fix: detect attachment mime from file contents (#23291)

packages/opencode/src/util/media.ts

@@ -0,0 +1,29 @@
+const startsWith = (bytes: Uint8Array, prefix: number[]) => prefix.every((value, index) => bytes[index] === value)
+
+export function isPdfAttachment(mime: string) {
+  return mime === "application/pdf"
+}
+
+export function isMedia(mime: string) {
+  return mime.startsWith("image/") || isPdfAttachment(mime)
+}
+
+export function isImageAttachment(mime: string) {
+  return mime.startsWith("image/") && mime !== "image/svg+xml" && mime !== "image/vnd.fastbidsheet"
+}
+
+export function sniffAttachmentMime(bytes: Uint8Array, fallback: string) {
+  if (startsWith(bytes, [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a])) return "image/png"
+  if (startsWith(bytes, [0xff, 0xd8, 0xff])) return "image/jpeg"
+  if (startsWith(bytes, [0x47, 0x49, 0x46, 0x38])) return "image/gif"
+  if (startsWith(bytes, [0x42, 0x4d])) return "image/bmp"
+  if (startsWith(bytes, [0x25, 0x50, 0x44, 0x46, 0x2d])) return "application/pdf"
+  if (
+    startsWith(bytes, [0x52, 0x49, 0x46, 0x46]) &&
+    startsWith(bytes.subarray(8), [0x57, 0x45, 0x42, 0x50])
+  ) {
+    return "image/webp"
+  }
+
+  return fallback
+}