nslookup: add support for search domains, closes 11161

function                                             old     new   delta
parse_resolvconf                                       -     311    +311
add_query_with_search                                  -     105    +105
nslookup_main                                        873     757    -116
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 0/1 up/down: 416/-116)          Total: 300 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 82 insertions, 22 deletions

diff --git a/networking/nslookup.c b/networking/nslookup.c
index 3a614b0c6..e153eb585 100644
--- a/networking/nslookup.c
+++ b/networking/nslookup.c
@@ -318,6 +318,8 @@ struct globals {
         unsigned serv_count;
         struct ns *server;
         struct query *query;
+        char *search;
+        smalluint have_search_directive;
 } FIX_ALIASING;
 #define G (*(struct globals*)bb_common_bufsiz1)
 #define INIT_G() do { \
@@ -667,24 +669,60 @@ static void parse_resolvconf(void)
 
         resolv = fopen("/etc/resolv.conf", "r");
         if (resolv) {
-                char line[128], *p;
+                char line[512]; /* "search" is defined to be up to 256 chars */
 
                 while (fgets(line, sizeof(line), resolv)) {
-                        p = strtok(line, " \t\n");
+                        char *p, *arg;
 
-                        if (!p || strcmp(p, "nameserver") != 0)
+                        p = strtok(line, " \t\n");
+                        if (!p)
+                                continue;
+                        dbg("resolv_key:'%s'\n", p);
+                        arg = strtok(NULL, "\n");
+                        dbg("resolv_arg:'%s'\n", arg);
+                        if (!arg)
                                 continue;
 
-                        p = strtok(NULL, " \t\n");
+                        if (strcmp(p, "domain") == 0) {
+                                /* domain DOM */
+                                if (!G.have_search_directive)
+                                        goto set_search;
+                                continue;
+                        }
+                        if (strcmp(p, "search") == 0) {
+                                /* search DOM1 DOM2... */
+                                G.have_search_directive = 1;
+ set_search:
+                                free(G.search);
+                                G.search = xstrdup(arg);
+                                dbg("search='%s'\n", G.search);
+                                continue;
+                        }
 
-                        if (!p)
+                        if (strcmp(p, "nameserver") != 0)
                                 continue;
 
-                        add_ns(xstrdup(p));
+                        /* nameserver DNS */
+                        add_ns(xstrdup(arg));
                 }
 
                 fclose(resolv);
         }
+
+        if (!G.search) {
+                /* default search domain is domain part of hostname */
+                char *h = safe_gethostname();
+                char *d = strchr(h, '.');
+                if (d) {
+                        G.search = d + 1;
+                        dbg("search='%s' (from hostname)\n", G.search);
+                }
+                /* else free(h); */
+        }
+
+        /* Cater for case of "domain ." in resolv.conf */
+        if (G.search && LONE_CHAR(G.search, '.'))
+                G.search = NULL;
 }
 
 static void add_query(int type, const char *dname)
@@ -695,7 +733,7 @@ static void add_query(int type, const char *dname)
 
         count = G.query_count++;
 
-        G.query = xrealloc_vector(G.query, /*2=2^1:*/ 1, count);
+        G.query = xrealloc_vector(G.query, /*4=2^2:*/ 2, count);
         new_q = &G.query[count];
 
         dbg("new query#%u type %u for '%s'\n", count, type, dname);
@@ -709,6 +747,28 @@ static void add_query(int type, const char *dname)
         new_q->qlen = qlen;
 }
 
+static void add_query_with_search(int type, const char *dname)
+{
+        char *s;
+
+        if (type == T_PTR || !G.search || strchr(dname, '.')) {
+                add_query(type, dname);
+                return;
+        }
+
+        s = G.search;
+        for (;;) {
+                char *fullname, *e;
+
+                e = skip_non_whitespace(s);
+                fullname = xasprintf("%s.%.*s", dname, (int)(e - s), s);
+                add_query(type, fullname);
+                s = skip_whitespace(e);
+                if (!*s)
+                        break;
+        }
+}
+
 static char *make_ptr(const char *addrstr)
 {
         unsigned char addr[16];
@@ -833,6 +893,18 @@ int nslookup_main(int argc UNUSED_PARAM, char **argv)
                 }
         }
 
+        /* Use given DNS server if present */
+        if (argv[1]) {
+                if (argv[2])
+                        bb_show_usage();
+                add_ns(argv[1]);
+        } else {
+                parse_resolvconf();
+                /* Fall back to localhost if we could not find NS in resolv.conf */
+                if (G.serv_count == 0)
+                        add_ns("127.0.0.1");
+        }
+
         if (types == 0) {
                 /* No explicit type given, guess query type.
                  * If we can convert the domain argument into a ptr (means that
@@ -846,31 +918,19 @@ int nslookup_main(int argc UNUSED_PARAM, char **argv)
                 if (ptr) {
                         add_query(T_PTR, ptr);
                 } else {
-                        add_query(T_A, argv[0]);
+                        add_query_with_search(T_A, argv[0]);
 #if ENABLE_FEATURE_IPV6
-                        add_query(T_AAAA, argv[0]);
+                        add_query_with_search(T_AAAA, argv[0]);
 #endif
                 }
         } else {
                 int c;
                 for (c = 0; c < ARRAY_SIZE(qtypes); c++) {
                         if (types & (1 << c))
-                                add_query(qtypes[c].type, argv[0]);
+                                add_query_with_search(qtypes[c].type, argv[0]);
                 }
         }
 
-        /* Use given DNS server if present */
-        if (argv[1]) {
-                if (argv[2])
-                        bb_show_usage();
-                add_ns(argv[1]);
-        } else {
-                parse_resolvconf();
-                /* Fall back to localhost if we could not find NS in resolv.conf */
-                if (G.serv_count == 0)
-                        add_ns("127.0.0.1");
-        }
-
         for (rc = 0; rc < G.serv_count;) {
                 int c;