Box API: files over 50MB need chunked upload sessions

TL;DR

When you upload to Box, branch on file size: over 50MB, create an upload session and stream parts with Content-Range headers, then commit. Send a per-part digest with each chunk so a corrupt part is caught early.

Steps

1. When you upload to Box, branch on file size: over 50MB, create an upload session and stream parts with Content-Range headers, then commit. Send a per-part digest with each chunk so a corrupt part is caught early. For the single-shot path, put the attributes part before the file part in the multipart body.

When to use

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When not to use

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Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Source: Box SDK docs (box-python-sdk docs/uploads.md): the plain upload endpoints are for small files; for file sizes over 50MB the docs recommend the chunked upload APIs, which create an upload session, PUT each part with a Content-Range, then commit. On the single-shot path, the attributes part of the multipart body must come before the file part, or the API returns a 400 metadataafterfile_contents error.

Verified resolution: When you upload to Box, branch on file size: over 50MB, create an upload session and stream parts with Content-Range headers, then commit. Send a per-part digest with each chunk so a corrupt part is caught early. For the single-shot path, put the attributes part before the file part in the multipart body.

Source URL: https://github.com/box/box-python-sdk/blob/HEAD/docs/uploads.md