fix gunicorn when used with musl libc

find_library('c') doesn't work in Alpine Linux. This happen because musl has a simpler implementation of libc.

This patch fix it by extending ctypes.util.find_library to search the libs using LD_LIBRARY_PATH.

Patch is based on e3f67780aa

See also https://bugs.python.org/issue21622

fix #2160

gunicorn/socketfromfd.py

@@ -12,7 +12,7 @@ import socket
 import sys
 import platform
 
-from ctypes.util import find_library
+from .util import find_library
 
 __all__ = ('fromfd',)
 

gunicorn/util.py

@@ -3,6 +3,7 @@
 # This file is part of gunicorn released under the MIT license.
 # See the NOTICE for more information.
 import ast
+import ctypes.util
 import email.utils
 import errno
 import fcntl
@@ -635,3 +636,32 @@ def bytes_to_str(b):
 
 def unquote_to_wsgi_str(string):
     return urllib.parse.unquote_to_bytes(string).decode('latin-1')
+
+
+def _findWalk_ldpath(name):
+    def _is_elf(filepath):
+        try:
+            with open(filepath, 'rb') as fh:
+                return fh.read(4) == b'\x7fELF'
+        except:
+            return False
+    from glob import glob
+    if os.path.isabs(name):
+        return name
+
+    # search LD_LIBRARY_PATH list
+    paths = os.environ.get('LD_LIBRARY_PATH', '').split(':')
+    if paths:
+        for d in paths:
+            f = os.path.join(d, name)
+            if _is_elf(f):
+                return os.path.basename(f)
+            prefix = os.path.join(d, 'lib'+name)
+            for suffix in ['.so', '.so.*']:
+                for f in glob('{0}{1}'.format(prefix, suffix)):
+                    if _is_elf(f):
+                        return os.path.basename(f)
+
+
+def find_library(name):
+    return ctypes.util.find_library(name) or _findWalk_ldpath(name)