SOLR-18079: Allow user to provide custom Implicit Plugins Mapping File #4067

epugh · 2026-01-20T22:13:07Z

https://issues.apache.org/jira/browse/SOLR-18079

Description

Allow user to provide their own ImplicitPlugins.json file via solr.xml setting.

Solution

Add a property to solr.xml that can be set via system property.

Tests

Added test for parsing of ImplicitPlugins.json and the two code paths.

Copilot

Pull request overview

This pull request implements the ability to provide a custom implicit plugins mapping file via solr.xml configuration, addressing JIRA issue SOLR-18079. The feature allows users to override the default ImplicitPlugins.json that ships with Solr, giving them control over which request handlers are registered for all cores.

Changes:

Added implicitPluginsFile configuration property to solr.xml that can be set via system property
Refactored the implicit plugins loading mechanism to support both default classpath resource and custom file paths
Added comprehensive unit tests and integration tests for the new functionality

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
solr/solr-ref-guide/modules/configuration-guide/pages/configuring-solr-xml.adoc	Added documentation for the new implicitPluginsFile configuration property
solr/server/solr/solr.xml	Added implicitPluginsFile property with empty default value
solr/packaging/test/test_start_solr.bats	Added integration test for starting Solr with custom implicit plugins configuration
solr/core/src/test/org/apache/solr/core/TestSolrXml.java	Added unit tests for parsing implicitPluginsFile from solr.xml
solr/core/src/test/org/apache/solr/core/SolrCoreTest.java	Added test for parsing custom implicit plugins JSON into PluginInfo objects
solr/core/src/test-files/solr/custom-implicit-plugins.json	Added test resource file with sample custom implicit plugins configuration
solr/core/src/java/org/apache/solr/core/SolrXmlConfig.java	Added parsing of implicitPluginsFile property from solr.xml
solr/core/src/java/org/apache/solr/core/SolrCore.java	Implemented custom implicit plugins loading with fallback to default, refactored ImplicitHolder to support dynamic loading
solr/core/src/java/org/apache/solr/core/RequestHandlers.java	Minor comment formatting improvement
solr/core/src/java/org/apache/solr/core/NodeConfig.java	Added implicitPluginsFile field and corresponding getter/setter

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Copilot · 2026-01-20T22:23:57Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+              customPluginsFile);
+        } catch (Exception e) {
+          log.warn(
+              "Failed to load custom implicit plugins file: {} (from solr.xml). Falling back to default.",
+              customPluginsFile,


The error message uses the string representation of the customPluginsFile variable instead of the actual path that was attempted to be loaded (customPluginsPath). This makes debugging harder since the user sees the input value, not the resolved path that was actually checked. Consider using customPluginsPath.toString() in the log messages.

Suggested change

customPluginsFile);

} catch (Exception e) {

log.warn(

"Failed to load custom implicit plugins file: {} (from solr.xml). Falling back to default.",

customPluginsFile,

customPluginsPath.toString());

} catch (Exception e) {

log.warn(

"Failed to load custom implicit plugins file: {} (from solr.xml). Falling back to default.",

customPluginsPath.toString(),

Copilot · 2026-01-20T22:23:58Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+    if (requestHandlers == null) {
+      throw new NullPointerException("No requestHandler section found in implicit plugins");


Using NullPointerException for control flow is not a best practice. The parseImplicitPlugins method throws NullPointerException when the requestHandler section is missing, which is then caught and logged. Consider using a more descriptive custom exception or IllegalArgumentException, which better conveys that this is a validation error rather than an unexpected null reference.

