libgo/go/net/http/cgi/host.go - gofrontend - Git at Google

 // Copyright 2011 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.

 // This file implements the host side of CGI (being the webserver
 // parent process).

 // Package cgi implements CGI (Common Gateway Interface) as specified
 // in RFC 3875.
 //
 // Note that using CGI means starting a new process to handle each
 // request, which is typically less efficient than using a
 // long-running server. This package is intended primarily for
 // compatibility with existing systems.
 package cgi

 import (
 	"bufio"
 	"fmt"
 	"io"
 	"log"
 	"net"
 	"net/http"
 	"net/textproto"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"regexp"
 	"runtime"
 	"strconv"
 	"strings"

 	"golang.org/x/net/http/httpguts"
 )

 var trailingPort = regexp.MustCompile(`:([0-9]+)$`)

 var osDefaultInheritEnv = func() []string {
 	switch runtime.GOOS {
 	case "darwin":
 		return []string{"DYLD_LIBRARY_PATH"}
 	case "linux", "freebsd", "openbsd":
 		return []string{"LD_LIBRARY_PATH"}
 	case "hpux":
 		return []string{"LD_LIBRARY_PATH", "SHLIB_PATH"}
 	case "irix":
 		return []string{"LD_LIBRARY_PATH", "LD_LIBRARYN32_PATH", "LD_LIBRARY64_PATH"}
 	case "solaris":
 		return []string{"LD_LIBRARY_PATH", "LD_LIBRARY_PATH_32", "LD_LIBRARY_PATH_64"}
 	case "windows":
 		return []string{"SystemRoot", "COMSPEC", "PATHEXT", "WINDIR"}
 	}
 	return nil
 }()

 // Handler runs an executable in a subprocess with a CGI environment.
 type Handler struct {
 	Path string // path to the CGI executable
 	Root string // root URI prefix of handler or empty for "/"

 	// Dir specifies the CGI executable's working directory.
 	// If Dir is empty, the base directory of Path is used.
 	// If Path has no base directory, the current working
 	// directory is used.
 	Dir string

 	Env        []string    // extra environment variables to set, if any, as "key=value"
 	InheritEnv []string    // environment variables to inherit from host, as "key"
 	Logger     *log.Logger // optional log for errors or nil to use log.Print
 	Args       []string    // optional arguments to pass to child process
 	Stderr     io.Writer   // optional stderr for the child process; nil means os.Stderr

 	// PathLocationHandler specifies the root http Handler that
 	// should handle internal redirects when the CGI process
 	// returns a Location header value starting with a "/", as
 	// specified in RFC 3875 § 6.3.2. This will likely be
 	// http.DefaultServeMux.
 	//
 	// If nil, a CGI response with a local URI path is instead sent
 	// back to the client and not redirected internally.
 	PathLocationHandler http.Handler
 }

 func (h *Handler) stderr() io.Writer {
 	if h.Stderr != nil {
 		return h.Stderr
 	}
 	return os.Stderr
 }

 // removeLeadingDuplicates remove leading duplicate in environments.
 // It's possible to override environment like following.
 //    cgi.Handler{
 //      ...
 //      Env: []string{"SCRIPT_FILENAME=foo.php"},
 //    }
 func removeLeadingDuplicates(env []string) (ret []string) {
 	for i, e := range env {
 		found := false
 		if eq := strings.IndexByte(e, '='); eq != -1 {
 			keq := e[:eq+1] // "key="
 			for _, e2 := range env[i+1:] {
 				if strings.HasPrefix(e2, keq) {
 					found = true
 					break
 				}
 			}
 		}
 		if !found {
 			ret = append(ret, e)
 		}
 	}
 	return
 }

 func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	root := h.Root
 	if root == "" {
 		root = "/"
 	}

 	if len(req.TransferEncoding) > 0 && req.TransferEncoding[0] == "chunked" {
 		rw.WriteHeader(http.StatusBadRequest)
 		rw.Write([]byte("Chunked request bodies are not supported by CGI."))
 		return
 	}

 	pathInfo := req.URL.Path
 	if root != "/" && strings.HasPrefix(pathInfo, root) {
 		pathInfo = pathInfo[len(root):]
 	}

 	port := "80"
 	if matches := trailingPort.FindStringSubmatch(req.Host); len(matches) != 0 {
 		port = matches[1]
 	}

