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util.go
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util.go
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/* Copyright (C) 2013 Matthias S. Benkmann
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this file (originally named util.go) and associated documentation files
* (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is furnished
* to do so, subject to the following conditions:
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
// Various re-usable utility functions.
package util // import "winterdrache.de/golib/util"
import (
"io"
"fmt"
"net"
"time"
"regexp"
"strings"
"crypto/md5"
"runtime/debug"
)
// Returns the md5sum of its argument as a string of hex digits.
func Md5sum(s string) string {
md5 := md5.New()
io.WriteString(md5, s)
return fmt.Sprintf("%x",md5.Sum(nil))
}
// Number of consecutive short writes before WriteAll() will give up
// ATTENTION! The wait time between tries increases exponetially, so don't
// blindly increase this number.
const write_all_max_tries = 8
// Calls g wrapped in a panic handler that logs the panic and recovers from it.
// Example:
// go util.WithPanicHandler(foobar)
// go util.WithPanicHandler(func(){ Send_foreign_job_updates(server, jobs) })
func WithPanicHandler(g func()) {
defer func() {
if x := recover(); x != nil {
Log(0, "PANIC! %v\n%v", x, string(debug.Stack()))
}
}()
g()
}
// Returns a new channel that will return start as first item and then
// always the next number.
func Counter(start uint64) chan uint64 {
c := make(chan uint64)
go func() {
for {
c<-start
start++
}
}()
return c
}
// Sleeps until time t. If clock is adjusted during the sleep, this will not
// cause more than 10 minutes extra sleep. In no case will this function return
// until time.Now() >= t.
func WaitUntil(t time.Time) {
// Wait in a for loop because clock might be adjusted while we're sleeping.
// ATTENTION! The check t.After(time.Now()) is NOT REDUNDANT with the check
// if dur <= 0 { return }
// A time.Duration has a limited range that can not express all differences
// between timestamps. Without the t.After(time.Now()) check, extreme timestamps
// in the past can cause large wait times due to overflow.
for ; t.After(time.Now()); {
dur := t.Sub(time.Now())
if dur <= 0 { return }
// wake up every 10 minutes to deal with clock adjustments (DST etc.)
if dur > 10*time.Minute { dur = 10*time.Minute }
time.Sleep(dur)
}
}
// Waits until either the duration timeout has passed or DNS is available
// ON A NON-LOOPBACK INTERFACE (so this waits until external interfaces are up).
// If timeout == 0, wait forever if necessary.
// Returns true if DNS is available.
func WaitForDNS(timeout time.Duration) bool {
var err error
endtime := time.Now().Add(timeout)
for {
var ifaces []net.Interface
ifaces, err = net.Interfaces()
if err == nil {
// find non-loopback interfaces that are up
for _, iface := range ifaces {
if iface.Flags & net.FlagLoopback != 0 { continue }
if iface.Flags & net.FlagUp == 0 { continue }
var addrs []net.Addr
addrs, err = iface.Addrs()
if err == nil {
// try to find a non-loopback IP address for that interface with rDNS
for _, addr := range addrs {
ip, _, err2 := net.ParseCIDR(addr.String())
if err2 == nil && !ip.IsLoopback() {
var names []string
names, err = net.LookupAddr(ip.String())
if err == nil && len(names) > 0 {
// sanity-check: lookup an address in the special reserved TEST IP range
// (this should never resolve to a name)
// and lookup the loopback address 127.0.0.1 (should always resolve)
_, err192 := net.LookupAddr("192.0.2.1")
_, err127 := net.LookupAddr("127.0.0.1")
if err192 != nil && err127 == nil { return true }
}
}
}
}
}
}
if timeout != 0 && time.Now().After(endtime) { break }
waittime := endtime.Sub(time.Now())
if waittime <= 0 || waittime > 1*time.Second { waittime = 1*time.Second }
time.Sleep(waittime)
}
return false
}
// Writes data to w, with automatic handling of short writes.
// A short write error will only be returned if multiple attempts
// failed in a row.
func WriteAll(w io.Writer, data []byte) (n int, err error) {
// Yeah, I know. Other people just ignore the issue of
// short writes. That's why their code fails more often than mine :-P
tries := write_all_max_tries
var bytes_written int
for n = 0; n < len(data); {
bytes_written, err = w.Write(data[n:])
n += bytes_written
if err != nil && err != io.ErrShortWrite {
return n, err
}
if bytes_written == 0 {
tries--
if tries <= 0 {
if err == nil {
err = io.ErrShortWrite
}
return n, err
}
// The first time we don't sleep. The 2nd time we sleep 1ms. The 3rd time 2ms.
// The 4th time 4ms. Then 8ms, 16ms, 32ms, 64ms,...
var wait time.Duration = (1 << (write_all_max_tries-2)) >> uint(tries)
time.Sleep(wait * time.Millisecond)
} else {
tries = write_all_max_tries // every time we succeed at writing we start tries again
}
}
return n, nil
}
// Opens a connection to target (e.g. "foo.example.com:20081"), sends msg followed
// by \r\n and then closes the connection.
// If timeout >= 0, then the connection will be terminated after at most this duration.
func SendLnTo(target string, msg string, timeout time.Duration) {
conn, err := net.Dial("tcp", target)
if err != nil {
Log(0, "ERROR! Dial: %v", err)
return
}
defer conn.Close()
SendLn(conn, msg, timeout)
}
// Sends strings via connection conn, followed by "\r\n"
// If timeout >= 0, then the send attempt will be aborted after at most this duration.