Copilot · 2026-01-20T22:23:58Z

solr/core/src/test/org/apache/solr/core/SolrCoreTest.java

+  @Test
+  public void testCustomImplicitPlugins() throws Exception {
+    // Test that the custom implicit plugins file can be loaded and parsed into PluginInfo objects
+    String customPluginsPath = TEST_HOME() + "/custom-implicit-plugins.json";
+    Path pluginsFile = Paths.get(customPluginsPath);
+
+    // Verify file exists
+    assertTrue(
+        "Custom implicit plugins file should exist: " + customPluginsPath,
+        Files.exists(pluginsFile));
+
+    // Load and parse the custom plugins file
+    try (InputStream is = Files.newInputStream(pluginsFile)) {
+      @SuppressWarnings("unchecked")
+      Map<String, ?> implicitPluginsInfo = (Map<String, ?>) Utils.fromJSON(is);
+
+      assertNotNull("Should parse custom plugins JSON", implicitPluginsInfo);
+
+      // Call parseImplicitPlugins to convert JSON to PluginInfo objects
+      List<PluginInfo> customHandlers = SolrCore.parseImplicitPlugins(implicitPluginsInfo);
+
+      assertNotNull("Should return list of PluginInfo objects", customHandlers);
+      assertEquals("Should have 3 custom handlers", 3, customHandlers.size());
+
+      // Build a map for easy verification
+      Map<String, String> pathToClassMap = new HashMap<>(customHandlers.size());
+      for (PluginInfo handler : customHandlers) {
+        assertEquals(
+            "All handlers should be of type requestHandler", SolrRequestHandler.TYPE, handler.type);
+        pathToClassMap.put(handler.name, handler.className);
+      }
+
+      // Verify custom handlers are present with correct classes
+      assertEquals(
+          "Custom update handler should be UpdateRequestHandler",
+          "solr.UpdateRequestHandler",
+          pathToClassMap.get("/custom-update"));
+      assertEquals(
+          "Custom select handler should be SearchHandler",
+          "solr.SearchHandler",
+          pathToClassMap.get("/custom-select"));
+      assertEquals(
+          "Custom ping handler should be PingRequestHandler",
+          "solr.PingRequestHandler",
+          pathToClassMap.get("/admin/ping"));
+
+      // Verify default handlers are NOT present (since we're using custom file)
+      assertNull(
+          "Default /debug/dump should not be present with custom plugins",
+          pathToClassMap.get("/debug/dump"));
+      assertNull(
+          "Default /update should not be present with custom plugins",
+          pathToClassMap.get("/update"));
+    }
+  }


The test coverage for the custom implicit plugins functionality is incomplete. While there are tests for the happy path (parsing a valid custom plugins file), there are no tests for error scenarios such as: (1) a non-existent file path, (2) malformed JSON, (3) missing requestHandler section, or (4) IOException during file reading. These error paths are implemented in SolrCore.loadImplicitPlugins but not tested. Consider adding test cases for these error scenarios to ensure proper fallback behavior and error logging.

Copilot · 2026-01-20T22:23:58Z

solr/solr-ref-guide/modules/configuration-guide/pages/configuring-solr-xml.adoc

+|Optional |Default: none
+|===
+
+The path relative to `$SOLR_HOME` for a custom implicit plugins file that lets you control exactly which endpoints are registerd for all cores. 


There is a spelling error: "registerd" should be "registered".

Suggested change

The path relative to `$SOLR_HOME` for a custom implicit plugins file that lets you control exactly which endpoints are registerd for all cores.

The path relative to `$SOLR_HOME` for a custom implicit plugins file that lets you control exactly which endpoints are registered for all cores.

solr/solr-ref-guide/modules/configuration-guide/pages/configuring-solr-xml.adoc

Copilot · 2026-01-20T22:23:59Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+    private static volatile List<PluginInfo> INSTANCE = null;

-    static {
+    static List<PluginInfo> getInstance(SolrCore core) {
+      if (INSTANCE == null) {
+        synchronized (ImplicitHolder.class) {
+          if (INSTANCE == null) {
+            INSTANCE = loadImplicitPlugins(core);
+          }
+        }
+      }
+      return INSTANCE;
+    }


The ImplicitHolder uses a static singleton pattern that is shared across all CoreContainer instances in the JVM. If multiple CoreContainer instances exist (e.g., in tests), they could have different implicitPluginsFile configurations, but only the first CoreContainer's configuration will be used for all of them. Consider making the implicit plugins configuration per-CoreContainer rather than using a static singleton, or document this limitation clearly.

Copilot · 2026-01-20T22:23:59Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+        } catch (NullPointerException e) {
+          log.warn(
+              "No requestHandler section found in custom implicit plugins file: {} (from solr.xml)",
+              customPluginsFile);


The error message uses the string representation of the customPluginsFile variable instead of the actual path that was attempted to be loaded (customPluginsPath). This makes debugging harder since the user sees the input value, not the resolved path that was actually checked. Consider using customPluginsPath.toString() in the log messages.

maybe, but we don't actually ahve this available to us in the catch

Copilot · 2026-01-20T22:23:59Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+            Path solrHome = core.getCoreContainer().getSolrHome();
+            customPluginsPath = solrHome.resolve(customPluginsFile);
+          }
+


The custom implicit plugins file path is not validated using the CoreContainer.assertPathAllowed() security check. While solr.xml is a privileged configuration file, it would be more consistent with Solr's security model to validate that the resolved customPluginsPath is within allowed paths, especially since this code reads from the filesystem. Consider adding a call to core.getCoreContainer().assertPathAllowed(customPluginsPath) after resolving the path but before checking if it exists.

