fix(io): Prevent hang in sliced BunFile stream on large files

src/bun.js/webcore/FileReader.zig

@@ -320,14 +320,18 @@ pub fn onReadChunk(this: *@This(), init_buf: []const u8, state: bun.io.ReadState
 
     if (buf.len > 0) {
         if (this.max_size) |max_size| {
-            if (this.total_readed >= max_size) return false;
+            if (this.total_readed >= max_size) {
+                close = true;
+                hasMore = false;
+                return false;
+            }
             const len = @min(max_size - this.total_readed, buf.len);
             if (buf.len > len) {
                 buf = buf[0..len];
             }
             this.total_readed += len;
 
-            if (buf.len == 0) {
+            if (this.total_readed >= max_size) {
                 close = true;
                 hasMore = false;
             }

test/regression/issue/18192.test.ts

@@ -0,0 +1,41 @@
+// https://github.com/oven-sh/bun/issues/18192
+// Bun.file().slice().stream() should not hang for files larger than 640KB
+
+import { expect, test } from "bun:test";
+import { tempDir } from "harness";
+import { join } from "path";
+
+test("Bun.file().slice().stream() should not hang for large files", async () => {
+  using tmpbase = tempDir("issue-18192", {});
+  const path = join(tmpbase, "large-file.bin");
+
+  const size = 1024 * 1024; // 1mb file
+  await Bun.write(path, new Uint8Array(size).fill(69));
+
+  const file = Bun.file(path);
+
+  // tiny slice
+  {
+    const sliced = file.slice(0, 1);
+    const bytes = await new Response(sliced.stream()).bytes();
+    expect(bytes.length).toBe(1);
+    expect(bytes).toEqual(new Uint8Array(1).fill(69));
+  }
+
+  // zero length slice
+  {
+    const sliced = file.slice(0, 0);
+    const bytes = await new Response(sliced.stream()).bytes();
+    expect(bytes.length).toBe(0);
+  }
+
+  // somewhere in the middle slice
+  {
+    const midStart = 500 * 1024;
+    const midEnd = midStart + 10;
+    const sliced = file.slice(midStart, midEnd);
+    const bytes = await new Response(sliced.stream()).bytes();
+    expect(bytes.length).toBe(10);
+    expect(bytes).toEqual(new Uint8Array(10).fill(69));
+  }
+});

test/regression/issue/21175.test.ts

@@ -0,0 +1,24 @@
+// https://github.com/oven-sh/bun/issues/21175
+// Bun.file().slice().stream() should not hang when consumed via iterator
+import { expect, test } from "bun:test";
+import { tempDir } from "harness";
+import { join } from "path";
+
+test("Bun.file().slice().stream() iterator consumption", async () => {
+  using tmpbase = tempDir("issue-21175", {});
+  const path = join(tmpbase, "large-file.bin");
+
+  const size = 1024 * 1024; // 1mb file
+  await Bun.write(path, new Uint8Array(size).fill(69));
+  const file = Bun.file(path);
+
+  const sliced = file.slice(0, 16384);
+  const stream = sliced.stream();
+
+  let totalLen = 0;
+  // @ts-expect-error: ReadableStream is async iterable
+  for await (const chunk of stream) {
+    totalLen += chunk.length;
+  }
+  expect(totalLen).toBe(16384);
+});