Return ErrorStatus from webdriver_handlers

1 files changed, 375 insertions, 321 deletions

diff --git a/components/script/webdriver_handlers.rs b/components/script/webdriver_handlers.rs
index 182f110c0c8..22d3e56fcaf 100644
--- a/components/script/webdriver_handlers.rs
+++ b/components/script/webdriver_handlers.rs
@@ -33,7 +33,7 @@ use crate::dom::nodelist::NodeList;
 use crate::dom::window::Window;
 use crate::dom::xmlserializer::XMLSerializer;
 use crate::script_runtime::JSContext as SafeJSContext;
-use crate::script_thread::Documents;
+use crate::script_thread::{Documents, ScriptThread};
 use cookie::Cookie;
 use euclid::default::{Point2D, Rect, Size2D};
 use hyper_serde::Serde;
@@ -52,18 +52,28 @@ use script_traits::webdriver_msg::{
 };
 use servo_url::ServoUrl;
 use webdriver::common::WebElement;
+use webdriver::error::ErrorStatus;
 
 fn find_node_by_unique_id(
     documents: &Documents,
     pipeline: PipelineId,
     node_id: String,
-) -> Option<DomRoot<Node>> {
-    documents.find_document(pipeline).and_then(|document| {
+) -> Result<DomRoot<Node>, ErrorStatus> {
+    match documents.find_document(pipeline).and_then(|document| {
         document
             .upcast::<Node>()
             .traverse_preorder(ShadowIncluding::Yes)
-            .find(|candidate| candidate.unique_id() == node_id)
-    })
+            .find(|node| node.unique_id() == node_id)
+    }) {
+        Some(node) => Ok(node),
+        None => {
+            if ScriptThread::has_node_id(&node_id) {
+                Err(ErrorStatus::StaleElementReference)
+            } else {
+                Err(ErrorStatus::NoSuchElement)
+            }
+        },
+    }
 }
 
 fn matching_links<'a>(
@@ -92,10 +102,10 @@ fn all_matching_links(
     root_node: &Node,
     link_text: String,
     partial: bool,
-) -> Result<Vec<String>, ()> {
+) -> Result<Vec<String>, ErrorStatus> {
     root_node
         .query_selector_all(DOMString::from("a"))
-        .map_err(|_| ())
+        .map_err(|_| ErrorStatus::UnknownError)
         .map(|nodes| matching_links(&nodes, link_text, partial).collect())
 }
 
@@ -103,10 +113,10 @@ fn first_matching_link(
     root_node: &Node,
     link_text: String,
     partial: bool,
-) -> Result<Option<String>, ()> {
+) -> Result<Option<String>, ErrorStatus> {
     root_node
         .query_selector_all(DOMString::from("a"))
-        .map_err(|_| ())
+        .map_err(|_| ErrorStatus::UnknownError)
         .map(|nodes| matching_links(&nodes, link_text, partial).take(1).next())
 }
 
@@ -243,45 +253,53 @@ pub fn handle_get_browsing_context_id(
     documents: &Documents,
     pipeline: PipelineId,
     webdriver_frame_id: WebDriverFrameId,
-    reply: IpcSender<Result<BrowsingContextId, ()>>,
+    reply: IpcSender<Result<BrowsingContextId, ErrorStatus>>,
 ) {
-    let result = match webdriver_frame_id {
-        WebDriverFrameId::Short(_) => {
-            // This isn't supported yet
-            Err(())
-        },
-        WebDriverFrameId::Element(x) => find_node_by_unique_id(documents, pipeline, x)
-            .and_then(|node| {
-                node.downcast::<HTMLIFrameElement>()
-                    .and_then(|elem| elem.browsing_context_id())
-            })
-            .ok_or(()),
-        WebDriverFrameId::Parent => documents
-            .find_window(pipeline)
-            .and_then(|window| {
-                window
-                    .window_proxy()
-                    .parent()
-                    .map(|parent| parent.browsing_context_id())
-            })
-            .ok_or(()),
-    };
-
-    reply.send(result).unwrap()
+    reply
+        .send(match webdriver_frame_id {
+            WebDriverFrameId::Short(_) => {
+                // This isn't supported yet
+                Err(ErrorStatus::UnsupportedOperation)
+            },
+            WebDriverFrameId::Element(element_id) => {
+                find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| {
+                    node.downcast::<HTMLIFrameElement>()
+                        .and_then(|element| element.browsing_context_id())
+                        .ok_or(ErrorStatus::NoSuchFrame)
+                })
+            },
+            WebDriverFrameId::Parent => documents
+                .find_window(pipeline)
+                .and_then(|window| {
+                    window
+                        .window_proxy()
+                        .parent()
+                        .map(|parent| parent.browsing_context_id())
+                })
+                .ok_or(ErrorStatus::NoSuchFrame),
+        })
+        .unwrap();
 }
 
