dns name compression a pointer bug

Author: yutianzuo

nativesock/src/main/cpp/netutils/dns.h

@@ -308,7 +308,7 @@ class DNSQuery final : public SimpleUdpClient
                     continue;
                 }
                 int ip = *((int *) (&str_respones[index_inner]));
-                std::string str_ip = NetHelper::int32_to_string_addr(ip);
+                std::string str_ip = NetHelper::ipv4_to_string_addr(ip);
                 ips.emplace_back(std::move(str_ip));
                 index_inner += 4;
             }
@@ -319,27 +319,27 @@ class DNSQuery final : public SimpleUdpClient
         return ret;
     }
 
-    bool analyze_queries(int &index, const std::string &str_respones, std::string &str_host)
+    int getName(const std::string &str_respones, int index_inner, std::string &str_host)
     {
-        bool ret = false;
-        int index_inner = index;
-        str_host.clear();
-        FUNCTION_BEGIN ;
+        int jump = 0;
+        while (str_respones[index_inner] != 0)
+        {
             if (!check_index(index_inner, str_respones))
             {
-                FUNCTION_LEAVE;
+                index_inner = str_respones.size();
+                break;
             }
-
-            int jump = 0;
-            while (str_respones[index_inner] != 0)
+            if (jump == 0)
             {
-                if (!check_index(index_inner, str_respones))
-                {
-                    break;
-                }
-                if (jump == 0)
+                jump = (unsigned char) str_respones[index_inner++];
+            }
+            else
+            {
+                if (jump & 0xc0) //encounter a pointer
                 {
-                    jump = (unsigned char) str_respones[index_inner++];
+                    //just move on
+                    ++index_inner;
+                    jump = 0;
                 }
                 else
                 {
@@ -352,11 +352,37 @@ class DNSQuery final : public SimpleUdpClient
                     jump = 0;
                 }
             }
-            if (str_host.size())
+        }
+        if (str_host.size())
+        {
+            str_host.erase(str_host.size() - 1);
+        }
+        ++index_inner; //jump '\0'
+        return index_inner;
+    }
+
+    bool analyze_queries(int &index, const std::string &str_respones, std::string &str_host)
+    {
+        bool ret = false;
+        int index_inner = index;
+        str_host.clear();
+        FUNCTION_BEGIN ;
+            if (!check_index(index_inner, str_respones))
+            {
+                FUNCTION_LEAVE;
+            }
+
+            if (str_respones[index_inner] & 0xc0) //name is a pointer
             {
-                str_host.erase(str_host.size() - 1);
+                int index_pointer = (((~0xc0 & 0xff) & str_respones[index_inner]) << 8) |
+                        (str_respones[index_inner + 1] & 0xff);
+                getName(str_respones, index_pointer, str_host);
+                index_inner += 2;
+            }
+            else
+            { //name can be labels combines pointer, which is not handled
+                index_inner = getName(str_respones, index_inner, str_host);
             }
-            ++index_inner; //jump '\0'
 
             if (!check_index(index_inner + 4, str_respones))
             {
@@ -472,7 +498,9 @@ class DNSQuery final : public SimpleUdpClient
 
     bool check_index(int index, const std::string &respones)
     {
-        if (index >= respones.size())
+        //如果index溢出，index将变为一个负数，但是respones.size()返回的是一个size_t（unsigned int），比较会隐式转换
+        //将index这个int提升为unsigned int, 这时会是一个巨大的数。从而可能带来意外的结果。这里不判断index>=0，结果也是正确的。
+        if (index >= 0 && index >= respones.size())
         {
             return false;
         }

nativesock/src/main/cpp/netutils/errorhunter.h

@@ -20,15 +20,42 @@
 #include "../toolbox/string_x.h"
 
 
+inline std::string get_error_info(const std::string& msg)
+{
+    std::ostringstream ss;
+    ss << "error(";
+    ss << msg;
+    ss << ") in";
+    ss << __FILE__;
+    ss << ", line:";
+    ss << __LINE__;
+    return ss.str();
+}
+
+inline std::string get_errorno_info(const std::string& msg)
+{
+    std::ostringstream ss;
+    ss << "error(";
+    ss << msg;
+    ss << ") errorno(";
+    ss << std::strerror(errno);
+    ss << ") in";
+    ss << __FILE__;
+    ss << ", line:";
+    ss << __LINE__;
+    return ss.str();
+}
+
+
+
 
 ///////////////////////////////////
 #ifndef NORMAL_ERROR_MSG
-#define NORMAL_ERROR_MSG(msg) (std::ostringstream() << "error(" << msg << ") in " << __FILE__ << ", line:" << __LINE__).str()
+#define NORMAL_ERROR_MSG(msg) get_error_info(msg)
 #endif
 
 #ifndef NORMAL_ERROR_NUM
-#define NORMAL_ERROR_NUM(msg) (std::ostringstream() << "error(" << msg << ") errorno(" << std::strerror(errno) << ") in "\
-<< __FILE__ << ", line:" << __LINE__).str()
+#define NORMAL_ERROR_NUM(msg) get_errorno_info(msg)
 #endif
 
 #ifndef STD_COUT_ERRORMSG
@@ -51,12 +78,27 @@ class NetHelper final
 {
 public:
     NetHelper() = delete;
-    static std::string int32_to_string_addr(int addr)
+    static std::string ipv4_to_string_addr(int addr)
     {
         in_addr addrin = {0};
         addrin.s_addr = addr;
         return stringxa(::inet_ntoa(addrin));
     }
+
+    static std::string safe_ipv4_to_string_addr(int addr)
+    {
+        const int len = 32;
+        char buff[len] = {0};
+        return stringxa(::inet_ntop(AF_INET, &addr, buff, len));
+    }
+
+    static std::string safe_ipv6_to_string_addr(const in6_addr* addr)
+    {
+        const int len = 64;
+        char buff[len] = {0};
+        return stringxa(::inet_ntop(AF_INET6, addr, buff, len));
+    }
+
 };
 
 #endif //SIMPLESOCKET_ERRORHUNTER_H