Remove symlink & just copy postBuild file instead

Temp fix for https://github.com/jupyter/repo2docker/issues/160.
Also includes a test to prevent drift

tests/memlimit.py

@@ -79,3 +79,21 @@ def test_memlimit_dockerfile_fail():
         512,
         256
     )
+
+
+def test_memlimit_same_postbuild():
+    """
+    Validate that the postBuild files for dockerfile & nondockerfile are same
+
+    Until https://github.com/jupyter/repo2docker/issues/160 gets fixed.
+    """
+    basedir = os.path.dirname(__file__)
+    filepaths = [
+        os.path.join(basedir, 'memlimit', t, "postBuild")
+        for t in ("dockerfile", "non-dockerfile")
+    ]
+    file_contents = []
+    for fp in filepaths:
+        with open(fp) as f:
+            file_contents.append(f.read())
+    assert all(c == file_contents[0] for c in file_contents)

tests/memlimit/dockerfile/postBuild

@@ -4,6 +4,11 @@ Simplest program that tries to allocate a large amount of RAM.
 
 malloc lies on Linux by default, so we use memset to force the
 kernel to actually give us real memory.
+
+NOTE: This file has to be duplicated & present in all the following locations:
+ - tests/memlimit/dockerfile/postBuild
+ - tests/memlimit/dockerfile/postBuild
+See https://github.com/jupyter/repo2docker/issues/160 for reason
 """
 from ctypes import cdll, c_void_p, memset
 import os

tests/memlimit/non-dockerfile/postBuild

@@ -1 +0,0 @@
-../dockerfile/postBuild

tests/memlimit/non-dockerfile/postBuild

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+"""
+Simplest program that tries to allocate a large amount of RAM.
+
+malloc lies on Linux by default, so we use memset to force the
+kernel to actually give us real memory.
+
+NOTE: This file has to be duplicated & present in all the following locations:
+ - tests/memlimit/dockerfile/postBuild
+ - tests/memlimit/dockerfile/postBuild
+See https://github.com/jupyter/repo2docker/issues/160 for reason
+"""
+from ctypes import cdll, c_void_p, memset
+import os
+
+libc = cdll.LoadLibrary("libc.so.6")
+libc.malloc.restype = c_void_p
+
+with open('mem_allocate_mb') as f:
+    mem_allocate_mb = int(f.read().strip())
+
+size = 1024 * 1024 * mem_allocate_mb
+print("trying to allocate {}MB".format(mem_allocate_mb))
+
+ret = libc.malloc(size)
+
+memset(ret, 0, size)