# BUD-10

## Chunked blobs

`draft` `optional`

Breaking large blobs into smaller chunks for distribution

### Chunking

The client MAY break large blobs into any number or size of chunks. although its recommended to use the size `1Mb` or `4Mb` for small and large chunks

Clients MUST NOT pad the remaining chunk, If clients need privacy they should use random chunk sizes and optionally encrypt the large blob

Clients MUST create a merkle tree using the chunk hashes as the leaf nodes

### Publishing

Clients should publish a `2001` kind event after chunking the file in order to store the list of chunks

The events `content` MUST be a new-line delimitated list of sha256 hashes

```txt
7e668b56a58c7891e0cf263ea3f093b75eebade23d663a45aa9920f347b3d671
9b9c44a91396f19fd8700986eb0586dff2dcccf96c75bc2caefef302bcd78da1
7a281548f1223664b855b10b08e59e84389ccabeb742517f6cd75eda2724a798
fadeccee86b123088bbc452df10e8fbc99d4c2f22a70ef7a35605ec8e439c345
5d62398419e6d136771541f3d2215e0ce31b1be45e99dbc64b43a4b734b447ca
```

The event MUST have an `x` tag with the sha256 hash of the ordered concatenated hashes of each chunk

Example using `xxd` and `sha256sum`:
```bash
#!/bin/bash
hashes=(
  "7e668b56a58c7891e0cf263ea3f093b75eebade23d663a45aa9920f347b3d671"
  "9b9c44a91396f19fd8700986eb0586dff2dcccf96c75bc2caefef302bcd78da1"
  "7a281548f1223664b855b10b08e59e84389ccabeb742517f6cd75eda2724a798"
  "fadeccee86b123088bbc452df10e8fbc99d4c2f22a70ef7a35605ec8e439c345"
  "5d62398419e6d136771541f3d2215e0ce31b1be45e99dbc64b43a4b734b447ca"
)

concatenated=""
for hex in "${hex_array[@]}"; do
  concatenated="${concatenated}${hex}"
done

echo "Chunks:"
printf '%s\n' "${hex_array[@]}"

echo -e "\nConcatenated:"
echo "$concatenated"

echo -e "\nRoot hash:"
echo "$concatenated" | xxd -r -p | sha256sum
```

### Metadata

The `2001` event MAY include additional metadata tags to help other clients know the filename, mime type or servers to download from

Metadata tags:
  - `name` Filename
  - `summary` A short summary of the file
  - `mime` Mime type of file
  - `size` Total size in bytes of the file
  - `server` (multiple) Recommended servers to download chunks from

### Examples

Example `2001` event
```json
{
  "id": "13dfd656bedaca1f5fbb5da3b585d9c13061aa6aee136a0dc7d534f4d2540941",
  "pubkey": "939e77d64e8eb5c240f60bf29f80a619d6057e70fcf5d25755da012fe1b9502e",
  "created_at": 1731405194,
  "kind": 2001,
  "content": "7e668b56a58c7891e0cf263ea3f093b75eebade23d663a45aa9920f347b3d671\n9b9c44a91396f19fd8700986eb0586dff2dcccf96c75bc2caefef302bcd78da1\n7a281548f1223664b855b10b08e59e84389ccabeb742517f6cd75eda2724a798\nfadeccee86b123088bbc452df10e8fbc99d4c2f22a70ef7a35605ec8e439c345\n5d62398419e6d136771541f3d2215e0ce31b1be45e99dbc64b43a4b734b447ca",
  "tags": [
    [ "x", "2d839865ac17d8bb10168490a88107637619f79dac21275fcec1705162581f39" ],
    [ "name", "example.mp4" ],
    [ "mime", "video/mp4" ],
    [ "size", "4823449" ],
    [ "server", "https://cdn.example.com" ],
    [ "server", "https://nostr.download" ]
  ],
  "sig": "949b52a12fcd788eb416069b231e106eeb36b4987052c29904b547cabf5a52ebb42acfbce1ae61139042064b6950e69e322c5edbe77603ac2241a4d0e953ddd4"
}
```