view mercurial/hgweb/wsgiheaders.py @ 39559:07b58266bce3

wireprotov2: implement commands as a generator of objects

Previously, wire protocol version 2 inherited version 1's model of
having separate types to represent the results of different wire
protocol commands.

As I implemented more powerful commands in future commits, I found
I was using a common pattern of returning a special type to hold a
generator. This meant the command function required a closure to
do most of the work. That made logic flow more difficult to follow.
I also noticed that many commands were effectively a sequence of
objects to be CBOR encoded.

I think it makes sense to define version 2 commands as generators.
This way, commands can simply emit the data structures they wish to
send to the client. This eliminates the need for a closure in
command functions and removes encoding from the bodies of commands.

As part of this commit, the handling of response objects has been
moved into the serverreactor class. This puts the reactor in the
driver's seat with regards to CBOR encoding and error handling.
Having error handling in the function that emits frames is
particularly important because exceptions in that function can lead
to things getting in a bad state: I'm fairly certain that uncaught
exceptions in the frame generator were causing deadlocks.

I also introduced a dedicated error type for explicit error reporting
in command handlers. This will be used in subsequent commits.

There's still a bit of work to be done here, especially around
formalizing the error handling "protocol." I've added yet another
TODO to track this so we don't forget.

Test output changed because we're using generators and no longer know
we are at the end of the data until we hit the end of the generator.
This means we can't emit the end-of-stream flag until we've exhausted
the generator. Hence the introduction of 0-sized end-of-stream frames.

Differential Revision: https://phab.mercurial-scm.org/D4472

"""This was forked from cpython's wsgiref.headers module to work on bytes.

Header from old file showing copyright is below.

Much of this module is red-handedly pilfered from email.message in the stdlib,
so portions are Copyright (C) 2001,2002 Python Software Foundation, and were
written by Barry Warsaw.
"""

# Regular expression that matches `special' characters in parameters, the
# existence of which force quoting of the parameter value.
from __future__ import absolute_import, print_function

import re
tspecials = re.compile(br'[ \(\)<>@,;:\\"/\[\]\?=]')

def _formatparam(param, value=None, quote=1):
    """Convenience function to format and return a key=value pair.
    This will quote the value if needed or if quote is true.
    """
    if value is not None and len(value) > 0:
        if quote or tspecials.search(value):
            value = value.replace('\\', '\\\\').replace('"', r'\"')
            return '%s="%s"' % (param, value)
        else:
            return '%s=%s' % (param, value)
    else:
        return param


class Headers(object):
    """Manage a collection of HTTP response headers"""

    def __init__(self, headers=None):
        headers = headers if headers is not None else []
        if type(headers) is not list:
            raise TypeError("Headers must be a list of name/value tuples")
        self._headers = headers
        if __debug__:
            for k, v in headers:
                self._convert_string_type(k)
                self._convert_string_type(v)

    def _convert_string_type(self, value):
        """Convert/check value type."""
        if type(value) is bytes:
            return value
        raise AssertionError(u"Header names/values must be"
                             u" of type bytes (got %s)" % repr(value))

    def __len__(self):
        """Return the total number of headers, including duplicates."""
        return len(self._headers)

    def __setitem__(self, name, val):
        """Set the value of a header."""
        del self[name]
        self._headers.append(
            (self._convert_string_type(name), self._convert_string_type(val)))

    def __delitem__(self, name):
        """Delete all occurrences of a header, if present.
        Does *not* raise an exception if the header is missing.
        """
        name = self._convert_string_type(name.lower())
        self._headers[:] = [kv for kv in self._headers if kv[0].lower() != name]

    def __getitem__(self, name):
        """Get the first header value for 'name'
        Return None if the header is missing instead of raising an exception.
        Note that if the header appeared multiple times, the first exactly which
        occurrence gets returned is undefined.  Use getall() to get all
        the values matching a header field name.
        """
        return self.get(name)

    def __contains__(self, name):
        """Return true if the message contains the header."""
        return self.get(name) is not None


    def get_all(self, name):
        """Return a list of all the values for the named field.
        These will be sorted in the order they appeared in the original header
        list or were added to this instance, and may contain duplicates.  Any
        fields deleted and re-inserted are always appended to the header list.
        If no fields exist with the given name, returns an empty list.
        """
        name = self._convert_string_type(name.lower())
        return [kv[1] for kv in self._headers if kv[0].lower()==name]


    def get(self, name, default=None):
        """Get the first header value for 'name', or return 'default'"""
        name = self._convert_string_type(name.lower())
        for k, v in self._headers:
            if k.lower()==name:
                return v
        return default


    def keys(self):
        """Return a list of all the header field names.
        These will be sorted in the order they appeared in the original header
        list, or were added to this instance, and may contain duplicates.
        Any fields deleted and re-inserted are always appended to the header
        list.
        """
        return [k for k, v in self._headers]

    def values(self):
        """Return a list of all header values.
        These will be sorted in the order they appeared in the original header
        list, or were added to this instance, and may contain duplicates.
        Any fields deleted and re-inserted are always appended to the header
        list.
        """
        return [v for k, v in self._headers]

    def items(self):
        """Get all the header fields and values.
        These will be sorted in the order they were in the original header
        list, or were added to this instance, and may contain duplicates.
        Any fields deleted and re-inserted are always appended to the header
        list.
        """
        return self._headers[:]

    def __repr__(self):
        return "%s(%r)" % (self.__class__.__name__, self._headers)

    def __str__(self):
        """str() returns the formatted headers, complete with end line,
        suitable for direct HTTP transmission."""
        return '\r\n'.join(["%s: %s" % kv for kv in self._headers]+['',''])

    def __bytes__(self):
        return str(self).encode('iso-8859-1')

    def setdefault(self, name, value):
        """Return first matching header value for 'name', or 'value'
        If there is no header named 'name', add a new header with name 'name'
        and value 'value'."""
        result = self.get(name)
        if result is None:
            self._headers.append((self._convert_string_type(name),
                self._convert_string_type(value)))
            return value
        else:
            return result

    def add_header(self, _name, _value, **_params):
        """Extended header setting.
        _name is the header field to add.  keyword arguments can be used to set
        additional parameters for the header field, with underscores converted
        to dashes.  Normally the parameter will be added as key="value" unless
        value is None, in which case only the key will be added.
        Example:
        h.add_header('content-disposition', 'attachment', filename='bud.gif')
        Note that unlike the corresponding 'email.message' method, this does
        *not* handle '(charset, language, value)' tuples: all values must be
        strings or None.
        """
        parts = []
        if _value is not None:
            _value = self._convert_string_type(_value)
            parts.append(_value)
        for k, v in _params.items():
            k = self._convert_string_type(k)
            if v is None:
                parts.append(k.replace('_', '-'))
            else:
                v = self._convert_string_type(v)
                parts.append(_formatparam(k.replace('_', '-'), v))
        self._headers.append(
            (self._convert_string_type(_name), "; ".join(parts)))