Validate/recognize version of string represented IP address

Question

Is there a clever/tricky way to analyze if a string represented IP address is valid and to recognize its version, so that to be able to convert it to the appropriate structure, just by using the UNIX API?

I don't want to use regex, no need to add dependency to additional libraries just about this.

My first approach was:

in_addr addr;
memset( &addr, 0, sizeof( in_addr ) );
// try to convert from standard numbers-and-dots notation into binary data
if( 0 != inet_aton( sIPAddress.c_str(), &addr ) )
{
    return Socket::enIPv4;      // valid IPv4
}

in6_addr addr6;
memset( &addr6, 0, sizeof( in6_addr ) );
if( inet_pton( AF_INET6, sIPAddress.c_str(), &addr6 ) > 0 )
{
    return Socket::enIPv6;      // valid IPv6
}

return Socket::enUnknown;

The problem here is, that if I pass string like 1, it's successfully converted to IPv4. String like 11111 is converted to IPv4, too. By documentation:

inet_aton() returns non-zero if the address is valid, zero if not.

Obviously, this function recognizes not only XXX.XXX.XXX.XXX format, but does something more internally.

Of course I can write my own function(and it's going to be fun, actually), by analyzing the string, but I wanted to use already existing and tested functions, instead. Is it possible or I should write my own?

Some programmer dude · Accepted Answer · 2011-11-21 13:52:14Z

4

As per the manual page, strings like "a", "a.b" and "a.b.c" are all valid addresses for inet_aton. If you only want the "normal" dotted-decimal, use inet_pton for those addresses too.

answered Nov 21, 2011 at 13:52

Some programmer dude

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4 Comments

Kiril Kirov Over a year ago

LOL, the info in this link is not in the man page of RHEL4/5 XD Anyway, inet_pton does the same thing. So no, it does not solve my issue :\

Some programmer dude Over a year ago

@KirilKirov In that case there is a bug in inet_pton, it should only recognize valid dotted-decimal.

Kiril Kirov Over a year ago

interesting. I'm testing on RHE5U3, it's not that old.

Kiril Kirov Over a year ago

OMFG :X This is totally my bad. You're terribly right about inet_pton. Thanks a lot, accepted and +1.

Joel · Accepted Answer · 2011-11-21 14:01:55Z

3

If you're open to Boost libraries check out Boost Asio

The boost::asio::ip::address class is very good at parsing IPv6 and IPv4 addresses and beats trying to come up with regexes and the like to verify input. It's also cross platform.

#include <boost/asio.hpp>
#include <boost/assert.hpp>

#include <iostream>
#include <string>

using namespace std;

int main(int argc, char* argv[]){

    std::string ipv4("192.168.1.1");
    std::string ipv6("::1");
    std::string notIP("1");

    boost::asio::ip::address ipv4Addr = boost::asio::ip::address::from_string(ipv4);
    BOOST_ASSERT(ipv4Addr.is_v4() == true);

    boost::asio::ip::address ipv6Addr = boost::asio::ip::address::from_string(ipv6);
    BOOST_ASSERT(ipv6Addr.is_v6() == true);

    boost::asio::ip::address badAddr;
    try{
        badAddr = boost::asio::ip::address::from_string(notIP);
    }
    catch(const std::exception& e){
        std::cout << "Bad Address:  " << e.what() << std::endl;
    }   

    return 0;
}

This prints:

$ g++ -Wall -I/usr/local/boost-1.47.0/include/ -L/usr/local/boost-1.47.0/lib -o ./asioTestIP ./asioTestIP.cpp -lboost_system
$ ./asioTestIP 
Bad Address:  Invalid argument

answered Nov 21, 2011 at 14:01

Joel

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1 Comment

Kiril Kirov Over a year ago

Thanks, but I clearly asked only about the standard UNIX API, as I don't want to add dependency to another library just about this, as I can write my own function, that will do this. Thanks anyway :)

bhawesh · Accepted Answer · 2013-09-18 14:34:50Z

This should work:

