dns: add verbatim option to dns.lookup()

When true, results from the DNS resolver are passed on as-is, without
the reshuffling that Node.js otherwise does that puts IPv4 addresses
before IPv6 addresses.

PR-URL: nodejs/node#14731
Ref: nodejs/node#6307
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/dns.md

@@ -140,6 +140,12 @@ changes:
     flags may be passed by bitwise `OR`ing their values.
   - `all` {boolean} When `true`, the callback returns all resolved addresses in
     an array. Otherwise, returns a single address. Defaults to `false`.
+  - `verbatim` {boolean} When `true`, the callback receives IPv4 and IPv6
+    addresses in the order the DNS resolver returned them.  When `false`,
+    IPv4 addresses are placed before IPv6 addresses.
+    Default: currently `false` (addresses are reordered) but this is expected
+    to change in the not too distant future.
+    New code should use `{ verbatim: true }`.
 - `callback` {Function}
   - `err` {Error}
   - `address` {string} A string representation of an IPv4 or IPv6 address.

lib/dns.js

@@ -131,6 +131,7 @@ function lookup(hostname, options, callback) {
   var hints = 0;
   var family = -1;
   var all = false;
+  var verbatim = false;
 
   // Parse arguments
   if (hostname && typeof hostname !== 'string') {
@@ -145,6 +146,7 @@ function lookup(hostname, options, callback) {
     hints = options.hints >>> 0;
     family = options.family >>> 0;
     all = options.all === true;
+    verbatim = options.verbatim === true;
 
     if (hints !== 0 &&
         hints !== cares.AI_ADDRCONFIG &&
@@ -185,7 +187,7 @@ function lookup(hostname, options, callback) {
   req.hostname = hostname;
   req.oncomplete = all ? onlookupall : onlookup;
 
-  var err = cares.getaddrinfo(req, hostname, family, hints);
+  var err = cares.getaddrinfo(req, hostname, family, hints, verbatim);
   if (err) {
     process.nextTick(callback, errnoException(err, 'getaddrinfo', hostname));
     return {};

src/cares_wrap.cc

@@ -196,15 +196,23 @@ void ChannelWrap::New(const FunctionCallbackInfo<Value>& args) {
 
 class GetAddrInfoReqWrap : public ReqWrap<uv_getaddrinfo_t> {
  public:
-  GetAddrInfoReqWrap(Environment* env, Local<Object> req_wrap_obj);
+  GetAddrInfoReqWrap(Environment* env,
+                     Local<Object> req_wrap_obj,
+                     bool verbatim);
   ~GetAddrInfoReqWrap();
 
   size_t self_size() const override { return sizeof(*this); }
+  bool verbatim() const { return verbatim_; }
+
+ private:
+  const bool verbatim_;
 };
 
 GetAddrInfoReqWrap::GetAddrInfoReqWrap(Environment* env,
-                                       Local<Object> req_wrap_obj)
-    : ReqWrap(env, req_wrap_obj, AsyncWrap::PROVIDER_GETADDRINFOREQWRAP) {
+                                       Local<Object> req_wrap_obj,
+                                       bool verbatim)
+    : ReqWrap(env, req_wrap_obj, AsyncWrap::PROVIDER_GETADDRINFOREQWRAP)
+    , verbatim_(verbatim) {
   Wrap(req_wrap_obj, this);
 }
 
@@ -1811,70 +1819,38 @@ void AfterGetAddrInfo(uv_getaddrinfo_t* req, int status, struct addrinfo* res) {
   };
 
   if (status == 0) {
-    // Success
-    struct addrinfo *address;
     int n = 0;
-
-    // Create the response array.
     Local<Array> results = Array::New(env->isolate());
 
