karlseguin.tngl.sh
A poolable string builder (aka string buffer) for Zig
zig 0.15
author
Karl Seguin
date
(Aug 21, 2025, 8:09 AM +0800)
commit
30f9512f
30f9512f61127efda1049c9064e533efa82c26f7
parent
fdd34230
fdd342308ba62c7f0711a51b6c5d40fa919b12e8
+20
-58
+1
-1
readme.md
+1
-1
readme.md
···
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buf.string(); // "over 9000!"
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```
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You can call `buf.writer()` to get an `std.io.Writer`.
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You can access `&buf.interface` to get an `*std.io.Writer`.
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You can use `writeU16Big`, `writeU32Big`, `writeU64Big` and `writeU16Little`, `writeU32Little`, `writeU64Little` to write integer values.
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src/buffer.zig
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src/buffer.zig
···
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// created when we try to write more than static.len
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dynamic: ?[]u8,
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interface: std.Io.Writer,
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pub fn init(allocator: Allocator, size: usize) !Buffer {
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const static = try allocator.alloc(u8, size);
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return .{
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.buf = static,
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.static = static,
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.dynamic = null,
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.interface = .{
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.buffer = &.{},
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.vtable = &.{
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.drain = drain,
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},
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}
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};
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}
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···
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if (self.dynamic) |dyn| {
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(self._da orelse allocator).free(dyn);
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}
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}
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pub fn drain(io_w: *std.io.Writer, data: []const []const u8, splat: usize) error{WriteFailed}!usize {
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_ = splat;
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const self: *Buffer = @alignCast(@fieldParentPtr("interface", io_w));
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self.write(data[0]) catch return error.WriteFailed;
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return data[0].len;
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}
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pub fn reset(self: *Buffer) void {
···
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@memcpy(c, self.buf[0..pos]);
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return c;
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}
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pub fn writer(self: *Buffer) Writer {
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return .init(self);
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}
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pub const Writer = struct {
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w: *Buffer,
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interface: std.io.Writer,
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pub const Error = Allocator.Error;
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fn init(w: *Buffer) Writer {
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return .{
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.w = w,
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.interface = .{
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.vtable = &.{
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.drain = drain,
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},
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.buffer = &.{},
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},
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};
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}
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pub fn adaptToNewApi(self: Writer) Adapter {
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return .{ .new_interface = self.interface };
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}
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pub fn drain(io_w: *std.io.Writer, data: []const []const u8, splat: usize) error{WriteFailed}!usize {
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_ = splat;
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const self: *Writer = @alignCast(@fieldParentPtr("interface", io_w));
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self.w.write(data[0]) catch return error.WriteFailed;
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return data[0].len;
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}
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// Legacy API
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pub fn writeByte(self: Writer, b: u8) !void {
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return self.w.writeByte(b);
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}
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pub fn writeByteNTimes(self: *Writer, b: u8, n: usize) !void {
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return self.w.writeByteNTimes(b, n);
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}
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pub fn print(self: *Writer, comptime fmt: []const u8, args: anytype) !void {
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return self.interface.print(fmt, args) catch return error.OutOfMemory;
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}
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pub fn writeAll(self: Writer, data: []const u8) !void {
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return self.w.write(data);
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}
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pub const Adapter = struct {
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err: ?Error = null,
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new_interface: std.Io.Writer,
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};
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};
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};
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pub const View = struct {
···
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}
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test "fuzz" {
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var control = std.ArrayList(u8).init(t.allocator);
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defer control.deinit();
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var control: std.ArrayList(u8) = .empty;
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defer control.deinit(t.allocator);
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var r = t.getRandom();
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const random = r.random();
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for (1..100) |_| {
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const input = testString(aa, random);
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try w.write(input);
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try control.appendSlice(input);
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try control.appendSlice(t.allocator, input);
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try t.expectString(control.items, w.string());
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}
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w.reset();
···
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var w = try Buffer.init(t.allocator, 10);
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defer w.deinit();
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try std.json.stringify(.{ .over = 9000, .spice = "must flow", .ok = true }, .{}, w.writer());
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try std.json.Stringify.value(.{ .over = 9000, .spice = "must flow", .ok = true }, .{}, &w.interface);
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try t.expectString("{\"over\":9000,\"spice\":\"must flow\",\"ok\":true}", w.string());
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}
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