Lib/CGIHTTPServer.py

"""CGI-savvy HTTP Server.

This module builds on SimpleHTTPServer by implementing GET and POST
requests to cgi-bin scripts.

If the os.fork() function is not present (e.g. on Windows),
os.popen2() is used as a fallback, with slightly altered semantics; if
that function is not present either (e.g. on Macintosh), only Python
scripts are supported, and they are executed by the current process.

In all cases, the implementation is intentionally naive -- all
requests are executed sychronously.

SECURITY WARNING: DON'T USE THIS CODE UNLESS YOU ARE INSIDE A FIREWALL
-- it may execute arbitrary Python code or external programs.

Note that status code 200 is sent prior to execution of a CGI script, so
scripts cannot send other status codes such as 302 (redirect).
"""


__version__ = "0.4"

__all__ = ["CGIHTTPRequestHandler"]

import os
import sys
import urllib
import BaseHTTPServer
import SimpleHTTPServer
import select


class CGIHTTPRequestHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):

    """Complete HTTP server with GET, HEAD and POST commands.

    GET and HEAD also support running CGI scripts.

    The POST command is *only* implemented for CGI scripts.

    """

    # Determine platform specifics
    have_fork = hasattr(os, 'fork')
    have_popen2 = hasattr(os, 'popen2')
    have_popen3 = hasattr(os, 'popen3')

    # Make rfile unbuffered -- we need to read one line and then pass
    # the rest to a subprocess, so we can't use buffered input.
    rbufsize = 0

    def do_POST(self):
        """Serve a POST request.

        This is only implemented for CGI scripts.

        """

        if self.is_cgi():
            self.run_cgi()
        else:
            self.send_error(501, "Can only POST to CGI scripts")

    def send_head(self):
        """Version of send_head that support CGI scripts"""
        if self.is_cgi():
            return self.run_cgi()
        else:
            return SimpleHTTPServer.SimpleHTTPRequestHandler.send_head(self)

    def is_cgi(self):
        """Test whether self.path corresponds to a CGI script.

        Returns True and updates the cgi_info attribute to the tuple
        (dir, rest) if self.path requires running a CGI script.
        Returns False otherwise.

        The default implementation tests whether the normalized url
        path begins with one of the strings in self.cgi_directories
        (and the next character is a '/' or the end of the string).
        """
        splitpath = _url_collapse_path_split(self.path)
        if splitpath[0] in self.cgi_directories:
            self.cgi_info = splitpath
            return True
        return False

    cgi_directories = ['/cgi-bin', '/htbin']

    def is_executable(self, path):
        """Test whether argument path is an executable file."""
        return executable(path)

    def is_python(self, path):
        """Test whether argument path is a Python script."""
        head, tail = os.path.splitext(path)
        return tail.lower() in (".py", ".pyw")

    def run_cgi(self):
        """Execute a CGI script."""
        path = self.path
        dir, rest = self.cgi_info

        i = path.find('/', len(dir) + 1)
        while i >= 0:
            nextdir = path[:i]
            nextrest = path[i+1:]

            scriptdir = self.translate_path(nextdir)
            if os.path.isdir(scriptdir):
                dir, rest = nextdir, nextrest
                i = path.find('/', len(dir) + 1)
            else:
                break

        # find an explicit query string, if present.
        i = rest.rfind('?')
        if i >= 0:
            rest, query = rest[:i], rest[i+1:]
        else:
            query = ''

        # dissect the part after the directory name into a script name &
        # a possible additional path, to be stored in PATH_INFO.
        i = rest.find('/')
        if i >= 0:
            script, rest = rest[:i], rest[i:]
        else:
            script, rest = rest, ''

        scriptname = dir + '/' + script
        scriptfile = self.translate_path(scriptname)
        if not os.path.exists(scriptfile):
            self.send_error(404, "No such CGI script (%r)" % scriptname)
            return
        if not os.path.isfile(scriptfile):
            self.send_error(403, "CGI script is not a plain file (%r)" %
                            scriptname)
            return
        ispy = self.is_python(scriptname)
        if not ispy:
            if not (self.have_fork or self.have_popen2 or self.have_popen3):
                self.send_error(403, "CGI script is not a Python script (%r)" %
                                scriptname)
                return
            if not self.is_executable(scriptfile):
                self.send_error(403, "CGI script is not executable (%r)" %
                                scriptname)
                return

