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gh-99948: Support ctypes.util.find_library in emscripten environment #138519

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22 changes: 22 additions & 0 deletions Lib/ctypes/util.py
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -173,6 +173,28 @@ def find_library(name):
fname = f"{directory}/lib{name}.so"
return fname if os.path.isfile(fname) else None

elif sys.platform == "emscripten":
def _is_wasm(filename):
# Return True if the given file is an WASM module
wasm_header = b"\x00asm"
with open(filename, 'br') as thefile:
return thefile.read(4) == wasm_header

def find_library(name):
candidates = [f"lib{name}.so", f"lib{name}.wasm"]
paths = os.environ.get("LD_LIBRARY_PATH", "")
for libdir in paths.split(":"):
for name in candidates:
libfile = os.path.join(libdir, name)

if os.path.isfile(libfile):
if not _is_wasm(libfile):
continue

return libfile
Comment on lines +190 to +194
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@freakboy3742 freakboy3742 Sep 8, 2025

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This seems overly complicated; suggest:

Suggested change
if os.path.isfile(libfile):
if not _is_wasm(libfile):
continue
return libfile
if os.path.isfile(libfile) and _is_wasm(libfile):
return libfile


return None

elif os.name == "posix":
# Andreas Degert's find functions, using gcc, /sbin/ldconfig, objdump
import re, tempfile
Expand Down
32 changes: 32 additions & 0 deletions Lib/test/test_ctypes/test_find.py
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Original file line number Diff line number Diff line change
Expand Up @@ -153,5 +153,37 @@ def test_find(self):
self.assertIsNone(find_library(name))


@unittest.skipUnless(test.support.is_emscripten,
'Test only valid for Emscripten')
class FindLibraryEmscripten(unittest.TestCase):
def test_find_on_libpath(self):
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@freakboy3742 freakboy3742 Sep 8, 2025

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There's a few cases missing from this test suite, including:

  • Ignoring non-WASM files
  • Finding a libdummy.wasm file
  • Finding nothing if LD_LIBRARY_PATH isn't defined
  • Finding nothing if LD_LIBRARY_PATH is defined, but doesn't include a WASM file.

It might be worth setting up a directory that contains libdummy.so and libother.wasm as a class-based startup fixture, and then adding tests that manipulate LD_LIBRARY_PATH to find (or not find) those two files.

import tempfile

# A very simple wasm module
# In WAT format: (module)
wasm_module = b'\x00asm\x01\x00\x00\x00\x00\x08\x04name\x02\x01\x00'

with tempfile.TemporaryDirectory() as d:
libname = 'dummy'
dstname = os.path.join(d, 'lib%s.so' % libname)
with open(dstname, 'wb') as f:
f.write(wasm_module)

# now check that the .so can't be found (since not in
# LD_LIBRARY_PATH)
self.assertIsNone(find_library(libname))
# now add the location to LD_LIBRARY_PATH
with os_helper.EnvironmentVarGuard() as env:
KEY = 'LD_LIBRARY_PATH'
if KEY not in env:
v = d
else:
v = '%s:%s' % (env[KEY], d)
env.set(KEY, v)
# now check that the .so can be found (since in
# LD_LIBRARY_PATH)
self.assertEqual(find_library(libname), dstname)


if __name__ == "__main__":
unittest.main()
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
:func:`ctypes.util.find_library` now works in Emscripten build.
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