dashboard: a subscribed node's message written out, read from it when shown

A subscribed node's messages come without being written out (their stream leaves the
text out: up to 8 KiB each, 500 at a time), so the figures box said only when, both
ends, type and size of one. Now the node answers for one message by its number,
`GET /admin/dashboard/messages/own/{seq}` (`{"text": …}`, `404` once it isn't kept),
which pages of other origins may call as they do its streams (`cors::open`), and the
page reads it when the message is shown, with its narrow token, and keeps it on the
message. Where it can't be read, the box says why.

7 files changed, 102 insertions, 18 deletions

diff --git a/docs/access.md b/docs/access.md
index a4c5375..38ae180 100644
--- a/docs/access.md
+++ b/docs/access.md
@@ -172,7 +172,8 @@ it may do.
 
 Pages of other origins, the dashboards of other members, may call a node with a token:
 its own links (`/admin/dashboard/links/own`, and its events) and messages
-(`/admin/dashboard/messages/own/events`), `/auth/refresh` and `/auth/whoami`, nothing
+(`/admin/dashboard/messages/own/events`, and one written out,
+`/admin/dashboard/messages/own/{seq}`), `/auth/refresh` and `/auth/whoami`, nothing
 else. A node allows the origins of the dashboards its member
 list names (`--dashboard-url`) and those of `--cors-origins`; without credentials (no
 cookie or password crosses origins: the page sends its token).
diff --git a/docs/dashboard.md b/docs/dashboard.md
index 5eee5c9..590f72f 100644
--- a/docs/dashboard.md
+++ b/docs/dashboard.md
@@ -399,8 +399,9 @@ A subscribed node's messages with its peers are listed too, as they come from it
 named by both ends, the receiver first (`b ← a`), each once, as on the map (those
 with this node only from this node, between two subscribed nodes from the sender); its
 tooltip names the node that logged it. Shown in the figures box, it says when, both
-ends, its type and size: the message itself is written out only on the node that
-logged it.
+ends, its type, size and address, and the message written out, read from the node that
+logged it as it is shown (`/admin/dashboard/messages/own/{seq}` there, with the page's
+token), while that node still keeps it (its latest 1000).
 
 A click on a message shows it in the figures box: when, with whom, its type and size,
 and the message written out (its bytes as sizes). A click on it again, or on anything on
diff --git a/docs/openapi.yaml b/docs/openapi.yaml
index 0fad136..03afa2f 100644
--- a/docs/openapi.yaml
+++ b/docs/openapi.yaml
@@ -1293,6 +1293,33 @@ paths:
         '401':
           $ref: '#/components/responses/Unauthorized'
 
+  /admin/dashboard/messages/own/{seq}:
+    get:
+      tags: [Admin]
+      summary: One of this node's messages, written out
+      description: |
+        The message `seq` (its number in `messages/own/events`) written out, as this
+        node's own console shows it, for a page subscribed to this node showing it (CORS,
+        with a token). Kept while the message log is: the latest 1000, while one looks.
+      parameters:
+        - name: seq
+          in: path
+          required: true
+          schema: { type: integer }
+      responses:
+        '200':
+          description: The message written out.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  text: { type: string }
+        '401':
+          $ref: '#/components/responses/Unauthorized'
+        '404':
+          description: Not kept any more.
+
   /admin/dashboard/refresh:
     post:
       tags: [Admin]
diff --git a/src/api/cors.rs b/src/api/cors.rs
index 406b7be..fc8270d 100644
--- a/src/api/cors.rs
+++ b/src/api/cors.rs
@@ -1,6 +1,6 @@
 //! Pages of other origins reading this node: the dashboards of other members, which a
 //! page subscribes to for their own links and messages (`/admin/dashboard/links/own`,
-//! `/admin/dashboard/messages/own/events`), refreshing its
+//! `/admin/dashboard/messages/own/events`, and one written out), refreshing its
 //! token on any node (`/auth/refresh`, `/auth/whoami`). Only those endpoints, only for
 //! the origins of the dashboards the member list names and those of `--cors-origins`,
 //! and without credentials: a page sends its token itself (`Authorization: Bearer`),
@@ -18,14 +18,19 @@ use crate::swarm::members;
 
