mara004
commented
7 months ago Dumping my lean string class replacement draft below as it's not very well visible in the PR diff. This may be a slightly updated version.
class _wraps_c_char_p:
def __init__(self, raw, value):
self.raw = raw
self.value = value
# provided for clarity, not actually necessary due to __getattr__ wrapper below
def decode(self, encoding="utf-8", errors="strict"):
return self.value.decode(encoding, errors=errors)
def __str__(self):
return self.decode()
def __getattr__(self, attr):
return getattr(self.value, attr)
class String(ctypes.c_char_p):
@classmethod
def _check_retval_(cls, result):
value = result.value
return value if value is None else _wraps_c_char_p(result, value)
@classmethod
def from_param(cls, obj):
if isinstance(obj, str):
obj = obj.encode("utf-8")
return super().from_param(obj)
See below for an overview of this fork. Note, this writeup is a non-exhaustive work in progress.
This information may be valuable for working towards a basis that could be merged back into upstream at some point, though this seems fairly hypothetical for the near term, given time constraints, and mismatched design intents (e.g. relating to backwards compatibility).
However, this fork of ctypesgen may be a good starting point for any active future development, with a significantly overhauled code base that should be nicer to work with.
Selection of improvements from this fork
.to the module directory, not the caller's CWD. Don't add compile libdirs to runtime.__slots__declaration. This fix should be fairly easy for upstream to pick. See also https://github.com/ctypesgen/ctypesgen/issues/183--link-modules, and library handle sharing with--no-embed-preamble, Removed incorrectPOINTERoverride. This properly fixes https://github.com/ctypesgen/ctypesgen/issues/86 (shared headers), and allows to divide bindings to a library in multiple outputs (e.g. translate each header to a separate python file).--symbol-rules.UNCHECKEDwrapper from preamble.c_void_p->intauto-conversion (see Readme or commit for background).small, self-contained fixes have usually been submitted upstream and may have been merged
[^no_symbol_guards]: Note, this is meant for use with inherently ABI correct packaging only
Points to consider
Restoring implicit UTF-8 string encoding/decoding as optional?
ctypesgen originally did implicit UTF-8 encoding/decoding of in/out strings. While that tends to be bad practice and callers had better handle strings explicitly instead, it would seem reasonable to retain an optional backward compatibility layer for existing callers. I also imagine it might be convenient for a library that consistently uses UTF-8 for everything.
Adding the old string classes back is certainly not an option for us. However, it may be possible to create a lean replacement. See https://github.com/ctypesgen/ctypesgen/pull/177 for a suggestion (copy below), or https://github.com/ctypesgen/ctypesgen/issues/77#issuecomment-570145399 for an alternative draft by @olsonse. Note that in/out must be handled in a single class.
The windows-specific stdcall convention
Our fork lost it for simplicity while rewriting the library loader. It should be fairly easy to add back, just wondering how to test (as this lies beyond our use case), and how to integrate it nicely.
Does the calling convention really have to be decided on function level with two library handles for cdecl/stdcall, or would it be sufficient to decide at library level, with a single handle? Is there any example of a single library actually exporting functions with different calling conventions? Note that the ctypes API is designed around deciding at library handle level, not at function level, which suggests the expected use case is a library ABI with homogeneous calling convention.
Possible resolution: Added an option to take a caller-given dll class. It requires a small user interaction and does not support mixed calling conventions, but seems like a nice bloatless way to support a pure stdcall binary.
Removal of support for multiple libraries in one bindings file
This feature was a significant complexity burden in some code areas, including pollution around symbols in printer/output code. For now we decided to remove it - callers can use
--no-embed-preambleand--link-modulesto create separate bindings files. This also encourages individual/explicit rather than unified loader config.However, see https://github.com/ctypesgen/ctypesgen/issues/86#issuecomment-1858834699 for some interesting considerations regarding a possible cleaner re-implementation.
Other notes
Shifts in design intent: We would prefer to stick with plain ctypes as much as possible and avoid cluttering the bindings with custom wrappers.
CLI: We changed the command-line interface from
action=appendtoaction=extendandnargs=+/*. This implied switching headers from positional to flag argument to avoid confusion/interference with flags that take multiple arguments. There are more CLI changes not listed here, see diff for details.Done tasks