Open-Generative-AI/app/api/upload-binary/route.js

import { NextResponse } from 'next/server';

export async function POST(request) {
    try {
        const formData = await request.formData();
        
        // Extract the original S3 target URL we injected earlier
        const targetUrl = formData.get('x-proxy-target-url');
        
        if (!targetUrl) {
            return NextResponse.json({ error: 'Missing proxy target URL' }, { status: 400 });
        }

        // Reconstruct the FormData for S3 (excluding our internal proxy marker)
        const s3FormData = new FormData();
        
        // S3 is very sensitive to field ordering. We must ensure 'file' is likely last
        // or at least that all signature fields come before what S3 expects.
        // The original library code appends 'file' last, so iterating should preserve that.
        for (const [key, value] of formData.entries()) {
            if (key !== 'x-proxy-target-url') {
                s3FormData.append(key, value);
            }
        }

        // Perform the server-to-server POST to S3
        // This bypasses browser CORS/Preflight security entirely
        const s3Response = await fetch(targetUrl, {
            method: 'POST',
            body: s3FormData,
        });

        if (s3Response.ok || s3Response.status === 204) {
            return new Response(null, { status: 204 });
        } else {
            const errorText = await s3Response.text();
            console.error('S3 Proxy Error:', errorText);
            return new Response(errorText, { status: s3Response.status });
        }
    } catch (error) {
        console.error('Upload Proxy Exception:', error);
        return NextResponse.json({ error: error.message }, { status: 500 });
    }
}