1 files changed, 64 insertions, 20 deletions
diff --git a/libgo/go/mime/type.go b/libgo/go/mime/type.go
index 00cff263ba..ffda1f0ce5 100644
--- a/libgo/go/mime/type.go
+++ b/libgo/go/mime/type.go
@@ -11,26 +11,41 @@ import (
 	"sync"
 )
 
-var mimeTypes = map[string]string{
-	".css":  "text/css; charset=utf-8",
-	".gif":  "image/gif",
-	".htm":  "text/html; charset=utf-8",
-	".html": "text/html; charset=utf-8",
-	".jpg":  "image/jpeg",
-	".js":   "application/x-javascript",
-	".pdf":  "application/pdf",
-	".png":  "image/png",
-	".xml":  "text/xml; charset=utf-8",
-}
+var (
+	mimeLock       sync.RWMutex
+	mimeTypesLower = map[string]string{
+		".css":  "text/css; charset=utf-8",
+		".gif":  "image/gif",
+		".htm":  "text/html; charset=utf-8",
+		".html": "text/html; charset=utf-8",
+		".jpg":  "image/jpeg",
+		".js":   "application/x-javascript",
+		".pdf":  "application/pdf",
+		".png":  "image/png",
+		".xml":  "text/xml; charset=utf-8",
+	}
+	mimeTypes = clone(mimeTypesLower)
+)
 
-var mimeLock sync.RWMutex
+func clone(m map[string]string) map[string]string {
+	m2 := make(map[string]string, len(m))
+	for k, v := range m {
+		m2[k] = v
+		if strings.ToLower(k) != k {
+			panic("keys in mimeTypesLower must be lowercase")
+		}
+	}
+	return m2
+}
 
-var once sync.Once
+var once sync.Once // guards initMime
 
 // TypeByExtension returns the MIME type associated with the file extension ext.
 // The extension ext should begin with a leading dot, as in ".html".
 // When ext has no associated type, TypeByExtension returns "".
 //
+// Extensions are looked up first case-sensitively, then case-insensitively.
+//
 // The built-in table is small but on unix it is augmented by the local
 // system's mime.types file(s) if available under one or more of these
 // names:
@@ -39,23 +54,49 @@ var once sync.Once
 //   /etc/apache2/mime.types
 //   /etc/apache/mime.types
 //
-// Windows system mime types are extracted from registry.
+// On Windows, MIME types are extracted from the registry.
 //
 // Text types have the charset parameter set to "utf-8" by default.
 func TypeByExtension(ext string) string {
 	once.Do(initMime)
 	mimeLock.RLock()
-	typename := mimeTypes[ext]
-	mimeLock.RUnlock()
-	return typename
+	defer mimeLock.RUnlock()
+
+	// Case-sensitive lookup.
+	v := mimeTypes[ext]
+	if v != "" {
+		return v
+	}
+
+	// Case-insensitive lookup.
+	// Optimistically assume a short ASCII extension and be
+	// allocation-free in that case.
+	var buf [10]byte
+	lower := buf[:0]
+	const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
+	for i := 0; i < len(ext); i++ {
+		c := ext[i]
+		if c >= utf8RuneSelf {
+			// Slow path.
+			return mimeTypesLower[strings.ToLower(ext)]
+		}
+		if 'A' <= c && c <= 'Z' {
+			lower = append(lower, c+('a'-'A'))
+		} else {
+			lower = append(lower, c)
+		}
+	}
+	// The conversion from []byte to string doesn't allocate in
+	// a map lookup.
+	return mimeTypesLower[string(lower)]
 }
 
 // AddExtensionType sets the MIME type associated with
-// the extension ext to typ.  The extension should begin with
+// the extension ext to typ. The extension should begin with
 // a leading dot, as in ".html".
 func AddExtensionType(ext, typ string) error {
-	if ext == "" || ext[0] != '.' {
-		return fmt.Errorf(`mime: extension "%s" misses dot`, ext)
+	if !strings.HasPrefix(ext, ".") {
+		return fmt.Errorf(`mime: extension %q misses dot`, ext)
 	}
 	once.Do(initMime)
 	return setExtensionType(ext, typ)
@@ -70,8 +111,11 @@ func setExtensionType(extension, mimeType string) error {
 		param["charset"] = "utf-8"
 		mimeType = FormatMediaType(mimeType, param)
 	}
+	extLower := strings.ToLower(extension)
+
 	mimeLock.Lock()
 	mimeTypes[extension] = mimeType
+	mimeTypesLower[extLower] = mimeType
 	mimeLock.Unlock()
 	return nil
 }