Cygnus is Swift package for embedding Lua into your projects.

Overview

Note

There is no Lua code in branch master (it will be cloned from official mirror and injected at CI). Please specify release branch when you install.

The simplest example: Execute Lua code passed as a string literal

// import Cygnus

let lua = Lua()
do {
    try lua.eval("print(\"Hello, Lua!\")")
} catch let luaError as LuaError {
    print(luaError)
} catch {
    print("Unexpected error: \(error)")
}

Console output:

Hello, Lua!

Application example: Capture data from Lua standard output

// import Cygnus

let lua = Lua()

// connect standard I/O to internal pipes
do {
    try lua.configureStandardIO()
} catch {
    print("Failed to configure standard I/O: \(error)")
}

// Invoke lua code that access to standard output
do {
    try lua.eval("print(\"This text will be emitted to Lua.stdout instead of standard output of host application.\")")
} catch let luaError as LuaError {
    print(luaError)
} catch {
    print("Unexpected error: \(error)")
}

// Capture standard output content
guard let outputData = lua.stdout?.availableData,
        let outputString = String(data: outputData, encoding: .utf8) else {return}
print("Lua output: \(outputString)")

Console output:

Lua output: This text will be emitted to Lua.stdout instead of standard output of host application.
Lua state 0x0000000000000000: stdout closed
Lua state 0x0000000000000000: stdin closed

Warning

Lua's print statement is replaced to custom function at lua.configureStandardIO. In details, see About print statement of Lua.

Application example: Inject data to Lua standard input

// import Cygnus

let lua = Lua()

// connect standard I/O to internal pipes
do {
    try lua.configureStandardIO()
} catch {
    print("Failed to configure standard I/O: \(error)")
}

let luaSemaphore = DispatchSemaphore(value: 0)
DispatchQueue.global().async {
    do {
        try lua.eval("print(string.lower(io.read()))")
    } catch let luaError as LuaError {
        print(luaError)
    } catch {
        print("Unexpected error: \(error)")
    }
    
    guard let outputData = lua.stdout?.availableData,
            let outputString = String(data: outputData, encoding: .utf8) else {return}
    print("Lua output: \(outputString)")
    luaSemaphore.signal()
}

let content = "HELLO, LUA!"
do {
    // The function `io.read` of Lua reads string until line break or EOF,
    // so you should to add '\n' to end of data.
    try lua.stdin?.write(contentsOf: (content + "\n").data(using: .utf8)!)
} catch let luaError as LuaError {
    print(luaError)
} catch {
    print("Unexpected error: \(error)")
}
luaSemaphore.wait()

Console output:

Lua output: hello, lua!
Lua state 0x0000000000000000: stdout closed
Lua state 0x0000000000000000: stdin closed

Warning

Lua's print statement is replaced to custom function at lua.configureStandardIO. In details, see About print statement of Lua.

Warning: About print statement of Lua

In default, Lua's statement print uses stdout defined at stdio.h. It means there is no way to capture output.
To avoid this, Cygnus internally replaces print to custom function calling io.write() and io.flush(). If you don't need this, set argument replacePrintStatement to false of function lua.configureStandardIO.

Details

This package contains following 3 modules:

• Cygnus : High-level Swift API
• CygnusCore : Lua core
• CygnusMacros : Lua macro definitions (lua_pop, lua_pcall, ...)

If you only use High-level API, just import Cygnus. To use Lua API directly or invoke function that is not implemented at Cygnus, please import CygnusCore (and CygnusCoreMacros if needed) additionaly.

Important

Cygnus is not API wrapper. It provides simpler method to use Lua from your app (such as I/O capture, executing code passed as a string) but not all functions of Lua C API.

License

This package is published under MIT License.

Lua is copyright (c) 1994–2023 Lua.org, PUC-Rio.