prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  v4 --replacements vs v5 --modify-headers
  I'm trying to replace the `User-Agent` request header if it contains a certain string.
  
  This works with "mitmproxy-4.0.4-linux":
  
  ```
  ./mitmproxy --replacements ":~hq User-Agent:Mozilla(.+):CUSTOMAGENT"
  ```
  
  With "mitmproxy-5.2-linux", this at least replaces the `User-Agent`, but is missing my "certain string condition":
  
  ```
  ./mitmproxy --modify-headers "|~hq .+|User-Agent|CUSTOMAGENT"
  ```
  
  How do I add my `Mozilla` condition in v5?
  
  None of these work:
  
  ```
  ./mitmproxy --modify-headers "|~hq ^(.*?)Mozilla(.*?)$|User-Agent|CUSTOMAGENT"
  
  ./mitmproxy --modify-headers "/~hq .*?Mozilla.*?/User-Agent/CUSTOMAGENT"
  
  ./mitmproxy --modify-headers "|~hq Mozilla|User-Agent|CUSTOMAGENT"
  
  ./mitmproxy --modify-headers "|~hq User-Agent: Mozilla|User-Agent|CUSTOMAGENT"
  
  ./mitmproxy --modify-headers "|~hq \"^(.*?)Mozilla(.*?)$\"|User-Agent|CUSTOMAGENT"
  ```
  
  I've been trying for hours, and I feel like I've tried every variation under the sun. There's a very small chance it's a bug, but most likely I'm just doing it wrong. If it matters, this system is Ubuntu 16.04.
  
  
  
