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use std::collections::HashSet;
use super::{common_header, ContentEncoding, Encoding, Preference, Quality, QualityItem};
use crate::http::header;
common_header! {
/// `Accept-Encoding` header, defined
/// in [RFC 7231](https://datatracker.ietf.org/doc/html/rfc7231#section-5.3.4)
///
/// The `Accept-Encoding` header field can be used by user agents to indicate what response
/// content-codings are acceptable in the response. An `identity` token is used as a synonym
/// for "no encoding" in order to communicate when no encoding is preferred.
///
/// # ABNF
/// ```plain
/// Accept-Encoding = #( codings [ weight ] )
/// codings = content-coding / "identity" / "*"
/// ```
///
/// # Example Values
/// * `compress, gzip`
/// * ``
/// * `*`
/// * `compress;q=0.5, gzip;q=1`
/// * `gzip;q=1.0, identity; q=0.5, *;q=0`
///
/// # Examples
/// ```
/// use actix_web::HttpResponse;
/// use actix_web::http::header::{AcceptEncoding, Encoding, Preference, QualityItem};
///
/// let mut builder = HttpResponse::Ok();
/// builder.insert_header(
/// AcceptEncoding(vec![QualityItem::max(Preference::Specific(Encoding::gzip()))])
/// );
/// ```
///
/// ```
/// use actix_web::HttpResponse;
/// use actix_web::http::header::{AcceptEncoding, Encoding, QualityItem};
///
/// let mut builder = HttpResponse::Ok();
/// builder.insert_header(
/// AcceptEncoding(vec![
/// "gzip".parse().unwrap(),
/// "br".parse().unwrap(),
/// ])
/// );
/// ```
(AcceptEncoding, header::ACCEPT_ENCODING) => (QualityItem<Preference<Encoding>>)*
test_parse_and_format {
common_header_test!(no_headers, [b""; 0], Some(AcceptEncoding(vec![])));
common_header_test!(empty_header, [b""; 1], Some(AcceptEncoding(vec![])));
common_header_test!(
order_of_appearance,
[b"br, gzip"],
Some(AcceptEncoding(vec![
QualityItem::max(Preference::Specific(Encoding::brotli())),
QualityItem::max(Preference::Specific(Encoding::gzip())),
]))
);
common_header_test!(any, [b"*"], Some(AcceptEncoding(vec![
QualityItem::max(Preference::Any),
])));
// Note: Removed quality 1 from gzip
common_header_test!(implicit_quality, [b"gzip, identity; q=0.5, *;q=0"]);
// Note: Removed quality 1 from gzip
common_header_test!(implicit_quality_out_of_order, [b"compress;q=0.5, gzip"]);
common_header_test!(
only_gzip_no_identity,
[b"gzip, *; q=0"],
Some(AcceptEncoding(vec![
QualityItem::max(Preference::Specific(Encoding::gzip())),
QualityItem::zero(Preference::Any),
]))
);
}
}
impl AcceptEncoding {
/// Selects the most acceptable encoding according to client preference and supported types.
///
/// The "identity" encoding is not assumed and should be included in the `supported` iterator
/// if a non-encoded representation can be selected.
///
/// If `None` is returned, this indicates that none of the supported encodings are acceptable to
/// the client. The caller should generate a 406 Not Acceptable response (unencoded) that
/// includes the server's supported encodings in the body plus a [`Vary`] header.
///
/// [`Vary`]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Vary
pub fn negotiate<'a>(&self, supported: impl Iterator<Item = &'a Encoding>) -> Option<Encoding> {
// 1. If no Accept-Encoding field is in the request, any content-coding is considered
// acceptable by the user agent.
let supported_set = supported.collect::<HashSet<_>>();
if supported_set.is_empty() {
return None;
}
if self.0.is_empty() {
// though it is not recommended to encode in this case, return identity encoding
return Some(Encoding::identity());
}
// 2. If the representation has no content-coding, then it is acceptable by default unless
// specifically excluded by the Accept-Encoding field stating either "identity;q=0" or
// "*;q=0" without a more specific entry for "identity".
let acceptable_items = self.ranked_items().collect::<Vec<_>>();
let identity_acceptable = is_identity_acceptable(&acceptable_items);
let identity_supported = supported_set.contains(&Encoding::identity());
if identity_acceptable && identity_supported && supported_set.len() == 1 {
return Some(Encoding::identity());
}
// 3. If the representation's content-coding is one of the content-codings listed in the
// Accept-Encoding field, then it is acceptable unless it is accompanied by a qvalue of 0.
