1 files changed, 345 insertions, 0 deletions
diff --git a/src/cmd/go/internal/vcweb/script.go b/src/cmd/go/internal/vcweb/script.go
new file mode 100644
index 0000000..c35b46f
--- /dev/null
+++ b/src/cmd/go/internal/vcweb/script.go
@@ -0,0 +1,345 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package vcweb
+
+import (
+	"bufio"
+	"bytes"
+	"cmd/go/internal/script"
+	"context"
+	"errors"
+	"fmt"
+	"internal/txtar"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/zip"
+)
+
+// newScriptEngine returns a script engine augmented with commands for
+// reproducing version-control repositories by replaying commits.
+func newScriptEngine() *script.Engine {
+	conds := script.DefaultConds()
+
+	interrupt := func(cmd *exec.Cmd) error { return cmd.Process.Signal(os.Interrupt) }
+	gracePeriod := 30 * time.Second // arbitrary
+
+	cmds := script.DefaultCmds()
+	cmds["at"] = scriptAt()
+	cmds["bzr"] = script.Program("bzr", interrupt, gracePeriod)
+	cmds["fossil"] = script.Program("fossil", interrupt, gracePeriod)
+	cmds["git"] = script.Program("git", interrupt, gracePeriod)
+	cmds["hg"] = script.Program("hg", interrupt, gracePeriod)
+	cmds["handle"] = scriptHandle()
+	cmds["modzip"] = scriptModzip()
+	cmds["svnadmin"] = script.Program("svnadmin", interrupt, gracePeriod)
+	cmds["svn"] = script.Program("svn", interrupt, gracePeriod)
+	cmds["unquote"] = scriptUnquote()
+
+	return &script.Engine{
+		Cmds:  cmds,
+		Conds: conds,
+	}
+}
+
+// loadScript interprets the given script content using the vcweb script engine.
+// loadScript always returns either a non-nil handler or a non-nil error.
+//
+// The script content must be a txtar archive with a comment containing a script
+// with exactly one "handle" command and zero or more VCS commands to prepare
+// the repository to be served.
+func (s *Server) loadScript(ctx context.Context, logger *log.Logger, scriptPath string, scriptContent []byte, workDir string) (http.Handler, error) {
+	ar := txtar.Parse(scriptContent)
+
+	if err := os.MkdirAll(workDir, 0755); err != nil {
+		return nil, err
+	}
+
+	st, err := s.newState(ctx, workDir)
+	if err != nil {
+		return nil, err
+	}
+	if err := st.ExtractFiles(ar); err != nil {
+		return nil, err
+	}
+
+	scriptName := filepath.Base(scriptPath)
+	scriptLog := new(strings.Builder)
+	err = s.engine.Execute(st, scriptName, bufio.NewReader(bytes.NewReader(ar.Comment)), scriptLog)
+	closeErr := st.CloseAndWait(scriptLog)
+	logger.Printf("%s:", scriptName)
+	io.WriteString(logger.Writer(), scriptLog.String())
+	io.WriteString(logger.Writer(), "\n")
+	if err != nil {
+		return nil, err
+	}
+	if closeErr != nil {
+		return nil, err
+	}
+
+	sc, err := getScriptCtx(st)
+	if err != nil {
+		return nil, err
+	}
+	if sc.handler == nil {
+		return nil, errors.New("script completed without setting handler")
+	}
+	return sc.handler, nil
+}
+
+// newState returns a new script.State for executing scripts in workDir.
+func (s *Server) newState(ctx context.Context, workDir string) (*script.State, error) {
+	ctx = &scriptCtx{
+		Context: ctx,
+		server:  s,
+	}
+
+	st, err := script.NewState(ctx, workDir, s.env)
+	if err != nil {
+		return nil, err
+	}
+	return st, nil
+}
+
+// scriptEnviron returns a new environment that attempts to provide predictable
+// behavior for the supported version-control tools.
+func scriptEnviron(homeDir string) []string {
+	env := []string{
+		"USER=gopher",
+		homeEnvName() + "=" + homeDir,
+		"GIT_CONFIG_NOSYSTEM=1",
+		"HGRCPATH=" + filepath.Join(homeDir, ".hgrc"),
+		"HGENCODING=utf-8",
+	}
+	// Preserve additional environment variables that may be needed by VCS tools.
+	for _, k := range []string{
+		pathEnvName(),
+		tempEnvName(),
+		"SYSTEMROOT",        // must be preserved on Windows to find DLLs; golang.org/issue/25210
+		"WINDIR",            // must be preserved on Windows to be able to run PowerShell command; golang.org/issue/30711
+		"ComSpec",           // must be preserved on Windows to be able to run Batch files; golang.org/issue/56555
+		"DYLD_LIBRARY_PATH", // must be preserved on macOS systems to find shared libraries
+		"LD_LIBRARY_PATH",   // must be preserved on Unix systems to find shared libraries
+		"LIBRARY_PATH",      // allow override of non-standard static library paths
+		"PYTHONPATH",        // may be needed by hg to find imported modules
+	} {
+		if v, ok := os.LookupEnv(k); ok {
+			env = append(env, k+"="+v)
+		}
+	}
+
+	if os.Getenv("GO_BUILDER_NAME") != "" || os.Getenv("GIT_TRACE_CURL") == "1" {
+		// To help diagnose https://go.dev/issue/52545,
+		// enable tracing for Git HTTPS requests.
+		env = append(env,
+			"GIT_TRACE_CURL=1",
+			"GIT_TRACE_CURL_NO_DATA=1",
+			"GIT_REDACT_COOKIES=o,SSO,GSSO_Uberproxy")
+	}
+
+	return env
+}
+
+// homeEnvName returns the environment variable used by os.UserHomeDir
+// to locate the user's home directory.