 pub fn handle_find_element_css(
     documents: &Documents,
     pipeline: PipelineId,
     selector: String,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
-    let node_id = documents
-        .find_document(pipeline)
-        .ok_or(())
-        .and_then(|doc| doc.QuerySelector(DOMString::from(selector)).map_err(|_| ()))
-        .map(|node| node.map(|x| x.upcast::<Node>().unique_id()));
-    reply.send(node_id).unwrap();
+    reply
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| {
+                    document
+                        .QuerySelector(DOMString::from(selector))
+                        .map_err(|_| ErrorStatus::InvalidSelector)
+                })
+                .map(|node| node.map(|x| x.upcast::<Node>().unique_id())),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_link_text(
@@ -289,54 +307,66 @@ pub fn handle_find_element_link_text(
     pipeline: PipelineId,
     selector: String,
     partial: bool,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
-    let node_id = documents
-        .find_document(pipeline)
-        .ok_or(())
-        .and_then(|doc| first_matching_link(&doc.upcast::<Node>(), selector.clone(), partial));
-    reply.send(node_id).unwrap();
+    reply
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| {
+                    first_matching_link(&document.upcast::<Node>(), selector.clone(), partial)
+                }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_tag_name(
     documents: &Documents,
     pipeline: PipelineId,
     selector: String,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
-    let node_id = documents
-        .find_document(pipeline)
-        .ok_or(())
-        .and_then(|doc| {
-            Ok(doc
-                .GetElementsByTagName(DOMString::from(selector))
-                .elements_iter()
-                .next())
-        })
-        .map(|node| node.map(|x| x.upcast::<Node>().unique_id()));
-    reply.send(node_id).unwrap();
+    reply
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| {
+                    Ok(document
+                        .GetElementsByTagName(DOMString::from(selector))
+                        .elements_iter()
+                        .next())
+                })
+                .map(|node| node.map(|x| x.upcast::<Node>().unique_id())),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_elements_css(
     documents: &Documents,
     pipeline: PipelineId,
     selector: String,
-    reply: IpcSender<Result<Vec<String>, ()>>,
+    reply: IpcSender<Result<Vec<String>, ErrorStatus>>,
 ) {
-    let node_ids = documents
-        .find_document(pipeline)
-        .ok_or(())
-        .and_then(|doc| {
-            doc.QuerySelectorAll(DOMString::from(selector))
-                .map_err(|_| ())
-        })
-        .map(|nodes| {
-            nodes
-                .iter()
-                .map(|x| x.upcast::<Node>().unique_id())
-                .collect()
-        });
-    reply.send(node_ids).unwrap();
+    reply
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| {
+                    document
+                        .QuerySelectorAll(DOMString::from(selector))
+                        .map_err(|_| ErrorStatus::InvalidSelector)
+                })
+                .map(|nodes| {
+                    nodes
+                        .iter()
+                        .map(|x| x.upcast::<Node>().unique_id())
+                        .collect()
+                }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_elements_link_text(
@@ -344,32 +374,40 @@ pub fn handle_find_elements_link_text(
     pipeline: PipelineId,
     selector: String,
     partial: bool,
-    reply: IpcSender<Result<Vec<String>, ()>>,
+    reply: IpcSender<Result<Vec<String>, ErrorStatus>>,
 ) {
-    let node_ids = documents
-        .find_document(pipeline)
-        .ok_or(())
-        .and_then(|doc| all_matching_links(&doc.upcast::<Node>(), selector.clone(), partial));
-    reply.send(node_ids).unwrap();
+    reply
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| {
+                    all_matching_links(&document.upcast::<Node>(), selector.clone(), partial)
+                }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_elements_tag_name(
     documents: &Documents,
     pipeline: PipelineId,
     selector: String,
-    reply: IpcSender<Result<Vec<String>, ()>>,
+    reply: IpcSender<Result<Vec<String>, ErrorStatus>>,
 ) {
-    let node_ids = documents
-        .find_document(pipeline)
-        .ok_or(())
-        .and_then(|doc| Ok(doc.GetElementsByTagName(DOMString::from(selector))))
-        .map(|nodes| {
-            nodes
-                .elements_iter()
-                .map(|x| x.upcast::<Node>().unique_id())
-                .collect::<Vec<String>>()
-        });
-    reply.send(node_ids).unwrap();
+    reply
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| Ok(document.GetElementsByTagName(DOMString::from(selector))))
+                .map(|nodes| {
+                    nodes
+                        .elements_iter()
+                        .map(|x| x.upcast::<Node>().unique_id())
+                        .collect::<Vec<String>>()
+                }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_element_css(
@@ -377,16 +415,17 @@ pub fn handle_find_element_element_css(
     pipeline: PipelineId,
     element_id: String,
     selector: String,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
-    let node_id = find_node_by_unique_id(documents, pipeline, element_id)
-        .ok_or(())
-        .and_then(|node| {
-            node.query_selector(DOMString::from(selector))
-                .map_err(|_| ())
-        })
-        .map(|node| node.map(|x| x.upcast::<Node>().unique_id()));
-    reply.send(node_id).unwrap();
+    reply
+        .send(
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| {
+                node.query_selector(DOMString::from(selector))
+                    .map_err(|_| ErrorStatus::InvalidSelector)
+                    .map(|node| node.map(|x| x.upcast::<Node>().unique_id()))
+            }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_element_link_text(
@@ -395,12 +434,14 @@ pub fn handle_find_element_element_link_text(
     element_id: String,
     selector: String,
     partial: bool,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
-    let node_id = find_node_by_unique_id(documents, pipeline, element_id)
-        .ok_or(())
-        .and_then(|node| first_matching_link(&node, selector.clone(), partial));
-    reply.send(node_id).unwrap();
+    reply
+        .send(
+            find_node_by_unique_id(documents, pipeline, element_id)
+                .and_then(|node| first_matching_link(&node, selector.clone(), partial)),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_element_tag_name(
@@ -408,19 +449,22 @@ pub fn handle_find_element_element_tag_name(
     pipeline: PipelineId,
     element_id: String,
     selector: String,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
-    let node_id = find_node_by_unique_id(documents, pipeline, element_id)
-        .ok_or(())
-        .and_then(|node| match node.downcast::<Element>() {
-            Some(elem) => Ok(elem
-                .GetElementsByTagName(DOMString::from(selector))
-                .elements_iter()
-                .next()),
-            None => Err(()),
-        })
-        .map(|node| node.map(|x| x.upcast::<Node>().unique_id()));
-    reply.send(node_id).unwrap();
+    reply
+        .send(
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| match node
+                .downcast::<Element>(
+            ) {
+                Some(element) => Ok(element
+                    .GetElementsByTagName(DOMString::from(selector))
+                    .elements_iter()
+                    .next()
+                    .map(|x| x.upcast::<Node>().unique_id())),
+                None => Err(ErrorStatus::UnknownError),
+            }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_elements_css(
@@ -428,21 +472,22 @@ pub fn handle_find_element_elements_css(
     pipeline: PipelineId,
     element_id: String,
     selector: String,
-    reply: IpcSender<Result<Vec<String>, ()>>,
+    reply: IpcSender<Result<Vec<String>, ErrorStatus>>,
 ) {
-    let node_ids = find_node_by_unique_id(documents, pipeline, element_id)
-        .ok_or(())
-        .and_then(|node| {
-            node.query_selector_all(DOMString::from(selector))
-                .map_err(|_| ())
-        })
-        .map(|nodes| {
-            nodes
-                .iter()
-                .map(|x| x.upcast::<Node>().unique_id())
-                .collect()
-        });
-    reply.send(node_ids).unwrap();
+    reply
+        .send(
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| {
+                node.query_selector_all(DOMString::from(selector))
+                    .map_err(|_| ErrorStatus::InvalidSelector)
+                    .map(|nodes| {
+                        nodes
+                            .iter()
+                            .map(|x| x.upcast::<Node>().unique_id())
+                            .collect()
+                    })
+            }),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_elements_link_text(
@@ -451,12 +496,14 @@ pub fn handle_find_element_elements_link_text(
     element_id: String,
     selector: String,
     partial: bool,
-    reply: IpcSender<Result<Vec<String>, ()>>,
+    reply: IpcSender<Result<Vec<String>, ErrorStatus>>,
 ) {
-    let node_ids = find_node_by_unique_id(documents, pipeline, element_id)
-        .ok_or(())
-        .and_then(|node| all_matching_links(&node, selector.clone(), partial));
-    reply.send(node_ids).unwrap();
+    reply
+        .send(
+            find_node_by_unique_id(documents, pipeline, element_id)
+                .and_then(|node| all_matching_links(&node, selector.clone(), partial)),
+        )
+        .unwrap();
 }
 
