WSGI OVERVIEW

# bottle.py
class Bottle(object):

    def wsgi(self, environ, start_response):
        """ The bottle WSGI-interface. """
        try:
            # out 是一个 list 类型
            out = self._cast(self._handle(environ)) # 1
            # rfc2616 section 4.3
            if response._status_code in (100, 101, 204, 304)\
            or environ['REQUEST_METHOD'] == 'HEAD':
                if hasattr(out, 'close'): out.close()
                out = []
            # 传入构建好的 response header
            start_response(response._status_line, response.headerlist)
            return out
        except (KeyboardInterrupt, SystemExit, MemoryError):
            raise
        except Exception:
            # ...

    def __call__(self, environ, start_response):
        ''' Each instance of :class:'Bottle' is a WSGI application. '''
        return self.wsgi(environ, start_response)

# /opt/python3.5/lib/python3.5/WSGIref/handler.py
class BaseHandler:
    # ...
    def run(self, application):
        """Invoke the application"""
        # Note to self: don't move the close()!  Asynchronous servers shouldn't
        # call close() from finish_response(), so if you close() anywhere but
        # the double-error branch here, you'll break asynchronous servers by
        # prematurely closing.  Async servers must return from 'run()' without
        # closing if there might still be output to iterate over.
        try:
            self.setup_environ()
            self.result = application(self.environ, self.start_response)
            self.finish_response()
        except:
            try:
                self.handle_error()
            except:
                # If we get an error handling an error, just give up already!
                self.close()
                raise   # ...and let the actual server figure it out.

    # ...

    def finish_response(self):
        """Send any iterable data, then close self and the iterable

        Subclasses intended for use in asynchronous servers will
        want to redefine this method, such that it sets up callbacks
        in the event loop to iterate over the data, and to call
        'self.close()' once the response is finished.
        """
        try:
            if not self.result_is_file() or not self.sendfile():
                for data in self.result:
                    self.write(data)
                self.finish_content()
        finally:
            self.close()

    # ...

    def start_response(self, status, headers,exc_info=None):
        """'start_response()' callable as specified by PEP 3333"""

        if exc_info:
            try:
                if self.headers_sent:
                    # Re-raise original exception if headers sent
                    raise exc_info[0](exc_info[1]).with_traceback(exc_info[2])
            finally:
                exc_info = None        # avoid dangling circular ref
        elif self.headers is not None:
            raise AssertionError("Headers already set!")

        self.status = status
        self.headers = self.headers_class(headers)
        status = self._convert_string_type(status, "Status")
        assert len(status)>=4,"Status must be at least 4 characters"
        assert status[:3].isdigit(), "Status message must begin w/3-digit code"
        assert status[3]==" ", "Status message must have a space after code"

        if __debug__:
            for name, val in headers:
                name = self._convert_string_type(name, "Header name")
                val = self._convert_string_type(val, "Header value")
                assert not is_hop_by_hop(name),"Hop-by-hop headers not allowed"

        return self.write

    # ...

    def write(self, data):
        """'write()' callable as specified by PEP 3333"""

        assert type(data) is bytes, \
            "write() argument must be a bytes instance"

        if not self.status:
            raise AssertionError("write() before start_response()")

        elif not self.headers_sent:
            # Before the first output, send the stored headers
            self.bytes_sent = len(data)    # make sure we know content-length
            self.send_headers()
        else:
            self.bytes_sent += len(data)

        # XXX check Content-Length and truncate if too many bytes written?
        self._write(data)
        self._flush()

from piglatin import piglatin

class LatinIter:

    """Transform iterated output to piglatin, if it's okay to do so

    Note that the "okayness" can change until the application yields
    its first non-empty bytestring, so 'transform_ok' has to be a mutable
    truth value.
    """

    def __init__(self, result, transform_ok):
        if hasattr(result, 'close'):
            self.close = result.close
        self._next = iter(result).__next__
        self.transform_ok = transform_ok

    def __iter__(self):
        return self

    def __next__(self):
        if self.transform_ok:
            return piglatin(self._next())   # call must be byte-safe on Py3
        else:
            return self._next()

class Latinator:

    # by default, don't transform output
    transform = False

    def __init__(self, application):
        self.application = application

    def __call__(self, environ, start_response):

        transform_ok = []

        def start_latin(status, response_headers, exc_info=None):

            # Reset ok flag, in case this is a repeat call
            del transform_ok[:]

            for name, value in response_headers:
                if name.lower() == 'content-type' and value == 'text/plain':
                    transform_ok.append(True)
                    # Strip content-length if present, else it'll be wrong
                    response_headers = [(name, value)
                        for name, value in response_headers
                            if name.lower() != 'content-length'
                    ]
                    break

            write = start_response(status, response_headers, exc_info)

            if transform_ok:
                def write_latin(data):
                    write(piglatin(data))   # call must be byte-safe on Py3
                return write_latin
            else:
                return write

        return LatinIter(self.application(environ, start_latin), transform_ok)


# Run foo_app under a Latinator's control, using the example CGI gateway
from foo_app import foo_app
run_with_cgi(Latinator(foo_app))