Fix memory leak in `await new Response(latin1String).arrayBuffer()` and `await Response.json(obj).json()` (#3656)

❯ mem bun --smol response-arrayBuffer.mjs
cpu: Apple M1 Max
runtime: bun 0.6.15 (arm64-darwin)

benchmark                                                        time (avg)             (min … max)       p75       p99      p995
--------------------------------------------------------------------------------------------------- -----------------------------
new Response().arrayBuffer() (new string each call, latin1)    12.9 µs/iter      (625 ns … 4.18 ms)      1 µs 567.17 µs 711.79 µs
new Response().arrayBuffer() (new string each call, utf16)    12.85 µs/iter     (1.67 µs … 1.56 ms)   2.17 µs 462.75 µs 621.13 µs
new Response().arrayBuffer() (existing string, latin1)         6.53 µs/iter     (6.21 µs … 7.07 µs)   6.64 µs   7.07 µs   7.07 µs

Peak memory usage: 49 MB

bun on  jarred/memory-leak-fix took 2s
❯ mem bun response-arrayBuffer.mjs
cpu: Apple M1 Max
runtime: bun 0.6.15 (arm64-darwin)

benchmark                                                        time (avg)             (min … max)       p75       p99      p995
--------------------------------------------------------------------------------------------------- -----------------------------
new Response().arrayBuffer() (new string each call, latin1)     1.2 µs/iter     (1.04 µs … 1.42 µs)   1.22 µs   1.42 µs   1.42 µs
new Response().arrayBuffer() (new string each call, utf16)     2.74 µs/iter     (2.42 µs … 6.37 µs)   2.68 µs   6.37 µs   6.37 µs
new Response().arrayBuffer() (existing string, latin1)       746.37 ns/iter   (643.82 ns … 1.04 µs) 776.11 ns   1.04 µs   1.04 µs

Peak memory usage: 104 MB

bun on  jarred/memory-leak-fix took 2s
❯ mem ~/.bun/bin/bun response-arrayBuffer.mjs
cpu: Apple M1 Max
runtime: bun 0.6.15 (arm64-darwin)

benchmark                                                        time (avg)             (min … max)       p75       p99      p995
--------------------------------------------------------------------------------------------------- -----------------------------
new Response().arrayBuffer() (new string each call, latin1)    1.69 µs/iter      (1.56 µs … 2.1 µs)   1.73 µs    2.1 µs    2.1 µs
new Response().arrayBuffer() (new string each call, utf16)     2.65 µs/iter     (2.47 µs … 3.17 µs)   2.69 µs   3.17 µs   3.17 µs
new Response().arrayBuffer() (existing string, latin1)       667.67 ns/iter   (547.67 ns … 1.28 µs) 694.21 ns   1.28 µs   1.28 µs

Peak memory usage: 2735 MB

bun on  jarred/memory-leak-fix took 2s
❯ mem ~/.bun/bin/bun --smol response-arrayBuffer.mjs
cpu: Apple M1 Max
runtime: bun 0.6.15 (arm64-darwin)

benchmark                                                        time (avg)             (min … max)       p75       p99      p995
--------------------------------------------------------------------------------------------------- -----------------------------
new Response().arrayBuffer() (new string each call, latin1)   13.51 µs/iter       (541 ns … 3.2 ms)   1.92 µs 553.42 µs 709.92 µs
new Response().arrayBuffer() (new string each call, utf16)    13.07 µs/iter     (1.71 µs … 3.43 ms)   2.13 µs 451.21 µs 651.67 µs
new Response().arrayBuffer() (existing string, latin1)         6.25 µs/iter     (5.79 µs … 6.81 µs)    6.4 µs   6.81 µs   6.81 µs

Peak memory usage: 292 MB

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

1 files changed, 4 insertions, 3 deletions

diff --git a/src/bun.js/javascript.zig b/src/bun.js/javascript.zig
index cfa791d63..2e6d61952 100644
--- a/src/bun.js/javascript.zig
+++ b/src/bun.js/javascript.zig
@@ -2431,9 +2431,10 @@ pub const VirtualMachine = struct {
                                 add_extra_line = true;
                             }
                         } else if (kind.isObject() or kind.isArray()) {
-                            var zig_str = ZigString.init("");
-                            value.jsonStringify(this.global, 2, &zig_str);
-                            try writer.print(comptime Output.prettyFmt(" {s}<d>: <r>{s}<r>\n", allow_ansi_color), .{ field, zig_str });
+                            var bun_str = bun.String.empty;
+                            defer bun_str.deref();
+                            value.jsonStringify(this.global, 2, &bun_str);
+                            try writer.print(comptime Output.prettyFmt(" {s}<d>: <r>{any}<r>\n", allow_ansi_color), .{ field, bun_str });
                             add_extra_line = true;
                         }
                     }