// 4. If multiple content-codings are acceptable, then the acceptable content-coding with
// the highest non-zero qvalue is preferred.
let matched = acceptable_items
.into_iter()
.filter(|q| q.quality > Quality::ZERO)
// search relies on item list being in descending order of quality
.find(|q| {
let enc = &q.item;
matches!(enc, Preference::Specific(enc) if supported_set.contains(enc))
})
.map(|q| q.item);
match matched {
Some(Preference::Specific(enc)) => Some(enc),
_ if identity_acceptable => Some(Encoding::identity()),
_ => None,
}
}
/// Extracts the most preferable encoding, accounting for [q-factor weighting].
///
/// If no q-factors are provided, we prefer brotli > zstd > gzip. Note that items without
/// q-factors are given the maximum preference value.
///
/// As per the spec, returns [`Preference::Any`] if acceptable list is empty. Though, if this is
/// returned, it is recommended to use an un-encoded representation.
///
/// If `None` is returned, it means that the client has signalled that no representations
/// are acceptable. This should never occur for a well behaved user-agent.
///
/// [q-factor weighting]: https://datatracker.ietf.org/doc/html/rfc7231#section-5.3.2
pub fn preference(&self) -> Option<Preference<Encoding>> {
// empty header indicates no preference
if self.0.is_empty() {
return Some(Preference::Any);
}
let mut max_item = None;
let mut max_pref = Quality::ZERO;
let mut max_rank = 0;
// uses manual max lookup loop since we want the first occurrence in the case of same
// preference but `Iterator::max_by_key` would give us the last occurrence
for pref in &self.0 {
// only change if strictly greater
// equal items, even while unsorted, still have higher preference if they appear first
let rank = encoding_rank(pref);
if (pref.quality, rank) > (max_pref, max_rank) {
max_pref = pref.quality;
max_item = Some(pref.item.clone());
max_rank = rank;
}
}
// Return max_item if any items were above 0 quality...
max_item.or_else(|| {
// ...or else check for "*" or "identity". We can elide quality checks since
// entering this block means all items had "q=0".
match self.0.iter().find(|pref| {
matches!(
pref.item,
Preference::Any
| Preference::Specific(Encoding::Known(ContentEncoding::Identity))
)
}) {
// "identity" or "*" found so no representation is acceptable
Some(_) => None,
// implicit "identity" is acceptable
None => Some(Preference::Specific(Encoding::identity())),
}
})
}
/// Returns a sorted list of encodings from highest to lowest precedence, accounting
/// for [q-factor weighting].
///
/// If no q-factors are provided, we prefer brotli > zstd > gzip.
///
/// [q-factor weighting]: https://datatracker.ietf.org/doc/html/rfc7231#section-5.3.2
pub fn ranked(&self) -> Vec<Preference<Encoding>> {
self.ranked_items().map(|q| q.item).collect()
}
fn ranked_items(&self) -> impl Iterator<Item = QualityItem<Preference<Encoding>>> {
if self.0.is_empty() {
return Vec::new().into_iter();
}
let mut types = self.0.clone();
// use stable sort so items with equal q-factor retain listed order
types.sort_by(|a, b| {
// sort by q-factor descending then server ranking descending
b.quality
.cmp(&a.quality)
.then(encoding_rank(b).cmp(&encoding_rank(a)))
});
types.into_iter()
}
}
/// Returns server-defined encoding ranking.
fn encoding_rank(qv: &QualityItem<Preference<Encoding>>) -> u8 {
// ensure that q=0 items are never sorted above identity encoding
// invariant: sorting methods calling this fn use first-on-equal approach
if qv.quality == Quality::ZERO {
return 0;
}
match qv.item {
Preference::Specific(Encoding::Known(ContentEncoding::Brotli)) => 5,
Preference::Specific(Encoding::Known(ContentEncoding::Zstd)) => 4,
Preference::Specific(Encoding::Known(ContentEncoding::Gzip)) => 3,
Preference::Specific(Encoding::Known(ContentEncoding::Deflate)) => 2,
Preference::Any => 0,
Preference::Specific(Encoding::Known(ContentEncoding::Identity)) => 0,
Preference::Specific(Encoding::Known(_)) => 1,
Preference::Specific(Encoding::Unknown(_)) => 1,
}
}
/// Returns true if "identity" is an acceptable encoding.
