Added file upload support

frontends/mizan-base/src/index.ts

@@ -386,6 +386,18 @@ async function resolveHeaders(): Promise<Record<string, string>> {
     }
 }
 
+/** Browser-safe `File` check — `File` is undefined under Node/SSR. */
+function isFile(value: unknown): boolean {
+    return typeof File !== 'undefined' && value instanceof File
+}
+
+/** True when any arg is a file (or an array containing a file). */
+function hasFileArg(args: Record<string, any>): boolean {
+    return Object.values(args).some(
+        (v) => isFile(v) || (Array.isArray(v) && v.some(isFile)),
+    )
+}
+
 /**
  * Default Mizan transport — POST `${baseUrl}/call/` and GET
  * `${baseUrl}/ctx/${name}/`. Compatible with `mizan-fastapi`,
@@ -397,13 +409,38 @@ export function httpTransport(): MizanTransport {
     return {
         async call(functionName, args) {
             const headers = await resolveHeaders()
-            headers['Content-Type'] = 'application/json'
+
+            // File-typed args switch the call to multipart/form-data: `fn` and a
+            // JSON `args` part for the non-file fields, plus one part per file
+            // (an array field repeats its part). Otherwise JSON as usual. The
+            // server reconstructs the args dict by merging the file parts back in.
+            let body: BodyInit
+            if (hasFileArg(args)) {
+                const form = new FormData()
+                form.append('fn', functionName)
+                const jsonArgs: Record<string, any> = {}
+                for (const [key, value] of Object.entries(args)) {
+                    if (isFile(value)) {
+                        form.append(key, value)
+                    } else if (Array.isArray(value) && value.some(isFile)) {
+                        for (const item of value) form.append(key, item as Blob)
+                    } else {
+                        jsonArgs[key] = value
+                    }
+                }
+                form.append('args', JSON.stringify(jsonArgs))
+                body = form
+                // Content-Type is set by the browser (with the multipart boundary).
+            } else {
+                headers['Content-Type'] = 'application/json'
+                body = JSON.stringify({ fn: functionName, args })
+            }
 
             const res = await fetch(`${config.baseUrl}/call/`, {
                 method: 'POST',
                 headers,
                 credentials: 'same-origin',
-                body: JSON.stringify({ fn: functionName, args }),
+                body,
             })
             if (!res.ok) throw new MizanError(res.status, await res.text())
             return res.json()