feat(#155): manual MIME checking for empty and single byte files

src/routes/viewer.ts

@@ -43,7 +43,7 @@ router.get(/.*/, async (req: Request, res: Response) => {
                 body = renderDirectory(path);
             } else {
                 const data = readFileSync(path);
-                const mime = pmime(path);
+                const mime = await pmime(path);
                 if (!shouldRender(mime)) {
                     res.setHeader('Content-Type', mime).send(data);
                     return;
@@ -99,7 +99,7 @@ router.post(/.*/, async (req: Request, res: Response) => {
     let { content } = req.body;
 
     if (reload) {
-        const mime = pmime(path);
+        const mime = await pmime(path);
         if (!shouldRender(mime)) {
             res.status(400).send('Reload is only permitted on rendered files');
             return;

src/utils/path.ts

@@ -1,9 +1,34 @@
-import { execSync } from 'child_process';
+import { exec } from 'child_process';
 import { homedir } from 'os';
 import { basename as pbasename, dirname as pdirname, parse as pparse } from 'path';
 import config from '../config.js';
+import { stat, readFile } from 'fs/promises';
+import { promisify } from 'util';
 
-export const pmime = (path: string) => execSync(`file --mime-type -b '${path}'`).toString().trim();
+const execPromise = promisify(exec);
+export const pmime = async (path: string) => {
+    const [{ stdout: mime }, stats] = await Promise.all([
+        execPromise(`file --mime-type -b '${path}'`),
+        stat(path),
+    ]);
+    // empty files can also be `application/x-empty`
+    // -> we unify to `inode/x-empty`
+    if (stats.size == 0) return 'inode/x-empty';
+    // single byte files don't work well for mime recognition as they will
+    // always be guessed as application/octet-stream
+    // -> we return `text/plain` if the single byte is a printable character
+    if (stats.size == 1) {
+        const content = await readFile(path);
+        const char = content.at(0);
+        if (
+            char !== undefined &&
+            // tab            line feed        carriage return   printable character range
+            (char === 0x09 || char === 0x0a || char === 0x0d || (char >= 0x20 && char <= 0x7e))
+        )
+            return 'text/plain';
+    }
+    return mime.trim();
+};
 
 export const pcomponents = (path: string) => {
     const parsed = pparse(path);