Fixes #5769 (#5775)

Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>

4 files changed, 46 insertions, 4 deletions

diff --git a/bun.lockb b/bun.lockb
index 635178a9c..fc33e014b 100755
--- a/bun.lockb
+++ b/bun.lockb
diff --git a/src/bun.js/node/types.zig b/src/bun.js/node/types.zig
index 72f1dff7e..7e9cdcd2d 100644
--- a/src/bun.js/node/types.zig
+++ b/src/bun.js/node/types.zig
@@ -2192,6 +2192,8 @@ pub const Path = struct {
         if (comptime is_bindgen) return JSC.JSValue.jsUndefined();
         if (args_len == 0) return JSC.ZigString.init("").toValue(globalThis);
         var arena = @import("root").bun.ArenaAllocator.init(heap_allocator);
+        defer arena.deinit();
+
         var arena_allocator = arena.allocator();
         var stack_fallback_allocator = std.heap.stackFallback(
             ((32 * @sizeOf(string)) + 1024),
@@ -2199,18 +2201,27 @@ pub const Path = struct {
         );
         var allocator = stack_fallback_allocator.get();
 
-        defer arena.deinit();
         var buf: [bun.MAX_PATH_BYTES]u8 = undefined;
+        var count: usize = 0;
         var to_join = allocator.alloc(string, args_len) catch unreachable;
         for (args_ptr[0..args_len], 0..) |arg, i| {
             const zig_str: JSC.ZigString = arg.getZigString(globalThis);
             to_join[i] = zig_str.toSlice(allocator).slice();
+            count += to_join[i].len;
+        }
+
+        var buf_to_use: []u8 = &buf;
+        if (count * 2 >= buf.len) {
+            buf_to_use = allocator.alloc(u8, count * 2) catch {
+                globalThis.throwOutOfMemory();
+                return .zero;
+            };
         }
 
         const out = if (!isWindows)
-            PathHandler.joinStringBuf(&buf, to_join, .posix)
+            PathHandler.joinStringBuf(buf_to_use, to_join, .posix)
         else
-            PathHandler.joinStringBuf(&buf, to_join, .windows);
+            PathHandler.joinStringBuf(buf_to_use, to_join, .windows);
 
         var str = bun.String.create(out);
         defer str.deref();
diff --git a/src/resolver/resolve_path.zig b/src/resolver/resolve_path.zig
index f74211709..381abc648 100644
--- a/src/resolver/resolve_path.zig
+++ b/src/resolver/resolve_path.zig
@@ -829,7 +829,25 @@ pub fn joinStringBuf(buf: []u8, _parts: anytype, comptime _platform: Platform) [
 
     var written: usize = 0;
     const platform = comptime _platform.resolve();
-    var temp_buf: [4096]u8 = undefined;
+    var temp_buf_: [4096]u8 = undefined;
+    var temp_buf: []u8 = &temp_buf_;
+    var free_temp_buf = false;
+    defer {
+        if (free_temp_buf) {
+            bun.default_allocator.free(temp_buf);
+        }
+    }
+
+    var count: usize = 0;
+    for (_parts) |part| {
+        count += if (part.len > 0) part.len + 1 else 0;
+    }
+
+    if (count * 2 > temp_buf.len) {
+        temp_buf = bun.default_allocator.alloc(u8, count * 2) catch @panic("Out of memory");
+        free_temp_buf = true;
+    }
+
     temp_buf[0] = 0;
 
     for (_parts) |part| {
diff --git a/test/js/node/path/path.test.js b/test/js/node/path/path.test.js
index 26b6a3b6d..1d14e1d9e 100644
--- a/test/js/node/path/path.test.js
+++ b/test/js/node/path/path.test.js
@@ -271,6 +271,19 @@ it("path.basename", () => {
   strictEqual(path.posix.basename(`/a/b/${controlCharFilename}`), controlCharFilename);
 });
 
+describe("path.join #5769", () => {
+  for (let length of [4096, 4095, 4097, 65_432, 65_431, 65_433]) {
+    it("length " + length, () => {
+      const tooLengthyFolderName = Array.from({ length }).fill("b").join("");
+      expect(path.join(tooLengthyFolderName)).toEqual("b".repeat(length));
+    });
+    it("length " + length + "joined", () => {
+      const tooLengthyFolderName = Array.from({ length }).fill("b");
+      expect(path.join(...tooLengthyFolderName)).toEqual("b/".repeat(length).substring(0, 2 * length - 1));
+    });
+  }
+});
+
 it("path.join", () => {
   const failures = [];
   const backslashRE = /\\/g;