From c0fdf64ecf3363ea2edaae275a614937a3d7d036 Mon Sep 17 00:00:00 2001
From: webreflection <andrea.giammarchi@gmail.com>
Date: Tue, 18 Aug 2026 09:57:39 +0200
Subject: [PATCH] Avoid throwing on blob: created via URL.createObjectURL()

---
 src/preamble.js                               | 25 +++++++++++++------
 .../test_codesize_file_preload.expected.js    |  7 +++++-
 .../test_codesize_minimal_O0.expected.js      | 25 +++++++++++++------
 3 files changed, 42 insertions(+), 15 deletions(-)

diff --git a/src/preamble.js b/src/preamble.js
index 79da5c867daa1..74fe8bdbcf1f5 100644
--- a/src/preamble.js
+++ b/src/preamble.js
@@ -100,6 +100,12 @@ function _free() {
 #endif // free
 #endif // ASSERTIONS
 
+/**
+ * Indicates whether filename is delivered via URL.createObjectURL()
+ * @noinline
+ */
+var isBlobURI = (filename) => filename.startsWith('blob:');
+
 /**
  * Indicates whether filename is delivered via file protocol (as opposed to http/https)
  * @noinline
@@ -685,13 +691,18 @@ async function instantiateAsync(binary, binaryFile, imports) {
       && !isFileURI(binaryFile)
 #endif
 #if ENVIRONMENT_MAY_BE_NODE
-      // Avoid instantiateStreaming() on Node.js environment for now, as while
-      // Node.js v18.1.0 implements it, it does not have a full fetch()
-      // implementation yet.
-      //
-      // Reference:
-      //   https://github.com/emscripten-core/emscripten/pull/16917
-      && !ENVIRONMENT_IS_NODE
+      && (
+        // Avoid instantiateStreaming() on Node.js environment for now, as while
+        // Node.js v18.1.0 implements it, it does not have a full fetch()
+        // implementation yet.
+        //
+        // Reference:
+        //   https://github.com/emscripten-core/emscripten/pull/16917
+        !ENVIRONMENT_IS_NODE
+        // On browsers this check won't be reached but on Node.js it is the only way to avoid
+        // throwing when URL.createObjectURL(blob) has been passed as the binaryFile.
+        || isBlobURI(binaryFile)
+      )
 #endif
 #if ENVIRONMENT_MAY_BE_SHELL
       // Shell environments don't have fetch.
diff --git a/test/codesize/test_codesize_file_preload.expected.js b/test/codesize/test_codesize_file_preload.expected.js
index 024496f7d7701..b3e691e8214c4 100644
--- a/test/codesize/test_codesize_file_preload.expected.js
+++ b/test/codesize/test_codesize_file_preload.expected.js
@@ -294,6 +294,11 @@ var ABORT = false;
 // but only when noExitRuntime is false.
 var EXITSTATUS;
 
+/**
+ * Indicates whether filename is delivered via URL.createObjectURL()
+ * @noinline
+ */ var isBlobURI = (filename) => filename.startsWith('blob:');
+
 /**
  * Indicates whether filename is delivered via file protocol (as opposed to http/https)
  * @noinline
@@ -415,7 +420,7 @@ async function instantiateArrayBuffer(binaryFile, imports) {
 }
 
 async function instantiateAsync(binary, binaryFile, imports) {
-  if (!binary && !isFileURI(binaryFile) && !ENVIRONMENT_IS_NODE) {
+  if (!binary && !isFileURI(binaryFile) && (!ENVIRONMENT_IS_NODE || isBlobURI(binaryFile))) {
     try {
       var response = fetch(binaryFile, {
         credentials: "same-origin"
diff --git a/test/codesize/test_codesize_minimal_O0.expected.js b/test/codesize/test_codesize_minimal_O0.expected.js
index 1b627a7f0a2cf..45677df6b3a7a 100644
--- a/test/codesize/test_codesize_minimal_O0.expected.js
+++ b/test/codesize/test_codesize_minimal_O0.expected.js
@@ -286,6 +286,12 @@ function _free() {
   abort('free() called but not included in the build - add `_free` to EXPORTED_FUNCTIONS');
 }
 
+/**
+ * Indicates whether filename is delivered via URL.createObjectURL()
+ * @noinline
+ */
+var isBlobURI = (filename) => filename.startsWith('blob:');
+
 /**
  * Indicates whether filename is delivered via file protocol (as opposed to http/https)
  * @noinline
@@ -651,13 +657,18 @@ async function instantiateAsync(binary, binaryFile, imports) {
   if (!binary
       // Don't use streaming for file:// delivered objects in a webview, fetch them synchronously.
       && !isFileURI(binaryFile)
-      // Avoid instantiateStreaming() on Node.js environment for now, as while
-      // Node.js v18.1.0 implements it, it does not have a full fetch()
-      // implementation yet.
-      //
-      // Reference:
-      //   https://github.com/emscripten-core/emscripten/pull/16917
-      && !ENVIRONMENT_IS_NODE
+      && (
+        // Avoid instantiateStreaming() on Node.js environment for now, as while
+        // Node.js v18.1.0 implements it, it does not have a full fetch()
+        // implementation yet.
+        //
+        // Reference:
+        //   https://github.com/emscripten-core/emscripten/pull/16917
+        !ENVIRONMENT_IS_NODE
+        // On browsers this check won't be reached but on Node.js it is the only way to avoid
+        // throwing when URL.createObjectURL(blob) has been passed as the binaryFile.
+        || isBlobURI(binaryFile)
+      )
      ) {
     try {
       var response = fetch(binaryFile, { credentials: 'same-origin' });