CGOEmitter (golang package)

What is it for?

The CGOEmitter package serves to obtain asynchronous C code response returns, facilitating the process of returning the data returned to the program in GO.

How to use?

1. Create the C header file

You must include the cgoemitter.h file to obtain the required methods.

File: (github.com/user/packagename/x/x.h)

#ifndef X_H_
#define X_H_

#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include "../../cgoemitter.h"

void say_message();

#endif

2. Create the C file with your logic

File: (github.com/user/packagename/x/x.c)

#include "x.h"

void check_err_cgoemitter_args_halloc_arg(void* value) {
  if (value == NULL) puts("Failed on cgoemitter_args_halloc_arg()");
}

void check_err_cgoemitter_args_add_arg(int code) {
  if (code == EXIT_FAILURE) puts("Failed on cgoemitter_args_add_arg()");
}

void say_message() {
  char* message = "Parameter sent from C language";

  cgoemitter_args_t cgoemitter_args = cgoemitter_new_args(1);
  
  void* message_arg = cgoemitter_args_halloc_arg(&message, (strlen(message)+1) * sizeof(char));
  check_err_cgoemitter_args_halloc_arg(message_arg);
  check_err_cgoemitter_args_add_arg(cgoemitter_args_add_arg(&cgoemitter_args, &message_arg));

  emit("message", &cgoemitter_args);
}

3. Create the package that will call this method

It is extremely important to add the flags below so that your code is compiled.

#cgo darwin LDFLAGS: -Wl,-undefined -Wl,dynamic_lookup
#cgo !darwin LDFLAGS: -Wl,-unresolved-symbols=ignore-all

File: (github.com/user/packagename/x/x.go)

package x

// The LDFLAGS lines below are needed to prevent linker errors
// since not all packages are present while building intermediate
// packages. The darwin build tag is used as a proxy for clang
// versus gcc because there doesn't seem to be a better way
// to detect this.

/*
#cgo darwin LDFLAGS: -Wl,-undefined -Wl,dynamic_lookup
#cgo !darwin LDFLAGS: -Wl,-unresolved-symbols=ignore-all
#include "x.h"
*/
import "C"

//SayMessage | Execute C function
func SayMessage() {
  C.say_message()
}

4. Using the CGOEmitter to receive the returned data

File: (github.com/user/packagename/main.go)

package main

import (
  "fmt"
  "sync"
  
  "github.com/supermock/cgoemitter"
  "github.com/user/packagename/x"
)

func main() {
  var wg sync.WaitGroup
  wg.Add(1)

  cgoemitter.On("message", cgoemitter.NewListener(func(args cgoemitter.Arguments) {
    fmt.Printf("Receveid message: %s\n", args.String(0))
    wg.Done()
  }))

  x.SayMessage()

  wg.Wait()
}

5. Just run your program and see the magic happening

$ go run main.go

Warnings Event

These warnings help you identify issues with your implementation, such as events triggered without manipulators.

Example:

cgoemitter.On("cgoemitter-warnings", cgoemitter.NewListener(func(args cgoemitter.Arguments) {
  fmt.Println("[WARNING]", args.String(0))
}))

Supported Methods:

On() => Add a new listener to the event.
Off() => Removes an existing listener in the event.
Once() => Add a new listener to the event with just one shot.
NewListener() => Creates a new listener.
GetListeners() => Returns all listeners to an event.
parser/CStructToGoStruct() => Transports data from a structure received from C to a structure in the GO.

CGO Security (go version >= 1.9.4)

From this version onwards a security measure was applied when using CGO, stay inside so you do not have problems.

For more details see:

If you have a problem compiling on account of an invalid flag warning. In the commands below, you allow the use of any flag, just for console session. (Not recommended, only for trusted code)

$ export CGO_CFLAGS_ALLOW='^.*\S'
$ export CGO_LDFLAGS_ALLOW='^.*\S'
$ go run main.go

Project with example of package usage:

https://github.com/supermock/cgoemitter-demo

Go documentation

https://godoc.org/github.com/supermock/cgoemitter

Roadmap

Add new conversions of types from C to GO in Arguments.
Add new treatments from C types to the GO in the CStructToGoStruct method

Read in another language

Clique aqui e leia em português

Contributions

Just download the code make your change and send a pull request explaining the purpose if it is a bug or an improvement and etc... After this will be analyzed to be approved. Note: If it is a major change, open a issue explaining what will be done so you do not waste your precious time developing something that will not be used. Make yourself at home!

License

MIT