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `mitmproxy/addons/modifyheaders.py`
  Content:
  ```
  1 import re
  2 import typing
  3 from pathlib import Path
  4 
  5 from mitmproxy import ctx, exceptions, flowfilter, http
  6 from mitmproxy.net.http import Headers
  7 from mitmproxy.utils import strutils
  8 from mitmproxy.utils.spec import parse_spec
  9 
  10 
  11 class ModifySpec(typing.NamedTuple):
  12     matches: flowfilter.TFilter
  13     subject: bytes
  14     replacement_str: str
  15 
  16     def read_replacement(self) -> bytes:
  17         """
  18         Process the replacement str. This usually just involves converting it to bytes.
  19         However, if it starts with `@`, we interpret the rest as a file path to read from.
  20 
  21         Raises:
  22             - IOError if the file cannot be read.
  23         """
  24         if self.replacement_str.startswith("@"):
  25             return Path(self.replacement_str[1:]).expanduser().read_bytes()
  26         else:
  27             # We could cache this at some point, but unlikely to be a problem.
  28             return strutils.escaped_str_to_bytes(self.replacement_str)
  29 
  30 
  31 def parse_modify_spec(option: str, subject_is_regex: bool) -> ModifySpec:
  32     flow_filter, subject_str, replacement = parse_spec(option)
  33 
  34     subject = strutils.escaped_str_to_bytes(subject_str)
  35     if subject_is_regex:
  36         try:
  37             re.compile(subject)
  38         except re.error as e:
  39             raise ValueError(f"Invalid regular expression {subject!r} ({e})")
  40 
  41     spec = ModifySpec(flow_filter, subject, replacement)
  42 
  43     try:
  44         spec.read_replacement()
  45     except OSError as e:
  46         raise ValueError(f"Invalid file path: {replacement[1:]} ({e})")
  47 
  48     return spec
  49 
  50 
  51 class ModifyHeaders:
  52     def __init__(self):
  53         self.replacements: typing.List[ModifySpec] = []
  54 
  55     def load(self, loader):
  56         loader.add_option(
  57             "modify_headers", typing.Sequence[str], [],
  58             """
  59             Header modify pattern of the form "[/flow-filter]/header-name/[@]header-value", where the
  60             separator can be any character. The @ allows to provide a file path that is used to read
  61             the header value string. An empty header-value removes existing header-name headers.
  62             """
  63         )
  64 
  65     def configure(self, updated):
  66         if "modify_headers" in updated:
  67             self.replacements = []
  68             for option in ctx.options.modify_headers:
  69                 try:
  70                     spec = parse_modify_spec(option, False)
  71                 except ValueError as e:
  72                     raise exceptions.OptionsError(f"Cannot parse modify_headers option {option}: {e}") from e
  73                 self.replacements.append(spec)
  74 
  75     def request(self, flow):
  76         if flow.response or flow.error or flow.reply.state == "taken":
  77             return
  78         self.run(flow, flow.request.headers)
  79 
  80     def response(self, flow):
  81         if flow.error or flow.reply.state == "taken":
  82             return
  83         self.run(flow, flow.response.headers)
  84 
  85     def run(self, flow: http.HTTPFlow, hdrs: Headers) -> None:
  86         # unset all specified headers
  87         for spec in self.replacements:
  88             if spec.matches(flow):
  89                 hdrs.pop(spec.subject, None)
  90 
  91         # set all specified headers if the replacement string is not empty
  92         for spec in self.replacements:
  93             if spec.matches(flow):
  94                 try:
  95                     replacement = spec.read_replacement()
  96                 except OSError as e:
  97                     ctx.log.warn(f"Could not read replacement file: {e}")
  98                     continue
  99                 else:
  100                     if replacement:
  101                         hdrs.add(spec.subject, replacement)
  102
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/mitmproxy/addons/modifyheaders.py b/mitmproxy/addons/modifyheaders.py
  --- a/mitmproxy/addons/modifyheaders.py
  +++ b/mitmproxy/addons/modifyheaders.py
  @@ -83,14 +83,21 @@
           self.run(flow, flow.response.headers)
   
       def run(self, flow: http.HTTPFlow, hdrs: Headers) -> None:
  -        # unset all specified headers
  +        matches = []
  +
  +        # first check all the filters against the original, unmodified flow
           for spec in self.replacements:
  -            if spec.matches(flow):
  +            matches.append(spec.matches(flow))
  +
  +        # unset all specified headers
  +        for i, spec in enumerate(self.replacements):
  +            if matches[i]:
                   hdrs.pop(spec.subject, None)
   
           # set all specified headers if the replacement string is not empty
  -        for spec in self.replacements:
  -            if spec.matches(flow):
  +
