Detailed Examples

Example 1: Proxy All Servers Except Local Hosts

In this example, Netscape Navigator connects directly to all hosts that are not fully qualified and the ones that are in the local domain. Everything else goes through the proxy called w3proxy.example.com:8080.

If the proxy goes down, connections become direct automatically.

    function FindProxyForURL(url, host)
    {
        if (isPlainhost name(host) ||
            dnsDomainIs(host, ".example.com") ||
            dnsDomainIs(host, ".mcom.com"))
            return "DIRECT";
        else
            return "PROXY w3proxy.example.com:8080; DIRECT";
    }

Example 2: Proxy Local Servers Outside the Firewall

This example is like the previous one, but it uses the proxy for local servers that are outside the firewall. If there are hosts (such as the main web server) that belong to the local domain but are outside the firewall and are only reachable through the proxy server, those exceptions are handled using the localHostOrDomainIs() function:

    function FindProxyForURL(url, host)
    {
        if ((isPlainhost name(host) ||
        dnsDomainIs(host, ".example.com")) &&
        !localHostOrDomainIs(host, "www.example.com") &&
        !localHostOrDoaminIs(host, "merchant.example.com"))
            return "DIRECT";
        else
            return "PROXY w3proxy.example.com:8080; DIRECT";
    }

This example uses the proxy for everything except local hosts in the example.com domain. The hosts www.example.com and merchant.example.com also go through the proxy.

The order of the exceptions increases efficiency: localHostOrDomainIs() functions get executed only for URLs that are in the local domain, not for every URL. In particular, notice the parentheses around the or expression before the and expression.

Example 3: Proxy Only Unresolved Hosts

This example works in an environment where internal DNS is set up so that it can resolve only internal host names, and the goal is to use a proxy only for hosts that aren’t resolvable:

    function FindProxyForURL(url, host)
    {
        if (isResolvable(host))
                return "DIRECT";
            else
                return "PROXY proxy.mydomain.com:8080";
    }

This example requires consulting the DNS every time, so it should be grouped with other rules so that DNS is consulted only if other rules do not yield a result:

    function FindProxyForURL(url, host)
    {
        if (isPlainhost name(host) ||
            dnsDomainIs(host, ".mydomain.com") ||
            isResolvable(host))
            return "DIRECT";
        else
            return "PROXY proxy.mydomain.com:8080";
    }

Example 4: Connect Directly to a Subnet

In this example all the hosts in a given subnet are connected to directly others go through the proxy:

    function FindProxyForURL(url, host)
    {
        if (isInNet(host, "198.95.0.0", "255.255.0.0"))
            return "DIRECT";
        else
            return "PROXY proxy.mydomain.com:8080";
    }

You can minimize the use of DNS in this example by adding redundant rules in the beginning:

    function FindProxyForURL(url, host)
    {
        if (isPlainhost name(host) ||
            dnsDomainIs(host, ".mydomain.com") ||
            isInNet(host, "198.95.0.0", "255.255.0.0"))
            return "DIRECT";
        else
            return "PROXY proxy.mydomain.com:8080";
    }

Example 5: Balance Proxy Load with dnsDomainIs()

This example is more sophisticated. There are four proxy servers, with one of them acting as a hot standby for the others, so if any of the remaining three goes down, the fourth one takes over. The three remaining proxy servers share the load based on URL patterns, which makes their caching more effective (there is only one copy of any document on the three servers, as opposed to one copy on each of them). The load is distributed as shown in Example 5: Balance Proxy Load with dnsDomainIs().

All local accesses should be direct. All proxy servers run on port 8080. You can concatenate strings by using the + operator in JavaScript.

function FindProxyForURL(url, host)
{
    if (isPlainhost name(host) || dnsDomainIs(host, ".mydomain.com"))
        return "DIRECT";

    else if (dnsDomainIs(host, ".com"))
        return "PROXY proxy1.mydomain.com:8080; " +
              "PROXY proxy4.mydomain.com:8080";

    else if (dnsDomainIs(host, ".edu"))
        return "PROXY proxy2.mydomain.com:8080; " +
              "PROXY proxy4.mydomain.com:8080";

    else
        return "PROXY proxy3.mydomain.com:8080; " +
              "PROXY proxy4.mydomain.com:8080";
}

Example 6: Balance Proxy Load with shExpMatch()

This example is essentially the same as example 5, but instead of using dnsDomainIs(), this example uses shExpMatch().

    function FindProxyForURL(url, host)
    {
    if (isPlainhost name(host) || dnsDomainIs(host, ".mydomain.com"))
        return "DIRECT";
    else if (shExpMatch(host, "*.com"))
        return "PROXY proxy1.mydomain.com:8080; " +
              "PROXY proxy4.mydomain.com:8080";
    else if (shExpMatch(host, "*.edu"))
        return "PROXY proxy2.mydomain.com:8080; " +
              "PROXY proxy4.mydomain.com:8080";
    else
        return "PROXY proxy3.mydomain.com:8080; " +
              "PROXY proxy4.mydomain.com:8080";
    }

Example 7: Proxying a Specific Protocol

You can set a proxy to be for a specific protocol. Most of the standard JavaScript functionality is available for use in the FindProxyForURL() function. For example, to set different proxies based on the protocol, you can use the substring() function:

    function FindProxyForURL(url, host)
    {
        if (url.substring(0, 5) == "http:") {
            return "PROXY http-proxy.mydomain.com:8080";
        }
        else if (url.substring(0, 4) == "ftp:") {
            return "PROXY ftp-proxy.mydomain.com:8080";
        }
        else if (url.substring(0, 7) == "gopher:") {
            return "PROXY gopher-proxy.mydomain.com:8080";
        }
        else if         (url.substring(0, 6) == "https:" ||
                url.substring(0, 6) == "snews:") {
            return "PROXY security-proxy.mydomain.com:8080";
        }
        else {
            return "DIRECT";
        }
    }

You can also accomplish this using the shExpMatch() function; for example:

    ...
    if (shExpMatch(url, "http:*")) {
        return "PROXY http-proxy.mydomain.com:8080;
    }
    ...