src/mime: Use os-generated mimetypes on unix systems

Related to bug on Solus bugtracker: https://dev.getsol.us/T9394

Mimetypes was incorrectly being looked up from custom mime.types files that were not generated by the systems.
This changes the mimetype loading and parsing on unix systems (except for darwin, see note below) to use the os-generated mimetypes instead.
It makes mimetype lookup work on systems that do not have those custom files and allows us to drop
the workarounds for FreeBSD, DragonflyBSD and OpenBSD. Mimetype lookup will now also work on Solus, a Linux distrubution.

The old lookup is used only for darwin, where the globs file is not present in later releases.

Author: Jacalz

src/mime/testdata/test.types

@@ -3,6 +3,6 @@
 # license that can be found in the LICENSE file.
 
 
- # mime package test
-application/test	t1	# Simple test
-text/test		t2	# Text test
+# mime package test
+application/test:*.t1
+text/test:*.t2

src/mime/testdata/test.types.darwin

@@ -0,0 +1,8 @@
+# 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.
+
+
+ # mime package test
+application/test	t1	# Simple test
+text/test		t2	# Text test

src/mime/type_darwin.go

@@ -0,0 +1,63 @@
+// Copyright 2021 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.
+
+//go:build darwin
+// +build darwin
+
+package mime
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+func init() {
+	osInitMime = initMimeDarwin
+}
+
+var typeFiles = []string{
+	"/etc/apache2/mime.types",
+}
+
+func loadMimeFile(filename string) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		fields := strings.Fields(scanner.Text())
+		if len(fields) <= 1 || fields[0][0] == '#' {
+			continue
+		}
+		mimeType := fields[0]
+		for _, ext := range fields[1:] {
+			if ext[0] == '#' {
+				break
+			}
+			setExtensionType("."+ext, mimeType)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+}
+
+func initMimeDarwin() {
+	for _, filename := range typeFiles {
+		loadMimeFile(filename)
+	}
+}
+
+func initMimeForTests() map[string]string {
+	typeFiles = []string{"testdata/test.types.darwin"}
+	return map[string]string{
+		".T1":  "application/test",
+		".t2":  "text/test; charset=utf-8",
+		".png": "image/png",
+	}
+}

src/mime/type_dragonfly.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build aix || darwin || dragonfly || freebsd || (js && wasm) || linux || netbsd || openbsd || solaris
-// +build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris
+//go:build aix || dragonfly || freebsd || (js && wasm) || linux || netbsd || openbsd || solaris
+// +build aix dragonfly freebsd js,wasm linux netbsd openbsd solaris
 
 package mime
 
@@ -18,10 +18,8 @@ func init() {
 }
 
 var typeFiles = []string{
-	"/etc/mime.types",
-	"/etc/apache2/mime.types",
-	"/etc/apache/mime.types",
-	"/etc/httpd/conf/mime.types",
+	"/usr/local/share/mime/globs",
+	"/usr/share/mime/globs", // Fallback for unix systems that don't use /usr/local.
 }
 
 func loadMimeFile(filename string) {
@@ -32,18 +30,19 @@ func loadMimeFile(filename string) {
 	defer f.Close()
 
 	scanner := bufio.NewScanner(f)
+	scanner.Split(bufio.ScanLines)
 	for scanner.Scan() {
-		fields := strings.Fields(scanner.Text())
-		if len(fields) <= 1 || fields[0][0] == '#' {
+		if scanner.Text() == "" || scanner.Text()[0] == '#' {
 			continue
 		}
-		mimeType := fields[0]
-		for _, ext := range fields[1:] {
-			if ext[0] == '#' {
-				break
-			}
-			setExtensionType("."+ext, mimeType)
+
+		// Each line should be of format: mimetype:*.ext
+		fields := strings.Split(scanner.Text(), ":")
+		if fields[1][0] != '*' {
+			continue // We only support getting mimetypes for extensions, not for filenames.
 		}
+
+		setExtensionType(fields[1][1:], fields[0])
 	}
 	if err := scanner.Err(); err != nil {
 		panic(err)