Chunked Uploads

Paaster uses chunked uploads at two levels: encryption chunks (client-side) and storage chunks (server-side).

Client-side encryption chunking

Text content is split into chunks of CHUNK_SIZE (1 MB) before encryption:

[raw text]  →  split into 1 MB chunks  →  encrypt each with secretstream  →  upload individually

Each chunk is encrypted with crypto_secretstream_xchacha20poly1305_push using either TAG_MESSAGE (intermediate) or TAG_FINAL (last chunk).

Upload protocol

1. Create paste — POST /api/paste with metadata (header, salt, etc.)
2. Upload chunks — POST /api/paste/{pasteId}/chunks for each chunk

Each chunk request sends:

Field	Description
chunkIndex	0-based index of the chunk
totalChunks	Total number of chunks
data	The raw encrypted chunk binary

When the last chunk (index totalChunks - 1) is uploaded, the server persists totalChunks on the paste document so the viewer knows how many chunks to fetch.

Download protocol

The viewer fetches each chunk individually:

GET /api/paste/{pasteId}/chunks/{chunkIndex}

Each response contains the raw encrypted chunk data, which is fed directly into crypto_secretstream_xchacha20poly1305_pull for decryption.

Maximum upload size

The maximum total upload size is configurable via the MAX_UPLOAD_SIZE environment variable (value in MB, default 10). The server enforces this limit per-chunk and the client checks against the value returned by the server.