terraform/config/module/get.go

package module

import (
	"bytes"
	"fmt"
	"net/url"
	"os/exec"
	"syscall"
)

// Getter defines the interface that schemes must implement to download
// and update modules.
type Getter interface {
	// Get downloads the given URL into the given directory. This always
	// assumes that we're updating and gets the latest version that it can.
	//
	// The directory may already exist (if we're updating). If it is in a
	// format that isn't understood, an error should be returned. Get shouldn't
	// simply nuke the directory.
	Get(string, *url.URL) error
}

// Getters is the mapping of scheme to the Getter implementation that will
// be used to get a dependency.
var Getters map[string]Getter

func init() {
	Getters = map[string]Getter{
		"file": new(FileGetter),
		"git":  new(GitGetter),
	}
}

// Get downloads the module specified by src into the folder specified by
// dst. If dst already exists, Get will attempt to update it.
//
// src is a URL, whereas dst is always just a file path to a folder. This
// folder doesn't need to exist. It will be created if it doesn't exist.
func Get(dst, src string) error {
	u, err := url.Parse(src)
	if err != nil {
		return err
	}

	g, ok := Getters[u.Scheme]
	if !ok {
		return fmt.Errorf(
			"module download not supported for scheme '%s'", u.Scheme)
	}

	err = g.Get(dst, u)
	if err != nil {
		err = fmt.Errorf("error downloading module '%s': %s", src, err)
	}

	return err
}

// getRunCommand is a helper that will run a command and capture the output
// in the case an error happens.
func getRunCommand(cmd *exec.Cmd) error {
	var buf bytes.Buffer
	cmd.Stdout = &buf
	cmd.Stderr = &buf
	err := cmd.Run()
	if err == nil {
		return nil
	}
	if exiterr, ok := err.(*exec.ExitError); ok {
		// The program has exited with an exit code != 0
		if status, ok := exiterr.Sys().(syscall.WaitStatus); ok {
			return fmt.Errorf(
				"%s exited with %d: %s",
				cmd.Path,
				status.ExitStatus(),
				buf.String())
		}
	}

	return fmt.Errorf("error running %s: %s", cmd.Path, buf.String())
}