unfinished partial work

1 files changed, 383 insertions, 0 deletions

diff --git a/src/hydrilla/proxy/flow_handlers.py b/src/hydrilla/proxy/flow_handlers.py
new file mode 100644
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--- /dev/null
+++ b/src/hydrilla/proxy/flow_handlers.py
@@ -0,0 +1,383 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Logic for modifying mitmproxy's HTTP flows.
+#
+# This file is part of Hydrilla&Haketilo.
+#
+# Copyright (C) 2022 Wojtek Kosior
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#
+#
+# I, Wojtek Kosior, thereby promise not to sue for violation of this
+# file's license. Although I request that you do not make use this code
+# in a proprietary program, I am not going to enforce this in court.
+
+"""
+This module's file gets passed to Mitmproxy as addon script and makes it serve
+as Haketilo proxy.
+"""
+
+# Enable using with Python 3.7.
+from __future__ import annotations
+
+import re
+import typing as t
+import dataclasses as dc
+
+import bs4 # type: ignore
+
+from mitmproxy import http
+from mitmproxy.net.http import Headers
+from mitmproxy.script import concurrent
+
+from .state import HaketiloState
+from . import policies
+
+StateUpdater = t.Callable[[HaketiloState], None]
+
+@dc.dataclass(frozen=True)
+class FlowHandler:
+    """...."""
+    flow:   http.HTTPFlow
+    policy: policies.Policy
+
+    stream_request:  bool = False
+    stream_response: bool = False
+
+    def on_requestheaders(self) -> t.Optional[StateUpdater]:
+        """...."""
+        if self.stream_request:
+            self.flow.request.stream = True
+
+        return None
+
+    def on_request(self) -> t.Optional[StateUpdater]:
+        """...."""
+        return None
+
+    def on_responseheaders(self) -> t.Optional[StateUpdater]:
+        """...."""
+        assert self.flow.response is not None
+
+        if self.stream_response:
+            self.flow.response.stream = True
+
+        return None
+
+    def on_response(self) -> t.Optional[StateUpdater]:
+        """...."""
+        return None
+
+@dc.dataclass(frozen=True)
+class FlowHandlerAllowScripts(FlowHandler):
+    """...."""
+    policy: policies.AllowPolicy
+
+    stream_request:  bool = True
+    stream_response: bool = True
+
+csp_header_names_and_dispositions = (
+    ('content-security-policy',             'enforce'),
+    ('content-security-policy-report-only', 'report'),
+    ('x-content-security-policy',           'enforce'),
+    ('x-content-security-policy',           'report'),
+    ('x-webkit-csp',                        'enforce'),
+    ('x-webkit-csp',                        'report')
+)
+
+csp_enforce_header_names_set = {
+    name for name, disposition in csp_header_names_and_dispositions
+    if disposition == 'enforce'
+}
+
+@dc.dataclass
+class ContentSecurityPolicy:
+    directives:  dict[str, list[str]]
+    header_name: str
+    disposition: str
+
+    @staticmethod
+    def deserialize(
+            serialized:  str,
+            header_name: str,
+            disposition: str = 'enforce'
+    ) -> 'ContentSecurityPolicy':
+        """...."""
+        # For more info, see:
+        # https://www.w3.org/TR/CSP3/#parse-serialized-policy
+        directives = {}
+
+        for serialized_directive in serialized.split(';'):
+            if not serialized_directive.isascii():
+                continue
+
+            serialized_directive = serialized_directive.strip()
+            if len(serialized_directive) == 0:
+                continue
+
+            tokens = serialized_directive.split()
+            directive_name = tokens.pop(0).lower()
+            directive_value = tokens
+
+            # Specs mention giving warnings for duplicate directive names but
+            # from our proxy's perspective this is not important right now.
+            if directive_name in directives:
+                continue
+
+            directives[directive_name] = directive_value
+
+        return ContentSecurityPolicy(directives, header_name, disposition)
+
+    def serialize(self) -> str:
+        """...."""