 /// The endpoints other origins may call.
 fn open(path: &str) -> bool {
-    matches!(
-        path,
-        "/admin/dashboard/links/own"
-            | "/admin/dashboard/links/own/events"
-            | "/admin/dashboard/messages/own/events"
-            | "/auth/refresh"
-            | "/auth/whoami"
-    )
+    // A message written out (`/admin/dashboard/messages/own/{seq}`).
+    let message = path
+        .strip_prefix("/admin/dashboard/messages/own/")
+        .is_some_and(|seq| !seq.is_empty() && seq.bytes().all(|byte| byte.is_ascii_digit()));
+    message
+        || matches!(
+            path,
+            "/admin/dashboard/links/own"
+                | "/admin/dashboard/links/own/events"
+                | "/admin/dashboard/messages/own/events"
+                | "/auth/refresh"
+                | "/auth/whoami"
+        )
 }
 
 /// `url`'s origin (`scheme://host[:port]`), if it is a URL with one.
@@ -138,6 +143,8 @@ mod tests {
     #[test]
     fn only_some_endpoints() {
         assert!(open("/admin/dashboard/links/own"));
+        assert!(open("/admin/dashboard/messages/own/42"));
+        assert!(!open("/admin/dashboard/messages/own/x"));
         assert!(open("/auth/refresh"));
         assert!(!open("/auth/login"));
         assert!(!open("/store"));
diff --git a/src/api/dashboard/dashboard.html b/src/api/dashboard/dashboard.html
index 9cfb384..6d32d55 100644
--- a/src/api/dashboard/dashboard.html
+++ b/src/api/dashboard/dashboard.html
@@ -876,8 +876,9 @@ function renderStats() {
       el("span", { class: "key" }, key + ": "), value);
     title.replaceChildren("Message: ", what);
     retitle(title, title.textContent);
-    // A subscribed node's: logged there, the message itself not read from it.
+    // A subscribed node's: logged there, written out as read from it.
     if (message.node) {
+      const text = el("pre", { class: "message" }, "reading it from " + name(message.node) + "…");
       document.getElementById("stats").replaceChildren(
         field("at", clockTime(new Date(message.at))),
         field("from", message.from),
@@ -886,7 +887,12 @@ function renderStats() {
         ...(message.address ? [field("address", message.address)] : []),
         field("type", message.type),
         field("bytes", String(message.bytes)),
-        el("div", { class: "note" }, "Written out only on the node that logged it (its console)."));
+        text);
+      writtenOut(message).then(written => { text.textContent = written; },
+        error => {
+          text.replaceWith(el("div", { class: "note" }, "Not read from " + name(message.node) +
+            ": " + (error.message || String(error))));
+        });
       return;
     }
     document.getElementById("stats").replaceChildren(
@@ -2842,9 +2848,7 @@ function follow(id, delay = 2000) {
   const member = state && state.graph.members[id];
   if (!member || !member.dashboard) return fail("it publishes no dashboard (--dashboard-url)");
   if (!narrowToken) return fail(tokenWhy);
-  // Its endpoints, beside its page (`…/admin/dashboard` → `…/admin/dashboard/…`).
-  const base = member.dashboard.split("#")[0].replace(/\/+$/, "");
-  const at = path => new URL(path, base).href;
+  const at = path => endpointOf(id, path);
   let url;
   try {
     url = at("dashboard/links/own/events");
@@ -2881,6 +2885,25 @@ function follow(id, delay = 2000) {
   };
   followMessages();
 }
+// A member's endpoint, beside the page it publishes (`…/admin/dashboard` →
+// `…/admin/dashboard/<path>`); throws where its address isn't one.
+function endpointOf(id, path) {
+  const member = state && state.graph.members[id];
+  const base = ((member && member.dashboard) || "").split("#")[0].replace(/\/+$/, "");
+  return new URL(path, base).href;
+}
+// A subscribed node's message written out, read from it (its console's
+// `messages/own/{seq}`) with this page's narrow token, kept on the message once read.
+async function writtenOut(message) {
+  if (typeof message.text === "string") return message.text;
+  if (!narrowToken) throw new Error(tokenWhy);
+  const response = await fetch(endpointOf(message.node, "dashboard/messages/own/" + message.ownSeq),
+    { cache: "no-store", headers: { Authorization: "Bearer " + narrowToken.token } });
+  const answer = await response.json().catch(() => ({}));
+  if (!response.ok) throw new Error(response.status + " " + (answer.error || response.statusText));
+  message.text = String(answer.text);
+  return message.text;
+}
 // Server-sent events from `url`, read with this page's narrow token (`EventSource`
 // can't send one): `opened` once answered, `event(kind, data)` for each; rejects when it
 // fails or ends (`offline`: the node stopped).
@@ -3581,7 +3604,7 @@ function remoteMessagesArrived(id, entry, list, sent) {
   for (const message of list) {
     if (message.way === "refused") continue;
     const [from, to] = message.way === "sent" ? [id, message.peer] : [message.peer, id];
-    const made = { ...message, seq: id + ":" + message.seq, node: id, from, to,
+    const made = { ...message, seq: id + ":" + message.seq, ownSeq: message.seq, node: id, from, to,
       related: message.related ? id + ":" + message.related : null };
     if (message.way === "sent") noteDelivery(from, to, message.counted, "sent");
     else noteDelivery(from, to, message.counted, "got");
diff --git a/src/api/dashboard/mod.rs b/src/api/dashboard/mod.rs
index 7a643d0..3a50ca6 100644
--- a/src/api/dashboard/mod.rs
+++ b/src/api/dashboard/mod.rs
@@ -509,6 +509,7 @@ pub(crate) fn router(state: AppState) -> Router<AppState> {
             "/admin/dashboard/messages/own/events",
             get(own_messages_events),
         )
+        .route("/admin/dashboard/messages/own/{seq}", get(own_message))
         .layer(Extension(Hub::new(state, closing)))
 }
 
