Parse JSON blobs more leniently

mullvad-daemon/src/settings/patch.rs

@@ -7,7 +7,7 @@
 //!    Attempting to edit prohibited or invalid settings results in an error.
 //! 2. Merging the changes. When the patch has been accepted, it can be applied to the existing
 //!    settings. How they're merged depends on the actual setting. See [MergeStrategy].
-//! 3. Deserialize the resulting JSON back to a [Settings] instance, and, if valid, replace the
+//! 3. Deserializing the resulting JSON back to a [Settings] instance, and, if valid, replacing the
 //!    existing settings.
 //!
 //! Permitted settings and merge strategies are defined in the [PERMITTED_SUBKEYS] constant.
@@ -133,8 +133,8 @@ pub async fn merge_validate_patch(
 ) -> Result<(), Error> {
     let mut settings_value: serde_json::Value =
         serde_json::to_value(settings.to_settings()).map_err(Error::SerializeSettings)?;
-    let patch_value: serde_json::Value =
-        serde_json::from_str(json_patch).map_err(Error::ParsePatch)?;
+
+    let patch_value = fixup_patch(json_patch)?;
 
     validate_patch_value(PERMITTED_SUBKEYS, &patch_value, 0)?;
     merge_patch_to_value(PERMITTED_SUBKEYS, &mut settings_value, &patch_value, 0)?;
@@ -150,6 +150,30 @@ pub async fn merge_validate_patch(
     Ok(())
 }
 
+/// Parse JSON input with some extra leniency.
+fn fixup_patch(json_patch: &str) -> Result<serde_json::Value, Error> {
+    let fixed_patch = add_missing_braces(&remove_comments(json_patch));
+    serde_json::from_str(&fixed_patch).map_err(Error::ParsePatch)
+}
+
+/// Remove lines beginning with '#'
+fn remove_comments(json_patch: &str) -> String {
+    json_patch
+        .lines()
+        .filter(|line| !line.trim_start().starts_with('#'))
+        .collect::<Vec<_>>()
+        .join("\n")
+}
+
+/// Wrap input in {} if it isn't already
+fn add_missing_braces(json_patch: &str) -> String {
+    let mut patch = json_patch.trim_start().to_owned();
+    if patch.get(0..1) != Some("{") {
+        patch = format!("{{\n{patch}\n}}");
+    }
+    patch
+}
+
 /// Replace overrides for existing values in the array if there's a matching hostname. For hostnames
 /// that do not exist, just append the overrides.
 fn merge_relay_overrides(
@@ -301,6 +325,53 @@ fn validate_patch_value(
     }
 }
 
+#[test]
+fn test_braces_json() {
+    let input = r#"
+        "a": [
+            {
+                "b": 1,
+                "c": 2
+            },
+            {}
+        ]
+    "#;
+    let expected = r#"
+        {
+        "a": [
+            {
+                "b": 1,
+                "c": 2
+            },
+            {}
+        ]
+        }
+    "#;
+
+    let fixed_json = add_missing_braces(input);
+
+    let expected_parsed: serde_json::Value = serde_json::from_str(expected).unwrap();
+    let trimmed_parsed: serde_json::Value = serde_json::from_str(&fixed_json).unwrap();
+
+    assert_eq!(trimmed_parsed, expected_parsed);
+}
+
+#[test]
+fn test_comment_json() {
+    let input = r#"
+        # This is a comment!
+        {}
+    "#;
+    let expected = "{}";
+
+    let fixed_json = remove_comments(input);
+
+    let expected_parsed: serde_json::Value = serde_json::from_str(expected).unwrap();
+    let trimmed_parsed: serde_json::Value = serde_json::from_str(&fixed_json).unwrap();
+
+    assert_eq!(trimmed_parsed, expected_parsed);
+}
+
 #[test]
 fn test_permitted_value() {
     const PERMITTED_SUBKEYS: &PermittedKey = &PermittedKey::object(&[(