# copybook-fixed
Fixed-length (LRECL) record framing primitives for copybook-rs.
## Overview
This crate provides streaming reader and writer types for fixed-length record framing.
`FixedRecordReader` consumes LRECL-sized records from a byte stream, while
`FixedRecordWriter` produces them with automatic null-byte padding for short payloads.
## Usage
```rust
use copybook_fixed::{FixedRecordReader, FixedRecordWriter};
use std::io::Cursor;
// Write fixed-length records (LRECL = 8)
let mut output = Vec::new();
let mut writer = FixedRecordWriter::with_lrecl(&mut output, 8).unwrap();
writer.write_record(b"ABCD").unwrap(); // padded to 8 bytes
writer.flush().unwrap();
// Read fixed-length records
let mut reader = FixedRecordReader::with_lrecl(Cursor::new(&output), 8).unwrap();
let record = reader.read_record().unwrap().unwrap();
assert_eq!(&record[..4], b"ABCD");
```
## Public API
- `FixedRecordReader<R>` — Streaming reader for fixed-length records
- `FixedRecordWriter<W>` — Streaming writer with automatic padding
The `with_lrecl` constructors are the canonical schema-independent framing
surface. Copybook schema compatibility is validated by `copybook-codec` before
it constructs these framing primitives.
## Standalone consumer proof
The repository includes a clean-room consumer that depends directly on only
`copybook-fixed` and `copybook-error`:
```text
cargo run --locked --manifest-path examples/copybook-fixed-clean-room/Cargo.toml
```
It proves multi-record read/write, zero padding, EOF, truncated-input rejection,
oversized-payload rejection, and the stable `CBKR101_FIXED_RECORD_ERROR`
identity without importing schema, codec, or CLI packages.
## Migration from the 0.5 schema-aware helper
The former `FixedRecordReader::validate_record_length` method was schema-aware
and is not part of the schema-independent framing API. Callers that need that
compatibility check should use
`copybook_codec::file::fixed::validate_record_length` with the parsed schema,
configured LRECL, record index, and record bytes; callers that only need
framing should use `with_lrecl`.
## License
AGPL-3.0-or-later