  +        for i, spec in enumerate(self.replacements):
  +            if matches[i]:
                   try:
                       replacement = spec.read_replacement()
                   except OSError as e:
  
verification_info: {"golden_diff": "diff --git a/mitmproxy/addons/modifyheaders.py b/mitmproxy/addons/modifyheaders.py\n--- a/mitmproxy/addons/modifyheaders.py\n+++ b/mitmproxy/addons/modifyheaders.py\n@@ -83,14 +83,21 @@\n         self.run(flow, flow.response.headers)\n \n     def run(self, flow: http.HTTPFlow, hdrs: Headers) -> None:\n-        # unset all specified headers\n+        matches = []\n+\n+        # first check all the filters against the original, unmodified flow\n         for spec in self.replacements:\n-            if spec.matches(flow):\n+            matches.append(spec.matches(flow))\n+\n+        # unset all specified headers\n+        for i, spec in enumerate(self.replacements):\n+            if matches[i]:\n                 hdrs.pop(spec.subject, None)\n \n         # set all specified headers if the replacement string is not empty\n-        for spec in self.replacements:\n-            if spec.matches(flow):\n+\n+        for i, spec in enumerate(self.replacements):\n+            if matches[i]:\n                 try:\n                     replacement = spec.read_replacement()\n                 except OSError as e:\n", "issue": "v4 --replacements vs v5 --modify-headers\nI'm trying to replace the `User-Agent` request header if it contains a certain string.\r\n\r\nThis works with \"mitmproxy-4.0.4-linux\":\r\n\r\n```\r\n./mitmproxy --replacements \":~hq User-Agent:Mozilla(.+):CUSTOMAGENT\"\r\n```\r\n\r\nWith \"mitmproxy-5.2-linux\", this at least replaces the `User-Agent`, but is missing my \"certain string condition\":\r\n\r\n```\r\n./mitmproxy --modify-headers \"|~hq .+|User-Agent|CUSTOMAGENT\"\r\n```\r\n\r\nHow do I add my `Mozilla` condition in v5?\r\n\r\nNone of these work:\r\n\r\n```\r\n./mitmproxy --modify-headers \"|~hq ^(.*?)Mozilla(.*?)$|User-Agent|CUSTOMAGENT\"\r\n\r\n./mitmproxy --modify-headers \"/~hq .*?Mozilla.*?/User-Agent/CUSTOMAGENT\"\r\n\r\n./mitmproxy --modify-headers \"|~hq Mozilla|User-Agent|CUSTOMAGENT\"\r\n\r\n./mitmproxy --modify-headers \"|~hq User-Agent: Mozilla|User-Agent|CUSTOMAGENT\"\r\n\r\n./mitmproxy --modify-headers \"|~hq \\\"^(.*?)Mozilla(.*?)$\\\"|User-Agent|CUSTOMAGENT\"\r\n```\r\n\r\nI've been trying for hours, and I feel like I've tried every variation under the sun. There's a very small chance it's a bug, but most likely I'm just doing it wrong. If it matters, this system is Ubuntu 16.04.\r\n\r\n\r\n\n", "before_files": [{"content": "import re\nimport typing\nfrom pathlib import Path\n\nfrom mitmproxy import ctx, exceptions, flowfilter, http\nfrom mitmproxy.net.http import Headers\nfrom mitmproxy.utils import strutils\nfrom mitmproxy.utils.spec import parse_spec\n\n\nclass ModifySpec(typing.NamedTuple):\n    matches: flowfilter.TFilter\n    subject: bytes\n    replacement_str: str\n\n    def read_replacement(self) -> bytes:\n        \"\"\"\n        Process the replacement str. This usually just involves converting it to bytes.\n        However, if it starts with `@`, we interpret the rest as a file path to read from.\n\n        Raises:\n            - IOError if the file cannot be read.\n        \"\"\"\n        if self.replacement_str.startswith(\"@\"):\n            return Path(self.replacement_str[1:]).expanduser().read_bytes()\n        else:\n            # We could cache this at some point, but unlikely to be a problem.\n            return strutils.escaped_str_to_bytes(self.replacement_str)\n\n\ndef parse_modify_spec(option: str, subject_is_regex: bool) -> ModifySpec:\n    flow_filter, subject_str, replacement = parse_spec(option)\n\n    subject = strutils.escaped_str_to_bytes(subject_str)\n    if subject_is_regex:\n        try:\n            re.compile(subject)\n        except re.error as e:\n            raise ValueError(f\"Invalid regular expression {subject!r} ({e})\")\n\n    spec = ModifySpec(flow_filter, subject, replacement)\n\n    try:\n        spec.read_replacement()\n    except OSError as e:\n        raise ValueError(f\"Invalid file path: {replacement[1:]} ({e})\")\n\n    return spec\n\n\nclass ModifyHeaders:\n    def __init__(self):\n        self.replacements: typing.List[ModifySpec] = []\n\n    def load(self, loader):\n        loader.add_option(\n            \"modify_headers\", typing.Sequence[str], [],\n            \"\"\"\n            Header modify pattern of the form \"[/flow-filter]/header-name/[@]header-value\", where the\n            separator can be any character. The @ allows to provide a file path that is used to read\n            the header value string. An empty header-value removes existing header-name headers.