-    char ip[INET6_ADDRSTRLEN];
-    const char *addr;
-
-    // Iterate over the IPv4 responses again this time creating javascript
-    // strings for each IP and filling the results array.
-    address = res;
-    while (address) {
-      CHECK_EQ(address->ai_socktype, SOCK_STREAM);
-
-      // Ignore random ai_family types.
-      if (address->ai_family == AF_INET) {
-        // Juggle pointers
-        addr = reinterpret_cast<char*>(&(reinterpret_cast<struct sockaddr_in*>(
-            address->ai_addr)->sin_addr));
-        int err = uv_inet_ntop(address->ai_family,
-                               addr,
-                               ip,
-                               INET6_ADDRSTRLEN);
-        if (err)
+    auto add = [&] (bool want_ipv4, bool want_ipv6) {
+      for (auto p = res; p != nullptr; p = p->ai_next) {
+        CHECK_EQ(p->ai_socktype, SOCK_STREAM);
+
+        const char* addr;
+        if (want_ipv4 && p->ai_family == AF_INET) {
+          addr = reinterpret_cast<char*>(
+              &(reinterpret_cast<struct sockaddr_in*>(p->ai_addr)->sin_addr));
+        } else if (want_ipv6 && p->ai_family == AF_INET6) {
+          addr = reinterpret_cast<char*>(
+              &(reinterpret_cast<struct sockaddr_in6*>(p->ai_addr)->sin6_addr));
+        } else {
           continue;
+        }
 
-        // Create JavaScript string
-        Local<String> s = OneByteString(env->isolate(), ip);
-        results->Set(n, s);
-        n++;
-      }
-
-      // Increment
-      address = address->ai_next;
-    }
-
-    // Iterate over the IPv6 responses putting them in the array.
-    address = res;
-    while (address) {
-      CHECK_EQ(address->ai_socktype, SOCK_STREAM);
-
-      // Ignore random ai_family types.
-      if (address->ai_family == AF_INET6) {
-        // Juggle pointers
-        addr = reinterpret_cast<char*>(&(reinterpret_cast<struct sockaddr_in6*>(
-            address->ai_addr)->sin6_addr));
-        int err = uv_inet_ntop(address->ai_family,
-                               addr,
-                               ip,
-                               INET6_ADDRSTRLEN);
-        if (err)
+        char ip[INET6_ADDRSTRLEN];
+        if (uv_inet_ntop(p->ai_family, addr, ip, sizeof(ip)))
           continue;
 
-        // Create JavaScript string
         Local<String> s = OneByteString(env->isolate(), ip);
         results->Set(n, s);
         n++;
       }
+    };
 
-      // Increment
-      address = address->ai_next;
-    }
+    const bool verbatim = req_wrap->verbatim();
+    add(true, verbatim);
+    if (verbatim == false)
+      add(false, true);
 
     // No responses were found to return
     if (n == 0) {
@@ -1965,6 +1941,7 @@ void GetAddrInfo(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[0]->IsObject());
   CHECK(args[1]->IsString());
   CHECK(args[2]->IsInt32());
+  CHECK(args[4]->IsBoolean());
   Local<Object> req_wrap_obj = args[0].As<Object>();
   node::Utf8Value hostname(env->isolate(), args[1]);
 
@@ -1985,7 +1962,7 @@ void GetAddrInfo(const FunctionCallbackInfo<Value>& args) {
     CHECK(0 && "bad address family");
   }
 
-  GetAddrInfoReqWrap* req_wrap = new GetAddrInfoReqWrap(env, req_wrap_obj);
+  auto req_wrap = new GetAddrInfoReqWrap(env, req_wrap_obj, args[4]->IsTrue());
 
   struct addrinfo hints;
   memset(&hints, 0, sizeof(struct addrinfo));

test/internet/test-dns.js

@@ -553,7 +553,7 @@ console.log('looking up nodejs.org...');
 
 const cares = process.binding('cares_wrap');
 const req = new cares.GetAddrInfoReqWrap();
-cares.getaddrinfo(req, 'nodejs.org', 4);
+cares.getaddrinfo(req, 'nodejs.org', 4, /* hints */ 0, /* verbatim */ true);
 
 req.oncomplete = function(err, domains) {
   assert.strictEqual(err, 0);