Function Examples

This section provides detailed examples of the JavaScript functions.

Example 1: Proxy All Servers Except Local Hosts

In this example, the browser connects directly to all hosts that are not fully qualified and the ones that are in the local domain. All other hosts go through the proxy called w3proxy.example.com:8080.

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Note –

If the proxy goes down, connections become direct automatically.

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    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 resembles Example 1: Proxy All Servers Except Local Hosts, but it uses the proxy for local servers that are outside the firewall. If hosts such as the main web server 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 all hosts 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 resolves only internal host names. 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. Therefore, you would group this example 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. Other hosts 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. The example uses four proxy servers, with one of them acting as a hot standby for the others. If any of the remaining three proxy servers 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. Only one copy of any document exists on the three servers, as opposed to one copy on each of them. The load is distributed as shown in the following table.

Table 17–3 Balance Proxy Load

Proxy	Purpose
#1	.com domain
#2	.edu domain
#3	all other domains
#4	hot standby

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

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: Balance Proxy Load With dnsDomainIs()(), 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 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 configuration by using the shExpMatch()() function; for example:

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