+        serialized_directives = []
+        for name, value_list in self.directives.items():
+            serialized_directives.append(f'{name} {" ".join(value_list)}')
+
+        return ';'.join(serialized_directives)
+
+def extract_csp(headers: Headers) -> tuple[ContentSecurityPolicy, ...]:
+    """...."""
+    csp_policies = []
+
+    for header_name, disposition in csp_header_names_and_dispositions:
+        for serialized_list in headers.get(header_name, ''):
+            for serialized in serialized_list.split(','):
+                policy = ContentSecurityPolicy.deserialize(
+                    serialized,
+                    header_name,
+                    disposition
+                )
+
+                if policy.directives != {}:
+                    csp_policies.append(policy)
+
+    return tuple(csp_policies)
+
+csp_script_directive_names = (
+    'script-src',
+    'script-src-elem',
+    'script-src-attr'
+)
+
+@dc.dataclass(frozen=True)
+class FlowHandlerBlockScripts(FlowHandler):
+    policy: policies.BlockPolicy
+
+    stream_request:  bool = True
+    stream_response: bool = True
+
+    def on_responseheaders(self) -> t.Optional[StateUpdater]:
+        """...."""
+        super().on_responseheaders()
+
+        assert self.flow.response is not None
+
+        csp_policies = extract_csp(self.flow.response.headers)
+
+        for header_name, _ in csp_header_names_and_dispositions:
+            del self.flow.response.headers[header_name]
+
+        for policy in csp_policies:
+            if policy.disposition != 'enforce':
+                continue
+
+            policy.directives.pop('report-to')
+            policy.directives.pop('report-uri')
+
+            self.flow.response.headers.add(
+                policy.header_name,
+                policy.serialize()
+            )
+
+        extra_csp = ';'.join((
+            "script-src 'none'",
+            "script-src-elem 'none'",
+            "script-src-attr 'none'"
+        ))
+
+        self.flow.response.headers.add('Content-Security-Policy', extra_csp)
+
+        return None
+
+# For details of 'Content-Type' header's structure, see:
+# https://datatracker.ietf.org/doc/html/rfc7231#section-3.1.1.1
+content_type_reg = re.compile(r'''
+^
+(?P<mime>[\w-]+/[\w-]+)
+\s*
+(?:
+    ;
+    (?:[^;]*;)* # match possible parameter other than "charset"
+)
+\s*
+charset=        # no whitespace allowed in parameter as per RFC
+(?P<encoding>
+    [\w-]+
+    |
+    "[\w-]+"    # quotes are optional per RFC
+)
+(?:;[^;]+)*     # match possible parameter other than "charset"
+$               # forbid possible dangling characters after closing '"'
+''', re.VERBOSE | re.IGNORECASE)
+
+def deduce_content_type(headers: Headers) \
+    -> tuple[t.Optional[str], t.Optional[str]]:
+    """...."""
+    content_type = headers.get('content-type')
+    if content_type is None:
+        return (None, None)
+
+    match = content_type_reg.match(content_type)
+    if match is None:
+        return (None, None)
+
+    mime, encoding = match.group('mime'), match.group('encoding')
+
+    if encoding is not None:
+        encoding = encoding.lower()
+
+    return mime, encoding
+
+UTF8_BOM = b'\xEF\xBB\xBF'
+BOMs = (
+    (UTF8_BOM,    'utf-8'),
+    (b'\xFE\xFF', 'utf-16be'),
+    (b'\xFF\xFE', 'utf-16le')
+)
+
+def block_attr(element: bs4.PageElement, atrr_name: str) -> None:
+    """...."""
+    # TODO: implement
+    pass
+
+@dc.dataclass(frozen=True)
+class FlowHandlerInjectPayload(FlowHandler):
+    """...."""
