How to Implement Reverse DNS Look Up Cache? - GeeksforGeeks

How to Implement Reverse DNS Look Up Cache? - GeeksforGeeks
How to Implement Reverse DNS Look Up Cache? Reverse DNS look up is using an internet IP address to find a domain name.

How to implement Reverse DNS Look Up cache? Following are the operations needed from cache.
1) Add a IP address to URL Mapping in cache.
2) Find URL for a given IP address.

One solution is to use Hashing.

In this post, a Trie based solution is discussed. 

void insert(struct trieNode *root, char *ipAdd, char *URL)

{

    // Length of the ip address

    int len = strlen(ipAdd);

    struct trieNode *pCrawl = root;

 

    // Traversing over the length of the ip address.

    for (int level=0; level<len; level++)

    {

        // Get index of child node from current character

        // in ipAdd[].  Index must be from 0 to 10 where

        // 0 to 9 is used for digits and 10 for dot

        int index = getIndex(ipAdd[level]);

 

        // Create a new child if not exist already

        if (!pCrawl->child[index])

            pCrawl->child[index] = newTrieNode();

 

        // Move to the child

        pCrawl = pCrawl->child[index];

    }

 

    //Below needs to be carried out for the last node.

    //Save the corresponding URL of the ip address in the

    //last node of trie.

    pCrawl->isLeaf = true;

    pCrawl->URL = new char[strlen(URL) + 1];

    strcpy(pCrawl->URL, URL);

}

 

// This function returns URL if given IP address is present in DNS cache.

// Else returns NULL

char  *searchDNSCache(struct trieNode *root, char *ipAdd)

{

    // Root node of trie.

    struct trieNode *pCrawl = root;

    int  len = strlen(ipAdd);

 

    // Traversal over the length of ip address.

    for (int level=0; level<len; level++)

    {

        int index = getIndex(ipAdd[level]);

        if (!pCrawl->child[index])

            return NULL;

        pCrawl = pCrawl->child[index];

    }

 

    // If we find the last node for a given ip address, print the URL.

    if (pCrawl!=NULL && pCrawl->isLeaf)

        return pCrawl->URL;

 

    return NULL;

}

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