encoded in a registered format.
+// The string returned is the format name used during format registration.
+// Format registration is typically done by the init method of the codec-
+// specific package.
+func Decode(r io.Reader) (Image, string, os.Error) {
+	rr := asReader(r)
+	f := sniff(rr)
+	if f.decode == nil {
+		return nil, "", UnknownFormatErr
+	}
+	m, err := f.decode(rr)
+	return m, f.name, err
+}
+
+// DecodeConfig decodes the color model and dimensions of an image that has
+// been encoded in a registered format. The string returned is the format name
+// used during format registration. Format registration is typically done by
+// the init method of the codec-specific package.
+func DecodeConfig(r io.Reader) (Config, string, os.Error) {
+	rr := asReader(r)
+	f := sniff(rr)
+	if f.decodeConfig == nil {
+		return Config{}, "", UnknownFormatErr
+	}
+	c, err := f.decodeConfig(rr)
+	return c, f.name, err
+}