+    policy: policies.PayloadPolicy
+
+    stream_request: bool = True
+
+    def __post_init__(self) -> None:
+        """...."""
+        script_src = f"script-src {self.policy.assets_base_url()}"
+        if self.policy.is_eval_allowed():
+            script_src = f"{script_src} 'unsafe-eval'"
+
+        self.new_csp = '; '.join((
+            script_src,
+            "script-src-elem 'none'",
+            "script-src-attr 'none'"
+        ))
+
+    def on_responseheaders(self) -> t.Optional[StateUpdater]:
+        """...."""
+        super().on_responseheaders()
+
+        assert self.flow.response is not None
+
+        for header_name, _ in csp_header_names_and_dispositions:
+            del self.flow.response.headers[header_name]
+
+        self.flow.response.headers.add('Content-Security-Policy', self.new_csp)
+
+        return None
+
+    def on_response(self) -> t.Optional[StateUpdater]:
+        """...."""
+        super().on_response()
+
+        assert self.flow.response is not None
+
+        if self.flow.response.content is None:
+            return None
+
+        mime, encoding = deduce_content_type(self.flow.response.headers)
+        if mime is None or 'html' not in mime:
+            return None
+
+        # A UTF BOM overrides encoding specified by the header.
+        for bom, encoding_name in BOMs:
+            if self.flow.response.content.startswith(bom):
+                encoding = encoding_name
+
+        soup = bs4.BeautifulSoup(
+            markup                   = self.flow.response.content,
+            from_encoding            = encoding,
+            features                 = 'html5lib'
+        )
+
+        # Inject scripts.
+        script_parent = soup.find('body') or soup.find('html')
+        if script_parent is None:
+            return None
+
+        for url in self.policy.script_urls():
+            script_parent.append(bs4.Tag(name='script', attrs={'src': url}))
+
+        # Remove Content Security Policy that could possibly block injected
+        # scripts.
+        for meta in soup.select('head meta[http-equiv]'):
+            header_name = meta.attrs.get('http-equiv', '').lower().strip()
+            if header_name in csp_enforce_header_names_set:
+                block_attr(meta, 'http-equiv')
+                block_attr(meta, 'content')
+
+        # Appending a three-byte Byte Order Mark (BOM) will force the browser to
+        # decode this as UTF-8 regardless of the 'Content-Type' header. See:
+        # https://www.w3.org/International/tests/repository/html5/the-input-byte-stream/results-basics#precedence
+        self.flow.response.content = UTF8_BOM + soup.encode()
+
+        return None
+
+@dc.dataclass(frozen=True)
+class FlowHandlerMetaResource(FlowHandler):
+    """...."""
+    policy: policies.MetaResourcePolicy
+
+    def on_request(self) -> t.Optional[StateUpdater]:
+        """...."""
+        super().on_request()
+        # TODO: implement
+        #self.flow.response = ....
+
+        return None
+
+def make_flow_handler(flow: http.HTTPFlow, policy: policies.Policy) \
+    -> FlowHandler:
+    """...."""
+    if isinstance(policy, policies.BlockPolicy):
+        return FlowHandlerBlockScripts(flow, policy)
+
+    if isinstance(policy, policies.AllowPolicy):
+        return FlowHandlerAllowScripts(flow, policy)
+
+    if isinstance(policy, policies.PayloadPolicy):
+        return FlowHandlerInjectPayload(flow, policy)
+
+    assert isinstance(policy, policies.MetaResourcePolicy)
+    # def response_creator(request: http.HTTPRequest) -> http.HTTPResponse:
+    #     """...."""
+    #     replacement_details = make_replacement_resource(
+    #         policy.replacement,
+    #         request.path
+    #     )
+
+    #     return http.HTTPResponse.make(
+    #         replacement_details.status_code,
+    #         replacement_details.content,
+    #         replacement_details.content_type
+    #     )
+    return FlowHandlerMetaResource(flow, policy)