 	env := []string{
 		"SERVER_SOFTWARE=go",
 		"SERVER_NAME=" + req.Host,
 		"SERVER_PROTOCOL=HTTP/1.1",
 		"HTTP_HOST=" + req.Host,
 		"GATEWAY_INTERFACE=CGI/1.1",
 		"REQUEST_METHOD=" + req.Method,
 		"QUERY_STRING=" + req.URL.RawQuery,
 		"REQUEST_URI=" + req.URL.RequestURI(),
 		"PATH_INFO=" + pathInfo,
 		"SCRIPT_NAME=" + root,
 		"SCRIPT_FILENAME=" + h.Path,
 		"SERVER_PORT=" + port,
 	}

 	if remoteIP, remotePort, err := net.SplitHostPort(req.RemoteAddr); err == nil {
 		env = append(env, "REMOTE_ADDR="+remoteIP, "REMOTE_HOST="+remoteIP, "REMOTE_PORT="+remotePort)
 	} else {
 		// could not parse ip:port, let's use whole RemoteAddr and leave REMOTE_PORT undefined
 		env = append(env, "REMOTE_ADDR="+req.RemoteAddr, "REMOTE_HOST="+req.RemoteAddr)
 	}

 	if req.TLS != nil {
 		env = append(env, "HTTPS=on")
 	}

 	for k, v := range req.Header {
 		k = strings.Map(upperCaseAndUnderscore, k)
 		if k == "PROXY" {
 			// See Issue 16405
 			continue
 		}
 		joinStr := ", "
 		if k == "COOKIE" {
 			joinStr = "; "
 		}
 		env = append(env, "HTTP_"+k+"="+strings.Join(v, joinStr))
 	}

 	if req.ContentLength > 0 {
 		env = append(env, fmt.Sprintf("CONTENT_LENGTH=%d", req.ContentLength))
 	}
 	if ctype := req.Header.Get("Content-Type"); ctype != "" {
 		env = append(env, "CONTENT_TYPE="+ctype)
 	}

 	envPath := os.Getenv("PATH")
 	if envPath == "" {
 		envPath = "/bin:/usr/bin:/usr/ucb:/usr/bsd:/usr/local/bin"
 	}
 	env = append(env, "PATH="+envPath)

 	for _, e := range h.InheritEnv {
 		if v := os.Getenv(e); v != "" {
 			env = append(env, e+"="+v)
 		}
 	}

 	for _, e := range osDefaultInheritEnv {
 		if v := os.Getenv(e); v != "" {
 			env = append(env, e+"="+v)
 		}
 	}

 	if h.Env != nil {
 		env = append(env, h.Env...)
 	}

 	env = removeLeadingDuplicates(env)

 	var cwd, path string
 	if h.Dir != "" {
 		path = h.Path
 		cwd = h.Dir
 	} else {
 		cwd, path = filepath.Split(h.Path)
 	}
 	if cwd == "" {
 		cwd = "."
 	}

 	internalError := func(err error) {
 		rw.WriteHeader(http.StatusInternalServerError)
 		h.printf("CGI error: %v", err)
 	}

 	cmd := &exec.Cmd{
 		Path:   path,
 		Args:   append([]string{h.Path}, h.Args...),
 		Dir:    cwd,
 		Env:    env,
 		Stderr: h.stderr(),
 	}
 	if req.ContentLength != 0 {
 		cmd.Stdin = req.Body
 	}
 	stdoutRead, err := cmd.StdoutPipe()
 	if err != nil {
 		internalError(err)
 		return
 	}

 	err = cmd.Start()
 	if err != nil {
 		internalError(err)
 		return
 	}
 	if hook := testHookStartProcess; hook != nil {
 		hook(cmd.Process)
 	}
 	defer cmd.Wait()
 	defer stdoutRead.Close()

