> ## Documentation Index
> Fetch the complete documentation index at: https://docsuncv2.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# crypt.lz4decompress

Decompresses `compressed` and returns exactly `expectedSize` bytes.

```luau theme={null}
crypt.lz4decompress(compressed: string, expectedSize: number): string
```

Input must be LZ4 Block format - see the page entry `crypt.lz4compress` to learn more.<br />  `expectedSize` is the length of the original plaintext in bytes, *not* the length of the compressed input - you have to track and pass it yourself.

There is no integrity check - if the bytes are damaged or `expectedSize` is wrong, <br />the function still returns a string of that length without raising an error.

## Parameters

| Parameter      | Type     | Description                                                          |
| -------------- | -------- | -------------------------------------------------------------------- |
| `compressed`   | `string` | An LZ4 Block-format payload.                                         |
| `expectedSize` | `number` | The desired output length in bytes (size of the original plaintext). |

## Returns

`string` - the decompressed bytes, padded or truncated to exactly `expectedSize` characters. <br />When `expectedSize` matches the original length, the result is the full plaintext.

## Aliases

* `lz4decompress`

## Example

In a chat-event-based Roblox game, stream Bad Apple as ASCII video over a remote at 30fps. <br /> Reason: storing >1800 frames and parsing them would be a lot more easier if you compress the data beforehand.

<CodeGroup>
  ```luau Example 1 theme={null}
  <<<<<<< HEAD
  local lz4decompress = crypt.lz4decompress("test", 10)
  =======
  -- crypt.lz4decompress(compressed: string, expectedSize: number): string
  >>>>>>> 50e30f53759b0538759af25c9b271514aa2c9290
  ```

  ```luau Example 2 theme={null}
  -- Example script; will not do anything

  local content = readfile("bad_apple/chunk_0001.txt")
  local headerEnd = content:find("\n", 1, true)
  local header = content:sub(1, headerEnd - 1)
  local bin = content:sub(headerEnd + 1)
  local offset = 1

  for _, pair in ipairs(header:split(",")) do
      local compLen, origLen = pair:match("^(%d+):(%d+)$")
      compLen, origLen = tonumber(compLen), tonumber(origLen)

      local compressed = bin:sub(offset, offset + compLen - 1)
      local frame = crypt.lz4decompress(compressed, origLen)
      offset += compLen

      someRemoteEvent:FireServer(`{frame}\0`)
      task.wait(1 / 30)
  end
  ```
</CodeGroup>

<Tip>
  There is no built-in integrity check.
  If the compressed string is malformed, or `expectedSize` is wrong, you get back a string that looks valid, but actually isn't. For any data, store a hash alongside the payload (`crypt.hash` works) and verify after decompressing.
</Tip>