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// SPDX-License-Identifier: MIT OR Apache-2.0
// This file is part of Static Web Server.
// See https://static-web-server.net/ for more information
// Copyright (C) 2019-present Jose Quintana <joseluisq.net>
//! Redirection module to handle config redirect URLs with pattern matching support.
//!
//! # Security: ReDoS / pattern complexity
//!
//! Redirect/rewrite source patterns are admin-supplied at startup. SWS
//! uses [`regex_lite`], which has **no backtracking** (linear-time NFA
//! engine), so the classic catastrophic-backtracking ReDoS class does
//! not apply. However:
//!
//! - Per-request work is still proportional to `pattern_size * uri_len`.
//! To bound it, requests with URIs longer than [`MAX_URI_LEN_FOR_REGEX`]
//! bytes are skipped (no regex evaluation, no redirect).
//! - Operators should treat redirect patterns as trusted configuration
//! and avoid loading them from untrusted sources.
use headers::HeaderValue;
use hyper::{Request, Response, StatusCode};
use regex_lite::Regex;
use crate::body::Body;
use crate::{Error, error_page, handler::RequestHandlerOpts, settings::Redirects};
/// Maximum URI length (bytes) that will be fed to the redirect regex
/// engine. Requests above this size skip redirect matching entirely.
///
/// 8 KiB matches the common HTTP-server URI cap and is more than the
/// largest realistic redirect source while still bounding per-request
/// regex work to a small constant.
pub(crate) const MAX_URI_LEN_FOR_REGEX: usize = 8 * 1024;
/// Applies redirect rules to a request if necessary.
pub(crate) fn pre_process<T>(
opts: &RequestHandlerOpts,
req: &Request<T>,
) -> Option<Result<Response<Body>, Error>> {
let redirects = opts.advanced_opts.as_ref()?.redirects.as_deref()?;
let uri = req.uri();
let uri_path = uri.path();
// SECURITY (ReDoS bound): refuse to run any regex against
// unreasonably long URIs. See module-level docs.
if uri_path.len() > MAX_URI_LEN_FOR_REGEX {
tracing::debug!(
"redirects: skipping match, uri path length {} exceeds cap {}",
uri_path.len(),
MAX_URI_LEN_FOR_REGEX
);
return None;
}
let host = req
.headers()
.get(http::header::HOST)
.and_then(|v| v.to_str().ok())
.unwrap_or("");
let mut uri_host = uri.host().unwrap_or(host).to_owned();
if let Some(uri_port) = uri.port_u16() {
uri_host.push_str(&format!(":{uri_port}"));
}
let matched = get_redirection(&uri_host, uri_path, Some(redirects))?;
let mut dest = match replace_placeholders(
uri_path,
&matched.source,
&matched.destination,
&matched.replacer,
) {
Ok(dest) => dest,
Err(err) => return handle_error(err, opts, req),
};
// Preserve the client's query string across the redirect
// in an Apache's QSA rewrite option fashion.
if let Some(query) = uri.query() {
if !dest.ends_with('?') && !dest.ends_with('&') {
dest.push(if dest.contains('?') { '&' } else { '?' });
}
dest.push_str(query);
}
match HeaderValue::from_str(&dest) {
Ok(loc) => {
let mut resp = Response::new(crate::body::empty());
resp.headers_mut().insert(hyper::header::LOCATION, loc);
*resp.status_mut() = matched.kind;
tracing::trace!(
"uri matches redirects glob pattern, redirecting with status '{}'",
matched.kind
);
Some(Ok(resp))
}
Err(err) => handle_error(
Error::new(err).context("invalid header value from current uri"),
opts,
req,
),
}
}
/// Replaces placeholders in the destination URI by matching capture groups from the original URI.
#[doc(hidden)]
pub fn replace_placeholders(
orig_uri: &str,
regex: &Regex,
dest_uri: &str,
ac: &aho_corasick::AhoCorasick,
) -> Result<String, Error> {
let regex_caps = if let Some(regex_caps) = regex.captures(orig_uri) {
regex_caps
} else {
return Err(Error::msg("regex didn't match, extracting captures failed"));
};
let caps: Vec<&str> = (0..regex_caps.len())
.map(|i| regex_caps.get(i).map(|s| s.as_str()).unwrap_or(""))
.collect();
tracing::debug!("url redirects/rewrites regex equivalent: {regex}");
tracing::debug!("url redirects/rewrites glob pattern captures: {caps:?}");
tracing::debug!("url redirects/rewrites glob pattern destination: {dest_uri:?}");
match ac.try_replace_all(dest_uri, &caps) {
Ok(dest) => {
tracing::debug!("url redirects/rewrites glob pattern destination replaced: {dest:?}");
Ok(dest)
}
Err(err) => Err(Error::new(err).context("failed replacing captures")),
}
}
/// Logs error and produces an Internal Server Error response.
