1 files changed, 64 insertions, 0 deletions
diff --git a/devtools/client/jsonview/Sniffer.sys.mjs b/devtools/client/jsonview/Sniffer.sys.mjs
new file mode 100644
index 0000000000..d585ce8ab2
--- /dev/null
+++ b/devtools/client/jsonview/Sniffer.sys.mjs
@@ -0,0 +1,64 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+const gPrefs = {};
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  gPrefs,
+  "gEnabled",
+  "devtools.jsonview.enabled"
+);
+
+const JSON_VIEW_MIME_TYPE = "application/vnd.mozilla.json.view";
+
+function getContentDisposition(channel) {
+  try {
+    return channel.contentDisposition;
+  } catch (e) {
+    // Channel doesn't support content dispositions
+    return null;
+  }
+}
+
+/**
+ * This component represents a sniffer (implements nsIContentSniffer
+ * interface) responsible for changing top level 'application/json'
+ * document types to: 'application/vnd.mozilla.json.view'.
+ *
+ * This internal type is consequently rendered by JSON View component
+ * that represents the JSON through a viewer interface.
+ *
+ * This is done in the .js file rather than a .jsm to avoid creating
+ * a compartment at startup when no JSON is being viewed.
+ */
+export class Sniffer {
+  getMIMETypeFromContent(request, data, length) {
+    if (request instanceof Ci.nsIChannel) {
+      // JSON View is enabled only for top level loads only.
+      if (
+        gPrefs.gEnabled &&
+        request.loadInfo?.isTopLevelLoad &&
+        request.loadFlags & Ci.nsIChannel.LOAD_DOCUMENT_URI &&
+        getContentDisposition(request) != Ci.nsIChannel.DISPOSITION_ATTACHMENT
+      ) {
+        // Check the response content type and if it's a valid type
+        // such as application/json or application/manifest+json
+        // change it to new internal type consumed by JSON View.
+        if (/^application\/(?:.+\+)?json$/.test(request.contentType)) {
+          return JSON_VIEW_MIME_TYPE;
+        }
+      } else if (request.contentType === JSON_VIEW_MIME_TYPE) {
+        return "application/json";
+      }
+    }
+
+    return "";
+  }
+}
+
+Sniffer.prototype.QueryInterface = ChromeUtils.generateQI([
+  "nsIContentSniffer",
+]);