Implement sockline!

1 files changed, 133 insertions, 0 deletions

diff --git a/sockline/sockline.go b/sockline/sockline.go
new file mode 100644
index 0000000..daa4766
--- /dev/null
+++ b/sockline/sockline.go
@@ -0,0 +1,133 @@
+// Copyright 2019  Luke Shumaker <lukeshu@parabola.nu>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"runtime"
+	"syscall"
+)
+
+func socketpair(domain, typ, proto int) (*os.File, *os.File, error) {
+	fd, err := syscall.Socketpair(domain, typ|syscall.SOCK_CLOEXEC|syscall.SOCK_NONBLOCK, proto)
+	// passing SOCK_CLOEXEC or SOCK_NONBLECK to socketpair()
+	// requires Linux 2.6.27 and Go's minimum requirement is
+	// 2.6.23, so it might not be implemented.  Similar story on
+	// FreeBSD.
+	if (runtime.GOOS == "linux" && err == syscall.ENOSYS) || (runtime.GOOS == "freebsd" && err == syscall.EPROTONOSUPPORT) {
+		syscall.ForkLock.RLock()
+		fd, err = syscall.Socketpair(domain, typ, proto)
+		if err != nil {
+			syscall.ForkLock.RUnlock()
+			return nil, nil, os.NewSyscallError("socketpair", err)
+		}
+		syscall.CloseOnExec(fd[0])
+		syscall.CloseOnExec(fd[1])
+		syscall.ForkLock.RUnlock()
+		if err = syscall.SetNonblock(fd[0], true); err != nil {
+			return nil, nil, os.NewSyscallError("setnonblock", err)
+		}
+		if err = syscall.SetNonblock(fd[1], true); err != nil {
+			return nil, nil, os.NewSyscallError("setnonblock", err)
+		}
+		return nil, nil, os.NewSyscallError("setnonblock", err)
+	} else if err != nil {
+		return nil, nil, os.NewSyscallError("socketpair", err)
+	}
+
+	return os.NewFile(uintptr(fd[0]), "|0"), os.NewFile(uintptr(fd[1]), "|1"), nil
+}
+
+func sockline(cmdlines []string) (err error) {
+	cmds := make([]*exec.Cmd, len(cmdlines))
+	defer func() {
+		for i := range cmds {
+			if cmds[i] == nil {
+				break
+			}
+			if cerr := cmds[i].Wait(); cerr != nil {
+				if err == nil {
+					err = cerr
+				}
+			}
+		}
+	}()
+
+	for i := range cmdlines {
+		cmds[i] = &exec.Cmd{
+			Path:   "/bin/sh",
+			Args:   []string{os.Args[0], "-c", cmdlines[i]},
+			Stderr: os.Stderr,
+		}
+		switch i {
+		case 0:
+			cmds[i].Stdin = os.Stdin
+		default:
+			if cmds[i].Stdin, cmds[i-1].Stdout, err = socketpair(syscall.AF_UNIX, syscall.SOCK_STREAM, 0); err != nil {
+				cmds[i-1] = nil
+				return
+			}
+			if err = cmds[i-1].Start(); err != nil {
+				cmds[i-1] = nil
+				return
+			}
+			_ = cmds[i-1].Stdin.(*os.File).Close()
+			_ = cmds[i-1].Stdout.(*os.File).Close()
+		}
+	}
+	cmds[len(cmds)-1].Stdout = os.Stdout
+	if err = cmds[len(cmds)-1].Start(); err != nil {
+		cmds[len(cmds)-1] = nil
+		return
+	}
+
+	return
+}
+
+func usage(w io.Writer) {
+	fmt.Fprintf(w, "Usage: %s 'COMMAND LINE 1' 'COMMAND LINE 2'...\n", os.Args[0])
+	fmt.Fprintf(w, "   or: %s <-h|--help>\n", os.Args[0])
+	fmt.Fprintf(w, "Like a shell pipeline, but uses AF_UNIX socket pairs instead of pipes\n")
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		usage(os.Stderr)
+		os.Exit(2)
+	}
+	if os.Args[1] == "-h" || os.Args[1] == "--help" {
+		usage(os.Stdout)
+		os.Exit(0)
+	}
+	err := sockline(os.Args[1:])
+	if err != nil {
+		if ee, ok := err.(*exec.ExitError); ok {
+			ws := ee.ProcessState.Sys().(syscall.WaitStatus)
+			switch {
+			case ws.Exited():
+				os.Exit(ws.ExitStatus())
+			case ws.Signaled():
+				os.Exit(128 + int(ws.Signal()))
+			}
+		} else {
+			fmt.Fprintf(os.Stderr, "%s: error: %v\n", os.Args[0], err)
+			os.Exit(255)
+		}
+	}
+}