feat: add Svg component (#15540)

A very trivial implementation that is capable of displaying static SVG at this point.

Co-authored-by: Soroosh Taefi <taefi.soroosh@gmail.com>

flow-server/src/main/java/com/vaadin/flow/component/Html.java

@@ -46,6 +46,9 @@
  * <p>
  * The HTML fragment cannot be changed after creation. You should create a new
  * instance to encapsulate another fragment.
+ * <p>
+ * Note that this component doesn't support svg element as a root node. See
+ * separate {@link Svg} component if you want to display SVG images.
  *
  * @author Vaadin Ltd
  * @since 1.0

flow-server/src/main/java/com/vaadin/flow/component/Svg.java

@@ -0,0 +1,134 @@
+/*
+ * Copyright 2000-2022 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow.component;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.UncheckedIOException;
+import org.jsoup.helper.DataUtil;
+
+import com.vaadin.flow.dom.Element;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+/**
+ * A component that displays a given SVG image.
+ * <p>
+ * Note that it is the developer's responsibility to sanitize and remove any
+ * dangerous parts of the SVG before sending it to the user through this
+ * component. Passing raw input data to the user will possibly lead to
+ * cross-site scripting attacks.
+ * <p>
+ * Note, because of implementation details, we currently wrap the SVG in a div
+ * element. This might change in the future.
+ *
+ * @author Vaadin Ltd
+ * @since 24.0
+ */
+public class Svg extends Component {
+
+    /**
+     * Creates an instance based on the given SVG input. The string must have
+     * exactly one root element.
+     *
+     * @param stream
+     *            the SVG to display
+     */
+    public Svg(InputStream stream) {
+        this();
+        setSvg(stream);
+    }
+
+    /**
+     * Creates an instance based on the given SVG string. The string must have
+     * exactly one root element.
+     *
+     * @param svg
+     *            the SVG to display
+     */
+    public Svg(String svg) {
+        this();
+        setSvg(svg);
+    }
+
+    /**
+     * Creates an empty Svg.
+     */
+    public Svg() {
+        super(new Element("div"));
+    }
+
+    /**
+     * Sets the graphics shown in this component.
+     *
+     * @param svg
+     *            the SVG string
+     */
+    public void setSvg(String svg) {
+        if (svg == null || svg.isEmpty()) {
+            setInnerHtml("");
+        } else {
+            validateAndSet(svg);
+        }
+    }
+
+    /**
+     * Sets the graphics shown in this component.
+     *
+     * @param stream
+     *            the input stream where SVG is read from
+     */
+    public void setSvg(InputStream stream) {
+        validateAndSet(readSvgStreamAsString(stream));
+    }
+
+    private String readSvgStreamAsString(InputStream stream) {
+        if (stream == null) {
+            throw new IllegalArgumentException("SVG stream cannot be null");
+        }
+        try {
+            /*
+             * Cannot use any of the methods that accept a stream since they all
+             * parse as a document rather than as a body fragment. The logic for
+             * reading a stream into a String is the same that is used
+             * internally by JSoup if you strip away all the logic to guess an
+             * encoding in case one isn't defined.
+             */
+            return UTF_8.decode(DataUtil.readToByteBuffer(stream, 0))
+                    .toString();
+        } catch (IOException e) {
+            throw new UncheckedIOException("Unable to read SVG from stream", e);
+        }
+    }
+
+    private void validateAndSet(String svgInput) {
+        if (!svgInput.startsWith("<svg")) {
+            // remove possible xml header & doc types
+            int startIndex = svgInput.indexOf("<svg");
+            if (startIndex == -1) {
+                throw new IllegalArgumentException(
+                        "The content don't appear to be SVG");
+            }
+            svgInput = svgInput.substring(startIndex);
+        }
+        setInnerHtml(svgInput);
+    }
+
+    private void setInnerHtml(String html) {
+        getElement().setProperty("innerHTML", html);
+    }
+
+}

flow-server/src/test/java/com/vaadin/flow/component/SvgTest.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2000-2022 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow.component;
+
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SvgTest {
+
+    @Test
+    public void attachedToElement() {
+        // This will throw an assertion error if the element is not attached to
+        // the component
+        new Svg("<svg></svg>").getParent();
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void nullStream() {
+        new Svg((InputStream) null);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void text() {
+        new Svg("hello");
+    }
+
+    static String TRIVIAL_SVG = """
+            <svg>
+                <circle cx="50" cy="50" r="40" stroke="green" stroke-width="4" fill="yellow" />
+            </svg>""";
+
+    static String TRIVIAL_SVG2 = """
+            <svg height="140" width="500">
+              <ellipse cx="200" cy="80" rx="100" ry="50"
+              style="fill:yellow;stroke:purple;stroke-width:2" />
+            </svg>""";
+
+    static String SVG_WITH_DOCTYPE_ET_AL = """
+            <?xml version="1.0" encoding="UTF-8" standalone="no"?>
+            <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+            <svg width="391" height="391" viewBox="-70.5 -70.5 391 391" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+            <rect fill="#fff" stroke="#000" x="-70" y="-70" width="390" height="390"/>
+            <g opacity="0.8">
+                 <rect x="25" y="25" width="200" height="200" fill="lime" stroke-width="4" stroke="pink" />
+                 <circle cx="125" cy="125" r="75" fill="orange" />
+                 <polyline points="50,150 50,200 200,200 200,100" stroke="red" stroke-width="4" fill="none" />
+                 <line x1="50" y1="50" x2="200" y2="200" stroke="blue" stroke-width="4" />
+            </g>
+            </svg>""";
+
+    @Test
+    public void simpleSvg() {
+        Svg svg = new Svg(TRIVIAL_SVG);
+        Assert.assertEquals(TRIVIAL_SVG, getSvgDocumentBody(svg));
+    }
+
+    @Test
+    public void withDocType() {
+        Svg svg = new Svg(SVG_WITH_DOCTYPE_ET_AL);
+        Assert.assertTrue(getSvgDocumentBody(svg).startsWith("<svg"));
+    }
+
+    @Test
+    public void resetSvg() {
+        Svg svg = new Svg(TRIVIAL_SVG);
+        Assert.assertEquals(TRIVIAL_SVG, getSvgDocumentBody(svg));
+        svg.setSvg(TRIVIAL_SVG2);
+        Assert.assertEquals(TRIVIAL_SVG2, getSvgDocumentBody(svg));
+    }
+
+    @Test
+    public void fromStream() {
+        Svg svg = new Svg(new ByteArrayInputStream(TRIVIAL_SVG.getBytes()));
+        Assert.assertEquals(TRIVIAL_SVG, getSvgDocumentBody(svg));
+    }
+
+    private static String getSvgDocumentBody(Svg svg) {
+        return svg.getElement().getProperty("innerHTML");
+    }
+
+}