 pub fn handle_find_element_elements_tag_name(
@@ -464,44 +511,42 @@ pub fn handle_find_element_elements_tag_name(
     pipeline: PipelineId,
     element_id: String,
     selector: String,
-    reply: IpcSender<Result<Vec<String>, ()>>,
+    reply: IpcSender<Result<Vec<String>, ErrorStatus>>,
 ) {
-    let node_ids = find_node_by_unique_id(documents, pipeline, element_id)
-        .ok_or(())
-        .and_then(|node| match node.downcast::<Element>() {
-            Some(elem) => Ok(elem.GetElementsByTagName(DOMString::from(selector))),
-            None => Err(()),
-        })
-        .map(|nodes| {
-            nodes
-                .elements_iter()
-                .map(|x| x.upcast::<Node>().unique_id())
-                .collect::<Vec<String>>()
-        });
-    reply.send(node_ids).unwrap();
+    reply
+        .send(
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| match node
+                .downcast::<Element>(
+            ) {
+                Some(element) => Ok(element
+                    .GetElementsByTagName(DOMString::from(selector))
+                    .elements_iter()
+                    .map(|x| x.upcast::<Node>().unique_id())
+                    .collect::<Vec<String>>()),
+                None => Err(ErrorStatus::UnknownError),
+            }),
+        )
+        .unwrap();
 }
 
