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On the latest Android API level (android-24), the if_nameindex function is now found by configure in Android libc. But the if_nameindex function and structure are still not defined in the Android net/if.h header.
The compilation fails with:
clang --sysroot=/opt/android-ndk/platforms/android-24/arch-x86 -target i686-none-linux-androideabi -gcc-toolchain /opt/android-ndk/toolchains/x86-4.9/prebuilt/linux-x86_64 -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -Wno-unused-value -Wno-empty-body -Qunused-arguments -Wno-parentheses-equality -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I. -IObjects -IInclude -IPython -I/home/xavier/src/android/pyona/build/python3.7-install-android-24-x86/org.bitbucket.pyona/include -I/opt/android-ndk/platforms/android-24/arch-x86/usr/include -I/path/to/android/cpython/Include -I/home/xavier/src/android/pyona/build/python3.7-android-24-x86 -c /path/to/android/cpython/Modules/socketmodule.c -o build/temp.linux-i686-3.7/path/to/android/cpython/Modules/socketmodule.o
/path/to/android/cpython/Modules/socketmodule.c:1034:29: warning: comparison of integers of different signs: 'socklen_t' (aka 'int') and 'size_t' (aka 'unsigned int') [-Wsign-compare]
 if (res->ai_addrlen < addr_ret_size)
 ~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
/path/to/android/cpython/Modules/socketmodule.c:1125:25: warning: comparison of integers of different signs: 'socklen_t' (aka 'int') and 'size_t' (aka 'unsigned int') [-Wsign-compare]
 if (res->ai_addrlen < addr_ret_size)
 ~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
/path/to/android/cpython/Modules/socketmodule.c:4925:15: warning: implicit declaration of function 'sethostname' is invalid in C99 [-Wimplicit-function-declaration]
 res = sethostname(buf.buf, buf.len);
 ^
/path/to/android/cpython/Modules/socketmodule.c:6242:10: warning: implicit declaration of function 'if_nameindex' is invalid in C99 [-Wimplicit-function-declaration]
 ni = if_nameindex();
 ^
/path/to/android/cpython/Modules/socketmodule.c:6242:8: warning: incompatible integer to pointer conversion assigning to 'struct if_nameindex *' from 'int' [-Wint-conversion]
 ni = if_nameindex();
 ^ ~~~~~~~~~~~~~~
/path/to/android/cpython/Modules/socketmodule.c:6250:9: warning: implicit declaration of function 'if_freenameindex' is invalid in C99 [-Wimplicit-function-declaration]
 if_freenameindex(ni);
 ^
/path/to/android/cpython/Modules/socketmodule.c:6254:19: error: subscript of pointer to incomplete type 'struct if_nameindex'
 for (i = 0; ni[i].if_index != 0 && i < INT_MAX; i++) {
 ~~^
/path/to/android/cpython/Modules/socketmodule.c:6240:12: note: forward declaration of 'struct if_nameindex'
 struct if_nameindex *ni;
 ^
/path/to/android/cpython/Modules/socketmodule.c:6256:19: error: subscript of pointer to incomplete type 'struct if_nameindex'
 ni[i].if_index, PyUnicode_DecodeFSDefault, ni[i].if_name);
 ~~^
/path/to/android/cpython/Modules/socketmodule.c:6240:12: note: forward declaration of 'struct if_nameindex'
 struct if_nameindex *ni;
 ^
/path/to/android/cpython/Modules/socketmodule.c:6256:62: error: subscript of pointer to incomplete type 'struct if_nameindex'
 ni[i].if_index, PyUnicode_DecodeFSDefault, ni[i].if_name);
 ~~^
/path/to/android/cpython/Modules/socketmodule.c:6240:12: note: forward declaration of 'struct if_nameindex'
 struct if_nameindex *ni;
 ^
6 warnings and 3 errors generated.

Patch attached.

New changeset e248bfb0f520 by Xavier de Gaye in branch '3.6':
Issue #28538: Fix the compilation error that occurs because if_nameindex() is
https://hg.python.org/cpython/rev/e248bfb0f520
New changeset 55bf0b79ec55 by Xavier de Gaye in branch 'default':
Issue #28538: Merge 3.6.
https://hg.python.org/cpython/rev/55bf0b79ec55 

These changes break the darwin platform, socket.if_nameindex() is not defined anymore. On Darwin, 'net/if.h' requires that 'sys/socket.h' be included beforehand (see the autoconf documentation).

New changeset f34dac552ad8 by Xavier de Gaye in branch '3.6':
Issue #28538: On Darwin net/if.h requires that sys/socket.h be included beforehand.
https://hg.python.org/cpython/rev/f34dac552ad8
New changeset c568b6ac5e89 by Xavier de Gaye in branch 'default':
Issue #28538: Merge 3.6.
https://hg.python.org/cpython/rev/c568b6ac5e89 

These changes are not needed anymore now that Unified Headers are supported by android-ndk-r14 (see issue 29040)

New changeset 5ad7ef8e420de8a54fb30ed37362194c6b96012c by xdegaye in branch 'master':
bpo-28538: Revert all the changes (now using Android Unified Headers) (GH-4479)
https://github.com/python/cpython/commit/5ad7ef8e420de8a54fb30ed37362194c6b96012c