pub(crate) fn handle_error<T>(
err: Error,
opts: &RequestHandlerOpts,
req: &Request<T>,
) -> Option<Result<Response<Body>, Error>> {
tracing::error!("{err:?}");
Some(error_page::error_response(
req.uri(),
req.method(),
&StatusCode::INTERNAL_SERVER_ERROR,
&opts.page404,
&opts.page50x,
))
}
/// It returns a redirect's destination path and status code if the current request uri
/// matches against the provided redirect's array.
pub fn get_redirection<'a>(
uri_host: &'a str,
uri_path: &'a str,
redirects_opts: Option<&'a [Redirects]>,
) -> Option<&'a Redirects> {
if let Some(redirects_vec) = redirects_opts {
for redirect_entry in redirects_vec {
// Match `host` redirect against `uri_host` if specified
if let Some(host) = &redirect_entry.host {
tracing::debug!(
"checking host '{host}' redirect entry against uri host '{uri_host}'"
);
if !host.eq(uri_host) {
continue;
}
}
// Match source glob pattern against the request uri path
if redirect_entry.source.is_match(uri_path) {
return Some(redirect_entry);
}
}
}
None
}
#[cfg(test)]
mod tests {
use super::pre_process;
use crate::body::Body;
use crate::{
Error,
handler::RequestHandlerOpts,
settings::{Advanced, Redirects, build_placeholder_replacer},
};
use hyper::{Request, Response, StatusCode};
use regex_lite::Regex;
fn make_request(host: &str, uri: &str) -> Request<Body> {
let mut builder = Request::builder();
if !host.is_empty() {
builder = builder.header("Host", host);
}
builder
.method("GET")
.uri(uri)
.body(crate::body::empty())
.unwrap()
}
fn get_redirects() -> Vec<Redirects> {
let s1 = Regex::new(r"/source1$").unwrap();
let r1 = build_placeholder_replacer(&s1);
let s2 = Regex::new(r"/source2$").unwrap();
let r2 = build_placeholder_replacer(&s2);
let s3 = Regex::new(r"/(prefix/)?(source3)/(.*)").unwrap();
let r3 = build_placeholder_replacer(&s3);
let s4 = Regex::new(r"/source4/(.*)").unwrap();
let r4 = build_placeholder_replacer(&s4);
vec![
Redirects {
host: None,
source: s1,
destination: "/destination1".into(),
kind: StatusCode::FOUND,
replacer: r1,
},
Redirects {
host: Some("example.com".into()),
source: s2,
destination: "/destination2".into(),
kind: StatusCode::MOVED_PERMANENTLY,
replacer: r2,
},
Redirects {
host: Some("example.info".into()),
source: s3,
destination: "/destination3/$2/$3".into(),
kind: StatusCode::MOVED_PERMANENTLY,
replacer: r3,
},
Redirects {
host: None,
source: s4,
destination: "/destination4?p=$1".into(),
kind: StatusCode::FOUND,
replacer: r4,
},
]
}
fn is_redirect(result: Option<Result<Response<Body>, Error>>) -> Option<(StatusCode, String)> {
if let Some(Ok(response)) = result {
let location = response.headers().get("Location")?.to_str().unwrap().into();
Some((response.status(), location))
} else {
None
}
}
#[test]
fn test_no_redirects() {
assert!(
pre_process(
&RequestHandlerOpts {
advanced_opts: None,
..Default::default()
},
&make_request("", "/")
)
.is_none()
);
assert!(
pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: None,
..Default::default()
}),
..Default::default()
},
&make_request("", "/")
)
.is_none()
);
}
#[test]
fn test_no_match() {
assert!(
pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("example.com", "/source2/whatever")
)
.is_none()
);
assert!(
pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("", "/source2")
)
.is_none()
);
}
#[test]
fn test_match() {
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("", "/source1")
)),
Some((StatusCode::FOUND, "/destination1".into()))
);
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("example.com", "/source2")
)),
Some((StatusCode::MOVED_PERMANENTLY, "/destination2".into()))
);
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("example.info", "/source3/whatever")
)),
Some((
StatusCode::MOVED_PERMANENTLY,
"/destination3/source3/whatever".into()
))
);
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("", "/source4/whatever")
)),
Some((StatusCode::FOUND, "/destination4?p=whatever".into()))
);
}
#[test]
fn test_query() {
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("", "/source1?q=query-string")
)),
Some((StatusCode::FOUND, "/destination1?q=query-string".into()))
);
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("example.com", "/source2?q=query-string")
)),
Some((
StatusCode::MOVED_PERMANENTLY,
"/destination2?q=query-string".into()
))
);
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("example.info", "/source3/whatever?q=query-string")
)),
Some((
StatusCode::MOVED_PERMANENTLY,
"/destination3/source3/whatever?q=query-string".into()
))
);
assert_eq!(
is_redirect(pre_process(
&RequestHandlerOpts {
advanced_opts: Some(Advanced {
redirects: Some(get_redirects()),
..Default::default()
}),
..Default::default()
},
&make_request("", "/source4/whatever?q=query-string")
)),
Some((
StatusCode::FOUND,
"/destination4?p=whatever&q=query-string".into()
))
);
}
// Property-based regression tests for `replace_placeholders` and the
// upstream URI length guard.
