[bugfix] fn:xml-to-json: enforce F&O 3.1 §17.4.2 structural validation (+10 XQTS HEAD)

exist-core/src/main/java/org/exist/xquery/functions/fn/FunXmlToJson.java

@@ -36,7 +36,9 @@
 import java.io.StringWriter;
 import java.io.Writer;
 import java.math.BigDecimal;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
+import java.util.Deque;
 
 import static org.exist.xquery.FunctionDSL.*;
 
@@ -106,6 +108,8 @@ private void nodeValueToJson(final NodeValue nodeValue, final Writer writer) thr
         final Integer stackSeparator = 0;
         //use ArrayList<Object> to store String type keys and non-string type separators
         final ArrayList<Object> mapkeyArrayList = new ArrayList<>();
+        //track parent element local names so we can validate child structure (F&O 3.1 §17.4.2 / §17.5.4)
+        final Deque<String> elementStack = new ArrayDeque<>();
         boolean elementKeyIsEscaped = false;
         boolean elementValueIsEscaped = false;
         XMLStreamReader reader = null;
@@ -127,6 +131,7 @@ private void nodeValueToJson(final NodeValue nodeValue, final Writer writer) thr
                                     "Invalid XML representation of JSON. Element '" + reader.getLocalName()
                                     + "' is not in the required namespace '" + Namespaces.XPATH_FUNCTIONS_NS + "'.");
                         }
+                        validateStartElement(reader, elementStack);
                         final String elementAttributeEscapedValue = reader.getAttributeValue(null, "escaped");
                         elementValueIsEscaped = "true".equals(elementAttributeEscapedValue);
                         final String elementAttributeEscapedKeyValue = reader.getAttributeValue(null, "escaped-key");
@@ -162,10 +167,15 @@ private void nodeValueToJson(final NodeValue nodeValue, final Writer writer) thr
                         break;
                     case XMLStreamReader.CHARACTERS:
                     case XMLStreamReader.CDATA:
-                        tempStringBuilder.append(reader.getText());
+                        final String charText = reader.getText();
+                        validateTextInContext(charText, elementStack.peek());
+                        tempStringBuilder.append(charText);
                         break;
                     case XMLStreamReader.END_ELEMENT:
                         final String tempString = tempStringBuilder.toString();
+                        if (!elementStack.isEmpty()) {
+                            elementStack.pop();
+                        }
                         switch (reader.getLocalName()) {
                             case "array":
                                 jsonGenerator.writeEndArray();
@@ -252,4 +262,122 @@ private String unescapeEscapedJsonString(final String escapedJsonString) throws
         unescapedJsonString = unescapedJsonStringBuilder.toString();
         return unescapedJsonString;
     }
+
+    /**
+     * Validate the current START_ELEMENT against the F&O 3.1 §17.4.2 / §17.5.4 structural rules
+     * and, on success, push the element's local name onto the parent-tracking stack.
+     */
+    private void validateStartElement(final XMLStreamReader reader, final Deque<String> elementStack) throws XPathException {
+        final String localName = reader.getLocalName();
+        if (!isJsonElementName(localName)) {
+            throw new XPathException(this, ErrorCodes.FOJS0006,
+                    "Invalid XML representation of JSON. Element '" + localName
+                    + "' is not one of [map, array, null, boolean, number, string].");
+        }
+        final String parentLocalName = elementStack.peek();
+        if (parentLocalName != null && isLeafElementName(parentLocalName)) {
+            throw new XPathException(this, ErrorCodes.FOJS0006,
+                    "Invalid XML representation of JSON. Element '" + parentLocalName
+                    + "' must not have element children.");
+        }
+        validateAttributes(reader, localName);
+        elementStack.push(localName);
+    }
+
+    /**
+     * Reject non-whitespace text node children of {@code map} and {@code array} per F&O 3.1 §17.4.2.
+     */
+    private void validateTextInContext(final String text, final String parentLocalName) throws XPathException {
+        if (parentLocalName == null) {
+            return;
+        }
+        if (!"map".equals(parentLocalName) && !"array".equals(parentLocalName)) {