 pub fn handle_focus_element(
     documents: &Documents,
     pipeline: PipelineId,
     element_id: String,
-    reply: IpcSender<Result<(), ()>>,
+    reply: IpcSender<Result<(), ErrorStatus>>,
 ) {
     reply
         .send(
-            match find_node_by_unique_id(documents, pipeline, element_id) {
-                Some(ref node) => {
-                    match node.downcast::<HTMLElement>() {
-                        Some(ref elem) => {
-                            // Need a way to find if this actually succeeded
-                            elem.Focus();
-                            Ok(())
-                        },
-                        None => Err(()),
-                    }
-                },
-                None => Err(()),
-            },
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| {
+                match node.downcast::<HTMLElement>() {
+                    Some(element) => {
+                        // Need a way to find if this actually succeeded
+                        element.Focus();
+                        Ok(())
+                    },
+                    None => Err(ErrorStatus::UnknownError),
+                }
+            }),
         )
         .unwrap();
 }
@@ -515,8 +560,8 @@ pub fn handle_get_active_element(
         .send(
             documents
                 .find_document(pipeline)
-                .and_then(|doc| doc.GetActiveElement())
-                .map(|elem| elem.upcast::<Node>().unique_id()),
+                .and_then(|document| document.GetActiveElement())
+                .map(|element| element.upcast::<Node>().unique_id()),
         )
         .unwrap();
 }
@@ -524,25 +569,28 @@ pub fn handle_get_active_element(
 pub fn handle_get_page_source(
     documents: &Documents,
     pipeline: PipelineId,
-    reply: IpcSender<Result<String, ()>>,
+    reply: IpcSender<Result<String, ErrorStatus>>,
 ) {
     reply
-        .send(documents.find_document(pipeline).ok_or(()).and_then(|doc| {
-            match doc.GetDocumentElement() {
-                Some(elem) => match elem.GetOuterHTML() {
-                    Ok(source) => Ok(source.to_string()),
-                    Err(_) => {
-                        match XMLSerializer::new(doc.window())
-                            .SerializeToString(elem.upcast::<Node>())
-                        {
-                            Ok(source) => Ok(source.to_string()),
-                            Err(_) => Err(()),
-                        }
+        .send(
+            documents
+                .find_document(pipeline)
+                .ok_or(ErrorStatus::UnknownError)
+                .and_then(|document| match document.GetDocumentElement() {
+                    Some(element) => match element.GetOuterHTML() {
+                        Ok(source) => Ok(source.to_string()),
+                        Err(_) => {
+                            match XMLSerializer::new(document.window())
+                                .SerializeToString(element.upcast::<Node>())
+                            {
+                                Ok(source) => Ok(source.to_string()),
+                                Err(_) => Err(ErrorStatus::UnknownError),
+                            }
+                        },
                     },
-                },
-                None => Err(()),
-            }
-        }))
+                    None => Err(ErrorStatus::UnknownError),
+                }),
+        )
         .unwrap();
 }
 
