pac.go

package main

import (
	"bytes"
	"fmt"
	"net"
	"text/template"
)

var pac struct {
	template *template.Template
}

func init() {
	const pacRawTmpl = `var direct = 'DIRECT';
var httpProxy = 'PROXY {{.ProxyAddr}}; DIRECT';

var domainList = [
"{{.DirectDomains}}"
];

var directAcc = [];
for (var i = 0; i < domainList.length; i += 1) {
	directAcc[domainList[i]] = true;
}

// hostIsIP determines whether a host address is an IP address and whether
// it is private. Currenly only handles IPv4 addresses.
function hostIsIP(host) {
	var part = host.split('.');
	if (part.length != 4) {
		return [false, false];
	}
	var n;
	for (var i = 3; i >= 0; i--) {
		if (part[i].length === 0 || part[i].length > 3) {
			return [false, false];
		}
		n = Number(part[i]);
		if (isNaN(n) || n < 0 || n > 255) {
			return [false, false];
		}
	}
	if (part[0] == '127' || part[0] == '10' || (part[0] == '192' && part[1] == '168')) {
		return [true, true];
	}
	if (part[0] == '172') {
		n = Number(part[1]);
		if (16 <= n && n <= 31) {
			return [true, true];
		}
	}
	return [true, false];
}

function host2Domain(host) {
	var arr, isIP, isPrivate;
	arr = hostIsIP(host);
	isIP = arr[0];
	isPrivate = arr[1];
	if (isPrivate) {
		return "";
	}
	if (isIP) {
		return host;
	}

	var lastDot = host.lastIndexOf('.');
	if (lastDot === -1) {
		return ""; // simple host name has no domain
	}
	// Find the second last dot
	dot2ndLast = host.lastIndexOf(".", lastDot-1);
	if (dot2ndLast === -1)
		return host;

	return host.substring(dot2ndLast+1);
}

function FindProxyForURL(url, host) {
	if (url.substring(0,4) == "ftp:")
		return direct;
	if (host.substring(0,7) == "::ffff:")
		return direct;
	if (host.indexOf(".local", host.length - 6) !== -1) {
		return direct;
	}
	return (directAcc[host] || directAcc[host2Domain(host)]) ? direct : httpProxy;
}
`
	var err error
	pac.template, err = template.New("pac").Parse(pacRawTmpl)
	if err != nil {
		Fatal("Internal error on generating pac file template:", err)
	}

}

// No need for content-length as we are closing connection
var pacHeader = []byte("HTTP/1.1 200 OK\r\nServer: meow-proxy\r\n" +
	"Content-Type: application/x-ns-proxy-autoconfig\r\nConnection: close\r\n\r\n")

// Different client will have different proxy URL, so generate it upon each request.
func genPAC(c *clientConn) []byte {
	buf := new(bytes.Buffer)

	hproxy, ok := c.proxy.(*httpProxy)
	if !ok {
		panic("sendPAC should only be called for http proxy")
	}

	proxyAddr := hproxy.addrInPAC
	if proxyAddr == "" {
		host, _, err := net.SplitHostPort(c.LocalAddr().String())
		// This is the only check to split host port on tcp addr's string
		// representation in meow. Keep it so we will notice if there's any
		// problem in the future.
		if err != nil {
			panic("split host port on local address error")
		}
		proxyAddr = net.JoinHostPort(host, hproxy.port)
	}

	directDomains := ""
	for k, v := range domainList.Domain {
		if v == domainTypeDirect {
			directDomains += k + "\",\n\""
		}
	}

	if directDomains == "" {
		// Empty direct domain list
		buf.Write(pacHeader)
		pacproxy := fmt.Sprintf("function FindProxyForURL(url, host) { return 'PROXY %s; DIRECT'; };",
			proxyAddr)
		buf.Write([]byte(pacproxy))
		return buf.Bytes()
	}

	data := struct {
		ProxyAddr     string
		DirectDomains string
	}{
		proxyAddr,
		directDomains,
	}

	buf.Write(pacHeader)
	if err := pac.template.Execute(buf, data); err != nil {
		errl.Println("Error generating pac file:", err)
		panic("Error generating pac file")
	}
	return buf.Bytes()
}

func sendPAC(c *clientConn) error {
	_, err := c.Write(genPAC(c))
	if err != nil {
		debug.Printf("cli(%s) error sending PAC: %s", c.RemoteAddr(), err)
	}
	return err
}