address review feedback: extend APPDATA check to reject empty/blank strings, add tests

Signed-off-by: anish k <ak8686@princeton.edu>

Author: anishesg

google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/GoogleAuthUtils.java

@@ -73,10 +73,10 @@ static final File getWellKnownCredentialsFile(DefaultCredentialsProvider provide
       cloudConfigPath = new File(envPath);
     } else if (provider.getOsName().indexOf("windows") >= 0) {
       String appDataEnv = provider.getEnv("APPDATA");
-      if (appDataEnv == null) {
+      if (appDataEnv == null || appDataEnv.trim().isEmpty()) {
         throw new UncheckedIOException(
             new FileNotFoundException(
-                "APPDATA environment variable is not set; cannot locate the well-known"
+                "APPDATA environment variable is not set or empty; cannot locate the well-known"
                     + " credentials file on Windows."));
       }
       File appDataPath = new File(appDataEnv);

google-auth-library-java/oauth2_http/javatests/com/google/auth/oauth2/GoogleAuthUtilsTest.java

@@ -56,6 +56,39 @@ void getWellKnownCredentialsFile_windows_nullAppData_throwsUncheckedIOException(
             () -> GoogleAuthUtils.getWellKnownCredentialsFile(provider));
     assertTrue(thrown.getCause() instanceof FileNotFoundException);
     assertTrue(thrown.getCause().getMessage().contains("APPDATA"));
+    assertTrue(thrown.getCause().getMessage().contains("not set or empty"));
+  }
+
+  @Test
+  void getWellKnownCredentialsFile_windows_emptyAppData_throwsUncheckedIOException() {
+    DefaultCredentialsProviderTest.TestDefaultCredentialsProvider provider =
+        new DefaultCredentialsProviderTest.TestDefaultCredentialsProvider();
+    provider.setProperty("os.name", "windows");
+    provider.setEnv("APPDATA", "");
+
+    UncheckedIOException thrown =
+        assertThrows(
+            UncheckedIOException.class,
+            () -> GoogleAuthUtils.getWellKnownCredentialsFile(provider));
+    assertTrue(thrown.getCause() instanceof FileNotFoundException);
+    assertTrue(thrown.getCause().getMessage().contains("APPDATA"));
+    assertTrue(thrown.getCause().getMessage().contains("not set or empty"));
+  }
+
+  @Test
+  void getWellKnownCredentialsFile_windows_blankAppData_throwsUncheckedIOException() {
+    DefaultCredentialsProviderTest.TestDefaultCredentialsProvider provider =
+        new DefaultCredentialsProviderTest.TestDefaultCredentialsProvider();
+    provider.setProperty("os.name", "windows");
+    provider.setEnv("APPDATA", "   ");
+
+    UncheckedIOException thrown =
+        assertThrows(
+            UncheckedIOException.class,
+            () -> GoogleAuthUtils.getWellKnownCredentialsFile(provider));
+    assertTrue(thrown.getCause() instanceof FileNotFoundException);
+    assertTrue(thrown.getCause().getMessage().contains("APPDATA"));
+    assertTrue(thrown.getCause().getMessage().contains("not set or empty"));
   }
 
   @Test