        # Reference: http://hoohoo.ncsa.uiuc.edu/cgi/env.html
        # XXX Much of the following could be prepared ahead of time!
        env = {}
        env['SERVER_SOFTWARE'] = self.version_string()
        env['SERVER_NAME'] = self.server.server_name
        env['GATEWAY_INTERFACE'] = 'CGI/1.1'
        env['SERVER_PROTOCOL'] = self.protocol_version
        env['SERVER_PORT'] = str(self.server.server_port)
        env['REQUEST_METHOD'] = self.command
        uqrest = urllib.unquote(rest)
        env['PATH_INFO'] = uqrest
        env['PATH_TRANSLATED'] = self.translate_path(uqrest)
        env['SCRIPT_NAME'] = scriptname
        if query:
            env['QUERY_STRING'] = query
        host = self.address_string()
        if host != self.client_address[0]:
            env['REMOTE_HOST'] = host
        env['REMOTE_ADDR'] = self.client_address[0]
        authorization = self.headers.getheader("authorization")
        if authorization:
            authorization = authorization.split()
            if len(authorization) == 2:
                import base64, binascii
                env['AUTH_TYPE'] = authorization[0]
                if authorization[0].lower() == "basic":
                    try:
                        authorization = base64.decodestring(authorization[1])
                    except binascii.Error:
                        pass
                    else:
                        authorization = authorization.split(':')
                        if len(authorization) == 2:
                            env['REMOTE_USER'] = authorization[0]
        # XXX REMOTE_IDENT
        if self.headers.typeheader is None:
            env['CONTENT_TYPE'] = self.headers.type
        else:
            env['CONTENT_TYPE'] = self.headers.typeheader
        length = self.headers.getheader('content-length')
        if length:
            env['CONTENT_LENGTH'] = length
        referer = self.headers.getheader('referer')
        if referer:
            env['HTTP_REFERER'] = referer
        accept = []
        for line in self.headers.getallmatchingheaders('accept'):
            if line[:1] in "\t\n\r ":
                accept.append(line.strip())
            else:
                accept = accept + line[7:].split(',')
        env['HTTP_ACCEPT'] = ','.join(accept)
        ua = self.headers.getheader('user-agent')
        if ua:
            env['HTTP_USER_AGENT'] = ua
        co = filter(None, self.headers.getheaders('cookie'))
        if co:
            env['HTTP_COOKIE'] = ', '.join(co)
        # XXX Other HTTP_* headers
        # Since we're setting the env in the parent, provide empty
        # values to override previously set values
        for k in ('QUERY_STRING', 'REMOTE_HOST', 'CONTENT_LENGTH',
                  'HTTP_USER_AGENT', 'HTTP_COOKIE', 'HTTP_REFERER'):
            env.setdefault(k, "")
        os.environ.update(env)

        self.send_response(200, "Script output follows")

        decoded_query = query.replace('+', ' ')

        if self.have_fork:
            # Unix -- fork as we should
            args = [script]
            if '=' not in decoded_query:
                args.append(decoded_query)
            nobody = nobody_uid()
            self.wfile.flush() # Always flush before forking
            pid = os.fork()
            if pid != 0:
                # Parent
                pid, sts = os.waitpid(pid, 0)
                # throw away additional data [see bug #427345]
                while select.select([self.rfile], [], [], 0)[0]:
                    if not self.rfile.read(1):
                        break
                if sts:
                    self.log_error("CGI script exit status %#x", sts)
                return
            # Child
            try:
                try:
                    os.setuid(nobody)
                except os.error:
                    pass
                os.dup2(self.rfile.fileno(), 0)
                os.dup2(self.wfile.fileno(), 1)
                os.execve(scriptfile, args, os.environ)
            except:
                self.server.handle_error(self.request, self.client_address)
                os._exit(127)

