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Wire Format and Message I/O

Header Layout

Each REPE message begins with a fixed 48-byte header (HEADER_SIZE) followed by the query payload and the body payload. All numeric fields are little-endian. The header length field equals 48 + query_length + body_length and is validated on parse. The header reserved field is validated and must be zero.

query_format and body_format use the enums in repe::constants. The suggested query format is JSON Pointer (/path/to/resource).

Streaming and Zero-Copy I/O

Message::to_vec and Message::from_slice are the convenient round-trip APIs, but for large bodies (e.g. multi-MiB binary chunks) they add a full-body memcpy you may not want. The streaming APIs let the body flow directly between the wire and a user-supplied encoder/decoder.

use repe::{write_message_streaming, BodyFormat, Header, QueryFormat};
use std::io::Write;

let mut header = Header::new();
header.id = 99;
header.query_format = QueryFormat::JsonPointer as u16;
header.body_format = BodyFormat::Beve as u16;
let body_len = beve_chunk_size(&chunk);

write_message_streaming(&mut socket, header, b"/collect/file_chunk", body_len, |w| {
    beve::to_writer_streaming(w, &chunk).map_err(std::io::Error::other)
})?;

use repe::MessageView;

let view = MessageView::from_slice(&frame_bytes)?;
let path = view.query_str()?;
// view.body is &[u8] pointing inside frame_bytes; pair with serde_bytes::Bytes<'a>
// on a Deserialize struct to keep the chunk payload borrowed end-to-end.

Message::write_to and Message::serialized_len are the owned-Message counterparts: emit a Message to a Write without going through to_vec, or query its wire size in O(1).

JSON Pointer Paths

Method paths follow RFC 6901: each /-separated segment names a step into the server's value tree, so /api/v1/counter reaches the field counter inside the object v1 inside the object api. The empty path "" (or just /) refers to the root. Two characters need escaping inside a segment: ~ becomes ~0 and / becomes ~1. Most REPE servers expose a flat namespace where the path is just a function or value name, but registry-backed servers may nest values arbitrarily deep.

Helpers:

  • parse_json_pointer splits a pointer into unescaped tokens.
  • eval_json_pointer indexes into a serde_json::Value using array indices or object keys.