Implement getAttribute for W3C-compliant remote ends.

Fix docs for WebElement.getAttribute to attempt to better reflect reality.

This shim is supposed to replicate the OSS behavior, but in terms of
W3C-compliant "Get Element Attribute" and "Get Element Property"
commands. (See #2301.)

java/client/src/org/openqa/selenium/WebElement.java

@@ -87,28 +87,37 @@ public interface WebElement extends SearchContext, TakesScreenshot {
   String getTagName();
 
   /**
-   * Get the value of a the given attribute of the element. Will return the current value, even if
-   * this has been modified after the page has been loaded. More exactly, this method will return
-   * the value of the given attribute, unless that attribute is not present, in which case the value
-   * of the property with the same name is returned (for example for the "value" property of a
-   * textarea element). If neither value is set, null is returned. The "style" attribute is
-   * converted as best can be to a text representation with a trailing semi-colon. The following are
-   * deemed to be "boolean" attributes, and will return either "true" or null:
-   *
-   * async, autofocus, autoplay, checked, compact, complete, controls, declare, defaultchecked,
+   * Get the value of the given attribute of the element. Will return the current value, even if
+   * this has been modified after the page has been loaded.
+   *
+   * <p>More exactly, this method will return the value of the property with the given name, if it
+   * exists. If it does not, then the value of the attribute with the given name is returned. If
+   * neither exists, null is returned.
+   *
+   * <p>The "style" attribute is converted as best can be to a text representation with a trailing
+   * semi-colon.
+   *
+   * <p>The following are deemed to be "boolean" attributes, and will return either "true" or null:
+   *
+   * <p>async, autofocus, autoplay, checked, compact, complete, controls, declare, defaultchecked,
    * defaultselected, defer, disabled, draggable, ended, formnovalidate, hidden, indeterminate,
    * iscontenteditable, ismap, itemscope, loop, multiple, muted, nohref, noresize, noshade,
    * novalidate, nowrap, open, paused, pubdate, readonly, required, reversed, scoped, seamless,
-   * seeking, selected, spellcheck, truespeed, willvalidate
+   * seeking, selected, truespeed, willvalidate
    *
-   * Finally, the following commonly mis-capitalized attribute/property names are evaluated as
+   * <p>Finally, the following commonly mis-capitalized attribute/property names are evaluated as
    * expected:
    *
    * <ul>
-   * <li>"class"
-   * <li>"readonly"
+   * <li>If the given name is "class", the "className" property is returned.
+   * <li>If the given name is "readonly", the "readOnly" property is returned.
    * </ul>
    *
+   * <i>Note:</i> The reason for this behavior is that users frequently confuse attributes and
+   * properties. If you need to do something more precise, e.g., refer to an attribute even when a
+   * property of the same name exists, then you should evaluate Javascript to obtain the result
+   * you desire.
+   *
    * @param name The name of the attribute.
    * @return The attribute/property's current value or null if the value is not set.
    */

java/client/src/org/openqa/selenium/remote/DriverCommand.java

@@ -89,6 +89,7 @@ public interface DriverCommand {
   String GET_ELEMENT_LOCATION_ONCE_SCROLLED_INTO_VIEW = "getElementLocationOnceScrolledIntoView";
   String GET_ELEMENT_SIZE = "getElementSize";
   String GET_ELEMENT_ATTRIBUTE = "getElementAttribute";
+  String GET_ELEMENT_PROPERTY = "getElementProperty";
   String GET_ELEMENT_VALUE_OF_CSS_PROPERTY = "getElementValueOfCssProperty";
   String ELEMENT_EQUALS = "elementEquals";
 

java/client/src/org/openqa/selenium/remote/RemoteWebElement.java

@@ -18,6 +18,7 @@
 package org.openqa.selenium.remote;
 
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 
 import org.openqa.selenium.Beta;
 import org.openqa.selenium.By;
@@ -48,12 +49,21 @@
 import java.io.IOException;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 public class RemoteWebElement implements WebElement, FindsByLinkText, FindsById, FindsByName,
                                          FindsByTagName, FindsByClassName, FindsByCssSelector,
                                          FindsByXPath, WrapsDriver, Locatable, HasIdentity,
                                          TakesScreenshot {
 
