src.elv.sh@v0.21.0-dev.0.20240515223629-06979efb9a2a/pkg/cli/examples/e3bc/bc/bc.go (about)

     1  package bc
     2  
     3  import (
     4  	"io"
     5  	"log"
     6  	"os"
     7  	"os/exec"
     8  )
     9  
    10  type Bc interface {
    11  	Exec(string) error
    12  	Quit()
    13  }
    14  
    15  type bc struct {
    16  	cmd    *exec.Cmd
    17  	stdin  io.WriteCloser
    18  	stdout io.ReadCloser
    19  }
    20  
    21  func Start() Bc {
    22  	cmd := exec.Command("bc")
    23  	stdin, err := cmd.StdinPipe()
    24  	if err != nil {
    25  		log.Fatal(err)
    26  	}
    27  	stdout, err := cmd.StdoutPipe()
    28  	if err != nil {
    29  		log.Fatal(err)
    30  	}
    31  	cmd.Stderr = os.Stderr
    32  	cmd.Start()
    33  	return &bc{cmd, stdin, stdout}
    34  }
    35  
    36  // TODO: Use a more robust marker
    37  var inputSuffix = []byte("\n\"\x04\"\n")
    38  
    39  func (bc *bc) Exec(code string) error {
    40  	bc.stdin.Write([]byte(code))
    41  	bc.stdin.Write(inputSuffix)
    42  	for {
    43  		b, err := readByte(bc.stdout)
    44  		if err != nil {
    45  			return err
    46  		}
    47  		if b == 0x04 {
    48  			break
    49  		}
    50  		os.Stdout.Write([]byte{b})
    51  	}
    52  	return nil
    53  }
    54  
    55  func readByte(r io.Reader) (byte, error) {
    56  	var buf [1]byte
    57  	_, err := r.Read(buf[:])
    58  	if err != nil {
    59  		return 0, err
    60  	}
    61  	return buf[0], nil
    62  }
    63  
    64  func (bc *bc) Quit() {
    65  	bc.stdin.Close()
    66  	bc.cmd.Wait()
    67  	bc.stdout.Close()
    68  }