vpython: Add VirtualEnv creation package.

vpython/venv/venv.go

Index: vpython/venv/venv.go
diff --git a/vpython/venv/venv.go b/vpython/venv/venv.go
new file mode 100644
index 0000000000000000000000000000000000000000..ae2aa4687b9ccf5ddd3316f63f407ba252841bdb
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+++ b/vpython/venv/venv.go
@@ -0,0 +1,385 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package venv
+
+import (
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/luci/luci-go/vpython/api/env"
+	"github.com/luci/luci-go/vpython/filesystem"
+	"github.com/luci/luci-go/vpython/python"
+	"github.com/luci/luci-go/vpython/spec"
+	"github.com/luci/luci-go/vpython/wheel"
+
+	"github.com/luci/luci-go/common/clock"
+	"github.com/luci/luci-go/common/errors"
+	"github.com/luci/luci-go/common/logging"
+
+	"github.com/danjacques/gofslock/fslock"
+	"golang.org/x/net/context"
+)
+
+const lockHeldDelay = 5 * time.Second
+
+// blocker is an fslock.Blocker implementation that sleeps lockHeldDelay in
+// between attempts.
+func blocker(c context.Context) fslock.Blocker {
+	return func() error {
+		logging.Debugf(c, "Lock is currently held. Sleeping %v and retrying...", lockHeldDelay)
+		clock.Sleep(c, lockHeldDelay)
+		return nil
+	}
+}
+
+// EnvRootFromSpecPath calculates the environment root from an exported
+// environment specification file path.
+//
+// The specification path is: <EnvRoot>/<SpecHash>/<spec>, so our EnvRoot
+// is two directories up.
+//
+// We export EnvSpecPath as an asbolute path. However, since someone else
+// could have overridden it or exported their own, let's make sure.
+func EnvRootFromSpecPath(path string) (string, error) {
+	if err := filesystem.AbsPath(&path); err != nil {
+		return "", errors.Annotate(err).
+			Reason("failed to get absolute path for specification file path: %(path)s").
+			Err()
+	}
+	return filepath.Dir(filepath.Dir(path)), nil
+}
+
+// Env is a fully set-up Python virtual enviornment. It is configured
+// based on the contents of an env.Spec file by Setup.
+//
+// Env should not be instantiated directly; it must be created by calling
+// Config.Env.
+//
+// All paths in Env are absolute.
+type Env struct {
+	// Config is this Env's Config, fully-resolved.
+	Config *Config
+
+	// Root is the Env container's root directory path.
+	Root string
+
+	// Python is the path to the Env Python interpreter.
+	Python string
+
+	// SepcPath is the path to the specification file that was used to construct
+	// this enviornment. It will be in text protobuf format, and, therefore,
+	// suitable for input to other "vpython" invocations.
+	SpecPath string
+
+	// name is the hash of the specification file for this Env.
+	name string
+	// lockPath is the path to this Env-specific lock file. It will be at:
+	// "<baseDir>/.<name>.lock".
+	lockPath string
+	// completeFlagPath is the path to this Env's complete flag.
+	// It will be at "<Root>/complete.flag".
+	completeFlagPath string
+}
+
+// Setup creates a new Env.
+//
+// It will lock around the Env to ensure that multiple processes do not
+// conflict with each other. If a Env for this specification already
+// exists, it will be used directly without any additional setup.
+//
+// If another process holds the lock and blocking is true, we will wait for our
+// turn at the lock. Otherwise, we will return immediately with a locking error.
+func (e *Env) Setup(c context.Context, blocking bool) error {
+	if err := e.setupImpl(c, blocking); err != nil {
+		return errors.Annotate(err).Err()
+	}
+
+	// Perform a pruning round. Failure is non-fatal.
+	if perr := prune(c, e.Config, e.name); perr != nil {
+		logging.WithError(perr).Warningf(c, "Failed to perform pruning round after initialization.")
+	}
+	return nil
+}
+
+func (e *Env) setupImpl(c context.Context, blocking bool) error {
+	// Repeatedly try and create our Env. We do this so that if we
+	// encounter a lock, we will let the other process finish and try and leverage
+	// its success.
+	for {
+		// Fast path: if our complete flag is present, assume that the environment
+		// is setup and complete. No locking or additional work necessary.
+		if _, err := os.Stat(e.completeFlagPath); err == nil {
+			logging.Debugf(c, "Completion flag found! Environment is set-up: %s", e.completeFlagPath)
+
+			// Update the complete flag so the timestamp reflects our usage of it.
+			// This is non-fatal if it fails.