@@ -551,21 +599,24 @@ pub fn handle_get_cookies(
     pipeline: PipelineId,
     reply: IpcSender<Vec<Serde<Cookie<'static>>>>,
 ) {
-    // TODO: Return an error if the pipeline doesn't exist?
-    let cookies = match documents.find_document(pipeline) {
-        None => Vec::new(),
-        Some(document) => {
-            let url = document.url();
-            let (sender, receiver) = ipc::channel().unwrap();
-            let _ = document
-                .window()
-                .upcast::<GlobalScope>()
-                .resource_threads()
-                .send(GetCookiesDataForUrl(url, sender, NonHTTP));
-            receiver.recv().unwrap()
-        },
-    };
-    reply.send(cookies).unwrap();
+    reply
+        .send(
+            // TODO: Return an error if the pipeline doesn't exist
+            match documents.find_document(pipeline) {
+                Some(document) => {
+                    let url = document.url();
+                    let (sender, receiver) = ipc::channel().unwrap();
+                    let _ = document
+                        .window()
+                        .upcast::<GlobalScope>()
+                        .resource_threads()
+                        .send(GetCookiesDataForUrl(url, sender, NonHTTP));
+                    receiver.recv().unwrap()
+                },
+                None => Vec::new(),
+            },
+        )
+        .unwrap();
 }
 
 // https://w3c.github.io/webdriver/webdriver-spec.html#get-cookie
@@ -575,22 +626,27 @@ pub fn handle_get_cookie(
     name: String,
     reply: IpcSender<Vec<Serde<Cookie<'static>>>>,
 ) {
-    // TODO: Return an error if the pipeline doesn't exist?
-    let cookies = match documents.find_document(pipeline) {
-        None => Vec::new(),
-        Some(document) => {
-            let url = document.url();
-            let (sender, receiver) = ipc::channel().unwrap();
-            let _ = document
-                .window()
-                .upcast::<GlobalScope>()
-                .resource_threads()
-                .send(GetCookiesDataForUrl(url, sender, NonHTTP));
-            receiver.recv().unwrap()
-        },
-    };
     reply
-        .send(cookies.into_iter().filter(|c| c.name() == &*name).collect())
+        .send(
+            // TODO: Return an error if the pipeline doesn't exist
+            match documents.find_document(pipeline) {
+                Some(document) => {
+                    let url = document.url();
+                    let (sender, receiver) = ipc::channel().unwrap();
+                    let _ = document
+                        .window()
+                        .upcast::<GlobalScope>()
+                        .resource_threads()
+                        .send(GetCookiesDataForUrl(url, sender, NonHTTP));
+                    let cookies = receiver.recv().unwrap();
+                    cookies
+                        .into_iter()
+                        .filter(|cookie| cookie.name() == &*name)
+                        .collect()
+                },
+                None => Vec::new(),
+            },
+        )
         .unwrap();
 }
 
