Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/rockfordwei/cswift

C Module for Swift, Swift Script and Dynamic Library Call;Swift中直接调用C语言源程序的展示程序
https://github.com/rockfordwei/cswift

c clang dll dynamic-programming hotfix module spm swift swift-script

Last synced: 2 days ago
JSON representation

C Module for Swift, Swift Script and Dynamic Library Call;Swift中直接调用C语言源程序的展示程序

Awesome Lists containing this project

README 

        
# C Module for Swift, Swift Script and Dynamic Library Call [简体中文](README.zh_CN.md)



Rockford Wei，2017-01-17



Last update: 2018-01-23



This project demonstrates how to call a customized C library in your swift project.

You can clone it from github, or follow the instruction below to generate it step by step.



Furthermore, this demo also shows how to use swift as a script, with examples of calling C api as dynamic libraries.

This practice makes it possible to patch hot fixes for server side swift without stopping the server, theoretically.



## Introduction



There are two C files: CSwift.c and CSwift.h. The objective is to build a CSwift library and export it to Swift.



## Quick Start



Please compile this project with Swift 4.0.3 toolchain.



### Build & Test



```

$ git clone https://github.com/RockfordWei/CSwift.git

$ cd CSwift

$ swift build

$ swift test

```



The sources are written in C while the test program is written in Swift. So if all tests passed, then congratulations! You've already mastered the process to call C api in a Swift source.



## Walk Through



However, even without the sources above, you can still start everything from blank:



### Start From An Empty Folder:



Assume the objective library is still CSwift, then find an empty folder and try these commands in a terminal:



```

mkdir CSwift && cd CSwift && swift package init

mkdir Sources/CSwift/include && rm Sources/CSwift/CSwift.swift

```



The above commands will set up the empty project template



### C Header File



Now edit the header file `Sources/CSwift/include/Swift.h`:



``` c

extern int c_add(int, int);

#define C_TEN 10

```



### C Source



Finishing the implementation of the C body `Sources/CSwift/CSwift.c`:



``` c

#include "include/CSwift.h"

int c_add(int a, int b) { return a + b ; }

```



### Module Map



Next, we will setup an umbrella file for swift: 

`Sources/CSwift/include/module.modulemap`



``` swift

module CSwift [system] {

  header "CSwift.h"

  export *

}

```



### Call C API in Swift



Now let's check if the library works by editing a test script:

`Tests/CSwiftTests/CSwiftTests.swift`



``` swift

import XCTest

@testable import CSwift

class CSwiftTests: XCTestCase {

  func testExample() {

    let three = c_add(1, 2)

    XCTAssertEqual(three, 3)

    XCTAssertEqual(C_TEN, 10)

  }

  static var allTests : [(String, (CSwiftTests) -> () throws -> Void)] {

      return [  ("testExample", testExample)  ]

  }

}

```



### Test



The final step is the easiest one - build & test:



```

$ swift build

$ swift test

```



If success, then perfect!



## Swift as Script and Call C lib dynamically



Beside the above classic static build & run, Swift also provide an interpreter to execute swift source as scripts, just like a playground in a terminal.

This project also makes an example for swift script, and even more, introduces how to call the same C api dynamically in such a script.



### Dynamic Link Library



The default linking object of Swift 4 is static, so it needs a bit modification to turn it into a dynamic one. 



To do this, edit the Package.swift file, and add a line:



``` swift

.library(

    name: "CSwift",

    type: .`dynamic`,  // <------------ Insert the dynamic type right here!

    targets: ["CSwift"]),

```



Please check a swift script `dll.swift.script`, actually it is a common swift with no difference to any other swift sources:



``` swift

// First thing first, make sure your dll path is an dynamic library in an ABSOLUTE path.

// on Mac, the suffix is ".dylib"; on Linux, it is ".so"

guard let lib = dlopen(dllpath,  RTLD_LAZY) else {

  exit(0)

}



// declare the api prototype to call

typealias AddFunc = @convention(c) (CInt, CInt) -> CInt



// look up the function in the library

guard let c_add = dlsym(lib, "c_add") else {

  dlclose(lib)

  exit(0)

}



// attache the function to the real API address

let add = unsafeBitCast(c_add, to: AddFunc.self)



// call the C method, dynamically

let x = add(1, 2)

print(x)



// release resources

dlclose(lib)

```



### Run the Swift Script



This project also provides a bash script `dll.sh` to run the swift script above.

```

# step one, build the C library

swift build



# then test what OS it is: .dylib for apple and .so for linux

if swift --version|grep apple

then

  SUFFIX=dylib

else

  SUFFIX=so

fi



# generate the full path of new library.

DLL=$PWD/.build/debug/libCSwift.$SUFFIX



# run the swift script and call the libray.

swift dll.swift.script $DLL

```



## More Info



If Xcode is preferred, then try command `swift package generate-xcodeproj` before building.