 	linebody := bufio.NewReaderSize(stdoutRead, 1024)
 	headers := make(http.Header)
 	statusCode := 0
 	headerLines := 0
 	sawBlankLine := false
 	for {
 		line, isPrefix, err := linebody.ReadLine()
 		if isPrefix {
 			rw.WriteHeader(http.StatusInternalServerError)
 			h.printf("cgi: long header line from subprocess.")
 			return
 		}
 		if err == io.EOF {
 			break
 		}
 		if err != nil {
 			rw.WriteHeader(http.StatusInternalServerError)
 			h.printf("cgi: error reading headers: %v", err)
 			return
 		}
 		if len(line) == 0 {
 			sawBlankLine = true
 			break
 		}
 		headerLines++
 		parts := strings.SplitN(string(line), ":", 2)
 		if len(parts) < 2 {
 			h.printf("cgi: bogus header line: %s", string(line))
 			continue
 		}
 		header, val := parts[0], parts[1]
 		if !httpguts.ValidHeaderFieldName(header) {
 			h.printf("cgi: invalid header name: %q", header)
 			continue
 		}
 		val = textproto.TrimString(val)
 		switch {
 		case header == "Status":
 			if len(val) < 3 {
 				h.printf("cgi: bogus status (short): %q", val)
 				return
 			}
 			code, err := strconv.Atoi(val[0:3])
 			if err != nil {
 				h.printf("cgi: bogus status: %q", val)
 				h.printf("cgi: line was %q", line)
 				return
 			}
 			statusCode = code
 		default:
 			headers.Add(header, val)
 		}
 	}
 	if headerLines == 0 || !sawBlankLine {
 		rw.WriteHeader(http.StatusInternalServerError)
 		h.printf("cgi: no headers")
 		return
 	}

 	if loc := headers.Get("Location"); loc != "" {
 		if strings.HasPrefix(loc, "/") && h.PathLocationHandler != nil {
 			h.handleInternalRedirect(rw, req, loc)
 			return
 		}
 		if statusCode == 0 {
 			statusCode = http.StatusFound
 		}
 	}

 	if statusCode == 0 && headers.Get("Content-Type") == "" {
 		rw.WriteHeader(http.StatusInternalServerError)
 		h.printf("cgi: missing required Content-Type in headers")
 		return
 	}

 	if statusCode == 0 {
 		statusCode = http.StatusOK
 	}

 	// Copy headers to rw's headers, after we've decided not to
 	// go into handleInternalRedirect, which won't want its rw
 	// headers to have been touched.
 	for k, vv := range headers {
 		for _, v := range vv {
 			rw.Header().Add(k, v)
 		}
 	}

 	rw.WriteHeader(statusCode)

 	_, err = io.Copy(rw, linebody)
 	if err != nil {
 		h.printf("cgi: copy error: %v", err)
 		// And kill the child CGI process so we don't hang on
 		// the deferred cmd.Wait above if the error was just
 		// the client (rw) going away. If it was a read error
 		// (because the child died itself), then the extra
 		// kill of an already-dead process is harmless (the PID
 		// won't be reused until the Wait above).
 		cmd.Process.Kill()
 	}
 }

 func (h *Handler) printf(format string, v ...interface{}) {
 	if h.Logger != nil {
 		h.Logger.Printf(format, v...)
 	} else {
 		log.Printf(format, v...)
 	}
 }

 func (h *Handler) handleInternalRedirect(rw http.ResponseWriter, req *http.Request, path string) {
 	url, err := req.URL.Parse(path)
 	if err != nil {
 		rw.WriteHeader(http.StatusInternalServerError)
 		h.printf("cgi: error resolving local URI path %q: %v", path, err)
 		return
 	}
 	// TODO: RFC 3875 isn't clear if only GET is supported, but it
 	// suggests so: "Note that any message-body attached to the
 	// request (such as for a POST request) may not be available
 	// to the resource that is the target of the redirect."  We
 	// should do some tests against Apache to see how it handles
 	// POST, HEAD, etc. Does the internal redirect get the same
 	// method or just GET? What about incoming headers?
 	// (e.g. Cookies) Which headers, if any, are copied into the
 	// second request?
 	newReq := &http.Request{
 		Method:     "GET",
 		URL:        url,
 		Proto:      "HTTP/1.1",
 		ProtoMajor: 1,
 		ProtoMinor: 1,
 		Header:     make(http.Header),
 		Host:       url.Host,
 		RemoteAddr: req.RemoteAddr,
 		TLS:        req.TLS,
 	}
 	h.PathLocationHandler.ServeHTTP(rw, newReq)
 }

 func upperCaseAndUnderscore(r rune) rune {
 	switch {
 	case r >= 'a' && r <= 'z':
 		return r - ('a' - 'A')
 	case r == '-':
 		return '_'
 	case r == '=':
 		// Maybe not part of the CGI 'spec' but would mess up
 		// the environment in any case, as Go represents the
 		// environment as a slice of "key=value" strings.
 		return '_'
 	}
 	// TODO: other transformations in spec or practice?
 	return r
 }

 var testHookStartProcess func(*os.Process) // nil except for some tests
	// Copyright 2011 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.

