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https://github.com/bjornbytes/trickle
Lua bitstream
https://github.com/bjornbytes/trickle
Last synced: 3 days ago
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Lua bitstream
- Host: GitHub
- URL: https://github.com/bjornbytes/trickle
- Owner: bjornbytes
- License: mit
- Archived: true
- Created: 2015-12-02T05:02:41.000Z (almost 9 years ago)
- Default Branch: master
- Last Pushed: 2020-01-15T22:30:59.000Z (almost 5 years ago)
- Last Synced: 2024-08-02T06:19:48.297Z (3 months ago)
- Language: Lua
- Size: 8.79 KB
- Stars: 31
- Watchers: 6
- Forks: 5
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- awesome-love2d - trickle - A bitstream library focused on high compression for use in networking. (Serialization)
README
Trickle
===
> **NOTE** - It's probably better to use Lua's built-in `string.pack` and `string.unpack` now.
Trickle is a bitstream for Lua. When writing data to a trickle stream, you must specify its size in
bits. The stream will automatically pack this data into compressed bytes, which often leads to
greatly reduced network bandwidth. This is useful in networking applications where it is necessary
to reduce network traffic, such as realtime multiplayer games.
Usage
---
```lua
local trickle = require 'trickle'
local stream = trickle.create()
stream:write(7, '3bits')
stream:write(true, 'bool')
stream:write(1.8, 'float')
-- send over the network
-- to convert a stream to a string, call tostring(stream)
-- to convert a string to a stream, call trickle.create(string)
stream:read('3bits') -- 7
stream:read('bool') -- true
stream:read('float') -- 1.8
```
Signatures
---
A signature describes a high level template for a message. It can be used to reduce duplication in
reading and writing of messages, and allows reading and writing of tables of data without having to
write each individual field in a specific order. First, define a signature:
```lua
local signature = {
{ 'playerId', '4bits' },
{ 'x', '8bits' },
{ 'y', '8bits' },
{ 'direction', '9bits' } -- direction in degrees
}
```
Then, pack a message into a trickle stream using the signature:
```lua
local playerData = {
playerId = 1,
x = 63,
y = 41,
direction = 270
}
stream:pack(playerData, signature)
```
`unpack` may be used to decode the stream:
```lua
local playerData = stream:unpack(signature)
```
### Delta Groups
Let's say we only want to send the position of the player if it has changed. Right now this isn't
possible with our signature, because we *have* to send 8 bits for the x position and 8 bits for the y
position to keep the structure of the signature uniform for the receiving end. **Delta groups**
provide a mechanism to specify these optional groups of data.
To declare a delta group, specify a `delta` key in the signature table:
```lua
local signature = {
{ 'playerId', '4bits'},
{ 'x', '8bits' },
{ 'y', '8bits' },
{ 'direction', '9bits' },
delta = {
{ 'x', 'y' },
'direction'
}
}
```
What we've done is defined two optional pieces of our message: a group for the position of the
player and a group for the direction of the player. Now, if we pack a message like this:
```lua
local playerData = {
playerId = 1,
x = nil,
y = nil,
direction = nil
}
stream:pack(playerData, signature)
```
trickle will only pack the 4 bit player id into the message, which saves 25 bits! Internally,
a single bit is added to the beginning of the message for each delta group, signifying whether or
not its data is present. This means that if a delta group contains more than one key (such as the
'x' and 'y' group above), either all of the data must be present or all of it must be `nil`. This,
for example, would result in an error:
```lua
local playerData = {
playerId = 1,
x = 17,
y = nil,
direction = 90
}
stream:pack(playerData, signature) -- Error: Only part of message delta group "x, y" was provided.
```
Documentation
---
- `trickle.create([str])` - Creates a stream. If `str` is provided then the contents of the stream
are set to this initial value.
- `tostring(stream)` - Serialize the stream's data to a string.
- `stream:clear()` - Resets the stream to contain no data.
- `stream:truncate()` - If a byte has been partially written, it will not be present in the stream
yet. `truncate` pads the rest of the byte with null data and adds it to the stream's data. This
is mostly for internal use, and is automatically called when converting the stream to a string.
#### Writing
- `stream:write(value, type)` - Writes a value to the stream. `type` can either be `string`,
`float`, `bool`, or `bits` for integers, where `n` is the number of bits the integer should use.
- `stream:writeString(str)` - Writes a string to the stream. Uses one byte per character.
- `stream:writeBool(bool)` - Writes a boolean to the stream. Uses one bit.
- `stream:writeFloat(float)` - Writes a float to the stream. Note that the float is currently
serialized as a string. This is suboptimal and should be improved in the future.
- `stream:writeBits(value, n)` - Writes a number to the stream, using `n` bits.
#### Reading
- `stream:read(type)` - Reads and returns a value from the stream.
- `stream:readString()` - Reads and returns a string.
- `stream:readBool()` - Reads and returns a boolean.
- `stream:readFloat()` - Reads and returns a float.
- `stream:readBits(n)` - Readss `n` bits from the string and returns them as a number.
#### Signatures
- `stream:pack(data, signature)` - Packs `data` into the stream according to the structure specified
by `signature`.
- `stream:unpack(signature)` - Uses `signature` to read data from the string, returning a table with
the data.
License
---
MIT, see [`LICENSE`](LICENSE) for details.