91 lines
2.8 KiB
Go
91 lines
2.8 KiB
Go
package codespaces
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import (
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"context"
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"fmt"
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"os"
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"os/exec"
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"strconv"
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"strings"
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)
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// Shell runs an interactive secure shell over an existing
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// port-forwarding session. It runs until the shell is terminated
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// (including by cancellation of the context).
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func Shell(ctx context.Context, log logger, sshArgs []string, port int, destination string, usingCustomPort bool) error {
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cmd, connArgs, err := newSSHCommand(ctx, port, destination, sshArgs)
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if err != nil {
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return fmt.Errorf("failed to create ssh command: %w", err)
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}
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if usingCustomPort {
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log.Println("Connection Details: ssh " + destination + " " + strings.Join(connArgs, " "))
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}
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return cmd.Run()
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}
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// NewRemoteCommand returns an exec.Cmd that will securely run a shell
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// command on the remote machine.
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func NewRemoteCommand(ctx context.Context, tunnelPort int, destination string, sshArgs ...string) (*exec.Cmd, error) {
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cmd, _, err := newSSHCommand(ctx, tunnelPort, destination, sshArgs)
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return cmd, err
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}
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// newSSHCommand populates an exec.Cmd to run a command (or if blank,
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// an interactive shell) over ssh.
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func newSSHCommand(ctx context.Context, port int, dst string, cmdArgs []string) (*exec.Cmd, []string, error) {
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connArgs := []string{"-p", strconv.Itoa(port), "-o", "NoHostAuthenticationForLocalhost=yes"}
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// The ssh command syntax is: ssh [flags] user@host command [args...]
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// There is no way to specify the user@host destination as a flag.
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// Unfortunately, that means we need to know which user-provided words are
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// SSH flags and which are command arguments so that we can place
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// them before or after the destination, and that means we need to know all
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// the flags and their arities.
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cmdArgs, command, err := parseSSHArgs(cmdArgs)
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if err != nil {
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return nil, nil, err
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}
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cmdArgs = append(cmdArgs, connArgs...)
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cmdArgs = append(cmdArgs, "-C") // Compression
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cmdArgs = append(cmdArgs, dst) // user@host
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if command != nil {
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cmdArgs = append(cmdArgs, command...)
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}
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cmd := exec.CommandContext(ctx, "ssh", cmdArgs...)
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cmd.Stdout = os.Stdout
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cmd.Stdin = os.Stdin
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cmd.Stderr = os.Stderr
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return cmd, connArgs, nil
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}
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// parseSSHArgs parses SSH arguments into two distinct slices of flags and command.
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// It returns an error if a unary flag is provided without an argument.
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func parseSSHArgs(args []string) (cmdArgs, command []string, err error) {
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for i := 0; i < len(args); i++ {
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arg := args[i]
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if strings.HasPrefix(arg, "-") {
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cmdArgs = append(cmdArgs, arg)
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if len(arg) == 2 && strings.Contains("bcDeFIiLlmOopRSWw", arg[1:2]) {
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if i++; i == len(args) {
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return nil, nil, fmt.Errorf("ssh flag: %s requires an argument", arg)
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}
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cmdArgs = append(cmdArgs, args[i])
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}
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continue
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}
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// if we've started parsing the command, set it to the rest of the args
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command = args[i:]
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break
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}
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return cmdArgs, command, nil
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}
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