@@ -601,7 +657,7 @@ pub fn handle_add_cookie(
     cookie: Cookie<'static>,
     reply: IpcSender<Result<(), WebDriverCookieError>>,
 ) {
-    // TODO: Return a different error if the pipeline doesn't exist?
+    // TODO: Return a different error if the pipeline doesn't exist
     let document = match documents.find_document(pipeline) {
         Some(document) => document,
         None => {
@@ -645,12 +701,12 @@ pub fn handle_add_cookie(
 pub fn handle_delete_cookies(
     documents: &Documents,
     pipeline: PipelineId,
-    reply: IpcSender<Result<(), ()>>,
+    reply: IpcSender<Result<(), ErrorStatus>>,
 ) {
     let document = match documents.find_document(pipeline) {
         Some(document) => document,
         None => {
-            return reply.send(Err(())).unwrap();
+            return reply.send(Err(ErrorStatus::UnknownError)).unwrap();
         },
     };
     let url = document.url();
@@ -660,62 +716,62 @@ pub fn handle_delete_cookies(
         .resource_threads()
         .send(DeleteCookies(url))
         .unwrap();
-    let _ = reply.send(Ok(()));
+    reply.send(Ok(())).unwrap();
 }
 
 pub fn handle_get_title(documents: &Documents, pipeline: PipelineId, reply: IpcSender<String>) {
-    // TODO: Return an error if the pipeline doesn't exist.
-    let title = documents
-        .find_document(pipeline)
-        .map(|doc| String::from(doc.Title()))
-        .unwrap_or_default();
-    reply.send(title).unwrap();
+    reply
+        .send(
+            // TODO: Return an error if the pipeline doesn't exist
+            documents
+                .find_document(pipeline)
+                .map(|document| String::from(document.Title()))
+                .unwrap_or_default(),
+        )
+        .unwrap();
 }
 
 pub fn handle_get_rect(
     documents: &Documents,
     pipeline: PipelineId,
     element_id: String,
-    reply: IpcSender<Result<Rect<f64>, ()>>,
+    reply: IpcSender<Result<Rect<f64>, ErrorStatus>>,
 ) {
     reply
         .send(
-            match find_node_by_unique_id(documents, pipeline, element_id) {
-                Some(elem) => {
-                    // https://w3c.github.io/webdriver/webdriver-spec.html#dfn-calculate-the-absolute-position
-                    match elem.downcast::<HTMLElement>() {
-                        Some(html_elem) => {
-                            // Step 1
-                            let mut x = 0;
-                            let mut y = 0;
-
-                            let mut offset_parent = html_elem.GetOffsetParent();
-
-                            // Step 2
-                            while let Some(element) = offset_parent {
-                                offset_parent = match element.downcast::<HTMLElement>() {
-                                    Some(elem) => {
-                                        x += elem.OffsetLeft();
-                                        y += elem.OffsetTop();
-                                        elem.GetOffsetParent()
-                                    },
-                                    None => None,
-                                };
-                            }
-                            // Step 3
-                            Ok(Rect::new(
-                                Point2D::new(x as f64, y as f64),
-                                Size2D::new(
-                                    html_elem.OffsetWidth() as f64,
-                                    html_elem.OffsetHeight() as f64,
-                                ),
-                            ))
-                        },
-                        None => Err(()),
-                    }
-                },
-                None => Err(()),
-            },
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| {
+                // https://w3c.github.io/webdriver/webdriver-spec.html#dfn-calculate-the-absolute-position
+                match node.downcast::<HTMLElement>() {
+                    Some(html_element) => {
+                        // Step 1
+                        let mut x = 0;
+                        let mut y = 0;
+
+                        let mut offset_parent = html_element.GetOffsetParent();
+
+                        // Step 2
+                        while let Some(element) = offset_parent {
+                            offset_parent = match element.downcast::<HTMLElement>() {
+                                Some(elem) => {
+                                    x += elem.OffsetLeft();
+                                    y += elem.OffsetTop();
+                                    elem.GetOffsetParent()
+                                },
+                                None => None,
+                            };
+                        }
+                        // Step 3
+                        Ok(Rect::new(
+                            Point2D::new(x as f64, y as f64),
+                            Size2D::new(
+                                html_element.OffsetWidth() as f64,
+                                html_element.OffsetHeight() as f64,
+                            ),
+                        ))
+                    },
+                    None => Err(ErrorStatus::UnknownError),
+                }
+            }),
         )
         .unwrap();
 }
@@ -724,13 +780,13 @@ pub fn handle_get_text(
     documents: &Documents,
     pipeline: PipelineId,
     node_id: String,
-    reply: IpcSender<Result<String, ()>>,
+    reply: IpcSender<Result<String, ErrorStatus>>,
 ) {
     reply
-        .send(match find_node_by_unique_id(documents, pipeline, node_id) {
-            Some(ref node) => Ok(node.GetTextContent().map_or("".to_owned(), String::from)),
-            None => Err(()),
-        })
+        .send(
+            find_node_by_unique_id(documents, pipeline, node_id)
+                .and_then(|node| Ok(node.GetTextContent().map_or("".to_owned(), String::from))),
+        )
         .unwrap();
 }
 