+            return;
+        }
+        if (!isXmlWhitespace(text)) {
+            throw new XPathException(this, ErrorCodes.FOJS0006,
+                    "Invalid XML representation of JSON. Element '" + parentLocalName
+                    + "' must not have non-whitespace text content.");
+        }
+    }
+
+    private static boolean isJsonElementName(final String name) {
+        return switch (name) {
+            case "map", "array", "string", "number", "boolean", "null" -> true;
+            default -> false;
+        };
+    }
+
+    private static boolean isLeafElementName(final String name) {
+        return switch (name) {
+            case "string", "number", "boolean", "null" -> true;
+            default -> false;
+        };
+    }
+
+    private static boolean isXmlWhitespace(final String text) {
+        for (int i = 0; i < text.length(); i++) {
+            final char c = text.charAt(i);
+            if (c != ' ' && c != '\t' && c != '\n' && c != '\r') {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Validate that the attributes on the current element conform to F&O 3.1 §17.4.2 (the schema for JSON).
+     * <p>
+     * Per the schema (Appendix C.2), the only allowed no-namespace attributes are:
+     * <ul>
+     *   <li>{@code key} and {@code escaped-key} on any of the six elements (when child of map; allowed at top-level too)</li>
+     *   <li>{@code escaped} on {@code string} only</li>
+     * </ul>
+     * Attributes in the {@code http://www.w3.org/2005/xpath-functions} namespace are disallowed
+     * ({@code anyAttribute namespace="##other"}); attributes in any other namespace are ignored.
+     * The {@code escaped} and {@code escaped-key} attributes must hold a valid {@code xs:boolean} value.
+     */
+    private void validateAttributes(final XMLStreamReader reader, final String localName) throws XPathException {
+        for (int i = 0; i < reader.getAttributeCount(); i++) {
+            final String attrNs = reader.getAttributeNamespace(i);
+            final String attrName = reader.getAttributeLocalName(i);
+            if (Namespaces.XPATH_FUNCTIONS_NS.equals(attrNs)) {
+                throw new XPathException(this, ErrorCodes.FOJS0006,
+                        "Invalid XML representation of JSON. Attribute '" + attrName
+                        + "' must not be in the namespace '" + Namespaces.XPATH_FUNCTIONS_NS + "'.");
+            }
+            if (attrNs != null && !attrNs.isEmpty()) {
+                continue;
+            }
+            switch (attrName) {
+                case "key", "escaped-key" -> {
+                    if ("escaped-key".equals(attrName) && !isValidXsBoolean(reader.getAttributeValue(i))) {
+                        throw new XPathException(this, ErrorCodes.FOJS0006,
+                                "Invalid XML representation of JSON. Attribute 'escaped-key' must have a valid xs:boolean value, but got '"
+                                + reader.getAttributeValue(i) + "'.");
+                    }
+                }
+                case "escaped" -> {
+                    // Per W3C bug 29917 / qt3tests xml-to-json-065, 'escaped' is tolerated on
+                    // non-string elements as a no-op; only the lexical value is enforced.
+                    if (!isValidXsBoolean(reader.getAttributeValue(i))) {
+                        throw new XPathException(this, ErrorCodes.FOJS0006,
+                                "Invalid XML representation of JSON. Attribute 'escaped' must have a valid xs:boolean value, but got '"
+                                + reader.getAttributeValue(i) + "'.");
+                    }
+                }
+                default -> throw new XPathException(this, ErrorCodes.FOJS0006,
+                        "Invalid XML representation of JSON. Attribute '" + attrName
+                        + "' is not allowed on element '" + localName + "'.");
+            }
+        }
+    }
+
+    private static boolean isValidXsBoolean(final String value) {
+        if (value == null) {
+            return false;
+        }
+        final String trimmed = value.trim();
+        return "true".equals(trimmed) || "false".equals(trimmed) || "1".equals(trimmed) || "0".equals(trimmed);
+    }
 }

exist-core/src/test/xquery/xquery3/xml-to-json.xql

@@ -479,6 +479,143 @@ function xtj:xmlmap-to-json-for-exponent($int as xs:string) as xs:string {
     )
 };
 
