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const std = @import("std");
const Allocator = std.mem.Allocator;
/// An allocator that rejects any single allocation or resize larger than a
/// configured byte limit. The limit applies to each request independently,
/// not to the total amount of memory currently allocated.
pub const LimitedAllocator = struct {
child: Allocator,
limit: usize,
/// Set after an allocation, resize, or remap is rejected for exceeding
/// the limit. This remains set until the caller clears it.
limit_exceeded: bool = false,
pub fn init(child: Allocator, limit: usize) LimitedAllocator {
return .{
.child = child,
.limit = limit,
};
}
pub fn allocator(self: *LimitedAllocator) Allocator {
return .{
.ptr = self,
.vtable = &.{
.alloc = alloc,
.resize = resize,
.remap = remap,
.free = free,
},
};
}
fn check(self: *LimitedAllocator, size: usize) bool {
if (size <= self.limit) return true;
self.limit_exceeded = true;
return false;
}
fn alloc(
ctx: *anyopaque,
len: usize,
alignment: std.mem.Alignment,
ret_addr: usize,
) ?[*]u8 {
const self: *LimitedAllocator = @ptrCast(@alignCast(ctx));
if (!self.check(len)) return null;
return self.child.rawAlloc(len, alignment, ret_addr);
}
fn resize(
ctx: *anyopaque,
memory: []u8,
alignment: std.mem.Alignment,
new_len: usize,
ret_addr: usize,
) bool {
const self: *LimitedAllocator = @ptrCast(@alignCast(ctx));
if (!self.check(new_len)) return false;
return self.child.rawResize(memory, alignment, new_len, ret_addr);
}
fn remap(
ctx: *anyopaque,
memory: []u8,
alignment: std.mem.Alignment,
new_len: usize,
ret_addr: usize,
) ?[*]u8 {
const self: *LimitedAllocator = @ptrCast(@alignCast(ctx));
if (!self.check(new_len)) return null;
return self.child.rawRemap(memory, alignment, new_len, ret_addr);
}
fn free(
ctx: *anyopaque,
memory: []u8,
alignment: std.mem.Alignment,
ret_addr: usize,
) void {
const self: *LimitedAllocator = @ptrCast(@alignCast(ctx));
self.child.rawFree(memory, alignment, ret_addr);
}
};
test "LimitedAllocator allows allocations through the limit" {
const testing = std.testing;
var limited: LimitedAllocator = .init(testing.allocator, 8);
const alloc = limited.allocator();
const data = try alloc.alloc(u8, 8);
defer alloc.free(data);
try testing.expect(!limited.limit_exceeded);
}
test "LimitedAllocator rejects allocations before the child" {
const testing = std.testing;
var failing = testing.FailingAllocator.init(testing.allocator, .{
.fail_index = 0,
});
var limited: LimitedAllocator = .init(failing.allocator(), 8);
try testing.expectError(error.OutOfMemory, limited.allocator().alloc(u8, 9));
try testing.expect(limited.limit_exceeded);
try testing.expect(!failing.has_induced_failure);
}
test "LimitedAllocator rejects oversized resize and remap" {
const testing = std.testing;
var limited: LimitedAllocator = .init(testing.allocator, 8);
const alloc = limited.allocator();
const data = try alloc.alloc(u8, 8);
defer alloc.free(data);
try testing.expect(!alloc.resize(data, 9));
try testing.expect(limited.limit_exceeded);
limited.limit_exceeded = false;
try testing.expect(alloc.remap(data, 9) == null);
try testing.expect(limited.limit_exceeded);
}
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