From d94b44952abc7175985f253db867eba7769ac2d8 Mon Sep 17 00:00:00 2001
From: George Blue <gblue@pivotal.io>
Date: Mon, 25 Oct 2021 14:17:14 +0100
Subject: [PATCH] fix: signal handling for Concourse 7.5

There seems to be a change (unidentified as yet) in Concourse 7.5 that
results in no longer being able to stop or time-out once Terraform is
running. This change introduces a wrapper around the Terraform command
that catches signals and kills the Terraform process group if one is
detected.
---
 src/terraform-resource/runner/runner.go    | 82 ++++++++++++++++++++++
 src/terraform-resource/terraform/client.go |  5 +-
 2 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 src/terraform-resource/runner/runner.go

diff --git a/src/terraform-resource/runner/runner.go b/src/terraform-resource/runner/runner.go
new file mode 100644
index 00000000..eb8f637a
--- /dev/null
+++ b/src/terraform-resource/runner/runner.go
@@ -0,0 +1,82 @@
+package runner
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"os/signal"
+	"syscall"
+)
+
+type Runner struct {
+	Stdout io.Writer
+	Stderr io.Writer
+	cmd    *exec.Cmd
+	sigs   chan os.Signal
+	logger io.Writer
+}
+
+func New(cmd *exec.Cmd, logger io.Writer) *Runner {
+	// Ensure that child is started in process group
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+
+	r := &Runner{
+		cmd:    cmd,
+		sigs:   make(chan os.Signal, 1),
+		logger: logger,
+	}
+	r.startSignalHandler()
+
+	return r
+}
+
+func (r *Runner) Run() error {
+	r.cmd.Stdout = r.Stdout
+	r.cmd.Stderr = r.Stderr
+	err := r.cmd.Run()
+
+	r.stopSignalHandler()
+	return err
+}
+
+func (r *Runner) CombinedOutput() ([]byte, error) {
+	out, err := r.cmd.CombinedOutput()
+	r.stopSignalHandler()
+	return out, err
+}
+
+func (r *Runner) Output() ([]byte, error) {
+	out, err := r.cmd.Output()
+	r.stopSignalHandler()
+	return out, err
+}
+
+func (r *Runner) terminate() {
+	if r.cmd.Process != nil {
+		processGroup := -r.cmd.Process.Pid
+		if err := syscall.Kill(processGroup, syscall.SIGKILL); err != nil {
+			fmt.Fprintf(r.logger, "** Error signaling process group %d: %s\n", processGroup, err)
+		}
+	} else {
+		fmt.Fprintln(r.logger, "** Process already terminated.")
+	}
+
+	fmt.Fprintln(r.logger, "** Exiting due to signal")
+	os.Exit(1)
+}
+
+func (r *Runner) startSignalHandler() {
+	signal.Notify(r.sigs, syscall.SIGINT, syscall.SIGTERM)
+	go func() {
+		for s := range r.sigs {
+			fmt.Fprintf(r.logger, "** Received signal: %s\n", s)
+			r.terminate()
+		}
+	}()
+}
+
+func (r *Runner) stopSignalHandler() {
+	signal.Reset(syscall.SIGINT, syscall.SIGTERM)
+	close(r.sigs)
+}
diff --git a/src/terraform-resource/terraform/client.go b/src/terraform-resource/terraform/client.go
index eab59f4b..168e7604 100644
--- a/src/terraform-resource/terraform/client.go
+++ b/src/terraform-resource/terraform/client.go
@@ -17,6 +17,7 @@ import (
 	"strings"
 
 	"github.com/ljfranklin/terraform-resource/models"
+	"github.com/ljfranklin/terraform-resource/runner"
 )
 
 const defaultWorkspace = "default"
@@ -868,7 +869,7 @@ func (c *client) resourceExistsLegacyStorage(tfID string) (bool, error) {
 	return (len(strings.TrimSpace(string(rawOutput))) > 0), nil
 }
 
-func (c *client) terraformCmd(args []string, env []string) (*exec.Cmd, error) {
+func (c *client) terraformCmd(args []string, env []string) (*runner.Runner, error) {
 	cmdPath, err := exec.LookPath("terraform")
 	if err != nil {
 		return nil, err
@@ -892,5 +893,5 @@ func (c *client) terraformCmd(args []string, env []string) (*exec.Cmd, error) {
 		cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%s", key, value))
 	}
 
-	return cmd, nil
+	return runner.New(cmd, c.logWriter), nil
 }