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wrapper.go
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wrapper.go
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package cmdio
import (
"io"
"log"
"os"
"strconv"
"strings"
"syscall"
"github.com/pkg/errors"
"github.com/rikonor/go-cmdio/rand"
"golang.org/x/sync/errgroup"
)
// CloseFunc needs to be called to clean up resources
type CloseFunc func() error
// Wrap wraps a command such that it uses named pipes attached to the given readers and writers
// instead of using actual files.
func Wrap(rs []io.Reader, ws []io.Writer, execArgs []string) ([]string, CloseFunc, error) {
// Keep track of files to remove later
toRemove := []string{}
eg := &errgroup.Group{}
// Setup a slice of tmp args
tmpArgs := make([]string, len(execArgs))
for i := 0; i < len(execArgs); i++ {
arg := execArgs[i]
switch {
// Handle input file
case strings.HasPrefix(arg, "INPUT"):
// Get reader index
idxStr := strings.TrimPrefix(arg, "INPUT")
idx, err := strconv.Atoi(idxStr)
if err != nil {
return nil, nil, errors.Wrap(err, "failed to parse reader index from arg name")
}
pipeName := rand.String()
tmpArgs[i] = pipeName
// Create pipe file
if err := syscall.Mkfifo(pipeName, 0644); err != nil {
return nil, nil, errors.Wrap(err, "failed to create pipe")
}
// Add pipe to removal list
toRemove = append(toRemove, pipeName)
// Start copying from reader to pipe
eg.Go(func() error {
fIn, err := os.OpenFile(pipeName, os.O_WRONLY, os.ModeNamedPipe)
if err != nil {
return errors.Wrap(err, "failed to open pipe")
}
defer fIn.Close()
_, err = io.Copy(fIn, rs[idx-1])
return errors.Wrap(err, "failed to copy from reader to pipe")
})
// Handle output file
case strings.HasPrefix(arg, "OUTPUT"):
// Get writer index
idxStr := strings.TrimPrefix(arg, "OUTPUT")
idx, err := strconv.Atoi(idxStr)
if err != nil {
return nil, nil, errors.Wrap(err, "failed to parse writer index from arg name")
}
pipeName := rand.String()
tmpArgs[i] = pipeName
// Create pipe file
if err := syscall.Mkfifo(pipeName, 0644); err != nil {
return nil, nil, errors.Wrap(err, "failed to create pipe")
}
// Add pipe to removal list
toRemove = append(toRemove, pipeName)
// Start copying from pipe to writer
eg.Go(func() error {
fOut, err := os.OpenFile(pipeName, os.O_RDONLY, os.ModeNamedPipe)
if err != nil {
return errors.Wrap(err, "failed to open pipe")
}
defer fOut.Close()
_, err = io.Copy(ws[idx-1], fOut)
return errors.Wrap(err, "failed to copy from pipe to writer")
})
// Use arg as-is
default:
tmpArgs[i] = arg
}
}
// Setup cleanup function
closeFn := func() error {
// Remove pipe files
for _, fPath := range toRemove {
if err := os.Remove(fPath); err != nil {
return errors.Wrap(err, "failed to remove pipe")
}
}
return eg.Wait()
}
return tmpArgs, closeFn, nil
}
// WrapSimple wraps a command such that it uses named pipes attached to the given reader
// and writer instead of using actual files.
func WrapSimple(r io.Reader, w io.Writer, execArgs []string) ([]string, CloseFunc, error) {
// Setup pipe names
inPipe := rand.String()
outPipe := rand.String()
// Setup a slice of tmp args
tmpArgs := make([]string, len(execArgs))
// Prepare args
for i := 0; i < len(execArgs); i++ {
switch execArgs[i] {
case "INPUT":
tmpArgs[i] = inPipe
case "OUTPUT":
tmpArgs[i] = outPipe
default:
tmpArgs[i] = execArgs[i]
}
}
// Setup named pipes
if err := syscall.Mkfifo(inPipe, 0644); err != nil {
return nil, nil, err
}
if err := syscall.Mkfifo(outPipe, 0644); err != nil {
return nil, nil, err
}
eg := &errgroup.Group{}
// Pipe input
eg.Go(func() error {
fIn, err := os.OpenFile(inPipe, os.O_WRONLY, os.ModeNamedPipe)
if err != nil {
log.Fatal(err)
}
defer fIn.Close()
_, err = io.Copy(fIn, r)
return err
})
// Pipe output
eg.Go(func() error {
fOut, err := os.OpenFile(outPipe, os.O_RDONLY, os.ModeNamedPipe)
if err != nil {
log.Fatal(err)
}
defer fOut.Close()
_, err = io.Copy(w, fOut)
return err
})
// Setup cleanup function
closeFn := func() error {
if err := os.Remove(inPipe); err != nil {
return err
}
if err := os.Remove(outPipe); err != nil {
return err
}
return eg.Wait()
}
return tmpArgs, closeFn, nil
}