image: allow "?" wildcards when registering image formats.

R=r, nigeltao_gnome
CC=golang-dev
https://golang.org/cl/4404041

diff --git a/src/pkg/image/format.go b/src/pkg/image/format.go
index 1d541b0940669d3efcb385ee96db5fe0e5e25e52..b4859325e1dbedb4d96d63a67d505c22d45885d7 100644 (file)
--- a/src/pkg/image/format.go
+++ b/src/pkg/image/format.go
@@ -25,7 +25,8 @@ 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.
+// Magic is the magic prefix that identifies the format's encoding. The magic
+// string can contain "?" wildcards that each match any one byte.
 // 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)) {
@@ -46,11 +47,24 @@ func asReader(r io.Reader) reader {
        return bufio.NewReader(r)
 }
 
-// sniff determines the format of r's data.
+// Match returns whether magic matches b. Magic may contain "?" wildcards.
+func match(magic string, b []byte) bool {
+       if len(magic) != len(b) {
+               return false
+       }
+       for i, c := range b {
+               if magic[i] != c && magic[i] != '?' {
+                       return false
+               }
+       }
+       return true
+}
+
+// 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 {
+               b, err := r.Peek(len(f.magic))
+               if err == nil && match(f.magic, b) {
                        return f
                }
        }