55 lines
2.2 KiB
Rust
55 lines
2.2 KiB
Rust
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//! Pre-sized JSON responses for listing endpoints.
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//!
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//! `axum::Json` serializes into a `BytesMut::with_capacity(128)` — a 500-row
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//! listing grows that seed through ~11 doubling reallocations, memcpy-ing
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//! ~1.3× the payload on every hot listing response (files, folder
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//! resources, photos timeline, search). `sized_json` serializes into one
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//! right-sized `Vec` instead: 2 allocations total and no copy chain
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//! (benches/ROUND12.md §M1, 1.40x / −11 allocs on a 500-row page).
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//!
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//! The per-row estimates are calibrated against the serialized DTOs (a
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//! realistic `FileDto` row measures ~380 B). Underestimates cost one extra
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//! doubling — still far better than the 128-byte seed; overestimates waste
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//! transient capacity only (the buffer is freed after the response).
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use axum::http::{HeaderValue, StatusCode, header};
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use axum::response::{IntoResponse, Response};
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use bytes::Bytes;
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use serde::Serialize;
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/// Serialized size estimate for one file/folder row (FileDto ≈ 380 B).
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pub const EST_ROW_BYTES: usize = 384;
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/// Serialized size estimate for one wrapped resource row (PhotoDto /
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/// FolderResourcesDto items carry a FileDto plus wrapper fields).
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pub const EST_WRAPPED_ROW_BYTES: usize = 448;
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/// Serialize `value` into a single pre-sized buffer and wrap it as an
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/// `application/json` response — drop-in for `Json(value).into_response()`
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/// (byte-identical body, gated in `bench_round12_micro` §1), minus the
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/// doubling-realloc chain.
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pub fn sized_json<T: Serialize>(estimated_bytes: usize, value: &T) -> Response {
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let mut buf = Vec::with_capacity(estimated_bytes.max(128));
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match serde_json::to_writer(&mut buf, value) {
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Ok(()) => (
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StatusCode::OK,
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[(
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header::CONTENT_TYPE,
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HeaderValue::from_static("application/json"),
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)],
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Bytes::from(buf),
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)
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.into_response(),
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// Mirror axum's Json error arm: 500 + plain-text serializer error.
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Err(err) => (
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StatusCode::INTERNAL_SERVER_ERROR,
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[(
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header::CONTENT_TYPE,
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HeaderValue::from_static("text/plain; charset=utf-8"),
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)],
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err.to_string(),
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)
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.into_response(),
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}
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}
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