fix: end-of-feed and all-type search semantics

src/providers/lemmyv0/compat.ts

@@ -505,8 +505,28 @@ export function toModlogView(
   }
 }
 
+/**
+ * Canonical pagination for the page-number softwares (Lemmy v0, PieFed).
+ *
+ * `next_page` has to mean "there is more" — handing one out unconditionally
+ * makes a consumer's `while (next_page)` loop spin forever. The server's own
+ * cursor wins when the endpoint returns one; otherwise a page at least as
+ * long as the limit implies there may be another, and a shorter one is the
+ * end.
+ *
+ * "At least" matters: endpoints that merge several requests (notifications,
+ * person content, all-type search, modlog) legitimately overshoot, because
+ * these servers apply the limit per bucket. A merged page shorter than the
+ * limit means every bucket was short — genuinely exhausted.
+ */
 export function toPageResponse(
   params: types.PageParams,
+  page?: {
+    /** How many items this page returned */
+    items: number;
+    /** The server's own cursor, for endpoints that return one */
+    next_page?: null | string;
+  },
 ): types.PagableResponse {
   const page_cursor = params.page_cursor;
 
@@ -515,9 +535,25 @@ export function toPageResponse(
       "lemmyv0 does not support string page_cursor",
     );
 
-  return {
-    next_page: (page_cursor ?? 1) + 1,
-  };
+  if (page?.next_page !== undefined) {
+    const serverCursor =
+      page.next_page === null ? undefined : Number(page.next_page);
+
+    // A cursor we can't use as a page number is no cursor at all — better
+    // to report end-of-feed than to send the server garbage
+    if (serverCursor === undefined || !Number.isFinite(serverCursor))
+      return { next_page: undefined };
+
+    return { next_page: serverCursor };
+  }
+
+  const nextPage = (page_cursor ?? 1) + 1;
+
+  // Without a limit there's nothing to compare a short page against, so
+  // keep assuming there's more
+  if (!page || params.limit === undefined) return { next_page: nextPage };
+
+  return { next_page: page.items >= params.limit ? nextPage : undefined };
 }
 
 export function toPerson(

src/providers/lemmyv0/index.ts

@@ -256,9 +256,11 @@ export class UnsafeLemmyV0Client implements BaseClient {
       options,
     );
 
+    const data = response.comments.map(compat.toCommentView);
+
     return {
-      ...compat.toPageResponse(payload),
-      data: response.comments.map(compat.toCommentView),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -308,13 +310,15 @@ export class UnsafeLemmyV0Client implements BaseClient {
       options,
     );
 
+    const data = Object.values(response)
+      .flat()
+      .map(compat.toModlogView)
+      .filter((m) => !!m)
+      .sort((a, b) => Date.parse(getLogDate(b)) - Date.parse(getLogDate(a)));
+
     return {
-      ...compat.toPageResponse(payload),
-      data: Object.values(response)
-        .flat()
-        .map(compat.toModlogView)
-        .filter((m) => !!m)
-        .sort((a, b) => Date.parse(getLogDate(b)) - Date.parse(getLogDate(a))),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -376,7 +380,7 @@ export class UnsafeLemmyV0Client implements BaseClient {
     }
 
     return {
-      ...compat.toPageResponse(payload),
+      ...compat.toPageResponse(payload, { items: data.length }),
       data,
     };
   }
@@ -539,9 +543,11 @@ export class UnsafeLemmyV0Client implements BaseClient {
       options,
     );
 
+    const data = response.comment_reports.map(compat.toCommentReportView);
+
     return {
-      ...compat.toPageResponse(payload),
-      data: response.comment_reports.map(compat.toCommentReportView),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -564,9 +570,11 @@ export class UnsafeLemmyV0Client implements BaseClient {
       options,
     );
 
+    const data = response.communities.map(compat.toCommunityView);
+
     return {
-      ...compat.toPageResponse(payload),
-      data: response.communities.map(compat.toCommunityView),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -604,7 +612,7 @@ export class UnsafeLemmyV0Client implements BaseClient {
     })();
 
     return {
-      ...compat.toPageResponse(payload),
+      ...compat.toPageResponse(payload, { items: data.length }),
       data,
     };
   }
@@ -625,12 +633,14 @@ export class UnsafeLemmyV0Client implements BaseClient {
       this.#client.getComments(v0Payload, options),
     ]);
 
+    const data = [
+      ...comments.map(compat.toCommentView),
+      ...posts.map(compat.toPostView),
+    ].sort(sortPostCommentByPublished);
+
     return {
-      data: [
-        ...comments.map(compat.toCommentView),
-        ...posts.map(compat.toPostView),
-      ].sort(sortPostCommentByPublished),
-      ...compat.toPageResponse(payload),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -657,9 +667,11 @@ export class UnsafeLemmyV0Client implements BaseClient {
       options,
     );
 
+    const data = response.post_reports.map(compat.toPostReportView);
+
     return {
-      ...compat.toPageResponse(payload),
-      data: response.post_reports.map(compat.toPostReportView),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -674,15 +686,17 @@ export class UnsafeLemmyV0Client implements BaseClient {
       this.#client.listPostReports(params, options),
     ]);
 
+    const data = [
+      ...comment_reports.map(compat.toCommentReportView),
+      ...post_reports.map(compat.toPostReportView),
+    ].sort(
+      (a, b) =>
+        getPostCommentItemCreatedDate(b) - getPostCommentItemCreatedDate(a),
+    );
+
     return {
-      ...compat.toPageResponse(payload),
-      data: [
-        ...comment_reports.map(compat.toCommentReportView),
-        ...post_reports.map(compat.toPostReportView),
-      ].sort(
-        (a, b) =>
-          getPostCommentItemCreatedDate(b) - getPostCommentItemCreatedDate(a),
-      ),
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }
 
@@ -856,14 +870,16 @@ export class UnsafeLemmyV0Client implements BaseClient {
       options,
     );
 
+    const data = [
+      ...response.comments.map(compat.toCommentView),
+      ...response.posts.map(compat.toPostView),
+      ...response.communities.map(compat.toCommunityView),
+      ...response.users.map(compat.toPersonView),
+    ];
+
     return {
-      ...compat.toPageResponse(payload),
-      data: [
-        ...response.comments.map(compat.toCommentView),
-        ...response.posts.map(compat.toPostView),
-        ...response.communities.map(compat.toCommunityView),
-        ...response.users.map(compat.toPersonView),
-      ],
+      ...compat.toPageResponse(payload, { items: data.length }),
+      data,
     };
   }