@@ -738,13 +794,13 @@ pub fn handle_get_name(
     documents: &Documents,
     pipeline: PipelineId,
     node_id: String,
-    reply: IpcSender<Result<String, ()>>,
+    reply: IpcSender<Result<String, ErrorStatus>>,
 ) {
     reply
-        .send(match find_node_by_unique_id(documents, pipeline, node_id) {
-            Some(node) => Ok(String::from(node.downcast::<Element>().unwrap().TagName())),
-            None => Err(()),
-        })
+        .send(
+            find_node_by_unique_id(documents, pipeline, node_id)
+                .and_then(|node| Ok(String::from(node.downcast::<Element>().unwrap().TagName()))),
+        )
         .unwrap();
 }
 
@@ -753,17 +809,18 @@ pub fn handle_get_attribute(
     pipeline: PipelineId,
     node_id: String,
     name: String,
-    reply: IpcSender<Result<Option<String>, ()>>,
+    reply: IpcSender<Result<Option<String>, ErrorStatus>>,
 ) {
     reply
-        .send(match find_node_by_unique_id(documents, pipeline, node_id) {
-            Some(node) => Ok(node
-                .downcast::<Element>()
-                .unwrap()
-                .GetAttribute(DOMString::from(name))
-                .map(String::from)),
-            None => Err(()),
-        })
+        .send(
+            find_node_by_unique_id(documents, pipeline, node_id).and_then(|node| {
+                Ok(node
+                    .downcast::<Element>()
+                    .unwrap()
+                    .GetAttribute(DOMString::from(name))
+                    .map(String::from))
+            }),
+        )
         .unwrap();
 }
 
@@ -773,11 +830,11 @@ pub fn handle_get_property(
     pipeline: PipelineId,
     node_id: String,
     name: String,
-    reply: IpcSender<Result<WebDriverJSValue, ()>>,
+    reply: IpcSender<Result<WebDriverJSValue, ErrorStatus>>,
 ) {
     reply
-        .send(match find_node_by_unique_id(documents, pipeline, node_id) {
-            Some(node) => {
+        .send(
+            find_node_by_unique_id(documents, pipeline, node_id).and_then(|node| {
                 let cx = documents.find_document(pipeline).unwrap().window().get_cx();
 
                 rooted!(in(*cx) let mut property = UndefinedValue());
@@ -800,9 +857,8 @@ pub fn handle_get_property(
                         Ok(WebDriverJSValue::Undefined)
                     },
                 }
-            },
-            None => Err(()),
-        })
+            }),
+        )
         .unwrap();
 }
 
