1 files changed, 131 insertions, 0 deletions
diff --git a/client/cmd.go b/client/cmd.go
new file mode 100644
index 0000000..b69880c
--- /dev/null
+++ b/client/cmd.go
@@ -0,0 +1,131 @@
+package client
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os/exec"
+	"strings"
+)
+
+func (c client) princExists(ctx context.Context, name string) (exists bool, err error) {
+	out, err := c.execKrbAdmin(ctx, fmt.Sprintf("getprinc \"%s\"", name), func(writer io.WriteCloser) error { return nil })
+	if err != nil {
+		err = fmt.Errorf("%s (output: %s)", err, out)
+		return
+	}
+
+	if strings.Contains(out, "Principal does not exist") {
+		exists = false
+	} else if strings.Contains(out, "Expiration date: ") {
+		exists = true
+	} else {
+		err = fmt.Errorf("unrecognised output format: %s", out)
+	}
+
+	return
+}
+
+func (c client) doCreatePrinc(ctx context.Context, name string, password string) (err error) {
+	out, err := c.execKrbAdmin(ctx, fmt.Sprintf("addprinc \"%s\"", name), func(writer io.WriteCloser) error {
+		toWrite := append([]byte(password), '\n')
+		for i := 0; i < 2; i++ {
+			n, err := writer.Write(toWrite)
+			if err != nil || n != len(toWrite) {
+				return fmt.Errorf("error writing to stdin: %s", err)
+			}
+		}
+		return nil
+	})
+
+	if err != nil {
+		return
+	}
+
+	if !strings.Contains(out, "created") {
+		err = fmt.Errorf("unrecognised output format: %s", out)
+	}
+
+	return
+}
+
+func (c client) doChangePassword(ctx context.Context, name string, password string) (err error) {
+	out, err := c.execKrbAdmin(ctx, fmt.Sprintf("cpw \"%s\"", name), func(writer io.WriteCloser) error {
+		toWrite := append([]byte(password), '\n')
+		for i := 0; i < 2; i++ {
+			n, err := writer.Write(toWrite)
+			if err != nil || n != len(toWrite) {
+				return fmt.Errorf("error writing to stdin: %s", err)
+			}
+		}
+		return nil
+	})
+
+	if err != nil {
+		return
+	}
+
+	if !strings.Contains(out, "changed") {
+		err = fmt.Errorf("unrecognised output format: %s", out)
+	}
+
+	return
+}
+
+// execKrbAdmin starts krbadmin with the appropriate commands, and tries to authenticate as the admin principal
+func (c client) execKrbAdmin(ctx context.Context, query string, writeFunc func(writer io.WriteCloser) error) (string, error) {
+	kadm, err := exec.LookPath("kadmin")
+	if err != nil {
+		return "", fmt.Errorf("error finding kadmin executable: %s", err)
+	}
+	cmd := exec.CommandContext(
+		ctx,
+		kadm,
+		"-p",
+		c.config.Username,
+		"-r",
+		c.config.Realm,
+		"-s",
+		c.config.KAdminServer,
+		"-q",
+		query,
+	)
+
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return "", fmt.Errorf("error getting stdin pipe: %s", err)
+	}
+
+	errChan := make(chan error)
+
+	go func() {
+		defer stdin.Close()
+		toWrite := append([]byte(c.config.Password), '\n')
+		n, err := stdin.Write(toWrite)
+
+		if err != nil || n != len(toWrite) {
+			errChan <- fmt.Errorf("error writing to stdin: %s", err)
+			return
+		}
+
+		err = writeFunc(stdin)
+		if err != nil || n != len(toWrite) {
+			errChan <- fmt.Errorf("error writing to stdin: %s", err)
+			return
+		}
+	}()
+
+	rawOut, err := cmd.CombinedOutput()
+	if err != nil {
+		return "", err
+	}
+	out := string(rawOut)
+
+	select {
+	case err = <-errChan:
+		return "", err
+	default:
+	}
+
+	return out, nil
+}