Reading files inside zip files

LuaZip

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Introduction

LuaZip is a lightweight Lua extension library that can be used to read files stored inside zip files. It uses zziplib to do all the hard work.

The API exposed to Lua is very simple and very similiar to the usual file handling functions provided by the I/O Lua standard library. In fact, the API is so similar that parts of this manual are extracted from the Lua manual, copyrighted by Tecgraf, PUC-Rio.

Building

LuaZip can be built for Lua 5.1, Lua 5.2, or Lua 5.3. In all cases, the language library and headers files for the target version must be installed properly.

LuaZip offers a Makefile and a separate configuration file, config, which should be edited to suit your installation before runnig make. The file has some definitions like paths to the external libraries, compiler options and the like. One important definition is the version of Lua language, which is not obtained from the installed software.

LuaZip compilation depends on zziplib 0.13.49 and zlib 1.2.3.

Installation

The LuaZip compiled binary should be copied to a directory in your C path.

Reference

zip.open (filename)

This function opens a zip file and returns a new zip file handle. In case of error it returns nil and an error message. Unlike io.open, there is no mode parameter, as the only supported mode is "read".

zip.openfile (filename [, extensions]])

This function opens a file and returns a file handle. In case of error it returns nil and an error message. Unlike io.open, there is no mode parameter, as the only supported mode is "read".
This function implements a virtual file system based on optionally compressed files. Instead of simply looking for a file at a given path, this function goes recursively up through all path separators ("/") looking for zip files there. If it finds a zip file, this function use the remaining path to open the requested file.
The optional parameter extensions allows the use of file extensions other than .zip during the lookup. It can be a string corresponding to the extension or an indexed table with the lookup extensions sequence.

zfile:close ()

This function closes a zfile opened by zip.open

zfile:files ()

Returns an iterator function that returns a new table containing the following information each time it is called:

• filename: the full path of a file
• compressed_size: the compressed size of the file in bytes
• uncompressed_size: the uncompressed size of the file in bytes

zfile:open (filename)

This function opens a file that is stored inside the zip file opened by zip.open.
The filename may contain the full path of the file contained inside the zip. The directory separator must be '/'.
Unlike f:open, there is no mode parameter, as the only supported mode is "read".

file:read (format1, ...)

Reads a file according to the given formats, which specify what to read.
For each format, the function returns a string with the characters read, or nil if it cannot read data with the specified format. When called without formats, it uses a default format that reads the entire next line (see below).
The available formats are:

• "*a": reads the whole file, starting at the current position. On end of file, it returns the empty string.
• "*l": reads the next line (skipping the end of line), returns nil on end of file. This is the default format.
• number: reads a string with up to that number of characters, returning nil on end of file. If number is zero, it reads nothing and returns an empty string, or nil on end of file.

Unlike the standard I/O read, the format "*n" is not supported.

file:seek ([whence] [, offset])

Sets and gets the file position, measured from the beginning of the file, to the position given by offset plus a base specified by the string whence, as follows:

• set: base is position 0 (beginning of the file);
• cur: base is current position;
• end: base is end of file;

In case of success, function seek returns the final file position, measured in bytes from the beginning of the file. If this function fails, it returns nil, plus an error string. The default value for whence is "cur", and for offset is 0. Therefore, the call file:seek() returns the current file position, without changing it; the call file:seek("set") sets the position to the beginning of the file (and returns 0); and the call file:seek("end") sets the position to the end of the file, and returns its size.

file:close ()

This function closes a file opened by zfile:open.

file:lines ()

Returns an iterator function that returns a new line from the file each time it is called. Therefore, the construction

for line in file:lines() do ... end

will iterate over all lines of the file.