augeas crud on /etc/network/interfaces

augparse.c

// Test CRUD of an iface in /etc/network/interfaces ( on Ubuntu)
// using the Augeas lib
// Aniruddha. A (aniruddha.a@gmail.com)
// Nov 1, 2014
#include <stdio.h>
#include <assert.h>
#include <stdarg.h>
#include <stddef.h>
#include <limits.h>
#include <string.h>
#include <augeas.h>


// using the .so installed from libaugeas-dev :
// gcc -I /usr/include/libxml2/  augparse.c  -laugeas 
//
// to run, just install libaugeas0 ( minus dev files )

#define LENS_PATH "/usr/share/augeas/lenses/dist/"

void if_create (augeas *aug, const char *ifname, int nfields, ...)
{
    char key[128] = {0}, val[128] = {0};
    char *p = NULL;
    char *kv = NULL;
    va_list  ap;
    int ret, i;
    char iffield_path[256]= {0};
    assert(aug && ifname && (nfields > 0));

    ret = aug_set(aug, "/files/etc/network/interfaces/iface[last()+1]", ifname);
    assert(ret == 0);

    va_start(ap, nfields);
    for (i = 0; i < nfields; i++) {
        kv = va_arg(ap,char*);
        p  = strchr(kv, '=');
        if (!p) continue;
        strncpy(key, kv, (ptrdiff_t)(p - kv));
        key[p - kv] = '\0';
        strcpy(val, p + 1);
        sprintf(iffield_path, "/files/etc/network/interfaces/iface[last()]/%s",
                key);
        ret = aug_set(aug, iffield_path, val);
        assert(ret == 0);
    }
    va_end(ap);
}

void if_update (augeas *aug, const char *ifname, int nfields, ...)
{
    char key[128] = {0}, val[128] = {0};
    char *p = NULL;
    char *kv = NULL;
    va_list  ap;
    int ret, i;
    char iffield_path[256]= {0};
    assert(aug && ifname && (nfields > 0));

    va_start(ap, nfields);
    for (i = 0; i < nfields; i++) {
        kv = va_arg(ap,char*);
        p  = strchr(kv, '=');
        if (!p) continue;
        strncpy(key, kv, (ptrdiff_t)(p - kv));
        key[p - kv] = '\0';
        strcpy(val, p + 1);
        sprintf(iffield_path, "/files/etc/network/interfaces/iface[. = '%s']/%s",
                ifname, key);
        ret = aug_set(aug, iffield_path, val);
        assert(ret == 0);
    }
    va_end(ap);
}

void if_rm (augeas *aug, const char *ifname)
{
    int ret;
    char ifpath[256]= {0};

    assert(aug && ifname);

    sprintf(ifpath, "/files/etc/network/interfaces/iface[. = '%s']", ifname);
    ret = aug_rm(aug, ifpath);
    assert(ret != -1);
}

// TEST
int main (int argc, char *argv[])
{
    augeas *aug = NULL;

    aug = aug_init("/", LENS_PATH, AUG_SAVE_BACKUP|AUG_NO_ERR_CLOSE);
    if (!aug || (aug_error(aug) != AUG_NOERROR)) {
        fprintf(stderr, "Init failed: %s\n", aug_error_message(aug));
        exit(1);
    }
    if_create(aug, "eth2", 5, 
                   "family=inet",     "method=static",
                   "address=1.1.1.1", "netmask=255.255.0.0",
                   "mtu=1500" );

    aug_save(aug);
    system("cat /etc/network/interfaces");

    if_update(aug, "eth2", 1, "address=2.2.2.2");
    aug_save(aug);
    system("cat /etc/network/interfaces");

    if_rm(aug, "eth2");
    aug_save(aug);
    system("cat /etc/network/interfaces");

    aug_close(aug);

    return 0;
}