The basis of gethostbyname

Makefile

@@ -1,10 +1,9 @@
 CC = gcc
-CFLAGS = -Wall -Werror -ggdb
+CFLAGS = -Wall -Werror -ggdb `pkg-config --cflags glib-2.0`
+LDFLAGS = `pkg-config --libs glib-2.0`
 
 OBJS = \
 	nss.o
 
 libnss_docker.so.2: $(OBJS)
-	$(CC) -shared -o $@ -Wl,-soname,$@ $<
-
-
+	$(CC) $(LDFLAGS) -shared -o $@ -Wl,-soname,$@ $<

nss.c

@@ -1,6 +1,22 @@
+/*
+ * NSS plugin for looking up Docker containers
+ *
+ * (c) 2014  Danielle Madeley  <danielle@madeley.id.au>
+ */
+
+#include <errno.h>
+#include <glib.h>
 #include <nss.h>
 #include <netdb.h>
 #include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include <arpa/inet.h>
+
+/* define a suffix that containers have */
+#define SUFFIX ".docker"
+
+#define ALIGN(a) (((a+sizeof(void*)-1)/sizeof(void*))*sizeof(void*))
 
 enum nss_status
 _nss_docker_gethostbyname2_r (const char *name,
@@ -11,7 +27,56 @@ _nss_docker_gethostbyname2_r (const char *name,
         int *errnop,
         int *h_errnop)
 {
-    return NSS_STATUS_NOTFOUND;
+    char *aliases, *addr, *addrlist;
+    size_t l, idx;
+
+    if (af != AF_INET)
+      {
+        *errnop = EAFNOSUPPORT;
+        *h_errnop = NO_DATA;
+        return NSS_STATUS_UNAVAIL;
+      }
+
+    if (!g_str_has_suffix(name, SUFFIX))
+      {
+        *errnop = ENOENT;
+        *h_errnop = HOST_NOT_FOUND;
+        return NSS_STATUS_NOTFOUND;
+      }
+
+    /* we can't allocate any memory, the buffer is where we need to
+     * return things we want to use
+     *
+     * 1st, the hostname */
+    l = strlen(name);
+    result->h_name = buffer;
+    memcpy (result->h_name, name, l);
+
+    idx = ALIGN (l+1);
+
+    /* 2nd, the empty aliases array */
+    aliases = buffer + idx;
+    *(char **) aliases = NULL;
+    idx += sizeof (char*);
+
+    result->h_aliases = (char **) aliases;
+
+    result->h_addrtype = af;
+    result->h_length = sizeof (struct in_addr);
+
+    /* 3rd, address */
+    addr = buffer + idx;
+    memcpy(addr, "AAAA", result->h_length);
+    idx += ALIGN (result->h_length);
+
+    /* 4th, the addresses ptr array */
+    addrlist = buffer + idx;
+    ((char **) addrlist)[0] = addr;
+    ((char **) addrlist)[1] = NULL;
+
+    result->h_addr_list = (char **) addrlist;
+
+    return NSS_STATUS_SUCCESS;
 }
 
 enum nss_status
@@ -22,7 +87,13 @@ _nss_docker_gethostbyname_r (const char *name,
         int *errnop,
         int *h_errnop)
 {
-    return NSS_STATUS_NOTFOUND;
+    return _nss_docker_gethostbyname2_r(name,
+            AF_INET,
+            result,
+            buffer,
+            buflen,
+            errnop,
+            h_errnop);
 }
 
 enum nss_status