SOLR-18085: Review use of "wt=standard" and see if we can remove it. #4080

Copilot · 2026-02-04T00:52:42Z

initWriters() no longer ensures a default response writer is set on responseWriters. If no <queryResponseWriter default="true"> is defined in solrconfig (e.g., configsets where response writers are only implicit), PluginBag's default (def) can remain null, which breaks default writer resolution and can change the default output unexpectedly. Consider restoring a safe default (e.g., set default to json) when responseWriters.getDefault() is null after init.

Suggested change

responseWriters.init(defaultWriters, this);

responseWriters.init(defaultWriters, this);

// Ensure there is always a default response writer configured.

// If no <queryResponseWriter default="true"> is defined and PluginBag

// did not pick a default, fall back to "json" when available.

if (responseWriters.getDefault() == null) {

QueryResponseWriter jsonWriter = responseWriters.get("json", false);

if (jsonWriter != null) {

responseWriters.setDefault("json");

}

}

dsmiley · 2026-02-04T06:05:16Z

nice and tidy :-)

dsmiley · 2026-02-04T06:08:15Z

minor: I prefer that we don't change source files for out-of-scope reasons that we aren't already touching for in-scope reasons.

yeah, I really struggle with seeing these things and not fixing them. I will try not to do it in the futre. I swear I went through the entire code base and fixed all the typos, and yet I keep finding them.

dsmiley · 2026-02-04T06:10:54Z

Are these changes in-scope?

Copilot · 2026-02-04T00:52:43Z

Grammar in this Javadoc is off: "Pass in a xml configuration" should be "Pass in an XML configuration" (and typically XML is capitalized).

Suggested change

* Pass in a xml configuration. A null configuration will enable everything with maximum values.

* Pass in an XML configuration. A null configuration will enable everything with maximum values.

-Original file line number
+Diff line change
@@ -0,0 +1,8 @@
+    # See https://github.com/apache/solr/blob/main/dev-docs/changelog.adoc
+    title: Removed the wt=standard concept that was used internally by Solr.
+    type: removed # added, changed, fixed, deprecated, removed, dependency_update, security, other
+    authors:
+      - name: Eric Pugh
+    links:
+      - name: SOLR-18085
+        url: https://issues.apache.org/jira/browse/SOLR-18085

-Original file line number
+Diff line change
@@ Expand Up / @@ -202,7 +202,7 @@ public T get(String name) { @@
        * Fetches a plugin by name , or the default
        *
        * @param name name using which it is registered
-       * @param useDefault Return the default , if a plugin by that name does not exist
+       * @param useDefault Return the default, if a plugin by that name does not exist
        */
       public T get(String name, boolean useDefault) {
         T result = get(name);
@@ Expand Down @@

-Original file line number
+Diff line change
@@ Expand Up / @@ -117,7 +117,7 @@ void initHandlersFromConfig(SolrConfig config) { @@
           modifiedInfos.add(applyInitParams(config, info));
         }
         handlers.init(Collections.emptyMap(), core, modifiedInfos);
-        handlers.alias(handlers.getDefault(), "");
         if (log.isDebugEnabled()) {
           log.debug("Registered paths: {}", StrUtils.join(new ArrayList<>(handlers.keySet()), ','));
         }
@@ Expand Down @@

-Original file line number
+Diff line change
@@ Expand Up / @@ -204,14 +204,7 @@ default CloudDescriptor getCloudDescriptor() { @@
        */
       default QueryResponseWriter getResponseWriter() {
         // it's weird this method is here instead of SolrQueryResponse, but it's practical/convenient
-        SolrCore core = getCore();
-        String wt = getParams().get(CommonParams.WT);
-        // Use core writers if available, otherwise fall back to built-in writers
-        if (core != null) {
-          return core.getQueryResponseWriter(wt);
-        } else {
-          return ResponseWritersRegistry.getWriter(wt);
-        }
+        return ResponseWritersRegistry.getWriter(getParams().get(CommonParams.WT), getCore());
       }
       /**
@@ Expand Down @@

-Original file line number
+Diff line change
@@ Expand Up @@
        */
       public static final String CONTENT = "content";
-      private String _baseWriter = null;
+      private String baseWriter = null;
       /**
        * A fallback writer used for requests that don't return raw content and that aren't associated
@@ Expand All / @@ -62,14 +62,17 @@ public void init(NamedList<?> n) { @@
         if (n != null) {
           Object base = n.get("base");
           if (base != null) {
-            _baseWriter = base.toString();
+            baseWriter = base.toString();
           }
         }
       }
       protected QueryResponseWriter getBaseWriter(SolrQueryRequest request) {
         if (request.getCore() != null) {
-          return request.getCore().getQueryResponseWriter(_baseWriter);
+          // When baseWriter is null, use the core's default writer (useDefault=true)
+          // Otherwise, look up the specific writer by name (useDefault=false for explicit lookups)
+          boolean useDefault = (baseWriter == null);
+          return request.getCore().getResponseWriters().get(baseWriter, useDefault);
         }
         // Requests to a specific core already have writers, but we still need a 'default writer' for
@@ Expand Down @@

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SOLR-18085: Review use of "wt=standard" and see if we can remove it. #4080