+func homeEnvName() string {
+	switch runtime.GOOS {
+	case "windows":
+		return "USERPROFILE"
+	case "plan9":
+		return "home"
+	default:
+		return "HOME"
+	}
+}
+
+// tempEnvName returns the environment variable used by os.TempDir
+// to locate the default directory for temporary files.
+func tempEnvName() string {
+	switch runtime.GOOS {
+	case "windows":
+		return "TMP"
+	case "plan9":
+		return "TMPDIR" // actually plan 9 doesn't have one at all but this is fine
+	default:
+		return "TMPDIR"
+	}
+}
+
+// pathEnvName returns the environment variable used by exec.LookPath to
+// identify directories to search for executables.
+func pathEnvName() string {
+	switch runtime.GOOS {
+	case "plan9":
+		return "path"
+	default:
+		return "PATH"
+	}
+}
+
+// A scriptCtx is a context.Context that stores additional state for script
+// commands.
+type scriptCtx struct {
+	context.Context
+	server      *Server
+	commitTime  time.Time
+	handlerName string
+	handler     http.Handler
+}
+
+// scriptCtxKey is the key associating the *scriptCtx in a script's Context..
+type scriptCtxKey struct{}
+
+func (sc *scriptCtx) Value(key any) any {
+	if key == (scriptCtxKey{}) {
+		return sc
+	}
+	return sc.Context.Value(key)
+}
+
+func getScriptCtx(st *script.State) (*scriptCtx, error) {
+	sc, ok := st.Context().Value(scriptCtxKey{}).(*scriptCtx)
+	if !ok {
+		return nil, errors.New("scriptCtx not found in State.Context")
+	}
+	return sc, nil
+}
+
+func scriptAt() script.Cmd {
+	return script.Command(
+		script.CmdUsage{
+			Summary: "set the current commit time for all version control systems",
+			Args:    "time",
+			Detail: []string{
+				"The argument must be an absolute timestamp in RFC3339 format.",
+			},
+		},
+		func(st *script.State, args ...string) (script.WaitFunc, error) {
+			if len(args) != 1 {
+				return nil, script.ErrUsage
+			}
+
+			sc, err := getScriptCtx(st)
+			if err != nil {
+				return nil, err
+			}
+
+			sc.commitTime, err = time.ParseInLocation(time.RFC3339, args[0], time.UTC)
+			if err == nil {
+				st.Setenv("GIT_COMMITTER_DATE", args[0])
+				st.Setenv("GIT_AUTHOR_DATE", args[0])
+			}
+			return nil, err
+		})
+}
+
+func scriptHandle() script.Cmd {
+	return script.Command(
+		script.CmdUsage{
+			Summary: "set the HTTP handler that will serve the script's output",
+			Args:    "handler [dir]",
+			Detail: []string{
+				"The handler will be passed the script's current working directory and environment as arguments.",
+				"Valid handlers include 'dir' (for general http.Dir serving), 'bzr', 'fossil', 'git', and 'hg'",
+			},
+		},
+		func(st *script.State, args ...string) (script.WaitFunc, error) {
+			if len(args) == 0 || len(args) > 2 {
+				return nil, script.ErrUsage
+			}
+
+			sc, err := getScriptCtx(st)
+			if err != nil {
+				return nil, err
+			}
+
+			if sc.handler != nil {
+				return nil, fmt.Errorf("server handler already set to %s", sc.handlerName)
+			}
+
+			name := args[0]
+			h, ok := sc.server.vcsHandlers[name]
+			if !ok {
+				return nil, fmt.Errorf("unrecognized VCS %q", name)
+			}
+			sc.handlerName = name
+			if !h.Available() {
+				return nil, ServerNotInstalledError{name}
+			}
+
+			dir := st.Getwd()
+			if len(args) >= 2 {
+				dir = st.Path(args[1])
+			}
+			sc.handler, err = h.Handler(dir, st.Environ(), sc.server.logger)
+			return nil, err
+		})
+}
+
+func scriptModzip() script.Cmd {
+	return script.Command(
+		script.CmdUsage{
+			Summary: "create a Go module zip file from a directory",
+			Args:    "zipfile path@version dir",
+		},
+		func(st *script.State, args ...string) (wait script.WaitFunc, err error) {
+			if len(args) != 3 {
+				return nil, script.ErrUsage
+			}
+			zipPath := st.Path(args[0])
+			mPath, version, ok := strings.Cut(args[1], "@")
+			if !ok {
+				return nil, script.ErrUsage
+			}
+			dir := st.Path(args[2])
+
+			if err := os.MkdirAll(filepath.Dir(zipPath), 0755); err != nil {
+				return nil, err
+			}
+			f, err := os.Create(zipPath)
+			if err != nil {
+				return nil, err
+			}
+			defer func() {
+				if closeErr := f.Close(); err == nil {
+					err = closeErr
+				}
+			}()
+
+			return nil, zip.CreateFromDir(f, module.Version{Path: mPath, Version: version}, dir)
+		})
+}
+
+func scriptUnquote() script.Cmd {
+	return script.Command(
+		script.CmdUsage{
+			Summary: "unquote the argument as a Go string",
+			Args:    "string",
+		},
+		func(st *script.State, args ...string) (script.WaitFunc, error) {
+			if len(args) != 1 {
+				return nil, script.ErrUsage
+			}
+
+			s, err := strconv.Unquote(`"` + args[0] + `"`)
+			if err != nil {
+				return nil, err
+			}
+
+			wait := func(*script.State) (stdout, stderr string, err error) {
+				return s, "", nil
+			}
+			return wait, nil
+		})
+}