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lockdownconn.go
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lockdownconn.go
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package debugserver
import (
"bufio"
"bytes"
"encoding/hex"
"errors"
"io"
)
var (
ErrInvalidGDBServerPayload = errors.New("invalid payload")
)
type GDBServer struct {
rw io.ReadWriter
scanner *bufio.Scanner
}
// Implements wire level GDBServer protocol
func NewGDBServer(rw io.ReadWriter) *GDBServer {
scanner := bufio.NewScanner(rw)
scanner.Split(func(data []byte, atEOF bool) (int, []byte, error) {
const lenPacketSuffix = 3 // len("#00")
if atEOF && len(data) == 0 {
return 0, nil, nil
}
start := bytes.IndexRune(data, '$')
end := bytes.IndexRune(data, '#')
// Need more data
if start < 0 || end < 0 || len(data) < end+lenPacketSuffix {
return 0, nil, nil
}
// Invalid data
if end < start {
return 0, nil, ErrInvalidGDBServerPayload
}
// Strip the $ prefix before returning
return end + lenPacketSuffix, data[start+1 : end], nil
})
return &GDBServer{
rw: rw,
scanner: scanner,
}
}
func (*GDBServer) chksum(pck string) string {
sum := 0
for _, b := range pck {
sum += int(b)
}
return hex.EncodeToString([]byte{byte(sum % 256)})
}
func (g *GDBServer) formatPacket(pck string) string {
return "+$" + pck + "#" + g.chksum(pck)
}
func (g *GDBServer) Recv() (string, error) {
if g.scanner.Scan() == false {
return "", g.scanner.Err()
}
return g.scanner.Text(), nil
}
func (g *GDBServer) Send(req string) error {
pck := g.formatPacket(req)
if _, err := g.rw.Write([]byte(pck)); err != nil {
return err
}
return nil
}
func (g *GDBServer) Request(req string) (string, error) {
if err := g.Send(req); err != nil {
return "", err
}
return g.Recv()
}