fix(BunFile.slice) fix slice when length is greater than the size (#5186)

* check the limits for file, when slicing

* check eof

* undo test

2 files changed, 15 insertions, 3 deletions

diff --git a/src/bun.js/webcore/blob.zig b/src/bun.js/webcore/blob.zig
index 54c37e679..7ce254ca8 100644
--- a/src/bun.js/webcore/blob.zig
+++ b/src/bun.js/webcore/blob.zig
@@ -1680,6 +1680,7 @@ pub const Blob = struct {
             read_completion: HTTPClient.NetworkThread.Completion = undefined,
             read_len: SizeType = 0,
             read_off: SizeType = 0,
+            read_eof: bool = false,
             size: SizeType = 0,
             buffer: []u8 = undefined,
             task: HTTPClient.NetworkThread.Task = undefined,
@@ -1797,8 +1798,7 @@ pub const Blob = struct {
 
             pub fn onRead(this: *ReadFile, completion: *HTTPClient.NetworkThread.Completion, result: AsyncIO.ReadError!usize) void {
                 defer this.doReadLoop();
-
-                this.read_len = @as(SizeType, @truncate(result catch |err| {
+                const read_len = @as(SizeType, @truncate(result catch |err| {
                     if (@hasField(HTTPClient.NetworkThread.Completion, "result")) {
                         this.errno = AsyncIO.asError(-completion.result);
                         this.system_error = (bun.sys.Error{
@@ -1821,6 +1821,8 @@ pub const Blob = struct {
                     this.read_len = 0;
                     return;
                 }));
+                this.read_eof = read_len == 0;
+                this.read_len = read_len;
             }
 
             fn runAsync(this: *ReadFile, task: *ReadFileTask) void {
@@ -1930,7 +1932,7 @@ pub const Blob = struct {
                 this.read_off += this.read_len;
                 var remain = this.buffer[@min(this.read_off, @as(Blob.SizeType, @truncate(this.buffer.len)))..];
 
-                if (remain.len > 0 and this.errno == null) {
+                if (remain.len > 0 and this.errno == null and !this.read_eof) {
                     this.doRead();
                     return;
                 }
diff --git a/test/js/bun/io/bun-write.test.js b/test/js/bun/io/bun-write.test.js
index f435d2ceb..a05fa283a 100644
--- a/test/js/bun/io/bun-write.test.js
+++ b/test/js/bun/io/bun-write.test.js
@@ -300,6 +300,16 @@ it("offset should work #4963", async () => {
   expect(contents).toBe("ntents");
 });
 
+it("length should be limited by file size #5080", async () => {
+  const filename = tmpdir() + "/bun.test.offset2.txt";
+  await Bun.write(filename, "contents");
+  const file = Bun.file(filename);
+  const slice = file.slice(2, 1024);
+  const contents = await slice.text();
+  expect(contents).toBe("ntents");
+  expect(contents.length).toBeLessThanOrEqual(file.size);
+});
+
 it("#2674", async () => {
   const file = path.join(import.meta.dir, "big-stdout.js");