From 93e7414f96aa2b27f3f0bf72f27967c83e6396ef Mon Sep 17 00:00:00 2001
From: Meghan Denny <hello@nektro.net>
Date: Sun, 31 May 2026 14:45:21 -0700
Subject: [PATCH] add LimitedReader

---
 limited_reader.zig | 73 ++++++++++++++++++++++++++++++++++++++++++++++
 nio.zig            |  2 ++
 2 files changed, 75 insertions(+)
 create mode 100644 limited_reader.zig

diff --git a/limited_reader.zig b/limited_reader.zig
new file mode 100644
index 0000000000000000000000000000000000000000..af8059c194c2277a03ba2fcd2b58699c4cf9df30
--- /dev/null
+++ b/limited_reader.zig
@@ -0,0 +1,73 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const extras = @import("extras");
+const nio = @import("./nio.zig");
+
+const sys = switch (builtin.target.os.tag) {
+    .linux => @import("sys-linux"),
+    .macos => @import("sys-darwin"),
+    else => unreachable,
+};
+
+pub fn LimitedReader(ReaderType: type) type {
+    return struct {
+        backing_reader: ReaderType,
+        bytes_left: u64,
+
+        const Self = @This();
+
+        pub fn init(backing_reader: ReaderType, bytes_left: u64) Self {
+            return .{
+                .backing_reader = backing_reader,
+                .bytes_left = bytes_left,
+            };
+        }
+
+        const R = nio.Readable(@This(), ._var);
+        pub const readAll = R.readAll;
+        pub const readAtLeast = R.readAtLeast;
+        pub const readNoEof = R.readNoEof;
+        pub const readAllAlloc = R.readAllAlloc;
+        pub const readArray = R.readArray;
+        pub const readByte = R.readByte;
+        pub const readUntilDelimiterArrayList = R.readUntilDelimiterArrayList;
+        pub const readUntilDelimiterAlloc = R.readUntilDelimiterAlloc;
+        pub const readUntilDelimiterOrEofAlloc = R.readUntilDelimiterOrEofAlloc;
+        pub const readUntilDelimitersBuf = R.readUntilDelimitersBuf;
+        pub const readUntilDelimitersArrayList = R.readUntilDelimitersArrayList;
+        pub const readAlloc = R.readAlloc;
+        pub const readInt = R.readInt;
+        pub const readUntilDelimitersAlloc = R.readUntilDelimitersAlloc;
+        pub const readUntilDelimiterOrEof = R.readUntilDelimiterOrEof;
+        pub const readExpected = R.readExpected;
+        pub const skipBytes = R.skipBytes;
+        pub const skipUntilDelimiterOrEof = R.skipUntilDelimiterOrEof;
+
+        pub const ReadError = extras.Pointee(ReaderType).ReadError;
+
+        pub fn read(self: *Self, bytes: []u8) ReadError!usize {
+            const max_read = @min(self.bytes_left, bytes.len);
+            const n = try self.backing_reader.read(bytes[0..max_read]);
+            self.bytes_left -= n;
+            return n;
+        }
+        // pub fn readv(self: *Self, iovec: []sys.struct_iovec) ReadError!usize {
+        //     const len = try self.backing_reader.readv(iovec);
+        //     self.bytes_read += len;
+        //     return len;
+        // }
+
+        pub fn anyReadable(self: *Self) nio.AnyReadable {
+            const S = struct {
+                fn read(s: *allowzero anyopaque, buffer: []u8) anyerror!usize {
+                    const fbs: *Self = @ptrCast(@alignCast(s));
+                    return fbs.read(buffer);
+                }
+            };
+            return .{
+                .vtable = &.{ .read = S.read },
+                .state = @ptrCast(self),
+            };
+        }
+    };
+}
diff --git a/nio.zig b/nio.zig
index bdc922099b4aff719fd68c4a0807f091af4ee913..b764a0c7291c8b5f9223340151b73921778119b0 100644
--- a/nio.zig
+++ b/nio.zig
@@ -395,3 +395,5 @@ pub const NullWriter = @import("./null_writer.zig").NullWriter;
 pub const AllocatingWriter = @import("./allocating_writer.zig").AllocatingWriter;
 
 pub const CountingReader = @import("./counting_reader.zig").CountingReader;
+
+pub const LimitedReader = @import("./limited_reader.zig").LimitedReader;
-- 
2.54.0