make kestrel a tak server, so that it can send and receive pois as cots data

server/api/me/avatar.put.js

@@ -8,6 +8,24 @@ const MAX_SIZE = 2 * 1024 * 1024
 const ALLOWED_TYPES = Object.freeze(['image/jpeg', 'image/png'])
 const EXT_BY_MIME = Object.freeze({ 'image/jpeg': 'jpg', 'image/png': 'png' })
 
+/**
+ * Validate image content using magic bytes to prevent MIME type spoofing.
+ * @param {Buffer} buffer - File data buffer
+ * @returns {string|null} Detected MIME type or null if invalid
+ */
+function validateImageContent(buffer) {
+  if (!buffer || buffer.length < 8) return null
+  // JPEG: FF D8 FF
+  if (buffer[0] === 0xFF && buffer[1] === 0xD8 && buffer[2] === 0xFF) {
+    return 'image/jpeg'
+  }
+  // PNG: 89 50 4E 47 0D 0A 1A 0A
+  if (buffer[0] === 0x89 && buffer[1] === 0x50 && buffer[2] === 0x4E && buffer[3] === 0x47) {
+    return 'image/png'
+  }
+  return null
+}
+
 export default defineEventHandler(async (event) => {
   const user = requireAuth(event)
   const form = await readMultipartFormData(event)
@@ -16,7 +34,14 @@ export default defineEventHandler(async (event) => {
   if (file.data.length > MAX_SIZE) throw createError({ statusCode: 400, message: 'File too large' })
   const mime = file.type ?? ''
   if (!ALLOWED_TYPES.includes(mime)) throw createError({ statusCode: 400, message: 'Invalid type; use JPEG or PNG' })
-  const ext = EXT_BY_MIME[mime] ?? 'jpg'
+  
+  // Validate file content matches declared MIME type
+  const actualMime = validateImageContent(file.data)
+  if (!actualMime || actualMime !== mime) {
+    throw createError({ statusCode: 400, message: 'File content does not match declared type' })
+  }
+  
+  const ext = EXT_BY_MIME[actualMime] ?? 'jpg'
   const filename = `${user.id}.${ext}`
   const dir = getAvatarsDir()
   const path = join(dir, filename)