secrets: add common secrets plugins impl (#26335)

Co-authored-by: Michael Schurter <mschurter@hashicorp.com>

client/commonplugins/commonplugins.go

@@ -0,0 +1,63 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package commonplugins
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os/exec"
+	"syscall"
+	"time"
+
+	"github.com/hashicorp/go-version"
+)
+
+var (
+	ErrPluginNotExists     error = errors.New("plugin not found")
+	ErrPluginNotExecutable error = errors.New("plugin not executable")
+)
+
+type CommonPlugin interface {
+	Fingerprint(ctx context.Context) (*PluginFingerprint, error)
+}
+
+// CommonPlugins are expected to respond to 'fingerprint' calls with json that
+// unmarshals to this struct.
+type PluginFingerprint struct {
+	Version *version.Version `json:"version"`
+	Type    *string          `json:"type"`
+}
+
+// runPlugin is a helper for executing the provided Cmd and capturing stdout/stderr.
+// This helper implements both the soft and hard timeouts defined by the common
+// plugins interface.
+func runPlugin(cmd *exec.Cmd, killTimeout time.Duration) (stdout, stderr []byte, err error) {
+	var errBuf bytes.Buffer
+	cmd.Stderr = &errBuf
+
+	done := make(chan error, 1)
+	cmd.Cancel = func() error {
+		var cancelErr error
+
+		_ = cmd.Process.Signal(syscall.SIGTERM)
+		killTimer := time.NewTimer(killTimeout)
+		defer killTimer.Stop()
+
+		select {
+		case <-killTimer.C:
+			cancelErr = cmd.Process.Kill()
+		case <-done:
+		}
+
+		return cancelErr
+	}
+
+	// start the command
+	stdout, err = cmd.Output()
+	done <- err
+
+	stderr = errBuf.Bytes()
+	return
+}