        elif self.have_popen2 or self.have_popen3:
            # Windows -- use popen2 or popen3 to create a subprocess
            import shutil
            if self.have_popen3:
                popenx = os.popen3
            else:
                popenx = os.popen2
            cmdline = scriptfile
            if self.is_python(scriptfile):
                interp = sys.executable
                if interp.lower().endswith("w.exe"):
                    # On Windows, use python.exe, not pythonw.exe
                    interp = interp[:-5] + interp[-4:]
                cmdline = "%s -u %s" % (interp, cmdline)
            if '=' not in query and '"' not in query:
                cmdline = '%s "%s"' % (cmdline, query)
            self.log_message("command: %s", cmdline)
            try:
                nbytes = int(length)
            except (TypeError, ValueError):
                nbytes = 0
            files = popenx(cmdline, 'b')
            fi = files[0]
            fo = files[1]
            if self.have_popen3:
                fe = files[2]
            if self.command.lower() == "post" and nbytes > 0:
                data = self.rfile.read(nbytes)
                fi.write(data)
            # throw away additional data [see bug #427345]
            while select.select([self.rfile._sock], [], [], 0)[0]:
                if not self.rfile._sock.recv(1):
                    break
            fi.close()
            shutil.copyfileobj(fo, self.wfile)
            if self.have_popen3:
                errors = fe.read()
                fe.close()
                if errors:
                    self.log_error('%s', errors)
            sts = fo.close()
            if sts:
                self.log_error("CGI script exit status %#x", sts)
            else:
                self.log_message("CGI script exited OK")

        else:
            # Other O.S. -- execute script in this process
            save_argv = sys.argv
            save_stdin = sys.stdin
            save_stdout = sys.stdout
            save_stderr = sys.stderr
            try:
                save_cwd = os.getcwd()
                try:
                    sys.argv = [scriptfile]
                    if '=' not in decoded_query:
                        sys.argv.append(decoded_query)
                    sys.stdout = self.wfile
                    sys.stdin = self.rfile
                    execfile(scriptfile, {"__name__": "__main__"})
                finally:
                    sys.argv = save_argv
                    sys.stdin = save_stdin
                    sys.stdout = save_stdout
                    sys.stderr = save_stderr
                    os.chdir(save_cwd)
            except SystemExit, sts:
                self.log_error("CGI script exit status %s", str(sts))
            else:
                self.log_message("CGI script exited OK")


# TODO(gregory.p.smith): Move this into an appropriate library.
def _url_collapse_path_split(path):
    """
    Given a URL path, remove extra '/'s and '.' path elements and collapse
    any '..' references.

    Implements something akin to RFC-2396 5.2 step 6 to parse relative paths.

    Returns: A tuple of (head, tail) where tail is everything after the final /
    and head is everything before it.  Head will always start with a '/' and,
    if it contains anything else, never have a trailing '/'.

    Raises: IndexError if too many '..' occur within the path.
    """
    # Similar to os.path.split(os.path.normpath(path)) but specific to URL
    # path semantics rather than local operating system semantics.
    path_parts = []
    for part in path.split('/'):
        if part == '.':
            path_parts.append('')
        else:
            path_parts.append(part)
    # Filter out blank non trailing parts before consuming the '..'.
    path_parts = [part for part in path_parts[:-1] if part] + path_parts[-1:]
    if path_parts:
        tail_part = path_parts.pop()
    else:
        tail_part = ''
    head_parts = []
    for part in path_parts:
        if part == '..':
            head_parts.pop()
        else:
            head_parts.append(part)
    if tail_part and tail_part == '..':
        head_parts.pop()
        tail_part = ''
    return ('/' + '/'.join(head_parts), tail_part)


nobody = None

def nobody_uid():
    """Internal routine to get nobody's uid"""
    global nobody
    if nobody:
        return nobody
    try:
        import pwd
    except ImportError:
        return -1
    try:
        nobody = pwd.getpwnam('nobody')[2]
    except KeyError:
        nobody = 1 + max(map(lambda x: x[2], pwd.getpwall()))
    return nobody


def executable(path):
    """Test for executable file."""
    try:
        st = os.stat(path)
    except os.error:
        return False
    return st.st_mode & 0111 != 0


def test(HandlerClass = CGIHTTPRequestHandler,
         ServerClass = BaseHTTPServer.HTTPServer):
    SimpleHTTPServer.test(HandlerClass, ServerClass)


if __name__ == '__main__':
    test()