+(: ===========================================================
+   F&O 3.1 §17.4.2 / §17.5.4 — structural validation tests
+   (parity with XQTS HEAD xml-to-json-{033,040,042,043,062,063,069,081,082})
+   =========================================================== :)
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-text-child-of-map() {
+    fn:xml-to-json(
+        <map xmlns="http://www.w3.org/2005/xpath-functions">
+            <string key="t">tab</string>blubber<string key="u">undo</string>
+        </map>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-text-child-of-array() {
+    fn:xml-to-json(
+        <array xmlns="http://www.w3.org/2005/xpath-functions">
+            <string>tab</string>blubber<string>undo</string>
+        </array>
+    )
+};
+
+declare
+    %test:assertEquals('{"a":null,"b":null}')
+function xtj:xml-to-json-whitespace-between-map-children-allowed() {
+    fn:xml-to-json(
+        <map xmlns="http://www.w3.org/2005/xpath-functions">
+            <null key="a"/>
+            <null key="b"/>
+        </map>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-disallowed-no-ns-attribute() {
+    fn:xml-to-json(
+        <map xmlns="http://www.w3.org/2005/xpath-functions">
+            <null key="a" yek="z"/>
+            <null key="b"/>
+        </map>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-attribute-in-json-namespace() {
+    fn:xml-to-json(
+        <j:map xmlns:j="http://www.w3.org/2005/xpath-functions" j:base="http://www.w3.org">
+            <j:string key="t">tab</j:string>
+        </j:map>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-invalid-escaped-key-value() {
+    fn:xml-to-json(
+        <map xmlns="http://www.w3.org/2005/xpath-functions">
+            <string escaped-key="bonkers" key="t">tab</string>
+        </map>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-invalid-escaped-value() {
+    fn:xml-to-json(
+        <map xmlns="http://www.w3.org/2005/xpath-functions">
+            <string escaped="potty" key="t">tab</string>
+        </map>
+    )
+};
+
+declare
+    %test:assertEquals('{"\\t":"tab"}')
+function xtj:xml-to-json-escaped-on-map-tolerated() {
+    fn:xml-to-json(
+        <map xmlns="http://www.w3.org/2005/xpath-functions" escaped="0">
+            <string key="\t">tab</string>
+        </map>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-element-child-of-string() {
+    fn:xml-to-json(
+        <string xmlns="http://www.w3.org/2005/xpath-functions">ok<null/></string>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-element-child-of-boolean() {
+    fn:xml-to-json(
+        <boolean xmlns="http://www.w3.org/2005/xpath-functions">true<string>qq</string></boolean>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-element-child-of-null() {
+    fn:xml-to-json(
+        <null xmlns="http://www.w3.org/2005/xpath-functions"><null/></null>
+    )
+};
+
+declare
+    %test:assertError('FOJS0006')
+function xtj:xml-to-json-element-child-of-number() {
+    fn:xml-to-json(
+        <number xmlns="http://www.w3.org/2005/xpath-functions">1<null/></number>
+    )
+};
+
+declare
+    %test:assertEquals('"ok"')
+function xtj:xml-to-json-foreign-ns-attribute-ignored() {
+    fn:xml-to-json(
+        <string xmlns="http://www.w3.org/2005/xpath-functions"
+                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+                xsi:type="xs:string">ok</string>
+    )
+};
+
+declare
+    %test:assertEquals('"ok"')
+function xtj:xml-to-json-escaped-numeric-boolean() {
+    fn:xml-to-json(
+        <string xmlns="http://www.w3.org/2005/xpath-functions" escaped="0">ok</string>
+    )
+};
+
 declare
     %test:arg("int", "1E9") %test:assertXPath('$result/fn:map/fn:number = ''1E9''')
     %test:arg("int", "1E+9") %test:assertXPath('$result/fn:map/fn:number = ''1E+9''')