events: Introduce RedactContent trait

crates/ruma-events-macros/src/event_content.rs

@@ -224,9 +224,10 @@ pub fn expand_event_content(
         quote! {
             // this is the non redacted event content's impl
             #[automatically_derived]
-            impl #ident {
-                /// Transforms the full event content into a redacted content according to spec.
-                pub fn redact(self, version: &#ruma_identifiers::RoomVersionId) -> #redacted_ident {
+            impl #ruma_events::RedactContent for #ident {
+                type Redacted = #redacted_ident;
+
+                fn redact(self, version: &#ruma_identifiers::RoomVersionId) -> #redacted_ident {
                     #redacted_ident {
                         #( #redaction_struct_fields: self.#redaction_struct_fields, )*
                     }

crates/ruma-events-macros/src/event_enum.rs

@@ -496,7 +496,7 @@ fn expand_redact(
                     match self {
                         #(
                             #self_variants(event) => {
-                                let content = event.content.redact(version);
+                                let content = #ruma_events::RedactContent::redact(event.content, version);
                                 #redaction_variants(#redacted_type {
                                     content,
                                     #fields
@@ -504,7 +504,7 @@ fn expand_redact(
                             }
                         )*
                         Self::Custom(event) => {
-                            let content = event.content.redact(version);
+                            let content = #ruma_events::RedactContent::redact(event.content, version);
                             #redacted_enum::Custom(#redacted_type {
                                 content,
                                 #fields

crates/ruma-events/src/custom.rs

@@ -8,7 +8,7 @@ use serde_json::{value::RawValue as RawJsonValue, Value as JsonValue};
 
 use crate::{
     EphemeralRoomEventContent, EventContent, GlobalAccountDataEventContent, HasDeserializeFields,
-    MessageEventContent, RedactedEventContent, RedactedMessageEventContent,
+    MessageEventContent, RedactContent, RedactedEventContent, RedactedMessageEventContent,
     RedactedStateEventContent, RoomAccountDataEventContent, RoomEventContent, StateEventContent,
     ToDeviceEventContent,
 };
@@ -25,9 +25,10 @@ pub struct CustomEventContent {
     pub data: BTreeMap<String, JsonValue>,
 }
 
-impl CustomEventContent {
-    /// Transforms the full event content into a redacted content according to spec.
-    pub fn redact(self, _: &RoomVersionId) -> RedactedCustomEventContent {
+impl RedactContent for CustomEventContent {
+    type Redacted = RedactedCustomEventContent;
+
+    fn redact(self, _: &RoomVersionId) -> RedactedCustomEventContent {
         RedactedCustomEventContent { event_type: self.event_type }
     }
 }

crates/ruma-events/src/lib.rs

@@ -118,7 +118,7 @@
 use std::fmt::Debug;
 
 use js_int::Int;
-use ruma_identifiers::EventEncryptionAlgorithm;
+use ruma_identifiers::{EventEncryptionAlgorithm, RoomVersionId};
 use ruma_serde::Raw;
 use serde::{
     de::{self, IgnoredAny},
@@ -275,6 +275,20 @@ pub trait EventContent: Sized + Serialize {
     fn from_parts(event_type: &str, content: Box<RawJsonValue>) -> Result<Self, serde_json::Error>;
 }
 
+/// Trait to define the behavior of redact an event's content object.
+pub trait RedactContent {
+    /// The redacted form of the event's content.
+    type Redacted;
+
+    /// Transform `self` into a redacted form (removing most or all fields) according to the spec.
+    ///
+    /// A small number of events have room-version specific redaction behavior, so a version has to
+    /// be specified.
+    ///
+    /// Where applicable, it is prefered to use [`Redact::redact`] on the outer event.
+    fn redact(self, version: &RoomVersionId) -> Self::Redacted;
+}
+
 /// Extension trait for Raw<EventContent>
 pub trait RawExt<T: EventContent> {
     /// Try to deserialize the JSON as event content

crates/ruma-events/src/room/aliases.rs

@@ -6,7 +6,8 @@ use serde::{Deserialize, Serialize};
 use serde_json::value::RawValue as RawJsonValue;
 
 use crate::{
-    EventContent, HasDeserializeFields, RedactedEventContent, RedactedStateEventContent, StateEvent,
+    EventContent, HasDeserializeFields, RedactContent, RedactedEventContent,
+    RedactedStateEventContent, StateEvent,
 };
 
 /// Informs the room about what room aliases it has been given.
@@ -26,9 +27,12 @@ impl AliasesEventContent {
     pub fn new(aliases: Vec<RoomAliasId>) -> Self {
         Self { aliases }
     }
+}
 
-    /// Redact an `AliasesEventContent` according to current Matrix spec.
-    pub fn redact(self, version: &RoomVersionId) -> RedactedAliasesEventContent {
+impl RedactContent for AliasesEventContent {
+    type Redacted = RedactedAliasesEventContent;
+
+    fn redact(self, version: &RoomVersionId) -> RedactedAliasesEventContent {
         // We compare the long way to avoid pre version 6 behavior if/when
         // a new room version is introduced.
         let aliases = match version {