AsciiStringCodec

Built-in Codec for 7-bit ASCII text (US-ASCII, RFC 20). One byte per character on the wire, range 0x00..0x7F.

Plug into a String field via com.ditchoom.buffer.codec.annotations.UseCodec, typically paired with com.ditchoom.buffer.codec.annotations.LengthPrefixed (or com.ditchoom.buffer.codec.annotations.RemainingBytes) so the framework narrows buffer.limit() to the field's body before calling decode:

@ProtocolMessage
data class StompFrame(
    @LengthPrefixed @UseCodec(AsciiStringCodec::class) val command: String,
)

Charset semantics

• Encode: every character in value must be in 0x00..0x7F. The first character outside that range raises EncodeException with the offending index and codepoint — the codec refuses to silently emit ? substitutes or platform-specific lossy fallbacks. After validation, encoding routes through WriteBuffer.writeString with Charset.UTF8: ASCII is a strict subset of UTF-8 (each 0x00..0x7F codepoint encodes to a single byte with the same value), so the wire form is identical and the codec inherits the platform's fast path (e.g. TextEncoder.encodeInto on JS).

• Decode: routed through ReadBuffer.readString with Charset.UTF8. ASCII-conformant input produces the same codepoints; bytes ≥ 0x80 are either replaced or rejected per the platform's UTF-8 decoder (JS uses {fatal: true} and throws). Producers conforming to RFC 20 will not emit those bytes.

The body length is owned by the surrounding annotation: @LengthPrefixed inserts the prefix in front of the body, @RemainingBytes consumes to buffer.limit(). decode reads buffer.remaining() bytes — i.e. the already-bounded region. Standalone callers must bound the buffer themselves (e.g. via setLimit) before invoking decode.

Adding other built-in charsets

This codec is the only built-in string codec. To support Latin-1, UTF-16, Modified UTF-8, etc., copy this class and swap the ASCII validation / wire-size formula for the target charset's encoding rules. See com.ditchoom.buffer.codec.annotations.UseCodec for the extension pattern.