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// Package params provides helpers for receiving setup payload from parent.
package params
import (
"encoding/gob"
"errors"
"os"
"strconv"
"syscall"
)
// ErrReceiveEnv is returned by [Receive] if setup fd is not present in environment.
var ErrReceiveEnv = errors.New("environment variable not set")
// Receive retrieves setup fd from the environment and receives params.
//
// The file descriptor written to the value pointed to by fdp must not be passed
// to any system calls. It is made available for ordering file descriptor only.
func Receive(key string, v any, fdp *int) (func() error, error) {
var setup *os.File
if s, ok := os.LookupEnv(key); !ok {
return nil, ErrReceiveEnv
} else {
if fd, err := strconv.Atoi(s); err != nil {
if _err := errors.Unwrap(err); _err != nil {
err = _err
}
return nil, err
} else {
setup = os.NewFile(uintptr(fd), "setup")
if setup == nil {
return nil, syscall.EDOM
}
if fdp != nil {
*fdp = fd
}
}
}
return setup.Close, gob.NewDecoder(setup).Decode(v)
}
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