fix #1030: work around a bug in go's mime types

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+* Fix incorrect MIME types on Windows ([#1030](https://github.com/evanw/esbuild/issues/1030))
+
+    The web server built into esbuild uses the file extension to determine the value of the `Content-Type` header. This was previously done using the `mime.TypeByExtension()` function from Go's standard library. However, this function is apparently broken on Windows because installed programs can change MIME types in the Windows registry: [golang/go#32350](https://github.com/golang/go/issues/32350). This release fixes the problem by using a copy of Go's `mime.TypeByExtension()` function without the part that reads from the Windows registry.
+
 * Using a top-level return inside an ECMAScript module is now forbidden
 
     The CommonJS module format is implemented as an anonymous function wrapper, so technically you can use a top-level `return` statement and it will actually work. Some packages in the wild use this to exit early from module initialization, so esbuild supports this. However, the ECMAScript module format doesn't allow top-level returns. With this release, esbuild no longer allows top-level returns in ECMAScript modules.

pkg/api/serve_other.go

@@ -4,7 +4,6 @@ package api
 
 import (
 	"fmt"
-	"mime"
 	"net"
 	"net/http"
 	"path"
@@ -111,6 +110,34 @@ func errorsToString(errors []Message) string {
 	return sb.String()
 }
 
+var builtinTypesLower = map[string]string{
+	".css":  "text/css; charset=utf-8",
+	".gif":  "image/gif",
+	".htm":  "text/html; charset=utf-8",
+	".html": "text/html; charset=utf-8",
+	".jpeg": "image/jpeg",
+	".jpg":  "image/jpeg",
+	".js":   "text/javascript; charset=utf-8",
+	".json": "application/json",
+	".mjs":  "text/javascript; charset=utf-8",
+	".pdf":  "application/pdf",
+	".png":  "image/png",
+	".svg":  "image/svg+xml",
+	".wasm": "application/wasm",
+	".webp": "image/webp",
+	".xml":  "text/xml; charset=utf-8",
+}
+
+// This is used instead of Go's built-in "mime.TypeByExtension" function because
+// this function is broken on Windows: https://github.com/golang/go/issues/32350.
+func mimeTypeByExtension(ext string) string {
+	contentType := builtinTypesLower[ext]
+	if contentType == "" {
+		contentType = builtinTypesLower[strings.ToLower(ext)]
+	}
+	return contentType
+}
+
 func (h *apiHandler) ServeHTTP(res http.ResponseWriter, req *http.Request) {
 	start := time.Now()
 
@@ -233,7 +260,7 @@ func (h *apiHandler) ServeHTTP(res http.ResponseWriter, req *http.Request) {
 
 		// Serve a file
 		if kind == fs.FileEntry {
-			if contentType := mime.TypeByExtension(path.Ext(queryPath)); contentType != "" {
+			if contentType := mimeTypeByExtension(path.Ext(queryPath)); contentType != "" {
 				res.Header().Set("Content-Type", contentType)
 			}