From cdd71a3f5056203085a272cc05b5f1bcbcabce16 Mon Sep 17 00:00:00 2001
From: Zaki Ahmed <zaki.ahmed@valka.ai>
Date: Thu, 13 Aug 2026 23:38:08 +0200
Subject: [PATCH] Load fragment keys only after fragment selection is finalized

Backports the ordering of #7874 to v1.6.x: extract key loading from the top
of _doFragLoad into loadKeyFor() and call it only once fragment selection
is final - after the LL-HLS part/hint swap in the parts branch, and after
the loading-parts fallback in the whole-fragment path.

Previously the key promise was armed with the fragment passed in, so when
the parts branch advanced the load onto the fragment hint, both
resolution-time context checks compared the stale pre-swap fragment against
the new fragCurrent, read the mismatch as an abort, and resolved silently -
leaving the stream-controller in FRAG_LOADING with no loader in flight and
no reachable timeout. Video fragment loading stopped permanently on
encrypted low-latency streams while the playlist kept polling.

Fixes #7975 on the v1.6.x line.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 src/controller/base-stream-controller.ts | 49 +++++++++++++++---------
 1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/src/controller/base-stream-controller.ts b/src/controller/base-stream-controller.ts
index 5b5873ec5b0..cacf06068a7 100644
--- a/src/controller/base-stream-controller.ts
+++ b/src/controller/base-stream-controller.ts
@@ -820,27 +820,16 @@ export default class BaseStreamController
     frag: PartsLoadedData | FragLoadedData,
   ) {}
 
-  protected _doFragLoad(
+  private loadKeyFor(
     frag: Fragment,
-    level: Level,
-    targetBufferTime: number | null = null,
-    progressCallback?: FragmentLoadProgressCallback,
-  ): Promise<PartsLoadedData | FragLoadedData | null> {
-    this.fragCurrent = frag;
-    const details = level.details;
-    if (!this.levels || !details) {
-      throw new Error(
-        `frag load aborted, missing level${details ? '' : ' detail'}s`,
-      );
-    }
-
+    details: LevelDetails,
+  ): Promise<KeyLoadedData | void> | null {
     let keyLoadingPromise: Promise<KeyLoadedData | void> | null = null;
     if (frag.encrypted && !frag.decryptdata?.key) {
       this.log(
         `Loading key for ${frag.sn} of [${details.startSN}-${details.endSN}], ${this.playlistLabel()} ${frag.level}`,
       );
       this.state = State.KEY_LOADING;
-      this.fragCurrent = frag;
       keyLoadingPromise = this.keyLoader.load(frag).then((keyLoadedData) => {
         if (!this.fragContextChanged(keyLoadedData.frag)) {
           this.hls.trigger(Events.KEY_LOADED, keyLoadedData);
@@ -851,10 +840,6 @@ export default class BaseStreamController
         }
       });
       this.hls.trigger(Events.KEY_LOADING, { frag });
-      if ((this.fragCurrent as Fragment | null) === null) {
-        this.log(`context changed in KEY_LOADING`);
-        return Promise.resolve(null);
-      }
     } else if (!frag.encrypted) {
       keyLoadingPromise = this.keyLoader.loadClear(
         frag,
@@ -865,6 +850,22 @@ export default class BaseStreamController
         this.log(`[eme] blocking frag load until media-keys acquired`);
       }
     }
+    return keyLoadingPromise;
+  }
+
+  protected _doFragLoad(
+    frag: Fragment,
+    level: Level,
+    targetBufferTime: number | null = null,
+    progressCallback?: FragmentLoadProgressCallback,
+  ): Promise<PartsLoadedData | FragLoadedData | null> {
+    this.fragCurrent = frag;
+    const details = level.details;
+    if (!this.levels || !details) {
+      throw new Error(
+        `frag load aborted, missing level${details ? '' : ' detail'}s`,
+      );
+    }
 
     const fragPrevious = this.fragPrevious;
     if (
@@ -892,6 +893,10 @@ export default class BaseStreamController
         if (partIndex > -1) {
           const part = partList[partIndex];
           frag = this.fragCurrent = part.fragment;
+          const keyLoadingPromise = this.loadKeyFor(frag, details);
+          if (this.fragContextChanged(frag)) {
+            return Promise.resolve(null);
+          }
           this.log(
             `Loading ${frag.type} sn: ${frag.sn} part: ${part.index} (${partIndex}/${partList.length - 1}) of ${this.fragInfo(frag, false, part)}) cc: ${
               frag.cc
@@ -962,6 +967,14 @@ export default class BaseStreamController
       return Promise.resolve(null);
     }
 
+    const keyLoadingPromise = this.loadKeyFor(frag, details);
+    if (this.fragContextChanged(frag)) {
+      this.log(
+        `Context changed in KEY_LOADING sn: ${frag.sn} ${frag.relurl} > ${this.fragCurrent?.relurl}`,
+      );
+      keyLoadingPromise?.catch(() => null);
+      return Promise.resolve(null);
+    }
     this.log(
       `Loading ${frag.type} sn: ${frag.sn} of ${this.fragInfo(frag, false)}) cc: ${frag.cc} ${
         '[' + details.startSN + '-' + details.endSN + ']'