From 87e5e3337e9123da3cd9cf6f0303fd391a0b7bc3 Mon Sep 17 00:00:00 2001
From: Paul Schneider <paulschneider@free.fr>
Date: Sat, 21 Jun 2025 15:37:10 +0100
Subject: [PATCH] ifaddr initial import

---
 .gitignore      |  2 ++
 README.adoc     |  3 +++
 src/Makefile    |  9 +++++++++
 src/getifaddr.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.c      | 24 ++++++++++++++++++++++
 5 files changed, 91 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 README.adoc
 create mode 100644 src/Makefile
 create mode 100644 src/getifaddr.c
 create mode 100644 src/main.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..495a75e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/build/
+
diff --git a/README.adoc b/README.adoc
new file mode 100644
index 0000000..b9b5b81
--- /dev/null
+++ b/README.adoc
@@ -0,0 +1,3 @@
+= Read me
+
+This command outputs the ipv4 address for the interface given by name in argument.
diff --git a/src/Makefile b/src/Makefile
new file mode 100644
index 0000000..2a541fd
--- /dev/null
+++ b/src/Makefile
@@ -0,0 +1,9 @@
+DESTDIR=../build
+
+$(DESTDIR)/ifaddr: main.c getifaddr.c
+	mkdir -p $(DESTDIR)
+	gcc  $^ -o $(DESTDIR)/ifaddr
+
+dist-clean:
+	rm -f ifaddr $(DESTDIR)/ifaddr
+
diff --git a/src/getifaddr.c b/src/getifaddr.c
new file mode 100644
index 0000000..03583af
--- /dev/null
+++ b/src/getifaddr.c
@@ -0,0 +1,53 @@
+#define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
+#include <ifaddrs.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <ifaddrs.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <linux/if_link.h>
+#include <string.h>
+
+char * get_if_addr(char *ifname)
+{
+
+  struct ifaddrs * list, * plist;
+  int family, s;
+
+	char host[NI_MAXHOST];
+  char *result;
+  if (getifaddrs (&list)==-1)
+  {
+    fprintf(stderr, "no info");
+    return NULL;
+  }
+  plist = list;
+  while (plist!=NULL)
+  {
+    if (strcmp(plist->ifa_name,ifname)==0) 
+		{
+      family = plist->ifa_addr->sa_family;
+      if (family == AF_INET || family == AF_INET6) {
+                   s = getnameinfo(plist->ifa_addr,
+                           (family == AF_INET) ? sizeof(struct sockaddr_in) :
+                                                 sizeof(struct sockaddr_in6),
+                           host, NI_MAXHOST,
+                           NULL, 0, NI_NUMERICHOST);
+                   if (s != 0) {
+                       fprintf(stderr, "getnameinfo() failed: %s\n", gai_strerror(s));
+                       exit(EXIT_FAILURE);
+                   }
+                   result = malloc(strlen(host)+1);
+                   strcpy(result,host);
+                   freeifaddrs (list);
+                   return result;
+               }
+    }
+    plist = plist->ifa_next;
+  }
+  freeifaddrs (list);
+  return NULL;
+
+}
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..84861e5
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include<stdlib.h>
+
+char * get_if_addr(char *ifname);
+
+int main(int argc, char ** argv)
+{
+
+  if (argc<2) {
+    fprintf(stderr, "usage: %s <ifname>\nOù `ifname` est le nom de l'interface, par exemple, `eth0`.", argv[0]);
+    
+    return 2;
+  }
+
+    char * addr = (char*) get_if_addr(argv[1]);
+    if (addr==NULL) {
+      printf("no addr found!\n");
+      return 1;
+    }
+    printf(addr);
+
+    free(addr);
+    return 0;
+}