[iannucci, 2017/02/23 00:54:21]

couldn't this mean that we return and this env might get pruned if we fail here?
Should we make this fatal if we're within some threshold of the prune time for
the mtime of this flag file? e.g. if the flag has < 1hour of life left, then
touching the flag requires a lock or something?

[dnj, 2017/02/23 20:38:50]

Hm, yeah that sounds reasonable.

+			if err := e.touchCompleteFlag(); err != nil {
+				logging.WithError(err).Warningf(c, "Failed to update complete flag.")
+			}
+
+			return nil
+		}
+
+		// We will be creating the Env. We will to lock around a file for this

[iannucci, 2017/02/23 00:54:21]

'will to lock'

[dnj, 2017/02/23 20:38:49]

Done.

+		// Env hash so that any other processes that may be trying to
+		// simultaneously create a Env will be forced to wait.
+		err := fslock.With(e.lockPath, func() error {
+			// Mark that we hit some lock contention. If we did, we will try again
+			// from scratch.
+			if err := e.createLocked(c); err != nil {
+				return errors.Annotate(err).Reason("failed to create new VirtualEnv").Err()
+			}
+			return nil
+		})
+		switch err {
+		case nil:
+			// Successfully created the environment! Mark this with a completion flag.
+			if err := e.touchCompleteFlag(); err != nil {
+				return errors.Annotate(err).Reason("failed to create complete flag").Err()

[iannucci, 2017/02/23 00:54:21]

shouldn't we loop? at least up to some limit?

[dnj, 2017/02/23 20:38:49]

I don't think so. Touching a file should be pretty soid.

+			}
+			return nil
+
+		case fslock.ErrLockHeld:
+			if !blocking {
+				return errors.Annotate(err).Reason("VirtualEnv lock is currently held (non-blocking)").Err()
+			}
+
+			// Some other process holds the lock. Sleep a little and retry.
+			logging.Warningf(c, "VirtualEnv lock is currently held. Retrying after delay (%s)...",
+				lockHeldDelay)
+			if tr := clock.Sleep(c, lockHeldDelay); tr.Incomplete() {
+				return tr.Err
+			}
+			continue
+
+		default:
+			return errors.Annotate(err).Reason("failed to create VirtualEnv").Err()
+		}
+	}
+}
+
+// Delete deletes this enviornment, if it exists.
+func (e *Env) Delete(c context.Context) error {
+	err := fslock.WithBlocking(e.lockPath, blocker(c), func() error {
+		if err := e.deleteLocked(c); err != nil {
+			return errors.Annotate(err).Err()
+		}
+		return nil
+	})
+	if err != nil {
+		errors.Annotate(err).Reason("failed to delete enviornment").Err()
+	}
+	return nil
+}
+
+func (e *Env) createLocked(c context.Context) error {
+	// If our root directory already exists, delete it.
+	if _, err := os.Stat(e.Root); err == nil {
+		logging.Warningf(c, "Deleting existing VirtualEnv: %s", e.Root)
+		if err := filesystem.RemoveAll(e.Root); err != nil {
+			return errors.Reason("failed to remove existing root").Err()
+		}
+	}
+
+	// Make sure our environment's base directory exists.
+	if err := filesystem.MakeDirs(e.Root); err != nil {
+		return errors.Annotate(err).Reason("failed to create environment root").Err()
+	}
+	logging.Infof(c, "Using virtual environment root: %s", e.Root)
+
+	// Build our package list. Always install our base VirtualEnv package.
+	// For resolution purposes, our VirtualEnv package will be index 0.