#include <iostream>
#include <string>
#include <vector>
#include <stdlib.h>

void printError(const std::string& errStr) {
    std::cerr << errStr << std::endl;
}

bool checkAddress(const std::string& address) {
    std::vector<std::string> arr;
    int k = 0;
    arr.push_back(std::string());
    for (std::string::const_iterator i = address.begin(); i != address.end(); ++i) {
        if (*i == '.') {
            ++k;
            arr.push_back(std::string());
            if (k == 4) {
                printError("too many '.'");
            }
            continue;
        }
        if (*i >= '0' && *i <= '9') {
            arr[k] += *i;
        } else {
            printError("wrong character");
            return false;
        }
        if (arr[k].size() > 3) {
            printError("size exceeded");
            return false;
        }
    }
    if (k != 3) {
        printError("not enough '.'");
        return false;
    }
    for (int i = 0; i != 4; ++i) {
        const char* nPtr = arr[i].c_str();
        char* endPtr = 0;
        const unsigned long a = ::strtoul(nPtr, &endPtr, 10);
        if (nPtr == endPtr) {
            printError("invalid numeric input");
            return false;
        }
        if (a > 255) {
            printError("out of range");
            return false;
        }
    }
    return true;
}

int main(int argc, char* argv[]) {
    if (argc < 2) {
        return -1;
    }
    std::string address = argv[1];
    if (checkAddress(address)) {
        std::cout << "address ok" << std::endl;
    } else {
        std::cout << "bad address" << std::endl;
    }
    return 0;
}

I know how to write it, this is not my question. Thanks anyway. And, btw, this will recognize only IPv4. IPv6 supports several formats (3, as far as I know), which could be very error prone

D. Pistorius · Accepted Answer · 2016-04-21 09:23:17Z

I solved this problem once in a project. First I made an EBNF of ip-addresses and then created the algorithm. It works quit fine and doesn't use any foreign libraries. You have to call the method CheckWholeIp and hand it the ip-string (example: CheckWholeIp("127.0.0.1"). It'll return int 0 if it fits in the ipv4 scheme and 1 if it's not. But it is imortand to note, that addresses like 127.055.008.001 would be accepted too. There was no need to filter foregoing zeros. Let me know your thoughts ;)

cpp file:

    #include "CheckIp.h"

CheckIp::CheckIp()
{
}

int CheckIp::CheckWholeIp(string s)
{

    int size = s.size();
    int psum = 0;
    //check amount of points
    for (int i = 0; i <= size; i++) {
        if (s[i] == '.')psum++;
    }
    if (psum != 3)return 1;

    //write stringblocks
    string sbl0 = "";
    string sbl1 = "";
    string sbl2 = "";
    string sbl3 = "";
    int ii = 0;

    while (s[ii] != '.') {
        sbl0 = sbl0 + s[ii];
        ii++;
    }
    ii++;
    while (s[ii] != '.') {
        sbl1 = sbl1 + s[ii];
        ii++;
    }
    ii++;
    while (s[ii] != '.') {
        sbl2 = sbl2 + s[ii];
        ii++;
    }
    ii++;
    while (s[ii] != NULL) {
        sbl3 = sbl3 + s[ii];
        ii++;
    }

    //checking the blocks
    if (CheckBlock(sbl0) == 1 | CheckBlock(sbl1) == 1 | CheckBlock(sbl2) == 1 | CheckBlock(sbl3) == 1) return 1;

    return 0;
}

int CheckIp::CheckBlock(string s)
{
    int sizeb = s.size();
    //checking size of block
    if (sizeb > 3) return 1;
    string ss;
    for (int i = 0; i < sizeb; i++) {
        ss = s[i];
        if (CheckNumber(ss) == 1) return 1;
    }

    return 0;
}

int CheckIp::CheckNumber(string s)
{
    if (s == "0" | s == "1" | s == "2" | s == "3" | s == "4" | s == "5" | s == "6" | s == "7" | s == "8" | s == "9") {
        return 0;
    }
    else {
        return 1;
    }

}

Header:

    #pragma once
#include <string>

using namespace std;

ref class CheckIp
{
public:
    CheckIp();

    static int CheckWholeIp(string s);

private: static int CheckBlock(string s);

        static int CheckNumber(string s);

};

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