ifaddrs.h in Swift 3

ifaddrs.h contains some useful information if you want to work with sockets. Using getifaddrs will enumerate all interfaces and the IP addresses they are bound to. However Swift does not include this header in either Darwin or Glibc.

Using Swift 3’s SPM, a first attempt would be to define a system module package like this:

module Cifaddrs [system] [extern_c] {
    header "/usr/include/ifaddrs.h"
    export *
}

However, this doesn’t work and gives the following error message in both Xcode 8 and SPM:

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/module.modulemap:7:8: error: redefinition of module 'Compression'
module Compression [system] [extern_c] {
^

A second attempt might be to define a new module that simply imports ifaddrs.h:

Sources/Cifaddrs/include/Cifaddrs.h:
#import <ifaddrs.h>

Sources/Cifaddrs/Cifaddrs.c:
(empty)

While this is OK for SPM, Xcode will give the following error message:

[…]Sources/Cifaddrs/include/Cifaddrs.h:1:9: Include of non-modular header inside framework module 'Cifaddrs'

Note that setting CLANG_ALLOW_NON_MODULAR_INCLUDES_IN_FRAMEWORK_MODULES doesn’t affect Swift compiler.

That got me thinking. In the header file I’m apparently not allowed to import non-modular header files. However in the implementation file, I could just forward to the actual implementation.

Sources/Cifaddrs/include/Cifaddrs.h:
/*  $FreeBSD: src/include/ifaddrs.h,v 1.3.32.1.4.1 2010/06/14 02:09:06 kensmith Exp $   */

/*
 + Copyright (c) 1995, 1999
 +  Berkeley Software Design, Inc.  All rights reserved.
 *
 + Redistribution and use in source and binary forms, with or without
 + modification, are permitted provided that the following conditions
 + are met:
 + 1. Redistributions of source code must retain the above copyright
 +    notice, this list of conditions and the following disclaimer.
 *
 + THIS SOFTWARE IS PROVIDED BY Berkeley Software Design, Inc. ``AS IS'' AND
 + ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 + IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 + ARE DISCLAIMED.  IN NO EVENT SHALL Berkeley Software Design, Inc. BE LIABLE
 + FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 + DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 + OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 + HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 + LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 + OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 + SUCH DAMAGE.
 *
 +  BSDI ifaddrs.h,v 2.5 2000/02/23 14:51:59 dab Exp
 */

#ifndef _IFADDRS_H_
#define _IFADDRS_H_

struct ifaddrs {
    struct ifaddrs  *ifa_next;
    char            *ifa_name;
    unsigned int     ifa_flags;
    struct sockaddr *ifa_addr;
    struct sockaddr *ifa_netmask;
    struct sockaddr *ifa_dstaddr;
    void            *ifa_data;
};

extern int getifaddrs(struct ifaddrs **);
extern void freeifaddrs(struct ifaddrs *);

#endif
Sources/Cifaddrs/Cifaddrs.c:
#include <sys/types.h>
#include <sys/socket.h>
#include <ifaddrs.h>

From Swift, enumerating the interfaces looks like this:

var addrs: UnsafeMutablePointer<ifaddrs>?
getifaddrs(&addrs)

And with Swift 3’s sequence the result can be transformed in a sequence:

for ifaddrs in sequence(first: addrs!, next: { $0.pointee.ifa_next }) {
    //...
}

New blog posts

I just check the last time that I have blogged. 9 years ago. Or actually a few programming languages ago. The very few blog posts I’ve written were about PHP. Since then I’ve had great fun with Python and more recently with Swift. Using the Internet Archive: Wayback Machine, I’ve restored the few posts I’d written.

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