statusbot: .well-known retry mechanism

1 files changed, 51 insertions, 14 deletions

diff --git a/modules/statusbot/statusbot.js b/modules/statusbot/statusbot.js
index da81d82..1af5804 100644
--- a/modules/statusbot/statusbot.js
+++ b/modules/statusbot/statusbot.js
@@ -110,6 +110,36 @@ class PRatelimit {
   }
 }
 
+// f: ((true, ...Args) => () | (false) => ()) => ()
+// cb: (true, ...Args) => () | (false) => ()
+// The callback to f should be invoked with 'true' plus further arguments if it
+// succeeded, and 'false' if it did not.
+// Based on this info, if f failed, f is retried a few times. Once ntimes has
+// been exhausted or a call succeeds, cb is invoked with respectively either
+// (false) or (true, ...args).
+function pretry(interval, multiplier, ntimes, f, cb) {
+  let tm = interval;
+  let ncalled = 0;
+
+  function schedule() {
+    setTimeout(() => {
+      f((success, ...args) => {
+        if (success) {
+          cb(true, ...args);
+          return;
+        }
+
+        ncalled++;
+        tm *= multiplier;
+        if (ncalled >= ntimes) cb(false);
+        else schedule();
+      });
+    }, tm);
+  }
+
+  schedule();
+}
+
 // cb: (state) => ()
 function augmentConfig(config, cb) {
   const m = config.user_id.match(/^@[^:]+:(.*)$/);
@@ -126,20 +156,27 @@ function augmentConfig(config, cb) {
   }
 
   // wait a bit with requesting this in case the homeserver in question is the same server as us
-  setTimeout(() => {
-    fetch("GET", {}, home_server, "/.well-known/matrix/server", "", (status, body) => {
-      if (status != 200) {
-        throw new Error(`statusbot: Failed getting https://${home_server}/.well-known/matrix/server`);
-      }
-      const mserver = JSON.parse(body)["m.server"];
-      const m = mserver.match(/^([^:]*)(:443)?$/);
-      if (!m) {
-        throw new Error(`statusbot: Matrix server port not 443 (sorry): <${mserver}>`);
-      }
-      const matrix_server = m[1];
-      cb({config, home_server, matrix_server, access_token, req_counter});
-    });
-  }, 100);
+  pretry(500, 1.2, 10,
+    cb => {
+      fetch("GET", {}, home_server, "/.well-known/matrix/server", "", (status, body) => {
+        if (status != 200) {
+          cb(false);  // attempt failed (perhaps a later attempt will succeed)
+        }
+        const mserver = JSON.parse(body)["m.server"];
+        const m = mserver.match(/^([^:]*)(:443)?$/);
+        if (!m) {
+          throw new Error(`statusbot: Matrix server port not 443 (sorry): <${mserver}>`);
+        }
+        const matrix_server = m[1];
+        // attempt succeeded!
+        cb(true, {config, home_server, matrix_server, access_token, req_counter});
+      });
+    },
+    (success, state) => {
+      if (success) cb(state);
+      else throw new Error(`statusbot: Failed getting https://${home_server}/.well-known/matrix/server`);
+    }
+  );
 }
 
 function updatePersist() {