Change newline when setting context.os to "windows" (#2330)

* Change newline when setting `context.os`

Windows uses `b'\r\n'` for newlines while unix uses `b'\n'`. Change the expected newline to `b'\r\n'` when setting `context.os = "windows"` automatically for convenience.

* Update CHANGELOG

* Fix other tests setting os

CHANGELOG.md

@@ -76,12 +76,14 @@ The table below shows which release corresponds to each branch, and what date th
 - [#2374][2374] libcdb.unstrip_libc: debug symbols are fetched only if not present
 - [#2327][2327] Add basic support to debug processes on Windows
 - [#2322][2322] Add basic RISCV64 shellcraft support
+- [#2330][2330] Change `context.newline` when setting `context.os` to `"windows"`
 
 [2360]: https://github.com/Gallopsled/pwntools/pull/2360
 [2356]: https://github.com/Gallopsled/pwntools/pull/2356
 [2374]: https://github.com/Gallopsled/pwntools/pull/2374
 [2327]: https://github.com/Gallopsled/pwntools/pull/2327
 [2322]: https://github.com/Gallopsled/pwntools/pull/2322
+[2330]: https://github.com/Gallopsled/pwntools/pull/2330
 
 ## 4.13.0 (`beta`)
 

pwnlib/context/__init__.py

@@ -302,7 +302,7 @@ class ContextType(object):
         >>> context.os == 'linux'
         True
         >>> context.arch = 'arm'
-        >>> vars(context) == {'arch': 'arm', 'bits': 32, 'endian': 'little', 'os': 'linux'}
+        >>> vars(context) == {'arch': 'arm', 'bits': 32, 'endian': 'little', 'os': 'linux', 'newline': b'\n'}
         True
         >>> context.endian
         'little'
@@ -376,8 +376,19 @@ class ContextType(object):
         'timeout': Timeout.maximum,
     }
 
-    #: Valid values for :meth:`pwnlib.context.ContextType.os`
-    oses = sorted(('linux','freebsd','windows','cgc','android','baremetal','darwin'))
+    unix_like    = {'newline': b'\n'}
+    windows_like = {'newline': b'\r\n'}
+
+    #: Keys are valid values for :meth:`pwnlib.context.ContextType.os`
+    oses = _longest({
+        'linux':     unix_like,
+        'freebsd':   unix_like,
+        'windows':   windows_like,
+        'cgc':       unix_like,
+        'android':   unix_like,
+        'baremetal': unix_like,
+        'darwin':    unix_like,
+    })
 
     big_32    = {'endian': 'big', 'bits': 32}
     big_64    = {'endian': 'big', 'bits': 64}
@@ -446,14 +457,14 @@ def __init__(self, **kwargs):
 
 
     def copy(self):
-        """copy() -> dict
+        r"""copy() -> dict
         Returns a copy of the current context as a dictionary.
 
         Examples:
 
             >>> context.clear()
             >>> context.os   = 'linux'
-            >>> vars(context) == {'os': 'linux'}
+            >>> vars(context) == {'os': 'linux', 'newline': b'\n'}
             True
         """
         return self._tls.copy()
@@ -1104,25 +1115,73 @@ def mask(self):
 
     @_validator
     def os(self, os):
-        """
+        r"""
         Operating system of the target machine.
 
         The default value is ``linux``.
 
         Allowed values are listed in :attr:`pwnlib.context.ContextType.oses`.
 
+        Side Effects:
+
+            If an os is specified some attributes will be set on the context
+            if a user has not already set a value.
+
+            The following property may be modified:
+
+            - :attr:`newline`
+
+        Raises:
+            AttributeError: An invalid os was specified
+
         Examples:
 
-            >>> context.os = 'linux'
+            >>> context.clear()
+            >>> context.os == 'linux' # Default os
+            True
+
+            >>> context.os = 'freebsd'
+            >>> context.os == 'freebsd'
+            True
+
             >>> context.os = 'foobar' #doctest: +ELLIPSIS
             Traceback (most recent call last):
             ...
             AttributeError: os must be one of ['android', 'baremetal', 'cgc', 'freebsd', 'linux', 'windows']
+
+            >>> context.clear()
+            >>> context.newline == b'\n' # Default value
+            True
+            >>> context.os = 'windows'
+            >>> context.newline == b'\r\n' # New value
+            True
+
+            Note that expressly setting :attr:`newline` means that we use
+            that value instead of the default
+
+            >>> context.clear()
+            >>> context.newline = b'\n'
+            >>> context.os = 'windows'
+            >>> context.newline == b'\n'
+            True
+
+            Setting the os can override the default for :attr:`newline`
+
+            >>> context.clear()
+            >>> context.os = 'windows'
+            >>> vars(context) == {'os': 'windows', 'newline': b'\r\n'}
+            True
         """
         os = os.lower()
 
-        if os not in self.oses:
-            raise AttributeError("os must be one of %r" % self.oses)
+        try:
+            defaults = self.oses[os]
+        except KeyError:
+            raise AttributeError("os must be one of %r" % sorted(self.oses))
+
+        for k,v in defaults.items():
+            if k not in self._tls:
+                self._tls[k] = v
 
         return os