Use build-specific settings for effect across windows and unix

- On Windows, we use the standard os/exec functionality. As Windows doesn't really have the concept of a PTY.
- On Unix, we use a PTY. This allows commands started through effect to appear like a user is actually running them. In many cases, this doesn't matter, but some commands will change their output if there is a user or pipe. The PTY fakes the spawned process into thinking it's a user. This will generally cause the spawned process to emite human-friendly output.
- This change is due to the fact that recent Windows builds of paketo-buildpacks/procfile have been failing. This traces back to creack/pty#50. It's not clear why this is happening now, since the issue is a few years old. With recent changes in libpak, we're now affected by this.
- Initial tests with paketo-buildpacks/procfile show that making the PTY stuff conditional on the OS, allows this to work as expected.

Signed-off-by: Daniel Mikusa <[email protected]>

effect/executor.go

@@ -17,13 +17,8 @@
 package effect
 
 import (
-	"fmt"
 	"io"
-	"os"
 	"os/exec"
-	"syscall"
-
-	"github.com/creack/pty"
 )
 
 // Execution is information about a command to run.
@@ -80,54 +75,3 @@ func (CommandExecutor) Execute(execution Execution) error {
 
 	return cmd.Run()
 }
-
-// TTYExecutor is an implementation of Executor that uses exec.Command and runs the command with a TTY.
-type TTYExecutor struct{}
-
-func (t TTYExecutor) Execute(execution Execution) error {
-	cmd := exec.Command(execution.Command, execution.Args...)
-
-	if execution.Dir != "" {
-		cmd.Dir = execution.Dir
-	}
-
-	if len(execution.Env) > 0 {
-		cmd.Env = execution.Env
-	}
-
-	cmd.Stdin = execution.Stdin
-
-	f, err := pty.Start(cmd)
-	if err != nil {
-		return fmt.Errorf("unable to start PTY\n%w", err)
-	}
-	defer f.Close()
-
-	if _, err := io.Copy(execution.Stdout, f); err != nil {
-		if !t.isEIO(err) {
-			return fmt.Errorf("unable to write output\n%w", err)
-		}
-	}
-
-	return cmd.Wait()
-}
-
-func (TTYExecutor) isEIO(err error) bool {
-	pe, ok := err.(*os.PathError)
-	if !ok {
-		return false
-	}
-
-	return pe.Err == syscall.EIO
-}
-
-// NewExecutor creates a new Executor.  If the buildpack is currently running in a TTY, returns a TTY-aware Executor.
-func NewExecutor() Executor {
-	// TODO: Remove once TTY support is in place
-	return TTYExecutor{}
-	// if isatty.IsTerminal(os.Stdout.Fd()) {
-	// 	return TTYExecutor{}
-	// } else {
-	// 	return CommandExecutor{}
-	// }
-}

effect/executor_unix.go

@@ -0,0 +1,81 @@
+//go:build aix && darwin && dragonfly && freebsd && linux && netbsd && openbsd && solaris
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+/*
+ * Copyright 2018-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package effect
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"syscall"
+
+	"github.com/creack/pty"
+)
+
+// TTYExecutor is an implementation of Executor that uses exec.Command and runs the command with a TTY.
+type TTYExecutor struct{}
+
+func (t TTYExecutor) Execute(execution Execution) error {
+	cmd := exec.Command(execution.Command, execution.Args...)
+
+	if execution.Dir != "" {
+		cmd.Dir = execution.Dir
+	}
+
+	if len(execution.Env) > 0 {
+		cmd.Env = execution.Env
+	}
+
+	cmd.Stdin = execution.Stdin
+
+	f, err := pty.Start(cmd)
+	if err != nil {
+		return fmt.Errorf("unable to start PTY\n%w", err)
+	}
+	defer f.Close()
+
+	if _, err := io.Copy(execution.Stdout, f); err != nil {
+		if !t.isEIO(err) {
+			return fmt.Errorf("unable to write output\n%w", err)
+		}
+	}
+
+	return cmd.Wait()
+}
+
+func (TTYExecutor) isEIO(err error) bool {
+	pe, ok := err.(*os.PathError)
+	if !ok {
+		return false
+	}
+
+	return pe.Err == syscall.EIO
+}
+
+// NewExecutor creates a new Executor.  If the buildpack is currently running in a TTY, returns a TTY-aware Executor.
+func NewExecutor() Executor {
+	// TODO: Remove once TTY support is in place
+	return TTYExecutor{}
+	// if isatty.IsTerminal(os.Stdout.Fd()) {
+	// 	return TTYExecutor{}
+	// } else {
+	// 	return CommandExecutor{}
+	// }
+}

effect/executor_windows.go

@@ -0,0 +1,25 @@
+//go:build windows
+// +build windows
+
+/*
+ * Copyright 2018-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package effect
+
+// NewExecutor creates a new Executor.
+func NewExecutor() Executor {
+	return CommandExecutor{}
+}