From 01deb085f8acbc4f173f63e2e7c36514cdc81df4 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Thu, 5 Feb 2026 16:04:45 +0100
Subject: [PATCH 1/2] Improve progress reporting in the `ChunkedStreamManager`

Currently there's two small bugs, which have existed around a decade, in the `loaded` property that's sent via the "DocProgress" message from the `ChunkedStreamManager.prototype.onReceiveData` method.

 - When the entire PDF has loaded the `loaded` property can become larger than the `total` property, which obviously doesn't make sense.
   This happens whenever the size of the PDF is *not* a multiple of the `rangeChunkSize` API-option, which is a very common situation.

 - When streaming is being used, the `loaded` property can become smaller than the actually loaded amount of data.
   This happens whenever the size of a streamed chunk is *not* a multiple of the `rangeChunkSize` API-option, which is a common situation.
---
 src/core/chunked_stream.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/core/chunked_stream.js b/src/core/chunked_stream.js
index 94c01fc03..e6ebf065c 100644
--- a/src/core/chunked_stream.js
+++ b/src/core/chunked_stream.js
@@ -14,7 +14,7 @@
  */
 
 import { arrayBuffersToBytes, MissingDataException } from "./core_utils.js";
-import { assert } from "../shared/util.js";
+import { assert, MathClamp } from "../shared/util.js";
 import { Stream } from "./stream.js";
 
 class ChunkedStream extends Stream {
@@ -511,7 +511,11 @@ class ChunkedStreamManager {
     }
 
     this.msgHandler.send("DocProgress", {
-      loaded: stream.numChunksLoaded * chunkSize,
+      loaded: MathClamp(
+        stream.numChunksLoaded * chunkSize,
+        stream.progressiveDataLength,
+        length
+      ),
       total: length,
     });
   }

From b3cd042ded4b0d0cca4f2469939dc587034b971f Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Thu, 5 Feb 2026 16:16:36 +0100
Subject: [PATCH 2/2] Prevent unnecessary data copy in
 `ChunkedStream.prototype.onReceiveData`

This method is only invoked via `ChunkedStreamManager.prototype.sendRequest`, which currently returns data in `Uint8Array` format (since it potentially combines multiple `ArrayBuffer`s).
Hence we end up doing a short-lived, but still completely unnecessary, data copy[1] in `ChunkedStream.prototype.onReceiveData` when handling range requests. In practice this is unlikely to be a big problem by default, given that streaming is used and the (low) value of the `rangeChunkSize` API-option. (However, in custom PDF.js deployments it might affect things more.)

Given that no data copy is better than a short lived one, let's fix this small oversight and add non-production `assert`s to keep it working as intended.
This way we also improve consistency, since all other streaming and range request methods (see e.g. `BasePDFStream` and related code) only return `ArrayBuffer` data.

---
[1] Remember that `new Uint8Array(arrayBuffer)` only creates a view of the underlying `arrayBuffer`, whereas `new Uint8Array(typedArray)` actually creates a copy of the `typedArray`.
---
 src/core/chunked_stream.js | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/core/chunked_stream.js b/src/core/chunked_stream.js
index e6ebf065c..642323fae 100644
--- a/src/core/chunked_stream.js
+++ b/src/core/chunked_stream.js
@@ -70,6 +70,12 @@ class ChunkedStream extends Stream {
       throw new Error(`Bad end offset: ${end}`);
     }
 
+    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
+      assert(
+        chunk instanceof ArrayBuffer,
+        "onReceiveData - expected an ArrayBuffer."
+      );
+    }
     this.bytes.set(new Uint8Array(chunk), begin);
     const beginChunk = Math.floor(begin / chunkSize);
     const endChunk = Math.floor((end - 1) / chunkSize) + 1;
@@ -85,6 +91,12 @@ class ChunkedStream extends Stream {
     let position = this.progressiveDataLength;
     const beginChunk = Math.floor(position / this.chunkSize);
 
+    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
+      assert(
+        data instanceof ArrayBuffer,
+        "onReceiveProgressiveData - expected an ArrayBuffer."
+      );
+    }
     this.bytes.set(new Uint8Array(data), position);
     position += data.byteLength;
     this.progressiveDataLength = position;
@@ -310,7 +322,7 @@ class ChunkedStreamManager {
       if (this.aborted) {
         return; // Ignoring any data after abort.
       }
-      this.onReceiveData({ chunk: data, begin });
+      this.onReceiveData({ chunk: data.buffer, begin });
     });
   }