Fix: os.readlink should raise when the file is not a symlink

Author: steve-s

graalpython/com.oracle.graal.python.test/src/com/oracle/graal/python/test/module/PosixTest.java

@@ -25,11 +25,11 @@
  */
 package com.oracle.graal.python.test.module;
 
-import static com.oracle.graal.python.test.PythonTests.assertPrints;
 import static com.oracle.graal.python.test.PythonTests.assertLastLineError;
+import static com.oracle.graal.python.test.PythonTests.assertLastLineErrorContains;
+import static com.oracle.graal.python.test.PythonTests.assertPrints;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
-import static com.oracle.graal.python.test.PythonTests.assertLastLineErrorContains;
 
 import java.io.IOException;
 import java.nio.file.Files;
@@ -184,7 +184,7 @@ public void printToFile() throws IOException {
     }
 
     @Test
-    public void readlink() throws IOException {
+    public void readlinkWithSymlink() throws IOException {
         Path realPath = tmpfile.toRealPath();
         Path symlinkPath = realPath.getParent().resolve(tmpfile.getFileName() + "__symlink");
         try {
@@ -196,6 +196,13 @@ public void readlink() throws IOException {
         }
     }
 
+    @Test
+    public void readlinkWithOriginalFile() throws IOException {
+        Path realPath = tmpfile.toRealPath();
+        assertLastLineErrorContains("OSError", "import posix\n" +
+                        "print(posix.readlink('" + realPath.toString() + "'))\n");
+    }
+
     @Test
     public void sysExcInfo0() {
         assertPrints("42\n", "import sys\n" +

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PosixModuleBuiltins.java

@@ -1900,7 +1900,12 @@ String readlink(VirtualFrame frame, Object str, @SuppressWarnings("unused") PNon
                         @CachedLibrary("str") PythonObjectLibrary lib) {
             String path = lib.asPath(str);
             try {
-                return getContext().getEnv().getPublicTruffleFile(path).getCanonicalFile().getPath();
+                TruffleFile original = getContext().getEnv().getPublicTruffleFile(path);
+                TruffleFile canonicalFile = original.getCanonicalFile();
+                if (original.equals(canonicalFile)) {
+                    throw raiseOSError(frame, OSErrorEnum.EINVAL, path);
+                }
+                return canonicalFile.getPath();
             } catch (Exception e) {
                 throw raiseOSError(frame, e, path);
             }