	// This file implements the host side of CGI (being the webserver
	// parent process).

	// Package cgi implements CGI (Common Gateway Interface) as specified
	// in RFC 3875.
	//
	// Note that using CGI means starting a new process to handle each
	// request, which is typically less efficient than using a
	// long-running server. This package is intended primarily for
	// compatibility with existing systems.
	package cgi

	import (
	"bufio"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"net/textproto"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"runtime"
	"strconv"
	"strings"

	"golang.org/x/net/http/httpguts"
	)

	var trailingPort = regexp.MustCompile(`:([0-9]+)$`)

	var osDefaultInheritEnv = func() []string {
	switch runtime.GOOS {
	case "darwin":
	return []string{"DYLD_LIBRARY_PATH"}
	case "linux", "freebsd", "openbsd":
	return []string{"LD_LIBRARY_PATH"}
	case "hpux":
	return []string{"LD_LIBRARY_PATH", "SHLIB_PATH"}
	case "irix":
	return []string{"LD_LIBRARY_PATH", "LD_LIBRARYN32_PATH", "LD_LIBRARY64_PATH"}
	case "solaris":
	return []string{"LD_LIBRARY_PATH", "LD_LIBRARY_PATH_32", "LD_LIBRARY_PATH_64"}
	case "windows":
	return []string{"SystemRoot", "COMSPEC", "PATHEXT", "WINDIR"}
	}
	return nil
	}()

	// Handler runs an executable in a subprocess with a CGI environment.
	type Handler struct {
	Path string // path to the CGI executable
	Root string // root URI prefix of handler or empty for "/"

	// Dir specifies the CGI executable's working directory.
	// If Dir is empty, the base directory of Path is used.
	// If Path has no base directory, the current working
	// directory is used.
	Dir string

	Env []string // extra environment variables to set, if any, as "key=value"
	InheritEnv []string // environment variables to inherit from host, as "key"
	Logger *log.Logger // optional log for errors or nil to use log.Print
	Args []string // optional arguments to pass to child process
	Stderr io.Writer // optional stderr for the child process; nil means os.Stderr

	// PathLocationHandler specifies the root http Handler that
	// should handle internal redirects when the CGI process
	// returns a Location header value starting with a "/", as
	// specified in RFC 3875 § 6.3.2. This will likely be
	// http.DefaultServeMux.
	//
	// If nil, a CGI response with a local URI path is instead sent
	// back to the client and not redirected internally.
	PathLocationHandler http.Handler
	}

	func (h *Handler) stderr() io.Writer {
	if h.Stderr != nil {
	return h.Stderr
	}
	return os.Stderr
	}

	// removeLeadingDuplicates remove leading duplicate in environments.
	// It's possible to override environment like following.
	// cgi.Handler{
	// ...
	// Env: []string{"SCRIPT_FILENAME=foo.php"},
	// }
	func removeLeadingDuplicates(env []string) (ret []string) {
	for i, e := range env {
	found := false
	if eq := strings.IndexByte(e, '='); eq != -1 {
	keq := e[:eq+1] // "key="
	for _, e2 := range env[i+1:] {
	if strings.HasPrefix(e2, keq) {
	found = true
	break
	}
	}
	}
	if !found {
	ret = append(ret, e)
	}
	}
	return
	}

	func (h Handler) ServeHTTP(rw http.ResponseWriter, req http.Request) {
	root := h.Root
	if root == "" {
	root = "/"
	}

	if len(req.TransferEncoding) > 0 && req.TransferEncoding[0] == "chunked" {
	rw.WriteHeader(http.StatusBadRequest)
	rw.Write([]byte("Chunked request bodies are not supported by CGI."))
	return
	}

	pathInfo := req.URL.Path
	if root != "/" && strings.HasPrefix(pathInfo, root) {
	pathInfo = pathInfo[len(root):]
	}

