LibCompress is a compression and decompression library implemented entirely in WoW-friendly Lua. It supports the LZW and Huffman algorithms, and can automatically choose the most efficient algorithm for your data. One popular usage for this library is to send a compressed table to another player or add-on. Doing this requires additional encoding to remove the \000 characters from the data stream.

Take a look at the forum post for more info and a development discussion:




The library is marked load on demand, so depend on it in your own addon or force load it using:


Follow it with:

libc = LibStub:GetLibrary("LibCompress")


Load the library with:

libc = LibStub:GetLibrary("LibCompress")

Compress data (must be in string form):

compressed_data = libc:Compress(data)

This will try all compression algorithms and return the best compressed result. It is possible to specify a specific compression algorithm like this:

compressed_data = libc:CompressHuffman(data)


compressed_data = libc:CompressLZW(data) Data will either be compressed with the Huffman compression algorithm or not at all. Data returned with a prefix byte identifying that the data is decompressed.

To decompress the data, simply use this:

decompressed_data = libc:Decompress(compressed_data)

Compress and Decompress can return an error and this is signaled by the first returned argument being nil and the second the error message. So checking for that would be appropriate.


LibCompress also has the possibility to encode and decode data, preparing it for transmission over the addon channel or chat channel (or a custom encoding). Two forms of encoding is provided:

Prefix encoding

The first form is prefix-encoding. Basically, reserved characters are replaced with a prefix/escape character followed by the suffix character, i.e. reserved bytes are replaced by a double-byte combination. This is how it is done:

table, msg = libc:GetEncodeTable(reservedChars, escapeChars, mapChars)

reservedChars: The characters in this string will not appear in the encoded data. escapeChars: A string of characters used as escape-characters (don't supply more than needed). #escapeChars >= 1 mapChars: First characters in reservedChars maps to first characters in mapChars. (#mapChars <= #reservedChars)

If table is nil, then msg holds an error message. Otherwise the usage is simple:

encoded_message = table:Encode(message)

message = table:Decode(encoded_message)

Two predefined setups have been included:

GetAddonEncodeTable: Sets up encoding for the addon channel (\000 is encoded)

GetChatEncodeTable: Sets up encoding for the chat channel (many bytes encoded, see the function for details)

7-bit encoding

This encoding packs bits, not bytes. It puts 7 bits into every byte, enlarging the data by approx 14%. Values from 0 to 127 (both inclusive) are present in the encoded data and therefor has to be prefix-encoded as well. This encoding generates a bit of string trash and should be used with consideration.

Encode data like this:

encoded_data = libc:Encode7bit(data)

Decode data like this:

decoded_data = libc:Decode7bit(encoded_data)

Checksum/hash algorithms

LibCompress also provides 2 reasonable fast hash algorithms. They are converted from a C-implementation to lua and are quite fast. The hash value is either 16 bit or 32 bit.

Use like this (data1, data2, data... = string):

code = libc:fcs16init()
code = libc:fcs16update(code, data1)
code = libc:fcs16update(code, data2)
code = libc:fcs16update(code, data...)
code = libc:fcs16final(code)

data = string fcs16 provides a 16 bit checksum, fcs32 provides a 32 bit checksum.