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gurl.go
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gurl.go
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package main
import (
"flag"
"io"
"log"
"log/slog"
"math"
"net"
"net/netip"
"net/url"
"os"
"strconv"
"strings"
"syscall"
"time"
"github.com/soypat/netif"
"github.com/soypat/seqs"
"github.com/soypat/seqs/eth/dns"
"github.com/soypat/seqs/httpx"
"github.com/soypat/seqs/stacks"
)
const connTimeout = 5 * time.Second
const ourHost = "gurl"
const dnsTimeout = 4 * time.Second
const arpTimeout = 1 * time.Second
func main() {
var (
flagInterface string
serverPort uint16
flagLogLevel int
flagRequestedIP string
flagDNS string
flagLocalport int
)
// Create device interface.
iface, err := netif.DefaultInterface()
if err != nil {
iface, err = net.InterfaceByIndex(1)
if err != nil {
log.Fatal("no interfaces found:", err)
}
}
flag.IntVar(&flagLocalport, "hostport", 8877, "Outgoing TCP port.")
flag.StringVar(&flagDNS, "dns", "", "DNS IP to seek.")
flag.StringVar(&flagInterface, "i", iface.Name, "Interface to use")
flag.StringVar(&flagRequestedIP, "hostip", "", "IP address to request by DHCP.")
flag.IntVar(&flagLogLevel, "l", int(slog.LevelInfo), "Log level")
flag.Parse()
if flag.NArg() > 1 {
log.Fatal("too many arguments")
} else if flagLocalport < 1 || flagLocalport > math.MaxUint16 {
log.Fatal("invalid port ", flagLocalport)
}
// Parse URL and validate it.
argURL := flag.Arg(0)
if argURL == "" {
log.Fatal("URL is required")
}
URL, err := url.Parse(argURL)
if err != nil {
log.Fatal(err)
}
svHostname := URL.Host
if newhost, sport, ok := strings.Cut(svHostname, ":"); ok {
svHostname = newhost
p, err := strconv.Atoi(sport)
if err != nil || p < 1 || p > 65535 {
log.Fatal("invalid port w/ parse err:", err)
}
serverPort = uint16(p)
}
if serverPort == 0 {
serverPort = 80 // Sensible default if not present.
}
// Create structured logger.
fp, _ := os.Create("http-client.log")
logger := slog.New(slog.NewTextHandler(io.MultiWriter(fp, os.Stdout), &slog.HandlerOptions{
Level: slog.Level(flagLogLevel),
}))
slog.Info("url", slog.String("url", URL.String()), slog.String("uri", URL.RequestURI()), slog.String("host", svHostname), slog.Uint64("port", uint64(serverPort)))
// Check whether we need to resolve hostname.
_, dnsErr := dns.NewName(svHostname)
serverAddr, ipErr := netip.ParseAddr(svHostname)
if dnsErr != nil && ipErr != nil {
log.Fatal("invalid hostname", dnsErr, ipErr)
}
// OK, all pre-processing is done, lets open the socket and start the client.
// This performs a DHCP setup to acquire network data.
ethsock, err := netif.NewEthSocket(flagInterface)
if err != nil {
log.Fatal("ethernet socket:" + err.Error())
}
var DNSServers []netip.Addr
if flagDNS != "" {
ip, err := netip.ParseAddr(flagDNS)
if err != nil {
log.Fatal("failed to parse dns flag:", err.Error())
}
DNSServers = append(DNSServers, ip)
}
engine, err := netif.NewEngine(ethsock, netif.EngineConfig{
MaxOpenPortsUDP: 1,
MaxOpenPortsTCP: 1,
Logger: logger,
Hostname: ourHost,
AddrMethod: netif.AddrMethodDHCP,
DNSServers: DNSServers,
})
if err != nil {
log.Fatal("netif.Engine create:" + err.Error())
}
go func() {
stalled := 0
for {
rx, tx, err := engine.HandlePoll()
if err != nil {
log.Println("engine poll:" + err.Error())
}
if rx == 0 && tx == 0 {
// Exponential backoff.
stalled += 1
sleep := time.Duration(1) << stalled
if sleep > 1*time.Second {
sleep = 1 * time.Second
}
time.Sleep(sleep)
} else {
stalled = 0
}
}
}()
err = engine.WaitForDHCP(5 * time.Second)
if err != nil {
log.Fatal("dhcp:" + err.Error())
}
if ipErr != nil {
// We have a hostname we must resolve.
resolver := engine.NewResolver(dns.ClientPort, dnsTimeout)
addrs, err := resolver.LookupNetIP(URL.Host)
if err != nil {
panic("DNS lookup failed:" + err.Error())
}
serverAddr = addrs[0]
}
// Create the HTTP request data.
var req httpx.RequestHeader
req.SetRequestURI(URL.RequestURI())
req.SetMethod("GET")
req.SetHost(svHostname)
reqbytes := req.Header()
// Reserve the underlying Linux socket so that
// the kernel does not reset the connection automatically.
// Bind TCP socket so underlying OS does not reset the connection.
// https://widu.tumblr.com/post/43624355124/suppressing-tcp-rst-on-raw-sockets
ourPort := uint16(flagLocalport)
err = bindTCPPort(netip.AddrPortFrom(engine.Addr(), ourPort))
if err != nil {
log.Fatal(err)
}
rxBuf := make([]byte, iface.MTU*8)
retries := 5
for retries > 0 {
retries--
slog.Info("dialing", slog.String("serveraddr", serverAddr.String()), slog.Uint64("our-port", uint64(ourPort)))
netconn, err := engine.DialTCP(ourPort, time.Now().Add(connTimeout), netip.AddrPortFrom(serverAddr, serverPort))
if err != nil {
panic("conn create:" + err.Error())
}
conn := netconn.(*stacks.TCPConn)
if conn.State() != seqs.StateEstablished {
panic("conn state:" + conn.State().String())
}
// Send the request.
_, err = conn.Write(reqbytes)
if err != nil {
log.Println("writing request:" + err.Error())
continue
}
// time.Sleep(500 * time.Millisecond)
conn.SetDeadline(time.Now().Add(connTimeout))
n, err := conn.Read(rxBuf)
if n == 0 && err != nil {
log.Println("reading response:" + err.Error())
continue
} else if n == 0 {
log.Println("no response:" + err.Error())
continue
}
logger.Info("response", slog.String("response", string(rxBuf[:n])))
os.Stdout.Write(rxBuf[:n])
return
}
os.Stderr.Write([]byte("failed to connect to server\n"))
os.Exit(1)
}
// This does not seem to be working.
func bindTCPPort(addr netip.AddrPort) error {
fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_STREAM, syscall.IPPROTO_TCP)
if err != nil {
return err
}
err = syscall.Bind(fd, &syscall.SockaddrInet4{
Port: int(addr.Port()),
Addr: addr.Addr().As4(),
})
if err != nil {
return err
}
return syscall.Listen(fd, 1)
}