1 files changed, 150 insertions, 0 deletions
diff --git a/src/lib/SyncMessage.js b/src/lib/SyncMessage.js
new file mode 100644
index 0000000..6d48b23
--- /dev/null
+++ b/src/lib/SyncMessage.js
@@ -0,0 +1,150 @@
+(() => {
+  let ENDPOINT_PREFIX = `https://sync-messages.invalid/${browser.extension.getURL("")}?`;
+  let MOZILLA = "mozSystem" in XMLHttpRequest.prototype;
+
+  if (browser.webRequest) {
+    if (typeof browser.runtime.onSyncMessage !== "object") {
+      // Background Script side
+
+      // cache of senders from unprivileged requests to track tab ids in Firefox
+      let pending = new Map();
+      let tabUrlCache = new Map();
+      let tabRemovalListener = null;
+      let CANCEL = {cancel: true};
+      let {TAB_ID_NONE} = browser.tabs;
+
+      let obrListener = request => {
+        let {url, tabId} = request;
+        let params = new URLSearchParams(url.split("?")[1]);
+        let msgId = params.get("id");
+        let msg = params.get("msg");
+        let documentUrl = params.get("url");
+        let sender;
+        if (tabId === TAB_ID_NONE) {
+          // Firefox sends privileged content script XHR without valid tab ids
+          // so we cache sender info from unprivileged XHR correlated by msgId
+          if (pending.has(msgId)) {
+            sender = pending.get(msgId);
+            pending.delete(msgId);
+          } else {
+            throw new Error(`sendSyncMessage: cannot correlate sender info for ${msgId}.`);
+          }
+        } else {
+          let {frameAncestors, frameId} = request;
+          let isTop = frameId === 0 || !!params.get("top");
+          let tabUrl = frameAncestors && frameAncestors.length
+            && frameAncestors[frameAncestors.length - 1].url;
+
+          if (!tabUrl) {
+            if (isTop) {
+              tabUrlCache.set(tabId, tabUrl = documentUrl);
+              if (!tabRemovalListener) {
+                browser.tabs.onRemoved.addListener(tabRemovalListener = tab => {
+                  tabUrlCache.delete(tab.id);
+                });
+              }
+            } else {
+              tabUrl = tabUrlCache.get(tabId);
+            }
+          }
+          sender = {
+            tab: {
+              id: tabId,
+              url: tabUrl
+            },
+            frameId,
+            url: documentUrl,
+            timeStamp: Date.now()
+          };
+          if (msg === null) {
+            // this was the unprivileged, messageless preliminary request
+            // to set tabId and frameId
+            pending.set(msgId, sender);
+          }
+        }
+        if (!(msg !== null && sender && url.startsWith(ENDPOINT_PREFIX))) {
+          return CANCEL;
+        }
+        // Just like in the async runtime.sendMessage() API,
+        // we process the listeners in order until we find a not undefined
+        // result, then we return it (or undefined if none returns anything).
+        let result;
+        for (let l of listeners) {
+          try {
+            if ((result = l(JSON.parse(msg), sender)) !== undefined) break;
+          } catch (e) {
+            console.error(e);
+          }
+        }
+        return {
+          redirectUrl: `data:application/json,${JSON.stringify(result)}`
+        };
+      };
+
+      let listeners = new Set();
+      browser.runtime.onSyncMessage = {
+        ENDPOINT_PREFIX,
+        addListener(l) {
+          listeners.add(l);
+          if (listeners.size === 1) {
+            browser.webRequest.onBeforeRequest.addListener(obrListener,
+              {urls: [`${ENDPOINT_PREFIX}*`, `*://*/${ENDPOINT_PREFIX}*`],
+                types: ["xmlhttprequest"]},
+              ["blocking"]
+            );
+          }
+        },
+        removeListener(l) {
+          listeners.remove(l);
+          if (listeners.size === 0) {
+            browser.webRequest.onBeforeRequest.removeListener(obrListener);
+          }
+        },
+        hasListener(l) {
+          return listeners.has(l);
+        }
+      };
+    }
+  } else if (typeof browser.runtime.sendSyncMessage !== "function") {
+    // Content Script side
+    if (typeof uuid !== "function") {
+      let uuid = () => (Math.random() * Date.now()).toString(16);
+    }
+    let docUrl = document.URL;
+    browser.runtime.sendSyncMessage = sendSyncMessage = msg => {
+      let msgId = `id=${encodeURIComponent(`${uuid()},${docUrl}`)}`;
+      let url = `${ENDPOINT_PREFIX}${msgId}` +
+        `&url=${encodeURIComponent(docUrl)}`;
+      if (window.top === window) {
+        // we add top URL information because Chromium doesn't know anything
+        // about frameAncestors
+        url += "&top=true";
+      }
+
+      if (MOZILLA) try {
+        // on Firefox first we send an unprivileged XHR to notify the listener
+        // about the tab ID, which is not sent in privileged XHR
+        let r = new content.XMLHttpRequest();
+        let unprivilegedUrl = docUrl.startsWith("http")
+          ? `${document.location.origin}/${url}` : url;
+        r.open("GET", unprivilegedUrl, false);
+        r.send(null);
+      } catch (e) {
+        // we ignore the likely CORS error
+      }
+      // adding the payload
+      url += `&msg=${encodeURIComponent(JSON.stringify(msg))}`;
+      try {
+        // then we send the payload using a privileged XHR, which is not subject
+        // to CORS but unfortunately doesn't carry any tab id except on Chromium
+        let r = new XMLHttpRequest();
+        r.open("GET", url, false);
+        r.send(null);
+        return JSON.parse(r.responseText);
+      } catch(e) {
+        console.error(`syncMessage error in ${document.URL}: ${e.message}`);
+      }
+      return null;
+    };
+  }
+})();