feat: added support for host whitelist from system property

CHANGELOG.md

@@ -24,6 +24,8 @@
 
 * Added fallback to binary mode on failure in zip digest computation
 
+* Added support for user defined host whitelist from system property
+
 ## 1.8.7 - May 24, 2022
 
 * Paths in classpath are specified relative to appdir to avoid excessively long command lines.

core/src/main/java/io/github/bekoenig/getdown/data/Build.java.tmpl

@@ -5,11 +5,6 @@
 
 package io.github.bekoenig.getdown.data;
 
-import java.util.Arrays;
-import java.util.List;
-
-import io.github.bekoenig.getdown.util.StringUtil;
-
 /**
  * Contains static data provided during the build process.
  */
@@ -26,7 +21,7 @@ public class Build {
     }
 
     /**
-     * <p>The hosts which Getdown is allowed to communicate with. An empty list indicates that
+     * <p>The hosts which Getdown is allowed to communicate with. An empty string indicates that
      * no whitelist is configured and there are no limitations. By default, no host whitelist
      * is added to the binary, so it can be used to download and run applications from any
      * server.
@@ -37,7 +32,7 @@ public class Build {
      * (e.g. {@code *.mycompany.com}) and multiple values can be separated by commas
      * (e.g. {@code app1.foo.com,app2.bar.com,app3.baz.com}).
      */
-    public static List<String> hostWhitelist () {
-        return Arrays.asList(StringUtil.parseStringArray("@host_whitelist@"));
+    public static String hostWhitelist () {
+        return "@host_whitelist@";
     }
 }

core/src/main/java/io/github/bekoenig/getdown/data/SysProps.java

@@ -175,6 +175,13 @@ public static int threadPoolSize() {
         return Integer.getInteger("thread_pool_size", defaultSize);
     }
 
+    /**
+     * Returns the host whitelist from system property.
+     */
+    public static String hostWhitelist() {
+        return System.getProperty("getdown.host.whitelist", "");
+    }
+
     /**
      * Parses a Java version system property using the supplied regular expression. The numbers
      * extracted from the regexp will be placed in each consecutive hundreds position in the

core/src/main/java/io/github/bekoenig/getdown/util/HostWhitelist.java

@@ -6,24 +6,44 @@
 package io.github.bekoenig.getdown.util;
 
 import io.github.bekoenig.getdown.data.Build;
+import io.github.bekoenig.getdown.data.SysProps;
 
 import java.net.MalformedURLException;
 import java.net.URL;
+import java.util.Arrays;
 import java.util.List;
 
 /**
- * Optional support for compiling a URL host whitelist into the Getdown JAR.
+ * Optional support for compiling a URL host whitelist into the Getdown JAR or defined by system
+ * property.
  * Useful if you're on the paranoid end of the security spectrum.
  *
  * @see Build#hostWhitelist()
+ * @see SysProps#hostWhitelist()
  */
 public final class HostWhitelist {
+
+    /**
+     * Returns the active host whitelist. If no host whitelist was set in the build (default
+     * behavior), the system property with the same name is used.
+     */
+    private static List<String> activeHostWhitelist() {
+        // The compiled host whitelist has the highest priority.
+        String hostWhitelist = Build.hostWhitelist();
+        // If the compiled host whitelist is blank, the system property can be used.
+        if (StringUtil.isBlank(hostWhitelist)) {
+            hostWhitelist = SysProps.hostWhitelist();
+        }
+
+        return Arrays.asList(StringUtil.parseStringArray(hostWhitelist));
+    }
+
     /**
      * Verifies that the specified URL should be accessible, per the built-in host whitelist.
      * See {@link Build#hostWhitelist()} and {@link #verify(List, URL)}.
      */
     public static URL verify(URL url) throws MalformedURLException {
-        return verify(Build.hostWhitelist(), url);
+        return verify(activeHostWhitelist(), url);
     }
 
     /**

core/src/test/java/io/github/bekoenig/getdown/data/SysPropsTest.java

@@ -7,7 +7,10 @@
 
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
+import org.junitpioneer.jupiter.ClearSystemProperty;
+import org.junitpioneer.jupiter.SetSystemProperty;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class SysPropsTest {
@@ -66,4 +69,29 @@ void testAppbaseOverride() {
             assertEquals("https://barbaz.com/newapp", SysProps.overrideAppbase(appbase));
         }
     }
+
+    @Test
+    @ClearSystemProperty(key = "getdown.host.whitelist")
+    void test_hostWhitelist_undefined() {
+        // GIVEN
+
+        // WHEN
+        String hostWhitelist = SysProps.hostWhitelist();
+
+        // THEN
+        assertThat(hostWhitelist).isEqualTo("");
+    }
+
+    @Test
+    @SetSystemProperty(key = "getdown.host.whitelist", value = "app1.foo.com,app2.bar.com,app3.baz.com")
+    void test_hostWhitelist_defined() {
+        // GIVEN
+
+        // WHEN
+        String hostWhitelist = SysProps.hostWhitelist();
+
+        // THEN
+        assertThat(hostWhitelist).isEqualTo("app1.foo.com,app2.bar.com,app3.baz.com");
+    }
+
 }