Initial commit
Add a work-in-progress demo chat server with TLS autodetection. It needs to be perfected before I move on to writing an IRCd on the foundations. If history is of any indication, this might lead towards a nice set of applications.
This commit is contained in:
commit
b5b64db075
GPG Key ID:
A0420B94F92B9493
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/build
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Copyright (c) 2018, Přemysl Janouch <p@janouch.name>
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Permission to use, copy, modify, and/or distribute this software for any
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purpose with or without fee is hereby granted.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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//
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// Copyright (c) 2018, Přemysl Janouch <p@janouch.name>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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//
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// This is an example TLS-autodetecting chat server.
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//
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// You may connect to it either using:
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// telnet localhost 1234
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// or
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// openssl s_client -connect localhost:1234
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package main
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import (
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"bufio"
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"crypto/tls"
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"flag"
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"fmt"
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"io"
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"log"
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"net"
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"os"
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"os/signal"
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"syscall"
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"time"
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)
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// --- Utilities ---------------------------------------------------------------
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// Trivial SSL/TLS autodetection. The first block of data returned by Recvfrom
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// must be at least three octets long for this to work reliably, but that should
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// not pose a problem in practice. We might try waiting for them.
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//
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// SSL2: 1xxx xxxx | xxxx xxxx | <1>
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// (message length) (client hello)
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// SSL3/TLS: <22> | <3> | xxxx xxxx
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// (handshake)| (protocol version)
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//
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func detectTLS(sysconn syscall.RawConn) bool {
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isTLS := false
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sysconn.Read(func(fd uintptr) (done bool) {
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var buf [3]byte
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n, _, err := syscall.Recvfrom(int(fd), buf[:], syscall.MSG_PEEK)
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switch {
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case n == 3:
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isTLS = buf[0]&0x80 != 0 && buf[2] == 1
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fallthrough
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case n == 2:
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isTLS = buf[0] == 22 && buf[1] == 3
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case n == 1:
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isTLS = buf[0] == 22
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case err == syscall.EAGAIN:
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return false
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}
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return true
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})
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return isTLS
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}
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// --- Declarations ------------------------------------------------------------
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type connCloseWrite interface {
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net.Conn
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CloseWrite() error
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}
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type client struct {
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transport net.Conn // underlying connection
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tls *tls.Conn // TLS, if detected
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conn connCloseWrite // high-level connection
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connReady bool // conn is safe to read from the main goroutine
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inQ []byte // unprocessed input
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outQ []byte // unprocessed output
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writing bool // whether a writing goroutine is running
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inShutdown bool // whether we're closing connection
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}
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type readEvent struct {
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client *client // client
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data []byte // new data from the client
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err error // read error
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}
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type writeEvent struct {
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client *client // client
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written int // amount of bytes written
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err error // write error
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}
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var (
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sigs = make(chan os.Signal, 1)
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conns = make(chan net.Conn)
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reads = make(chan readEvent)
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writes = make(chan writeEvent)
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tlsConf *tls.Config
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clients = make(map[*client]bool)
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listener net.Listener
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inShutdown bool
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shutdownTimer <-chan time.Time
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)
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// --- Server ------------------------------------------------------------------
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// Broadcast to all /other/ clients (telnet-friendly, also in accordance to
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// the plan of extending this to an IRCd).
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func broadcast(line string, except *client) {
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for c := range clients {
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if c != except {
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c.send(line)
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}
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}
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}
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func initiateShutdown() {
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log.Println("shutting down")
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if err := listener.Close(); err != nil {
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log.Println(err)
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}
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for c := range clients {
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c.kill()
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}
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shutdownTimer = time.After(3 * time.Second)
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inShutdown = true
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}
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func forceShutdown(reason string) {
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log.Printf("forced shutdown (%s)\n", reason)
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for c := range clients {
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c.destroy()
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}
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}
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// --- Client ------------------------------------------------------------------
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func (c *client) send(line string) {
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if !c.inShutdown {
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c.outQ = append(c.outQ, (line + "\r\n")...)
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c.flushOutQ()
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}
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}
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func (c *client) shutdown() {
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if c.inShutdown {
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log.Println("client double shutdown")
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return
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}
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// TODO: We must set a timer and destroy the client on timeout. Since we
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// have a central event loop, we probably need an event. Since we also
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// seem to need an event for TLS autodetection because of conn, we might
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// want to send an enumeration value.
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c.inShutdown = true
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c.conn.CloseWrite()
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}
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// Tear down the client connection, trying to do so in a graceful manner.
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func (c *client) kill() {
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if c.connReady {
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c.send("Goodbye")
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c.shutdown()
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} else {
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c.destroy()
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}
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}
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// Close the connection and forget about the client.
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func (c *client) destroy() {
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// Try to send a "close notify" alert if the TLS object is ready,
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// otherwise just tear down the transport.
