tiny.closure.receipt.json

1const std = @import("std");2const pretty_json = @import("pretty").json;34pub const Error = error{ReceiptCapacityExceeded};56const measurement_buffer_bytes: usize = 256;78pub fn measure(9    comptime write: anytype,10    args: anytype,11) Error!usize {12    var buffer: [measurement_buffer_bytes]u8 = undefined;13    var discarding = std.Io.Writer.Discarding.init(&buffer);14    @call(.auto, write, .{&discarding.writer} ++ args) catch15        return error.ReceiptCapacityExceeded;16    return std.math.cast(usize, discarding.fullCount()) orelse17        error.ReceiptCapacityExceeded;18}1920pub fn render(21    output: []u8,22    expected: usize,23    comptime write: anytype,24    args: anytype,25) Error![]const u8 {26    if (expected > output.len) return error.ReceiptCapacityExceeded;27    var writer = std.Io.Writer.fixed(output);28    @call(.auto, write, .{&writer} ++ args) catch29        return error.ReceiptCapacityExceeded;30    if (writer.end != expected) return error.ReceiptCapacityExceeded;31    return output[0..writer.end];32}3334fn writeFixture(writer: *std.Io.Writer, value: []const u8) std.Io.Writer.Error!void {35    var json = pretty_json.Writer.init(writer, .minified);36    const object = try json.object();37    try object.byteString("value", value);38    try object.endLine();39}4041test "bounded JSON measures and renders arbitrary byte strings exactly" {42    const expected = "{\"value\":\"quote\\\"\\n\\u0080\\u00ff\"}\n";43    const length = try measure(writeFixture, .{"quote\"\n\x80\xff"});44    try std.testing.expectEqual(expected.len, length);45    var output: [expected.len]u8 = undefined;46    const rendered = try render(47        &output,48        length,49        writeFixture,50        .{"quote\"\n\x80\xff"},51    );52    try std.testing.expectEqualStrings(expected, rendered);53}5455test "bounded JSON rejects short output without mutation" {56    const length = try measure(writeFixture, .{"value"});57    var output: [1]u8 = .{0xa5};58    try std.testing.expectError(59        error.ReceiptCapacityExceeded,60        render(&output, length, writeFixture, .{"value"}),61    );62    try std.testing.expectEqual(@as(u8, 0xa5), output[0]);63}

1pub const json = @import("json.zig");