systemprompt_api/services/static_content/static_files/
cache.rs

1//! Cache-control constants and `ETag` computation/matching for static file
2//! responses.
3//!
4//! Assets are classified by URL shape, not by how they were built, so
5//! `/css/content.css` and `/css/content.4f3a9c1e.css` reach the same handler.
6//! Only a name carrying a content hash may be answered with `immutable`: a
7//! client that believes that promise will not revalidate for the lifetime of
8//! the `max-age`, leaving the `ETag` computed here unreachable.
9//!
10//! Copyright (c) systemprompt.io — Business Source License 1.1.
11//! See <https://systemprompt.io> for licensing details.
12
13use axum::http::{HeaderMap, StatusCode, header};
14use axum::response::IntoResponse;
15use std::hash::{Hash, Hasher};
16use std::path::Path;
17
18pub const CACHE_STATIC_ASSET: &str = "public, max-age=31536000, immutable";
19pub const CACHE_STATIC_ASSET_REVALIDATE: &str = "public, max-age=0, must-revalidate";
20pub const CACHE_HTML: &str = "no-cache";
21pub const CACHE_METADATA: &str = "public, max-age=3600";
22
23const CONTENT_HASH_MIN_LEN: usize = 8;
24const CONTENT_HASH_MAX_LEN: usize = 32;
25
26/// The hash predicate is deliberately conservative: a missed hash costs one
27/// conditional request, whereas a false positive pins a mutable URL in client
28/// and CDN caches for a year.
29pub fn asset_cache_policy(path: &Path) -> &'static str {
30    let hashed = path
31        .file_name()
32        .and_then(|name| name.to_str())
33        .is_some_and(has_content_hash_segment);
34
35    if hashed {
36        CACHE_STATIC_ASSET
37    } else {
38        CACHE_STATIC_ASSET_REVALIDATE
39    }
40}
41
42fn has_content_hash_segment(file_name: &str) -> bool {
43    let segments: Vec<&str> = file_name.split(['.', '-']).collect();
44    let Some(interior) = segments.get(1..segments.len().saturating_sub(1)) else {
45        return false;
46    };
47    interior.iter().copied().any(is_content_hash)
48}
49
50fn is_content_hash(segment: &str) -> bool {
51    if !(CONTENT_HASH_MIN_LEN..=CONTENT_HASH_MAX_LEN).contains(&segment.len())
52        || !segment.chars().all(|c| c.is_ascii_alphanumeric())
53    {
54        return false;
55    }
56    let all_hex = segment.chars().all(|c| c.is_ascii_hexdigit());
57    let mixed = segment.chars().any(|c| c.is_ascii_digit())
58        && segment.chars().any(|c| c.is_ascii_alphabetic());
59    all_hex || mixed
60}
61
62pub fn compute_etag(content: &[u8]) -> String {
63    let mut hasher = std::collections::hash_map::DefaultHasher::new();
64    content.hash(&mut hasher);
65    format!("\"{}\"", hasher.finish())
66}
67
68pub(super) fn etag_matches(headers: &HeaderMap, etag: &str) -> bool {
69    headers
70        .get(header::IF_NONE_MATCH)
71        .and_then(|v| v.to_str().ok())
72        == Some(etag)
73}
74
75pub(super) fn not_modified_response(etag: &str, cache_control: &str) -> axum::response::Response {
76    (
77        StatusCode::NOT_MODIFIED,
78        [
79            (header::ETAG, etag.to_owned()),
80            (header::CACHE_CONTROL, cache_control.to_owned()),
81        ],
82    )
83        .into_response()
84}
85
86fn serve_file_response(
87    content: Vec<u8>,
88    content_type: String,
89    cache_control: &str,
90    etag: String,
91) -> axum::response::Response {
92    (
93        StatusCode::OK,
94        [
95            (header::CONTENT_TYPE, content_type),
96            (header::CACHE_CONTROL, cache_control.to_owned()),
97            (header::ETAG, etag),
98        ],
99        content,
100    )
101        .into_response()
102}
103
104pub(super) async fn serve_cached_file(
105    file_path: &Path,
106    headers: &HeaderMap,
107    content_type: &str,
108    cache_control: &str,
109) -> axum::response::Response {
110    match tokio::fs::read(file_path).await {
111        Ok(content) => {
112            let etag = compute_etag(&content);
113            if etag_matches(headers, &etag) {
114                return not_modified_response(&etag, cache_control);
115            }
116            serve_file_response(content, content_type.to_owned(), cache_control, etag)
117        },
118        Err(_) => (StatusCode::INTERNAL_SERVER_ERROR, "Error reading file").into_response(),
119    }
120}
systemprompt_api/services/static_content/static_files/cache.rs

systemprompt_api/services/static_content/static_files/
cache.rs