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if c.connReady {
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_ = c.conn.Close()
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} else {
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_ = c.transport.Close()
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}
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delete(clients, c)
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}
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// Handle the results from trying to read from the client connection.
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func (c *client) onRead(data []byte, readErr error) {
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c.inQ = append(c.inQ, data...)
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for {
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advance, token, _ := bufio.ScanLines(c.inQ, false /* atEOF */)
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c.inQ = c.inQ[advance:]
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if advance == 0 {
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break
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}
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line := string(token)
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fmt.Println(line)
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broadcast(line, c)
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}
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// TODO: Inform the client about the inQ overrun in the farewell message.
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if len(c.inQ) > 8192 {
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c.kill()
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return
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}
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if readErr == io.EOF {
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// TODO: What if we're already in shutdown?
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c.shutdown()
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} else if readErr != nil {
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log.Println(readErr)
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c.destroy()
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}
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}
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// Spawn a goroutine to flush the outQ if possible and necessary. If the
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// connection is not ready yet, it needs to be retried as soon as it becomes.
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func (c *client) flushOutQ() {
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if c.connReady && !c.writing {
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go write(c, c.outQ)
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c.writing = true
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}
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}
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// Handle the results from trying to write to the client connection.
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func (c *client) onWrite(written int, writeErr error) {
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c.outQ = c.outQ[written:]
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c.writing = false
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if writeErr != nil {
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log.Println(writeErr)
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c.destroy()
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} else if len(c.outQ) > 0 {
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c.flushOutQ()
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} else if c.inShutdown {
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c.destroy()
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}
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}
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// --- Worker goroutines -------------------------------------------------------
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func accept(ln net.Listener) {
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// TODO: Consider specific cases in error handling, some errors
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// are transitional while others are fatal.
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for {
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if conn, err := ln.Accept(); err != nil {
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log.Println(err)
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} else {
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conns <- conn
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}
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}
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}
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func read(client *client) {
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// TODO: Either here or elsewhere we need to set a timeout.
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client.conn = client.transport.(connCloseWrite)
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if sysconn, err := client.transport.(syscall.Conn).SyscallConn(); err != nil {
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// This is just for the TLS detection and doesn't need to be fatal.
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log.Println(err)
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} else if detectTLS(sysconn) {
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client.tls = tls.Server(client.transport, tlsConf)
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client.conn = client.tls
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}
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// TODO: Signal the main goroutine that conn is ready. In fact, the upper
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// part could be mostly moved to the main goroutine and we'd only spawn
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// a thin wrapper around detectTLS, sending back {*client, bool}. Heck,
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// I could get rid of connReady.
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// A new buffer is allocated each time we receive some bytes, because of
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// thread-safety. Therefore the buffer shouldn't be too large, or we'd
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// need to copy it each time into a precisely sized new buffer.
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var err error
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for err == nil {
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var (
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buf [512]byte
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n int
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)
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n, err = client.conn.Read(buf[:])
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reads <- readEvent{client, buf[:n], err}
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}
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}
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// Flush outQ, which is passed by parameter so that there are no data races.
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func write(client *client, data []byte) {
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// We just write as much as we can, the main goroutine does the looping.
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n, err := client.conn.Write(data)
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writes <- writeEvent{client, n, err}
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}
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// --- Main --------------------------------------------------------------------
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func processOneEvent() {
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select {
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case <-sigs:
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if inShutdown {
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forceShutdown("requested by user")
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} else {
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initiateShutdown()
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}
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case <-shutdownTimer:
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forceShutdown("timeout")
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case conn := <-conns:
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log.Println("accepted client connection")
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c := &client{transport: conn}
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clients[c] = true
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go read(c)
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case ev := <-reads:
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log.Println("received data from client")
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if _, ok := clients[ev.client]; ok {
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ev.client.onRead(ev.data, ev.err)
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}
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case ev := <-writes:
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log.Println("sent data to client")
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if _, ok := clients[ev.client]; ok {
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ev.client.onWrite(ev.written, ev.err)
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}
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}
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}
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func main() {
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// Just deal with unexpected flags, we don't use any ourselves.
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flag.Parse()
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if len(flag.Args()) != 3 {
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log.Fatalf("usage: %s KEY CERT ADDRESS\n", os.Args[0])
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}
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cert, err := tls.LoadX509KeyPair(flag.Arg(1), flag.Arg(0))
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if err != nil {
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log.Fatalln(err)
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}
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tlsConf = &tls.Config{Certificates: []tls.Certificate{cert}}
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listener, err = net.Listen("tcp", flag.Arg(2))
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if err != nil {
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log.Fatalln(err)
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}
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go accept(listener)
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signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
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for !inShutdown || len(clients) > 0 {
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processOneEvent()
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}
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}
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