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-Original file line number
+Diff line change
@@ Expand Up / @@ -20,7 +20,9 @@ @@
     import static org.apache.solr.util.stats.MetricUtils.PROMETHEUS_METRICS_WT;
     import java.util.Map;
+    import org.apache.solr.common.SolrException;
     import org.apache.solr.common.params.CommonParams;
+    import org.apache.solr.core.SolrCore;
     import org.apache.solr.handler.admin.api.ReplicationAPIBase;
     /**
@@ Expand All / @@ -46,21 +48,14 @@ private ResponseWritersRegistry() { @@
         PrometheusResponseWriter prometheusWriter = new PrometheusResponseWriter();
         BUILTIN_WRITERS =
-            Map.of(
-                CommonParams.JAVABIN,
-                new JavaBinResponseWriter(),
-                CommonParams.JSON,
-                jsonWriter,
-                "standard",
-                jsonWriter, // Alias for JSON
-                "xml",
-                new XMLResponseWriter(),
-                PROMETHEUS_METRICS_WT,
-                prometheusWriter,
-                OPEN_METRICS_WT,
-                prometheusWriter,
-                ReplicationAPIBase.FILE_STREAM,
-                new FileStreamResponseWriter());
+            Map.ofEntries(
+                Map.entry(CommonParams.JAVABIN, new JavaBinResponseWriter()),
+                Map.entry(CommonParams.JSON, jsonWriter),
+                Map.entry("xml", new XMLResponseWriter()),
+                Map.entry("raw", new RawResponseWriter()),
+                Map.entry(PROMETHEUS_METRICS_WT, prometheusWriter),
+                Map.entry(OPEN_METRICS_WT, prometheusWriter),
+                Map.entry(ReplicationAPIBase.FILE_STREAM, new FileStreamResponseWriter()));
       }
       /**
@@ Expand All / @@ -69,17 +64,68 @@ private ResponseWritersRegistry() { @@
        * <p>Built-in writers are always available and provide essential formats needed by admin APIs and
        * core functionality. They do not depend on core configuration or ImplicitPlugins.json settings.
        *
-       * <p>If the requested writer is not available, returns the "standard" (JSON) writer as a
-       * fallback. This ensures requests always get a valid response format.
+       * <p>If the requested writer is not available, returns the JSON writer as a fallback. This
+       * ensures requests always get a valid response format.
        *
        * @param writerName the writer name (e.g., "json", "xml", "javabin"), or null for default
-       * @return the response writer, never null (returns "standard"/JSON if not found)
+       * @return the response writer, never null (returns JSON if not found)
        */
       public static QueryResponseWriter getWriter(String writerName) {
         if (writerName == null || writerName.isEmpty()) {
-          return BUILTIN_WRITERS.get("standard");
+          writerName = CommonParams.JSON;
         }
-        return BUILTIN_WRITERS.getOrDefault(writerName, BUILTIN_WRITERS.get("standard"));
+        return BUILTIN_WRITERS.get(writerName);
+      }
+      /**
+       * Gets a response writer, trying the core's registry first, then falling back to built-in
+       * writers. This is the unified entry point for all writer resolution.
+       *
+       * <p>Resolution order:
+       *
+       * <ol>
+       *   <li>If core is provided, check core's writer registry
+       *   <li>If not found in core (or no core), check built-in writers
+       *   <li>If writer name is explicitly specified but not found anywhere, throw exception
+       *   <li>If writer name is null/empty, return default (JSON)
+       * </ol>
+       *
+       * @param writerName the writer name (e.g., "json", "xml", "javabin"), or null for default
+       * @param core the SolrCore to check first, or null for node-level requests
+       * @return the response writer, never null
+       * @throws SolrException if an explicitly requested writer type is not found
+       */
+      public static QueryResponseWriter getWriter(String writerName, SolrCore core) {
+        QueryResponseWriter writer = null;
+        // Try core registry first if available
+        if (core != null) {
+          writer = core.getQueryResponseWriter(writerName);
+        }
+        // If not found and writer is explicitly requested, validate it exists in built-in
+        if (writer == null) {
+          if (!hasWriter(writerName)) {
+            throw new SolrException(
+                SolrException.ErrorCode.SERVER_ERROR, "Unknown response writer type: " + writerName);
+          } else {
+            writer = getWriter(writerName);
+          }
+        }
+        return writer;
+      }
+      /**
+       * Checks if a writer with the given name exists in the built-in writers.
+       *
+       * @param writerName the writer name to check
+       * @return true if the writer exists, false otherwise
+       */
+      public static boolean hasWriter(String writerName) {
+        if (writerName == null || writerName.isEmpty()) {
+          return true; // null/empty is valid, will use default
+        }
+        return BUILTIN_WRITERS.containsKey(writerName);
       }
       /**
@@ Expand Down @@

-Original file line number
+Diff line change
@@ Expand Up / @@ -727,7 +727,7 @@ private void handleAdminRequest() throws IOException { @@
       protected void logAndFlushAdminRequest(SolrQueryResponse solrResp) throws IOException {
         if (solrResp.getToLog().size() > 0) {
-          // has to come second and in it's own if to keep ./gradlew check happy.
+          // has to come second and in its own "if" to keep ./gradlew check happy.
           if (log.isInfoEnabled()) {
             log.info(
                 handler != null
@@ Expand Down @@

SOLR-18085: Review use of "wt=standard" and see if we can remove it. #4080

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