[iannucci, 2017/02/23 00:54:21]

why? why not just sort them?

The Spec_Package are the fully resolved ones, right (no ${platform}, no
tag:name)? should we assert that?

[dnj, 2017/02/23 20:38:49]

Doesn't really matter. The comment isn't too useful, so I will just delete it.
This is now an implementation detail.
That's a precondition, so I don't think we need to assert here.

+	packages := make([]*env.Spec_Package, 1, 1+len(e.Config.Spec.Wheel))
+	packages[0] = e.Config.Spec.Virtualenv
+	packages = append(packages, e.Config.Spec.Wheel...)
+
+	bootstrapDir := filepath.Join(e.Root, ".vpython_bootstrap")
+	pkgDir := filepath.Join(bootstrapDir, "packages")

[iannucci, 2017/02/23 00:54:21]

we should make sure to delete this directory after were done, right?

[dnj, 2017/02/23 20:38:50]

We do, yeah. See "finalize".

+	if err := filesystem.MakeDirs(pkgDir); err != nil {
+		return errors.Annotate(err).Reason("could not create bootstrap packages directory").Err()
+	}
+
+	if err := e.downloadPackages(c, pkgDir, packages); err != nil {
+		return errors.Annotate(err).Reason("failed to download packages").Err()
+	}
+
+	// Installing base VirtualEnv.
+	if err := e.installVirtualEnv(c, pkgDir); err != nil {
+		return errors.Annotate(err).Reason("failed to install VirtualEnv").Err()
+	}
+
+	// Download our wheel files.

[iannucci, 2017/02/23 00:54:21]

Install?

[dnj, 2017/02/23 20:38:50]

Done.

+	if len(e.Config.Spec.Wheel) > 0 {
+		// Install wheels into our VirtualEnv.
+		if err := e.installWheels(c, bootstrapDir, pkgDir); err != nil {
+			return errors.Annotate(err).Reason("failed to install wheels").Err()
+		}
+	}
+
+	// Write our specification file.
+	if err := spec.Write(e.Config.Spec, e.SpecPath); err != nil {
+		return errors.Annotate(err).Reason("failed to write spec file to: %(path)s").
+			D("path", e.SpecPath).
+			Err()
+	}
+	logging.Debugf(c, "Wrote specification file to: %s", e.SpecPath)
+
+	// Finalize our VirtualEnv for bootstrap execution.
+	if err := e.finalize(c, bootstrapDir); err != nil {
+		return errors.Annotate(err).Reason("failed to prepare VirtualEnv").Err()
+	}
+
+	return nil
+}
+
+func (e *Env) downloadPackages(c context.Context, dst string, packages []*env.Spec_Package) error {
+	// Create a wheel sub-directory underneath of root.
+	logging.Debugf(c, "Loading %d package(s) into: %s", len(packages), dst)
+	if err := e.Config.Loader.Ensure(c, dst, packages); err != nil {
+		return errors.Annotate(err).Reason("failed to download packages").Err()

[iannucci, 2017/02/23 00:54:21]

pro tip: errors.Annotate(nil).Reason(...).D(...).Err() == nil (and is a fast
path)

[dnj, 2017/02/23 20:38:50]

For me, this is too much on a single line :)

