initial commit

3 files changed, 171 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..518a4e8
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/hose
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..5d66d44
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module git.samanthony.xyz/hose
+
+go 1.20
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..3c893f0
--- /dev/null
+++ b/main.go
@@ -0,0 +1,167 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"time"
+)
+
+const (
+	port    = 60321
+	timeout = time.Minute
+	usage   = "Usage: hose <host>"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Fprintf(os.Stderr, "%s\n", usage)
+		os.Exit(1)
+	}
+
+	remote, err := parseHost(os.Args[1])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to resolve host '%s'\n", os.Args[1])
+		os.Exit(1)
+	} else if remote == nil {
+		fmt.Fprintf(os.Stderr, "%s is not a valid IP address or host name\n",
+			os.Args[1])
+		os.Exit(1)
+	}
+
+	ifs, err := netIfs()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	} else if ifs == nil {
+		fmt.Fprintf(os.Stderr, "no suitable network interfaces\n")
+		os.Exit(1)
+	}
+
+	local, err := ip(ifs)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	} else if local == nil {
+		fmt.Fprintf(os.Stderr, "no suitable ip addresses\n")
+		os.Exit(1)
+	}
+
+	errs := make(chan error)
+	go listen(local, remote, errs)
+	go send(addr(remote, port), errs)
+
+	// Wait for goroutines.
+	nroutines := 2
+	for i := 0; i < nroutines; i++ {
+		if err := <-errs; err != nil {
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+		}
+	}
+}
+
+// listen listens on local for connections from remote and copies received data
+// to stdout. Sends exactly one (possible nil) error to errs.
+func listen(local, remote net.IP, errs chan error) {
+	l, err := net.Listen("tcp", addr(local, port))
+	if err != nil {
+		errs <- err
+		return
+	}
+
+	var c net.Conn
+	for {
+		c, err = l.Accept()
+		if err != nil {
+			errs <- err
+			return
+		}
+		host, _, err := net.SplitHostPort(c.RemoteAddr().String())
+		if err != nil {
+			errs <- err
+			return
+		}
+		if host := net.ParseIP(host); host != nil && host.Equal(remote) {
+			break
+		}
+	}
+
+	io.Copy(os.Stdout, c)
+
+	c.Close()
+	l.Close()
+	errs <- nil
+}
+
+// send sends data from stdin to addr. addr has the form "host:port" (see
+// net.Dial). Sends exactly one (possible nil) error to errs.
+func send(addr string, errs chan<- error) {
+	var d net.Dialer
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	c, err := d.DialContext(ctx, "tcp", addr)
+	if err != nil {
+		errs <- err
+		return
+	}
+
+	io.Copy(c, os.Stdin)
+
+	c.Close()
+	cancel()
+	errs <- nil
+}
+
+// addr joins an IP address and a port number into a full address. See net.Dial.
+func addr(ip net.IP, port uint) string {
+	return net.JoinHostPort(fmt.Sprintf("%s", ip), fmt.Sprintf("%d", port))
+}
+
+// s is either an IP address or a host name. Returns nil if is s neither a
+// valid IP nor hostname. Returns error if host lookup fails.
+func parseHost(s string) (net.IP, error) {
+	if ip := net.ParseIP(s); ip != nil {
+		return ip, nil
+	}
+	addrs, err := net.LookupIP(s)
+	if err != nil {
+		return nil, err
+	}
+	if len(addrs) < 1 {
+		return nil, nil
+	}
+	return addrs[0], nil
+}
+
+// netIfs returns a network interface that is up, running and not a loopback
+// interface. Returns nil if no such interface exists on the system.
+func netIfs() (*net.Interface, error) {
+	ifs, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	for _, i := range ifs {
+		if (i.Flags&net.FlagUp != 0) &&
+			(i.Flags&net.FlagRunning != 0) &&
+			(i.Flags&net.FlagLoopback == 0) {
+			return &i, nil
+		}
+	}
+	return nil, nil
+}
+
+// ip returns the first IP address bound to ifs or nil if none are bound.
+func ip(ifs *net.Interface) (net.IP, error) {
+	addrs, err := ifs.Addrs()
+	if err != nil {
+		return nil, err
+	} else if len(addrs) < 1 {
+		return nil, nil
+	}
+	ip, _, err := net.ParseCIDR(addrs[0].String())
+	if err != nil {
+		return nil, err
+	}
+	return ip, nil
+}