@@ -811,48 +867,49 @@ pub fn handle_get_css(
     pipeline: PipelineId,
     node_id: String,
     name: String,
-    reply: IpcSender<Result<String, ()>>,
+    reply: IpcSender<Result<String, ErrorStatus>>,
 ) {
     reply
-        .send(match find_node_by_unique_id(documents, pipeline, node_id) {
-            Some(node) => {
+        .send(
+            find_node_by_unique_id(documents, pipeline, node_id).and_then(|node| {
                 let window = window_from_node(&*node);
-                let elem = node.downcast::<Element>().unwrap();
+                let element = node.downcast::<Element>().unwrap();
                 Ok(String::from(
                     window
-                        .GetComputedStyle(&elem, None)
+                        .GetComputedStyle(&element, None)
                         .GetPropertyValue(DOMString::from(name)),
                 ))
-            },
-            None => Err(()),
-        })
+            }),
+        )
         .unwrap();
 }
 
 pub fn handle_get_url(documents: &Documents, pipeline: PipelineId, reply: IpcSender<ServoUrl>) {
-    // TODO: Return an error if the pipeline doesn't exist.
-    let url = documents
-        .find_document(pipeline)
-        .map(|document| document.url())
-        .unwrap_or_else(|| ServoUrl::parse("about:blank").expect("infallible"));
-    reply.send(url).unwrap();
+    reply
+        .send(
+            // TODO: Return an error if the pipeline doesn't exist.
+            documents
+                .find_document(pipeline)
+                .map(|document| document.url())
+                .unwrap_or_else(|| ServoUrl::parse("about:blank").expect("infallible")),
+        )
+        .unwrap();
 }
 
 pub fn handle_is_enabled(
     documents: &Documents,
     pipeline: PipelineId,
     element_id: String,
-    reply: IpcSender<Result<bool, ()>>,
+    reply: IpcSender<Result<bool, ErrorStatus>>,
 ) {
     reply
         .send(
-            match find_node_by_unique_id(&documents, pipeline, element_id) {
-                Some(ref node) => match node.downcast::<Element>() {
-                    Some(elem) => Ok(elem.enabled_state()),
-                    None => Err(()),
-                },
-                None => Err(()),
-            },
+            find_node_by_unique_id(&documents, pipeline, element_id).and_then(|node| match node
+                .downcast::<Element>(
+            ) {
+                Some(element) => Ok(element.enabled_state()),
+                None => Err(ErrorStatus::UnknownError),
+            }),
         )
         .unwrap();
 }
@@ -861,24 +918,21 @@ pub fn handle_is_selected(
     documents: &Documents,
     pipeline: PipelineId,
     element_id: String,
-    reply: IpcSender<Result<bool, ()>>,
+    reply: IpcSender<Result<bool, ErrorStatus>>,
 ) {
     reply
         .send(
-            match find_node_by_unique_id(documents, pipeline, element_id) {
-                Some(ref node) => {
-                    if let Some(input_element) = node.downcast::<HTMLInputElement>() {
-                        Ok(input_element.Checked())
-                    } else if let Some(option_element) = node.downcast::<HTMLOptionElement>() {
-                        Ok(option_element.Selected())
-                    } else if node.is::<HTMLElement>() {
-                        Ok(false) // regular elements are not selectable
-                    } else {
-                        Err(())
-                    }
-                },
-                None => Err(()),
-            },
+            find_node_by_unique_id(documents, pipeline, element_id).and_then(|node| {
+                if let Some(input_element) = node.downcast::<HTMLInputElement>() {
+                    Ok(input_element.Checked())
+                } else if let Some(option_element) = node.downcast::<HTMLOptionElement>() {
+                    Ok(option_element.Selected())
+                } else if node.is::<HTMLElement>() {
+                    Ok(false) // regular elements are not selectable
+                } else {
+                    Err(ErrorStatus::UnknownError)
+                }
+            }),
         )
         .unwrap();
 }