\n            \"\"\"\n        )\n\n    def configure(self, updated):\n        if \"modify_headers\" in updated:\n            self.replacements = []\n            for option in ctx.options.modify_headers:\n                try:\n                    spec = parse_modify_spec(option, False)\n                except ValueError as e:\n                    raise exceptions.OptionsError(f\"Cannot parse modify_headers option {option}: {e}\") from e\n                self.replacements.append(spec)\n\n    def request(self, flow):\n        if flow.response or flow.error or flow.reply.state == \"taken\":\n            return\n        self.run(flow, flow.request.headers)\n\n    def response(self, flow):\n        if flow.error or flow.reply.state == \"taken\":\n            return\n        self.run(flow, flow.response.headers)\n\n    def run(self, flow: http.HTTPFlow, hdrs: Headers) -> None:\n        # unset all specified headers\n        for spec in self.replacements:\n            if spec.matches(flow):\n                hdrs.pop(spec.subject, None)\n\n        # set all specified headers if the replacement string is not empty\n        for spec in self.replacements:\n            if spec.matches(flow):\n                try:\n                    replacement = spec.read_replacement()\n                except OSError as e:\n                    ctx.log.warn(f\"Could not read replacement file: {e}\")\n                    continue\n                else:\n                    if replacement:\n                        hdrs.add(spec.subject, replacement)\n", "path": "mitmproxy/addons/modifyheaders.py"}], "after_files": [{"content": "import re\nimport typing\nfrom pathlib import Path\n\nfrom mitmproxy import ctx, exceptions, flowfilter, http\nfrom mitmproxy.net.http import Headers\nfrom mitmproxy.utils import strutils\nfrom mitmproxy.utils.spec import parse_spec\n\n\nclass ModifySpec(typing.NamedTuple):\n    matches: flowfilter.TFilter\n    subject: bytes\n    replacement_str: str\n\n    def read_replacement(self) -> bytes:\n        \"\"\"\n        Process the replacement str. This usually just involves converting it to bytes.\n        However, if it starts with `@`, we interpret the rest as a file path to read from.\n\n        Raises:\n            - IOError if the file cannot be read.\n        \"\"\"\n        if self.replacement_str.startswith(\"@\"):\n            return Path(self.replacement_str[1:]).expanduser().read_bytes()\n        else:\n            # We could cache this at some point, but unlikely to be a problem.\n            return strutils.escaped_str_to_bytes(self.replacement_str)\n\n\ndef parse_modify_spec(option: str, subject_is_regex: bool) -> ModifySpec:\n    flow_filter, subject_str, replacement = parse_spec(option)\n\n    subject = strutils.escaped_str_to_bytes(subject_str)\n    if subject_is_regex:\n        try:\n            re.compile(subject)\n        except re.error as e:\n            raise ValueError(f\"Invalid regular expression {subject!r} ({e})\")\n\n    spec = ModifySpec(flow_filter, subject, replacement)\n\n    try:\n        spec.read_replacement()\n    except OSError as e:\n        raise ValueError(f\"Invalid file path: {replacement[1:]} ({e})\")\n\n    return spec\n\n\nclass ModifyHeaders:\n    def __init__(self):\n        self.replacements: typing.List[ModifySpec] = []\n\n    def load(self, loader):\n        loader.add_option(\n            \"modify_headers\", typing.Sequence[str], [],\n            \"\"\"\n            Header modify pattern of the form \"[/flow-filter]/header-name/[@]header-value\", where the\n            separator can be any character. The @ allows to provide a file path that is used to read\n            the header value string. An empty header-value removes existing header-name headers.\n            \"\"\"\n        )\n\n    def configure(self, updated):\n        if \"modify_headers\" in updated:\n            self.replacements = []\n            for option in ctx.options.modify_headers:\n                try:\n                    spec = parse_modify_spec(option, False)\n                except ValueError as e:\n                    raise exceptions.OptionsError(f\"Cannot parse modify_headers option {option}: {e}\") from e\n                self.replacements.append(spec)\n\n    def request(self, flow):\n        if flow.response or flow.error or flow.reply.state == \"taken\":\n            return\n        self.run(flow, flow.request.headers)\n\n    def response(self, flow):\n        if flow.error or flow.reply.state == \"taken\":\n            return\n        self.run(flow, flow.response.headers)\n\n    def run(self, flow: http.HTTPFlow, hdrs: Headers) -> None:\n        matches = []\n\n        # first check all the filters against the original, unmodified flow\n        for spec in self.replacements:\n            matches.append(spec.matches(flow))\n\n        # unset all specified headers\n        for i, spec in enumerate(self.replacements):\n            if matches[i]:\n                hdrs.pop(spec.subject, None)\n\n        # set all specified headers if the replacement string is not empty\n\n        for i, spec in enumerate(self.replacements):\n            if matches[i]:\n                try:\n                    replacement = spec.read_replacement()\n                except OSError as e:\n                    ctx.log.warn(f\"Could not read replacement file: {e}\")\n                    continue\n                else:\n                    if replacement:\n                        hdrs.add(spec.subject, replacement)\n", "path": "mitmproxy/addons/modifyheaders.py"}]}