//
// The guard exists so adversarial inputs cannot pin the CPU on
// regex matching; the property is "calls never panic and respect
// the cap". `replace_placeholders` itself must also be total over
// any byte-length input bounded by `MAX_URI_LEN_FOR_REGEX`.
use super::{MAX_URI_LEN_FOR_REGEX, replace_placeholders};
use proptest::prelude::*;
proptest! {
#![proptest_config(ProptestConfig {
cases: 128, ..ProptestConfig::default()
})]
/// `replace_placeholders` must never panic on arbitrary input
/// pairs (orig URI, destination template) within the URI cap,
/// regardless of whether the regex matches.
#[test]
fn prop_replace_placeholders_never_panics(
orig in "\\PC{0,512}",
dest in "\\PC{0,512}",
) {
// A representative source pattern with 5 capture groups
// \u2014 mirrors realistic redirect rules.
let re = Regex::new(r"^/(.*)/(.*)/(.*)/(.*)/(.*)$").unwrap();
let ac = build_placeholder_replacer(&re);
let _ = replace_placeholders(&orig, &re, &dest, &ac);
}
/// When the regex does NOT match, `replace_placeholders` MUST
/// return an `Err` (no silent fallthrough).
#[test]
fn prop_replace_placeholders_no_match_returns_err(
// A leading char that prevents the regex from anchoring.
tail in "[a-zA-Z0-9_.-]{0,64}",
dest in "\\PC{0,64}",
) {
let orig = format!("no-leading-slash-{tail}");
let re = Regex::new(r"^/(.*)/(.*)/(.*)/(.*)/(.*)$").unwrap();
let ac = build_placeholder_replacer(&re);
prop_assert!(replace_placeholders(&orig, &re, &dest, &ac).is_err());
}
/// On a successful match, the produced destination MUST contain
/// only the captured substrings (or original literals) — i.e.
/// no `$N` placeholders survive for `N < captures_len()`.
#[test]
fn prop_replace_placeholders_substitutes_all_indices(
a in "[a-zA-Z0-9]{1,16}",
b in "[a-zA-Z0-9]{1,16}",
c in "[a-zA-Z0-9]{1,16}",
d in "[a-zA-Z0-9]{1,16}",
e in "[a-zA-Z0-9]{1,16}",
) {
let orig = format!("/{a}/{b}/{c}/{d}/{e}");
let re = Regex::new(r"^/(.*)/(.*)/(.*)/(.*)/(.*)$").unwrap();
let ac = build_placeholder_replacer(&re);
let dest = "/$0|$1|$2|$3|$4|$5".to_string();
let out = replace_placeholders(&orig, &re, &dest, &ac).unwrap();
// $0 = whole match (orig), then capture groups 1..=5.
let expected = format!("/{orig}|{a}|{b}|{c}|{d}|{e}");
prop_assert_eq!(out, expected);
}
}
/// `MAX_URI_LEN_FOR_REGEX` is a security/perf invariant; this test
/// keeps it as a tripwire if anyone ever lowers it accidentally.
#[test]
fn max_uri_len_for_regex_is_at_least_8kib() {
const { assert!(MAX_URI_LEN_FOR_REGEX >= 8 * 1024) };
}
}