cgolmnl

Go wrapper of libmnl using cgo, under heavy development

sample

see examples

installation

Need running mktypes.sh before build.

requires

• libmnl
• test reqs (optional): **ginkgo (http://onsi.github.io/ginkgo/)

links

• libmnl: http://netfilter.org/projects/libmnl/

struct

mnl_nlmsg_batch and mnl_socket are opaque as NlmsgBatch and Socket (cgo say [0]byte). Nlattr is same as C struct but Nlmsg seems a little bit strange. It has buf and real Nlmsghdr.

errno

I currently use an incredibly childish C function in set_errno.c

void SetErrno(int n) { errno = n; }

I can not find the way of tossing up Go callback error, in other words set C's errno from Go. I am not good at English, let me show why I need to do in the code snippets below:

• C library header (lib.h)

    typedef int cbf_t(void *data);
    extern int c_func(cbf_t cbfunc, void *data);

• wrapper header

    #include "lib.h"
    #include "_cgo_export.h"
    extern int wrap(void *data);

• C wrapper source

    #include "cblib.h"
    int wrap(void *data)
    {
        return c_func((cbf_t)CallFromC, data);
    }

• Go

    /*
    #include "cbwrap.h"
    */
    import "C"
    import "unsafe"

    type Cb_t func(interface {}) (int, error)

    func Doit(cbfunc Cb_t, data interface{}) (int, error) {
        // multiplexing
        pseudo_data := [2]unsafe.Pointer{unsafe.Pointer(&cbfunc), unsafe.Pointer(&data)}
        return C.wrap(unsafe.Pointer(&pseudo_data))
    }

    //export CallFromC
    func CallFromC(pseudo_data interface) C.int {
        // demultiplexing
        args := *(*[2]unsafe.Porinter)(pseudo_data)
        cbfunc := *(*Cb_t)(args[0])
        real_data := *(*interface{})(args[1])
        ret, err := cbfunc(real_data)
	// set C errno here
    }

    func cb(data interface{}) (int, error) {
        i := data.(int)
        if i < 0:
	    return -1, syscall.Errno(-i)
        else:
	    return i, syscall.Errno(0)
    }

    func main() {
        Doit(cb, 7)
    }

call chain will be: Go main() -> Go Doit() -> C wrap() -> C c_func() -> Go CallFromC() -> Go cb()

I need to know the way of tossing last Go cb() error up to Go Doit() or C c_func().

comparison

original	cgolmnl	remarks
mnl_attr_get_type	Nlattr.GetType
mnl_attr_get_len	Nlattr.GetLen
mnl_attr_get_payload_len	Nlattr.GetPayloadLen
mnl_attr_get_payload	Nlattr.GetPayload
(add)	Nlattr.GetPayloadBytes	returns []byte
mnl_attr_ok	Nlattr.Ok
mnl_attr_next	Nlattr.Next
mnl_attr_type_valid	Nlattr.TypeValid	returns ret, error
mnl_attr_validate	Nlattr.Validate	returns ret, errno
mnl_attr_validate2	Nlattr.Validate2	returns ret, errno
mnl_attr_parse	Nlattr.Parse	returns ret, errno
mnl_attr_parse_nested	Nlattr.ParseNested	returns ret, errno
mnl_attr_parse_payload	Nlattr.ParsePayload	returns ret, errno
mnl_attr_get_u8	Nlattr.GetU8
mnl_attr_get_u16	Nlattr.GetU16
mnl_attr_get_u32	Nlattr.GetU32
mnl_attr_get_u64	Nlattr.GetU64
mnl_attr_get_str	Nlattr.GetStr
mnl_attr_put	Nlattr.Put
(add)	Nlattr.PutPtr
(add)	Nlattr.PutBytes
mnl_attr_put_u8	Nlattr.PutU8
mnl_attr_put_u16	Nlattr.PutU16
mnl_attr_put_u32	Nlattr.PutU32
mnl_attr_put_u64	Nlattr.PutU64
mnl_attr_put_str	Nlattr.Putstr
mnl_attr_put_strz	Nlattr.Putstrz
mnl_attr_nest_start	Nlattr.NestStart
mnl_attr_put_check	Nlattr.PutCheck
mnl_attr_put_u8_check	Nlattr.PutU8Check
mnl_attr_put_u16_check	Nlattr.PutU16Check
mnl_attr_put_u32_check	Nlattr.PutU32Check
mnl_attr_put_u64_check	Nlattr.PutU64Check
mnl_attr_put_str_check	Nlattr.PutStrCheck
mnl_attr_put_strz_check	Nlattr.PutStrzCheck
mnl_attr_nest_start_check	Nlattr.nestStartCheck
mnl_attr_nest_end	Nlattr.nestEnd
mnl_attr_nest_cancel	Nlattr.nestCancel
-------------------------------------	-----------------------------	-----------------------------
mnl_nlmsg_size	NlmsgSize
mnl_nlmsg_get_payload_len	Nlmsg.GetPayloadLen
mnl_nlmsg_put_header	Nlmsg.PutHeader
(add)	NlmsgBytes	build new nlmsg from []byte
(add)	NewNlmsg	build new nlmsg
mnl_nlmsg_put_extra_header	Nlmsg.PutExtraHeader
mnl_nlmsg_get_paylod	Nlmsg.GetPayload
(add)	Nlmsg.GetPayloadBytes	returns []byte
mnl_nlmsg_get_payload_offset	Nlmsg.GetPayloadOffset
(add)	Nlmsg.GetPayloadOffsetBytes	returns []byte
mnl_nlmsg_ok	Nlmsg.Ok
mnl_nlmsg_next	Nlmsg.Next
mnl_nlmsg_get_payload_tail	Nlmsg.GetPayloadTail
mnl_nlmsg_seq_ok	Nlmsg.SeqOk
mnl_nlmsg_portid_ok	Nlmsg.PortidOk
mnl_nlmsg_fprintf	Nlmsg.Fprint	*os.File, not descriptor
mnl_nlmsg_batch_start	NewNlmsgBatch
mnl_nlmsg_batch_stop	NlmsgBatch.Stop
mnl_nlmsg_batch_next	NlmsgBatch.Next
mnl_nlmsg_batch_reset	NlmsgBatch.Reset
mnl_nlmsg_batch_size	NlmsgBatch.Size
mnl_nlmsg_batch_head	NlmsgBatch.Head
(add)	NlmsgBatch.HeadBytes	returns []byte
mnl_nlmsg_batch_current	NlmsgBatch.Current
mnl_nlmsg_batch_is_empty	NlmsgBatch.IsEmpty
-------------------------------------	-----------------------------	-----------------------------
mnl_cb_run	CbRun
mnl_cb_run2	CbRun2	changed signature
-------------------------------------	-----------------------------	-----------------------------
mnl_socket_get_fd	Socket.GgetFd
mnl_socket_get_portid	Socket.GetPortid
mnl_socket_open	NewSocket
mnl_socket_open2	NewSocket2
mnl_socket_fdopen	NewSocketFd
mnl_socket_bind	Socket.Bind
mnl_socket_sendto	Socket.Sendto
(add)	Socket.SendNlmsg
mnl_socket_recvfrom	Socket.Recvfrom
mnl_socket_close	Socket.Close
mnl_socket_setsockopt	Socket.Setsockopt
mnl_socket_getsockopt	Socket.Getsockopt