	port := "80"
	if matches := trailingPort.FindStringSubmatch(req.Host); len(matches) != 0 {
	port = matches[1]
	}

	env := []string{
	"SERVER_SOFTWARE=go",
	"SERVER_NAME=" + req.Host,
	"SERVER_PROTOCOL=HTTP/1.1",
	"HTTP_HOST=" + req.Host,
	"GATEWAY_INTERFACE=CGI/1.1",
	"REQUEST_METHOD=" + req.Method,
	"QUERY_STRING=" + req.URL.RawQuery,
	"REQUEST_URI=" + req.URL.RequestURI(),
	"PATH_INFO=" + pathInfo,
	"SCRIPT_NAME=" + root,
	"SCRIPT_FILENAME=" + h.Path,
	"SERVER_PORT=" + port,
	}

	if remoteIP, remotePort, err := net.SplitHostPort(req.RemoteAddr); err == nil {
	env = append(env, "REMOTE_ADDR="+remoteIP, "REMOTE_HOST="+remoteIP, "REMOTE_PORT="+remotePort)
	} else {
	// could not parse ip:port, let's use whole RemoteAddr and leave REMOTE_PORT undefined
	env = append(env, "REMOTE_ADDR="+req.RemoteAddr, "REMOTE_HOST="+req.RemoteAddr)
	}

	if req.TLS != nil {
	env = append(env, "HTTPS=on")
	}

	for k, v := range req.Header {
	k = strings.Map(upperCaseAndUnderscore, k)
	if k == "PROXY" {
	// See Issue 16405
	continue
	}
	joinStr := ", "
	if k == "COOKIE" {
	joinStr = "; "
	}
	env = append(env, "HTTP_"+k+"="+strings.Join(v, joinStr))
	}

	if req.ContentLength > 0 {
	env = append(env, fmt.Sprintf("CONTENT_LENGTH=%d", req.ContentLength))
	}
	if ctype := req.Header.Get("Content-Type"); ctype != "" {
	env = append(env, "CONTENT_TYPE="+ctype)
	}

	envPath := os.Getenv("PATH")
	if envPath == "" {
	envPath = "/bin:/usr/bin:/usr/ucb:/usr/bsd:/usr/local/bin"
	}
	env = append(env, "PATH="+envPath)

	for _, e := range h.InheritEnv {
	if v := os.Getenv(e); v != "" {
	env = append(env, e+"="+v)
	}
	}

	for _, e := range osDefaultInheritEnv {
	if v := os.Getenv(e); v != "" {
	env = append(env, e+"="+v)
	}
	}

	if h.Env != nil {
	env = append(env, h.Env...)
	}

	env = removeLeadingDuplicates(env)

	var cwd, path string
	if h.Dir != "" {
	path = h.Path
	cwd = h.Dir
	} else {
	cwd, path = filepath.Split(h.Path)
	}
	if cwd == "" {
	cwd = "."
	}

	internalError := func(err error) {
	rw.WriteHeader(http.StatusInternalServerError)
	h.printf("CGI error: %v", err)
	}

	cmd := &exec.Cmd{
	Path: path,
	Args: append([]string{h.Path}, h.Args...),
	Dir: cwd,
	Env: env,
	Stderr: h.stderr(),
	}
	if req.ContentLength != 0 {
	cmd.Stdin = req.Body
	}
	stdoutRead, err := cmd.StdoutPipe()
	if err != nil {
	internalError(err)
	return
	}

	err = cmd.Start()
	if err != nil {
	internalError(err)
	return
	}
	if hook := testHookStartProcess; hook != nil {
	hook(cmd.Process)
	}
	defer cmd.Wait()
	defer stdoutRead.Close()

