1 files changed, 62 insertions, 0 deletions
diff --git a/src/cmd/godoc/utils.go b/src/cmd/godoc/utils.go
index 55cf87841..a032bd331 100644
--- a/src/cmd/godoc/utils.go
+++ b/src/cmd/godoc/utils.go
@@ -15,11 +15,13 @@ import (
 	"strings"
 	"sync"
 	"time"
+	"utf8"
 )
 
 
 // An RWValue wraps a value and permits mutually exclusive
 // access to it and records the time the value was last set.
+//
 type RWValue struct {
 	mutex     sync.RWMutex
 	value     interface{}
@@ -107,3 +109,63 @@ func writeFileAtomically(filename string, data []byte) os.Error {
 	}
 	return os.Rename(f.Name(), filename)
 }
+
+
+// isText returns true if a significant prefix of s looks like correct UTF-8;
+// that is, if it is likely that s is human-readable text.
+//
+func isText(s []byte) bool {
+	const max = 1024 // at least utf8.UTFMax
+	if len(s) > max {
+		s = s[0:max]
+	}
+	for i, c := range string(s) {
+		if i+utf8.UTFMax > len(s) {
+			// last char may be incomplete - ignore
+			break
+		}
+		if c == 0xFFFD || c < ' ' && c != '\n' && c != '\t' {
+			// decoding error or control character - not a text file
+			return false
+		}
+	}
+	return true
+}
+
+
+// TODO(gri): Should have a mapping from extension to handler, eventually.
+
+// textExt[x] is true if the extension x indicates a text file, and false otherwise.
+var textExt = map[string]bool{
+	".css": false, // must be served raw
+	".js":  false, // must be served raw
+}
+
+
+// isTextFile returns true if the file has a known extension indicating
+// a text file, or if a significant chunk of the specified file looks like
+// correct UTF-8; that is, if it is likely that the file contains human-
+// readable text.
+//
+func isTextFile(filename string) bool {
+	// if the extension is known, use it for decision making
+	if isText, found := textExt[pathutil.Ext(filename)]; found {
+		return isText
+	}
+
+	// the extension is not known; read an initial chunk
+	// of the file and check if it looks like text
+	f, err := os.Open(filename, os.O_RDONLY, 0)
+	if err != nil {
+		return false
+	}
+	defer f.Close()
+
+	var buf [1024]byte
+	n, err := f.Read(buf[0:])
+	if err != nil {
+		return false
+	}
+
+	return isText(buf[0:n])
+}