+  private static final Set<String> BOOLEAN_ATTRIBUTES = ImmutableSet.of(
+      "async", "autofocus", "autoplay", "checked", "compact", "complete", "controls", "declare",
+      "defaultchecked", "defaultselected", "defer", "disabled", "draggable", "ended",
+      "formnovalidate", "hidden", "indeterminate", "iscontenteditable", "ismap", "itemscope",
+      "loop", "multiple", "muted", "nohref", "noresize", "noshade", "novalidate", "nowrap", "open",
+      "paused", "pubdate", "readonly", "required", "reversed", "scoped", "seamless", "seeking",
+      "selected", "truespeed", "willvalidate");
+
   private String foundBy;
   protected String id;
   protected RemoteWebDriver parent;
@@ -146,13 +156,88 @@ public String getTagName() {
   }
 
   public String getAttribute(String name) {
-    Object value =
+    if (parent.getW3CStandardComplianceLevel() == 0) {
+      return stringValueOf(
+          execute(DriverCommand.GET_ELEMENT_ATTRIBUTE, ImmutableMap.of("id", id, "name", name))
+          .getValue());
+    }
+
+    // Return a normalized version of the element's inline style. This excludes, e.g., properties
+    // inherited from parents or set via style sheets. This inline style is generally what people
+    // want when they ask for the "style" attribute; there is a separate WebDriver command for
+    // inspecting computed CSS properties.
+    if (name.equals("style")) {
+      return stringValueOf(parent.executeScript("return arguments[0].style.cssText", this));
+    }
+
+    // Special cases for selectable elements, i.e., radio buttons, checkboxes, and select options.
+    // When a user calls getAttribute("checked"), they generally want to know whether the element
+    // is *currently* checked, as opposed to the value of the "checked" attribute, which indicates
+    // the element's default checkedness.
+    if ("checked".equalsIgnoreCase(name) || "selected".equalsIgnoreCase(name)) {
+      String tagName = getTagName();
+      if ("option".equalsIgnoreCase(tagName)) {
+        return isSelected() ? "true" : null;
+      }
+      if ("input".equalsIgnoreCase(tagName)) {
+        String type = getAttribute("type");
+        if ("checkbox".equalsIgnoreCase(type) || "radio".equalsIgnoreCase(type)) {
+          return isSelected() ? "true" : null;
+        }
+      }
+    }
+
+    if (BOOLEAN_ATTRIBUTES.contains(name)) {
+      return getElementAttribute(name) != null ? "true" : null;
+    }
+
+    String attrValue = getElementProperty(name);
+    if ((attrValue != null && !attrValue.isEmpty()) || name.equals("value")) {
+      return attrValue;
+    }
+
+    attrValue = getElementAttribute(name);
+    if (attrValue != null) {
+      // We might be receiving a default value of the attribute (e.g., getting the "src" attribute
+      // for an <img> tag that lacks a src will return the empty string). If the attribute is
+      // absent, we are supposed to return null.
+      Object hasAttr =
+          parent.executeScript("return arguments[0].hasAttribute(arguments[1])", this, name);
+      if (hasAttr instanceof Boolean && !((Boolean) hasAttr)) {
+        attrValue = null;
+      }
+    }
+
+    return attrValue;
+  }
+
+  private String getElementAttribute(String name) {
+    return stringValueOf(
         execute(DriverCommand.GET_ELEMENT_ATTRIBUTE, ImmutableMap.of("id", id, "name", name))
-            .getValue();
-    if (value == null) {
+            .getValue());
+  }
+
+  private String getElementProperty(String name) {
+    try {
+      return stringValueOf(
+          execute(DriverCommand.GET_ELEMENT_PROPERTY, ImmutableMap.of("id", id, "name", name))
+              .getValue());
+    } catch (WebDriverException e) {
+      // In Firefox 48, Marionette returns a malformed response if the property is missing.
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=1281397
+      // Delete this after we stop supporting Firefox 48.
+      if (e.getMessage().contains("Failed to find value field")) {
+        return null;
+      }
+      throw e;
+    }
+  }
+
+  private static String stringValueOf(Object o) {
+    if (o == null) {
       return null;
     }
-    return String.valueOf(value);
+    return String.valueOf(o);
   }
 
   public boolean isSelected() {

java/client/src/org/openqa/selenium/remote/http/JsonHttpCommandCodec.java

@@ -128,6 +128,7 @@ public JsonHttpCommandCodec() {
     defineCommand(FIND_ELEMENTS, post("/session/:sessionId/elements"));
     defineCommand(GET_ACTIVE_ELEMENT, post("/session/:sessionId/element/active"));
     defineCommand(GET_ELEMENT_ATTRIBUTE, get("/session/:sessionId/element/:id/attribute/:name"));
+    defineCommand(GET_ELEMENT_PROPERTY, get("/session/:sessionId/element/:id/property/:name"));
     defineCommand(CLICK_ELEMENT, post("/session/:sessionId/element/:id/click"));
     defineCommand(CLEAR_ELEMENT, post("/session/:sessionId/element/:id/clear"));
     defineCommand(