@@ -573,6 +574,20 @@ impl Drop for Watching {
     }
 }
 
+/// `GET /admin/dashboard/messages/own/{seq}`: the message `seq` of this node's
+/// (`messages/own/events`, which leaves it out) written out, `{"text": …}`, for a page
+/// subscribed to this node showing it; `404` once it isn't kept any more (the latest
+/// 1000, while someone looks).
+async fn own_message(
+    Extension(hub): Extension<Arc<Hub>>,
+    axum::extract::Path(seq): axum::extract::Path<u64>,
+) -> axum::response::Response {
+    match hub.state.traffic.log.text_of(seq) {
+        Some(text) => axum::Json(json!({ "text": text })).into_response(),
+        None => super::error_response(axum::http::StatusCode::NOT_FOUND, "not kept any more", None),
+    }
+}
+
 /// `GET /admin/dashboard/messages/own/events`: server-sent events, `messages` with the
 /// messages this node sent and received since the last, as they come (gathered for
 /// `MESSAGES_GATHERED` after the first), as the page's own `messages` events have them,
diff --git a/src/transport/traffic.rs b/src/transport/traffic.rs
index bac0da7..5ff588e 100644
--- a/src/transport/traffic.rs
+++ b/src/transport/traffic.rs
@@ -325,6 +325,16 @@ impl MessageLog {
     }
 
     /// The messages after `seq`, the latest `most` of them.
+    /// The message `seq` written out, while it is kept.
+    pub(crate) fn text_of(&self, seq: u64) -> Option<String> {
+        let inner = self.inner.lock_or_recover();
+        inner
+            .entries
+            .iter()
+            .find(|entry| entry.seq == seq)
+            .map(|entry| entry.text.clone())
+    }
+
     pub(crate) fn after(&self, seq: u64, most: usize) -> Vec<Logged> {
         let inner = self.inner.lock_or_recover();
         let newer: Vec<&Logged> = inner.entries.iter().filter(|e| e.seq > seq).collect();