Allow potential compilation into wasm

The modified file was the only thing in boxo erroring when attempting to build a wasm target

Author: hsanjuan

CHANGELOG.md

@@ -24,8 +24,10 @@ The following emojis are used to highlight certain changes:
 
 ### Fixed
 
+- Improvements to support WASM builds
 - `gateway`: Fixed suffix range-requests and updated tests to [gateway-conformance v0.8](https://github.com/ipfs/gateway-conformance/releases/tag/v0.8.0) [#922](https://github.com/ipfs/boxo/pull/922)
 
+
 ### Security
 
 

files/filewriter_js.go

@@ -0,0 +1,18 @@
+//go:build js
+
+package files
+
+import (
+	"os"
+	"strings"
+)
+
+var invalidChars = `/` + "\x00"
+
+func isValidFilename(filename string) bool {
+	return !strings.ContainsAny(filename, invalidChars)
+}
+
+func createNewFile(path string) (*os.File, error) {
+	return os.OpenFile(path, os.O_EXCL|os.O_CREATE|os.O_WRONLY, 0o666)
+}

files/filewriter_unix.go

@@ -1,4 +1,4 @@
-//go:build darwin || linux || netbsd || openbsd || freebsd || dragonfly || js || wasip1
+//go:build darwin || linux || netbsd || openbsd || freebsd || dragonfly
 
 package files