// Returns nil if sending was successful, an error otherwise. The error will also
// be sent to the log, so the caller does not have to log it.
func SendLn(conn net.Conn, s string, timeout time.Duration) error {
sendbuf := make([]byte, len(s)+2)
copy(sendbuf, s)
sendbuf[len(s)]='\r'
sendbuf[len(s)+1]='\n'
var deadline time.Time // zero value means "no deadline"
if timeout >= 0 { deadline = time.Now().Add(timeout) }
conn.SetWriteDeadline(deadline)
var no_deadline time.Time
defer conn.SetWriteDeadline(no_deadline)
_, err := WriteAll(conn, sendbuf)
if err != nil {
Log(0, "ERROR! WriteAll: %v", err)
}
return err
}
// Reads from the connection until \n is seen (or timeout or error) and
// returns the read data without any trailing \n or \r.
//
// If timeout > 0, then reading will stop after at most this duration and
// the function will return with an error. If timeout <= 0 there will be
// no timeout (any pre-existing read deadline will be cleared).
//
// If an error (or timeout) occurs before \n is seen, the data read up to
// the error is returned (without any trailing \r).
//
// You should probably give special treatment to the case of an io.EOF error
// being returned. This happens when the last line of the connection is not
// terminated by \n. It often makes sense to not treat this as an error.
//
// NOTE: This function reads individual bytes which means that data following
// the line read is still available for reading (in particular you can read
// subsequent lines by calling ReadLn() again). The drawback, however, is
// lower throughput compared to reading in chunks.
func ReadLn(conn net.Conn, timeout time.Duration) (string, error) {
var deadline time.Time // zero value means "no deadline"
if timeout > 0 { deadline = time.Now().Add(timeout) }
conn.SetReadDeadline(deadline)
var no_deadline time.Time
defer conn.SetReadDeadline(no_deadline)
var buf = make([]byte, 128)
var i int
var n int
var err error
for err == nil {
if i == len(buf) {
buf_new := make([]byte, len(buf)<<1)
copy(buf_new, buf)
buf = buf_new
}
n, err = conn.Read(buf[i:i+1]) // read one byte
i += n
// Did we read \n ?
if i > 0 && buf[i-1] == '\n' {
for ; i > 0 && (buf[i-1] == '\n' || buf[i-1] == '\r') ; { i-- }
return string(buf[0:i]), nil
}
}
for ; i > 0 && buf[i-1] == '\r' ; { i-- }
return string(buf[0:i]), err
}
// Sends a UDP wake-on-lan packet coded for the given macaddress to the
// broadcast address for the given host or network.
// host_or_net can be:
// a) a host name (with or without ":<port>")
// b) a host's IP address from which the broadcast address will be
// derived by setting final byte to 255
// c) a network's broadcast IP address
// If host_or_net includes a port that port will be used, otherwise the
// default port 40000 is used.
func Wake(macaddress string, host_or_net string) error {
hwaddr, err := net.ParseMAC(macaddress)
if err != nil { return err }
if strings.Index(host_or_net,":") < 0 { host_or_net += ":40000" }
udpaddr,err := net.ResolveUDPAddr("udp", host_or_net)
if err != nil { return err }
udpaddr.IP[len(udpaddr.IP)-1] = 255
udpconn,err := net.DialUDP("udp", nil, udpaddr)
if err != nil { return err }
payload := []byte{0xff,0xff,0xff,0xff,0xff,0xff}
for i := 0; i < 16; i++ { payload = append(payload, hwaddr...) }
_, err = udpconn.Write(payload)
return err
}
const re_1xx = "(1([0-9]?[0-9]?))"
const re_2xx = "(2([6-9]|([0-4][0-9]?)|(5[0-5]?))?)"
const re_xx = "([3-9][0-9]?)"
const re_port = "(0|([1-6][0-9]{0,4})|([7-9][0-9]{0,3}))"
const ip_part = "(0|"+re_1xx+"|"+re_2xx+"|"+re_xx+")"
var startsWithIPv4Regexp = regexp.MustCompile("^"+ip_part+"([.]"+ip_part+"){3}")
var endsWithPort = regexp.MustCompile(":"+re_port+"$")
// Takes either a HOST or a HOST:IP pair and replaces the HOST part with
// that machine's IP address (preferring an IPv4 address if there is one).
// If HOST is "localhost" or "::1", it will be replaced with "127.0.0.1".
// If HOST is already an IPv4 address, it will be kept.
// If there is only an IPv6 address available, it will be enclosed in "[...]"
// in the result (even if there is no port).
//
// If localip != "" in the result "127.0.0.1" will be replaced with localip.
//
// Returns the modified address or the original address with an error.
func Resolve(addr string, localip string) (string, error) {
if localip == "" { localip = "127.0.0.1" }
addr = strings.Replace(addr, "127.0.0.1", localip, 1)
if startsWithIPv4Regexp.MatchString(addr) { return addr, nil }
host := addr
port := ""
var err error
// the net.ParseIP() check tries to prevent confusing an IPv6 address for a port
if endsWithPort.MatchString(addr) && net.ParseIP(addr) == nil {
host, port, err = net.SplitHostPort(addr)
if err != nil { return addr, err }
port = ":" + port
}
if host == "localhost" || host == "::1" || host == "[::1]" {
return localip + port, nil
}
addrs, err := net.LookupIP(host)
if err != nil {
return addr, err
}
if len(addrs) == 0 { // I don't think this is possible but just in case...
return addr, fmt.Errorf("No IP address for %v", host)
}
// try to find an IPv4 non-loopback address
for _, a := range addrs {
if !a.IsLoopback() && a.To4() != nil { return a.String() + port, nil }
}
// try to find an IPv4 address (possibly loopback)
for _, a := range addrs {
if a.To4() != nil { return strings.Replace(a.String(), "127.0.0.1", localip, 1) + port, nil }
}
// take the first address (which is IPv6)
return "[" + addrs[0].String() + "]" + port, nil
}