+	}
+	return nil
+}
+
+func (e *Env) installVirtualEnv(c context.Context, pkgDir string) error {
+	// Create our VirtualEnv package staging sub-directory underneath of root.
+	bsDir := filepath.Join(e.Root, ".virtualenv")
+	if err := filesystem.MakeDirs(bsDir); err != nil {
+		return errors.Annotate(err).Reason("failed to create VirtualEnv bootstrap directory").
+			D("path", bsDir).
+			Err()
+	}
+
+	// Identify the virtualenv directory: will have "virtualenv-" prefix.
+	matches, err := filepath.Glob(filepath.Join(pkgDir, "virtualenv-*"))
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to glob for 'virtualenv-' directory").Err()
+	}
+	if len(matches) == 0 {
+		return errors.Reason("no 'virtualenv-' directory provided by package").Err()
+	}
+
+	logging.Debugf(c, "Creating VirtualEnv at: %s", e.Root)
+	i := e.Config.systemInterpreter()
+	i.WorkDir = matches[0]
+	err = i.Run(c,
+		"virtualenv.py",
+		"--no-download",
+		e.Root)
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to create VirtualEnv").Err()
+	}
+
+	return nil
+}
+
+func (e *Env) installWheels(c context.Context, bootstrapDir, pkgDir string) error {
+	// Identify all downloaded wheels and parse them.
+	wheels, err := wheel.ScanDir(pkgDir)
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to load wheels").Err()
+	}
+
+	// Build a "wheel" requirements file.
+	reqPath := filepath.Join(bootstrapDir, "requirements.txt")
+	logging.Debugf(c, "Rendering requirements file to: %s", reqPath)
+	if err := wheel.WriteRequirementsFile(reqPath, wheels); err != nil {
+		return errors.Annotate(err).Reason("failed to render requirements file").Err()
+	}
+
+	cmd := e.venvInterpreter()
+	err = cmd.Run(c,
+		"-m", "pip",
+		"install",
+		"--use-wheel",
+		"--compile",
+		"--no-index",
+		"--find-links", pkgDir,
+		"--requirement", reqPath)
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to install wheels").Err()
+	}
+	return nil
+}
+
+func (e *Env) finalize(c context.Context, bootstrapDir string) error {
+	// Uninstall "pip" and "wheel", preventing (easy) augmentation of the
+	// enviornment.
+	cmd := e.venvInterpreter()
+	err := cmd.Run(c,
+		"-m", "pip",
+		"uninstall",
+		"--quiet",
+		"--yes",
+		"pip", "wheel")
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to install wheels").Err()
+	}
+
+	// Delete our bootstrap directory (non-fatal).

[iannucci, 2017/02/23 00:54:21]

ah, this is the place we delete it

[dnj, 2017/02/23 20:38:50]

Acknowledged.

+	if err := filesystem.RemoveAll(bootstrapDir); err != nil {
+		logging.WithError(err).Warningf(c, "Failed to delete bootstrap directory: %s", bootstrapDir)
+	}
+
+	// Change all files to read-only, except:
+	// - Our root directory, which must be writable in order to update our
+	//   completion flag.
+	// - Our completion flag, which must be trivially re-writable.
+	err = filesystem.MakeReadOnly(e.Root, func(path string) bool {
+		switch path {
+		case e.Root, e.completeFlagPath:
+			return false
+		default:
+			return true
+		}
+	})
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to mark environment read-only").Err()
+	}
+	return nil
+}
+
+func (e *Env) venvInterpreter() *python.Command {
+	cmd := e.InterpreterCommand()
+	cmd.WorkDir = e.Root
+	return cmd
+}
+
+// InterpreterCommand returns a Python interpreter Command pointing to the
+// VirtualEnv's Python installation.
+func (e *Env) InterpreterCommand() *python.Command {
+	i := python.Interpreter{
+		Python: e.Python,
+	}
+	cmd := i.Command()
+	cmd.Isolated = true
+	return cmd
+}
+
+// touchCompleteFlag touches the complete flag, creating it and/or updating its
+// timestamp.
+//
+// This is safe to call without the lock held, since worst-case an update is
+// overwritten if contested.
+func (e *Env) touchCompleteFlag() error {
+	if err := filesystem.Touch(e.completeFlagPath, 0644); err != nil {
+		return errors.Annotate(err).Err()
+	}
+	return nil
+}
+
+func (e *Env) deleteLocked(c context.Context) error {
+	// Delete our environment directory.
+	if err := filesystem.RemoveAll(e.Root); err != nil {
+		return errors.Annotate(err).Reason("failed to delete environment root").Err()
+	}
+
+	// Delete our lock path.
+	if err := os.Remove(e.lockPath); err != nil {
+		return errors.Annotate(err).Reason("failed to delete lock").Err()
+	}
+	return nil
+}