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storage
Binary Files Corrupted During Upload or Processing
Files uploaded to or processed by your application come out corrupted. PDFs are unreadable, images show as broken, ZIP archives can't be extracted, and Excel files fail to open. The files appear to be the right size but their contents are garbled.
Binary file corruption typically happens when the application treats binary data as text (applying encoding transformations that destroy the data), when streams are not properly piped, or when files are read and written with mismatched encoding settings.
This issue is particularly insidious because it may only affect certain file types or file sizes, making it hard to reproduce consistently during testing.
Error Messages You Might See
Error: Invalid PDF structure
The file is corrupted and cannot be opened
Error: incorrect header check (zlib)
CairoError: invalid image surface
Corrupted ZIP: unexpected end of data
Common Causes
- UTF-8 encoding applied to binary data — Reading binary files with encoding: 'utf-8' instead of as a Buffer or bytes object
- Base64 double-encoding — File data is base64 encoded during upload and encoded again during storage, doubling the corruption
- Multipart parsing misconfigured — The file upload middleware converts binary data to strings instead of preserving raw buffers
- Stream not set to binary mode — HTTP response or file stream uses text mode instead of binary mode
- Chunked transfer truncation — Large files are cut off because the receiving end closes the connection before all chunks arrive
How to Fix It
- Always use binary mode for file operations — Use fs.readFile without encoding option (returns Buffer) or open files with 'rb'/'wb' in Python
- Verify multipart parsing configuration — Ensure multer, busboy, or your upload library preserves raw binary buffers
- Test with actual binary files — Upload a real PDF, image, and ZIP file and verify they open correctly after download. Compare checksums
- Use streams correctly — Pipe readable streams directly to writable streams without intermediate string conversion
- Check Content-Type headers — Ensure the response sets application/octet-stream or the correct MIME type, not text/plain
Real developers can help you.
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Full stack dev w/ 20+ years of experience
Victor Denisov
Developer
Costea Adrian
Embedded Engineer specilizing in perception systems. Latest project was a adas camera calibration system.
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I’m a product-focused engineer and tech leader who builds scalable systems and turns ideas into production-ready platforms.
Over the past years, I’ve worked across startups and fast-moving teams, leading backend architecture, improving system reliability, and shipping products used by thousands of users. My strength is not just writing code — but connecting product vision, technical execution, and business impact.
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Been around fixing other peoples code for 20 years.
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Milan Surelia is a Mobile App Developer with 5+ years of experience crafting scalable, cross-platform apps at 7Span and Meticha. At 7Span, he engineers feature-rich Flutter apps with smooth performance and modern UI. As the Co-Founder of Meticha, he builds open-source tools and developer-focused products that solve real-world problems.
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SWE with 15+ years of experience building and maintaining web apps and extensive BE infrastructure
Caio Rodrigues
I'm a full-stack developer focused on building practical and scalable web applications. My main experience is with **React, TypeScript, and modern frontend architectures**, where I prioritize clean code, component reusability, and maintainable project structures.
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You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.
Get HelpFrequently Asked Questions
Why are my uploaded files corrupted?
The most common cause is reading binary files as text (UTF-8). Ensure your upload handler preserves raw binary buffers. In Node.js, don't pass an encoding option to fs.readFile for binary files.
How do I verify file integrity after upload?
Compare MD5 or SHA256 checksums of the original file and the stored file. If they differ, the data was modified during transit or storage. Use crypto.createHash in Node.js or hashlib in Python.