	linebody := bufio.NewReaderSize(stdoutRead, 1024)
	headers := make(http.Header)
	statusCode := 0
	headerLines := 0
	sawBlankLine := false
	for {
	line, isPrefix, err := linebody.ReadLine()
	if isPrefix {
	rw.WriteHeader(http.StatusInternalServerError)
	h.printf("cgi: long header line from subprocess.")
	return
	}
	if err == io.EOF {
	break
	}
	if err != nil {
	rw.WriteHeader(http.StatusInternalServerError)
	h.printf("cgi: error reading headers: %v", err)
	return
	}
	if len(line) == 0 {
	sawBlankLine = true
	break
	}
	headerLines++
	parts := strings.SplitN(string(line), ":", 2)
	if len(parts) < 2 {
	h.printf("cgi: bogus header line: %s", string(line))
	continue
	}
	header, val := parts[0], parts[1]
	if !httpguts.ValidHeaderFieldName(header) {
	h.printf("cgi: invalid header name: %q", header)
	continue
	}
	val = textproto.TrimString(val)
	switch {
	case header == "Status":
	if len(val) < 3 {
	h.printf("cgi: bogus status (short): %q", val)
	return
	}
	code, err := strconv.Atoi(val[0:3])
	if err != nil {
	h.printf("cgi: bogus status: %q", val)
	h.printf("cgi: line was %q", line)
	return
	}
	statusCode = code
	default:
	headers.Add(header, val)
	}
	}
	if headerLines == 0 \|\| !sawBlankLine {
	rw.WriteHeader(http.StatusInternalServerError)
	h.printf("cgi: no headers")
	return
	}

	if loc := headers.Get("Location"); loc != "" {
	if strings.HasPrefix(loc, "/") && h.PathLocationHandler != nil {
	h.handleInternalRedirect(rw, req, loc)
	return
	}
	if statusCode == 0 {
	statusCode = http.StatusFound
	}
	}

	if statusCode == 0 && headers.Get("Content-Type") == "" {
	rw.WriteHeader(http.StatusInternalServerError)
	h.printf("cgi: missing required Content-Type in headers")
	return
	}

	if statusCode == 0 {
	statusCode = http.StatusOK
	}

	// Copy headers to rw's headers, after we've decided not to
	// go into handleInternalRedirect, which won't want its rw
	// headers to have been touched.
	for k, vv := range headers {
	for _, v := range vv {
	rw.Header().Add(k, v)
	}
	}

	rw.WriteHeader(statusCode)

	_, err = io.Copy(rw, linebody)
	if err != nil {
	h.printf("cgi: copy error: %v", err)
	// And kill the child CGI process so we don't hang on
	// the deferred cmd.Wait above if the error was just
	// the client (rw) going away. If it was a read error
	// (because the child died itself), then the extra
	// kill of an already-dead process is harmless (the PID
	// won't be reused until the Wait above).
	cmd.Process.Kill()
	}
	}

	func (h *Handler) printf(format string, v ...interface{}) {
	if h.Logger != nil {
	h.Logger.Printf(format, v...)
	} else {
	log.Printf(format, v...)
	}
	}

	func (h Handler) handleInternalRedirect(rw http.ResponseWriter, req http.Request, path string) {
	url, err := req.URL.Parse(path)
	if err != nil {
	rw.WriteHeader(http.StatusInternalServerError)
	h.printf("cgi: error resolving local URI path %q: %v", path, err)
	return
	}
	// TODO: RFC 3875 isn't clear if only GET is supported, but it
	// suggests so: "Note that any message-body attached to the
	// request (such as for a POST request) may not be available
	// to the resource that is the target of the redirect." We
	// should do some tests against Apache to see how it handles
	// POST, HEAD, etc. Does the internal redirect get the same
	// method or just GET? What about incoming headers?
	// (e.g. Cookies) Which headers, if any, are copied into the
	// second request?
	newReq := &http.Request{
	Method: "GET",
	URL: url,
	Proto: "HTTP/1.1",
	ProtoMajor: 1,
	ProtoMinor: 1,
	Header: make(http.Header),
	Host: url.Host,
	RemoteAddr: req.RemoteAddr,
	TLS: req.TLS,
	}
	h.PathLocationHandler.ServeHTTP(rw, newReq)
	}

	func upperCaseAndUnderscore(r rune) rune {
	switch {
	case r >= 'a' && r <= 'z':
	return r - ('a' - 'A')
	case r == '-':
	return '_'
	case r == '=':
	// Maybe not part of the CGI 'spec' but would mess up
	// the environment in any case, as Go represents the
	// environment as a slice of "key=value" strings.
	return '_'
	}
	// TODO: other transformations in spec or practice?
	return r
	}

	var testHookStartProcess func(*os.Process) // nil except for some tests