Initialize the document locator before starting tokenization

Problem: When a caller supplies its own ContentHandler, the Document
system identifier is null.

Cause: tokenizer.initLocation() wasn’t getting called until after
Driver.tokenize() called tokenizer.start(). So the tokenizer’s systemId/
publicId were still null when start() delivered the first SAX events.

Fix: Call initLocation() before start(). The locator carries the input
source’s public/system IDs before any downstream handler observes it.

Fixes #123

Author: sideshowbarker

src/nu/validator/htmlparser/io/Driver.java

@@ -194,10 +194,10 @@ public void tokenize(InputSource is, int bufferSize)
         if (is == null) {
             throw new IllegalArgumentException("InputSource was null.");
         }
+        tokenizer.initLocation(is.getPublicId(), is.getSystemId());
         tokenizer.start();
         confidence = Confidence.TENTATIVE;
         rewindableInputStream = null;
-        tokenizer.initLocation(is.getPublicId(), is.getSystemId());
         this.reader = is.getCharacterStream();
         this.characterEncoding = encodingFromExternalDeclaration(is.getEncoding());
         if (this.reader == null) {

test-src/nu/validator/htmlparser/test/SystemIdTester.java

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2026 Mozilla Foundation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package nu.validator.htmlparser.test;
+
+import java.io.IOException;
+import java.io.StringReader;
+
+import org.xml.sax.InputSource;
+import org.xml.sax.Locator;
+import org.xml.sax.SAXException;
+import org.xml.sax.helpers.DefaultHandler;
+
+import nu.validator.htmlparser.common.XmlViolationPolicy;
+import nu.validator.htmlparser.sax.HtmlParser;
+
+/**
+ * Regression test for
+ * <a href="https://github.com/validator/htmlparser/issues/123">issue&nbsp;#123</a>:
+ * the document system identifier must be available to a caller-supplied
+ * {@link org.xml.sax.ContentHandler} by the time {@code startDocument()} fires.
+ *
+ * <p>Both SAX configurations are exercised, because they surface the system
+ * identifier by different mechanisms: the default buffered path snapshots the
+ * locator when the root node is created, whereas the streaming path hands the
+ * live tokenizer to the handler directly.
+ */
+public class SystemIdTester {
+
+    private static final String SYSTEM_ID = "http://example.org/doc.html";
+
+    private static final String DOCUMENT = "<!DOCTYPE html><html><head><title>Test</title></head><body><p>Hello</p></body></html>";
+
+    /**
+     * Records the system identifier reported by the {@link Locator} at
+     * {@code startDocument()} time, i.e. the earliest point at which a
+     * content handler can reasonably read it.
+     */
+    private static final class SystemIdRecorder extends DefaultHandler {
+
+        private Locator locator;
+
+        private String systemIdAtStartDocument = "<startDocument() not called>";
+
+        @Override public void setDocumentLocator(Locator locator) {
+            this.locator = locator;
+        }
+
+        @Override public void startDocument() throws SAXException {
+            systemIdAtStartDocument = (locator == null) ? null
+                    : locator.getSystemId();
+        }
+    }
+
+    private static void check(XmlViolationPolicy streamabilityViolationPolicy,
+            String label) throws SAXException, IOException {
+        HtmlParser parser = new HtmlParser();
+        parser.setStreamabilityViolationPolicy(streamabilityViolationPolicy);
+        SystemIdRecorder recorder = new SystemIdRecorder();
+        parser.setContentHandler(recorder);
+
+        InputSource in = new InputSource(new StringReader(DOCUMENT));
+        in.setSystemId(SYSTEM_ID);
+        parser.parse(in);
+
+        if (!SYSTEM_ID.equals(recorder.systemIdAtStartDocument)) {
+            throw new AssertionError(label
+                    + ": expected system identifier \"" + SYSTEM_ID
+                    + "\" at startDocument() but got \""
+                    + recorder.systemIdAtStartDocument + "\"");
+        }
+        System.out.println(label + ": OK");
+    }
+
+    public static void main(String[] args) throws SAXException, IOException {
+        // Default configuration: the SAXTreeBuilder path, which replays a
+        // buffered tree to the content handler.
+        check(XmlViolationPolicy.ALLOW, "buffered (SAXTreeBuilder)");
+        // Any non-ALLOW policy selects the direct SAXStreamer path.
+        check(XmlViolationPolicy.ALTER_INFOSET, "streaming (SAXStreamer)");
+        System.out.println("issue #123 regression test passed");
+    }
+}