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, 43 insertions, 0 deletions

diff --git a/src/string.zig b/src/string.zig
index 5f107197f..26cd86d8c 100644
--- a/src/string.zig
+++ b/src/string.zig
@@ -128,6 +128,22 @@ pub const WTFStringImplStruct = extern struct {
         return .{};
     }
 
+    pub fn toUTF8WithoutRef(this: WTFStringImpl, allocator: std.mem.Allocator) ZigString.Slice {
+        if (this.is8Bit()) {
+            if (bun.strings.toUTF8FromLatin1(allocator, this.latin1Slice()) catch null) |utf8| {
+                return ZigString.Slice.init(allocator, utf8.items);
+            }
+
+            return ZigString.Slice.fromUTF8NeverFree(this.latin1Slice());
+        }
+
+        if (bun.strings.toUTF8Alloc(allocator, this.utf16Slice()) catch null) |utf8| {
+            return ZigString.Slice.init(allocator, utf8);
+        }
+
+        return .{};
+    }
+
     pub fn toUTF8IfNeeded(this: WTFStringImpl, allocator: std.mem.Allocator) ?ZigString.Slice {
         if (this.is8Bit()) {
             if (bun.strings.toUTF8FromLatin1(allocator, this.latin1Slice()) catch null) |utf8| {
@@ -533,6 +549,16 @@ pub const String = extern struct {
         return false;
     }
 
+    extern fn BunString__toJSON(
+        globalObject: *bun.JSC.JSGlobalObject,
+        this: *String,
+    ) JSC.JSValue;
+
+    pub fn toJSForParseJSON(self: *String, globalObject: *JSC.JSGlobalObject) JSC.JSValue {
+        JSC.markBinding(@src());
+        return BunString__toJSON(globalObject, self);
+    }
+
     pub fn encodeInto(self: String, out: []u8, comptime enc: JSC.Node.Encoding) !usize {
         if (self.isUTF16()) {
             return JSC.WebCore.Encoder.encodeIntoFrom16(self.utf16(), out, enc, true);
@@ -581,6 +607,23 @@ pub const String = extern struct {
         return ZigString.Slice.empty;
     }
 
+    /// This is the same as toUTF8, but it doesn't increment the reference count for latin1 strings
+    pub fn toUTF8WithoutRef(this: String, allocator: std.mem.Allocator) ZigString.Slice {
+        if (this.tag == .WTFStringImpl) {
+            return this.value.WTFStringImpl.toUTF8WithoutRef(allocator);
+        }
+
+        if (this.tag == .ZigString) {
+            return this.value.ZigString.toSlice(allocator);
+        }
+
+        if (this.tag == .StaticZigString) {
+            return ZigString.Slice.fromUTF8NeverFree(this.value.StaticZigString.slice());
+        }
+
+        return ZigString.Slice.empty;
+    }
+
     pub fn toSlice(this: String, allocator: std.mem.Allocator) SliceWithUnderlyingString {
         return SliceWithUnderlyingString{
             .utf8 = this.toUTF8(allocator),