Suggested change

// Ensure the resolved path is within allowed locations

core.getCoreContainer().assertPathAllowed(customPluginsPath);

Good find by copilot! (The fact that assertPathAllowed is not called before using the string)

well, heck, I went and fussed aroudn for a while and missed this fix, which was what i did eventually!

solr/packaging/test/test_start_solr.bats

Copilot · 2026-01-20T22:24:00Z

solr/packaging/test/test_start_solr.bats

+  run curl -s "http://localhost:${SOLR_PORT}/solr/custom_plugins_test/update"
+  assert_output --partial 'Searching for Solr'


The test verifies that the /update endpoint is not available by checking for "Searching for Solr" in the response. This appears to be checking for a 404 error page. However, this is fragile as the error page content could change. Consider checking the HTTP status code directly (e.g., using curl's -w flag) or checking for a more specific error indicator.

Suggested change

run curl -s "http://localhost:${SOLR_PORT}/solr/custom_plugins_test/update"

assert_output --partial 'Searching for Solr'

run curl -s -o /dev/null -w "%{http_code}" "http://localhost:${SOLR_PORT}/solr/custom_plugins_test/update"

assert_output "404"

thanks for suggestion.

janhoy

Quick review

janhoy · 2026-01-21T12:05:49Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+            Path solrHome = core.getCoreContainer().getSolrHome();
+            customPluginsPath = solrHome.resolve(customPluginsFile);
+          }
+


Good find by copilot! (The fact that assertPathAllowed is not called before using the string)

janhoy · 2026-01-21T12:07:34Z

solr/core/src/java/org/apache/solr/core/SolrCore.java

+          if (!customPluginsPath.isAbsolute()) {
+            // Resolve relative paths against SOLR_HOME
+            Path solrHome = core.getCoreContainer().getSolrHome();
+            customPluginsPath = solrHome.resolve(customPluginsFile);


Wasn't it suggested to disallow path.resolve due to how it will resolve ../../.. patterns perhaps unexpectedly? However, if calling assertPathAllowed before use, we should be safe anyway

I couldn't remember how to do the assert! We need it in our prompt.md ;-)

janhoy · 2026-01-21T12:09:44Z

solr/server/solr/solr.xml

  <str name="allowUrls">${solr.security.allow.urls:}</str>
  <str name="hideStackTrace">${solr.hideStackTrace:false}</str>
  <int name="indexSearcherExecutorThreads">${solr.searchThreads:0}</int>
+  <str name="implicitPluginsFile">${solr.implicitPluginsFile:}</str>


Did you consider a "modern" property name?

Not really because all the other ones are the same. So kept the existing style. In another PR I'd love to get these all renamed!

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

…ing-solr-xml.adoc Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

epugh added 2 commits January 20, 2026 15:07

Introduce solr.xml level implicitPluginsFile

be6f3eb

Enahnce the testing of the loading of implicit plugins.

342d5c7

epugh requested review from Copilot and dsmiley January 20, 2026 22:13

github-actions bot added documentation Improvements or additions to documentation configs tests labels Jan 20, 2026

Copilot started reviewing on behalf of epugh January 20, 2026 22:13 View session

Copilot AI reviewed Jan 20, 2026

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janhoy reviewed Jan 21, 2026

View reviewed changes

epugh and others added 5 commits January 21, 2026 09:19

Update solr/packaging/test/test_start_solr.bats

11cee64

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update solr/solr-ref-guide/modules/configuration-guide/pages/configur…

c47060d

…ing-solr-xml.adoc Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Respond to feedback

b4633ff

Merge branch 'SOLR-18079' of github.com:epugh/solr into SOLR-18079

bbc6e21

More targeted exception

3a11769

		if (requestHandlers == null) {
		throw new NullPointerException("No requestHandler section found in implicit plugins");

	The path relative to `$SOLR_HOME` for a custom implicit plugins file that lets you control exactly which endpoints are registerd for all cores.
	The path relative to `$SOLR_HOME` for a custom implicit plugins file that lets you control exactly which endpoints are registered for all cores.



	// Ensure the resolved path is within allowed locations
	core.getCoreContainer().assertPathAllowed(customPluginsPath);

		run curl -s "http://localhost:${SOLR_PORT}/solr/custom_plugins_test/update"
		assert_output --partial 'Searching for Solr'

SOLR-18079: Allow user to provide custom Implicit Plugins Mapping File #4067

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SOLR-18079: Allow user to provide custom Implicit Plugins Mapping File #4067

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epugh commented Jan 20, 2026

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