awaforge

fontWriter

AGPL-3.0-onlyRelease 2L4

Big-endian binary writer — symmetric counterpart of fontReader.

Module fontWriter | Source packages/front/office/fonts/src/primitives/writer.js | Deps fontErrors, binaryWriter, fontFixed | Worker-safe yes

Grows an internal Uint8Array (doubling strategy) and exposes finalize(), which returns a tightly-sized copy of the bytes written. Used by table encoders, the SFNT packer and the subsetter.

Resolve

const { BinaryWriter, writer } = runtime.resolve('fontWriter');
const w = writer(initialCapacity);

API

Constructor

new BinaryWriter(initialCapacity = 256) — initial buffer size.

Properties

Property Type Description
pos number Current write offset.
length number Logical length (== pos).

Write methods

Method Signature Description
writeUint8 / writeInt8 (v) => this 1 byte.
writeUint16 / writeInt16 (v) => this 2 bytes BE.
writeUint24 (v) => this 3 bytes BE.
writeUint32 / writeInt32 (v) => this 4 bytes BE.
writeFixed (v) => this Fixed 16.16.
writeF2Dot14 (v) => this Saturated F2Dot14.
writeTag (v: string|number) => this 4-char ASCII or uint32.
writeLongDateTime (seconds) => this 64-bit seconds since 1904.
writeBytes (u8: Uint8Array) => this Raw append.
padTo4 () => this Zero-pad to a multiple of 4 (OT alignment).
padTo (align) => this Zero-pad to an arbitrary alignment.

Positioning methods

Method Signature Description
seek (p) => this Must stay within the already-written area.
patchUint32 (pos, value) => this Back-patches a uint32 without moving the cursor.
patchUint16 (pos, value) => this Back-patches a uint16.
finalize () => Uint8Array Tightly-sized copy of the bytes written.

Examples

Building a table

const { writer } = runtime.resolve('fontWriter');
const w = writer(54);
w.writeUint16(1).writeUint16(0).writeFixed(1.0);
const bytes = w.finalize();

Deferred offset patch

const offsetPos = w.pos;
w.writeUint32(0);          // placeholder
// ... bytes later ...
w.patchUint32(offsetPos, actualOffset);

Notes

  • All write methods are chainable (return this).
  • writeBytes requires a Uint8Array — otherwise ContractError('fonts/writer-input').
  • seek does not allow moving past the written area — to reserve and patch later, write a placeholder then use patchUint*.
  • writeTag(string) rejects any non-ASCII character (> 0x7F) — ContractError('fonts/bad-tag'). Avoids the historical silent-truncation issue.
  • v1.0.0 migration: implementation delegated to @awacloud/fw/io/binary/writer.js. The fonts package's BinaryWriter facade keeps the historical API (writeFixed, writeF2Dot14, writeTag, writeLongDateTime, padTo4/padTo, patchUint16/32).

See also