///
/// Internal algorithm relies on item list being in descending order of quality.
fn is_identity_acceptable(items: &'_ [QualityItem<Preference<Encoding>>]) -> bool {
if items.is_empty() {
return true;
}
// Loop algorithm depends on items being sorted in descending order of quality. As such, it
// is sufficient to return (q > 0) when reaching either an "identity" or "*" item.
for q in items {
match (q.quality, &q.item) {
// occurrence of "identity;q=n"; return true if quality is non-zero
(q, Preference::Specific(Encoding::Known(ContentEncoding::Identity))) => {
return q > Quality::ZERO
}
// occurrence of "*;q=n"; return true if quality is non-zero
(q, Preference::Any) => return q > Quality::ZERO,
_ => {}
}
}
// implicit acceptable identity
true
}
#[cfg(test)]
mod tests {
use super::*;
use crate::http::header::*;
macro_rules! accept_encoding {
() => { AcceptEncoding(vec![]) };
($($q:expr),+ $(,)?) => { AcceptEncoding(vec![$($q.parse().unwrap()),+]) };
}
/// Parses an encoding string.
fn enc(enc: &str) -> Preference<Encoding> {
enc.parse().unwrap()
}
#[test]
fn detect_identity_acceptable() {
macro_rules! accept_encoding_ranked {
() => { accept_encoding!().ranked_items().collect::<Vec<_>>() };
($($q:expr),+ $(,)?) => { accept_encoding!($($q),+).ranked_items().collect::<Vec<_>>() };
}
let test = accept_encoding_ranked!();
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip");
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "br");
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "*;q=0.1");
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "identity;q=0.1");
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "identity;q=0.1", "*;q=0");
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "*;q=0", "identity;q=0.1");
assert!(is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "*;q=0");
assert!(!is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "identity;q=0");
assert!(!is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "identity;q=0", "*;q=0");
assert!(!is_identity_acceptable(&test));
let test = accept_encoding_ranked!("gzip", "*;q=0", "identity;q=0");
assert!(!is_identity_acceptable(&test));
}
#[test]
fn encoding_negotiation() {
// no preference
let test = accept_encoding!();
assert_eq!(test.negotiate([].iter()), None);
let test = accept_encoding!();
assert_eq!(
test.negotiate([Encoding::identity()].iter()),
Some(Encoding::identity()),
);
let test = accept_encoding!("identity;q=0");
assert_eq!(test.negotiate([Encoding::identity()].iter()), None);
let test = accept_encoding!("*;q=0");
assert_eq!(test.negotiate([Encoding::identity()].iter()), None);
let test = accept_encoding!();
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::identity()),
);
let test = accept_encoding!("gzip");
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::gzip()),
);
assert_eq!(
test.negotiate([Encoding::brotli(), Encoding::identity()].iter()),
Some(Encoding::identity()),
);
assert_eq!(
test.negotiate([Encoding::brotli(), Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::gzip()),
);
let test = accept_encoding!("gzip", "identity;q=0");
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::gzip()),
);
assert_eq!(
test.negotiate([Encoding::brotli(), Encoding::identity()].iter()),
None
);
let test = accept_encoding!("gzip", "*;q=0");
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::gzip()),
);
assert_eq!(
test.negotiate([Encoding::brotli(), Encoding::identity()].iter()),
None
);
let test = accept_encoding!("gzip", "deflate", "br");
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::gzip()),
);
assert_eq!(
test.negotiate([Encoding::brotli(), Encoding::identity()].iter()),
Some(Encoding::brotli())
);
assert_eq!(
test.negotiate([Encoding::deflate(), Encoding::identity()].iter()),
Some(Encoding::deflate())
);
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::deflate(), Encoding::identity()].iter()),
Some(Encoding::gzip())
);
assert_eq!(
test.negotiate([Encoding::gzip(), Encoding::brotli(), Encoding::identity()].iter()),
Some(Encoding::brotli())
);
assert_eq!(
test.negotiate([Encoding::brotli(), Encoding::gzip(), Encoding::identity()].iter()),
Some(Encoding::brotli())
);
}
#[test]
fn ranking_precedence() {
let test = accept_encoding!();
assert!(test.ranked().is_empty());
let test = accept_encoding!("gzip");
assert_eq!(test.ranked(), vec![enc("gzip")]);
let test = accept_encoding!("gzip;q=0.900", "*;q=0.700", "br;q=1.0");
assert_eq!(test.ranked(), vec![enc("br"), enc("gzip"), enc("*")]);
let test = accept_encoding!("br", "gzip", "*");
assert_eq!(test.ranked(), vec![enc("br"), enc("gzip"), enc("*")]);
let test = accept_encoding!("gzip", "br", "*");
assert_eq!(test.ranked(), vec![enc("br"), enc("gzip"), enc("*")]);
}
#[test]
fn preference_selection() {
assert_eq!(accept_encoding!().preference(), Some(Preference::Any));
assert_eq!(accept_encoding!("identity;q=0").preference(), None);
assert_eq!(accept_encoding!("*;q=0").preference(), None);
assert_eq!(accept_encoding!("compress;q=0", "*;q=0").preference(), None);
assert_eq!(accept_encoding!("identity;q=0", "*;q=0").preference(), None);
let test = accept_encoding!("*;q=0.5");
assert_eq!(test.preference().unwrap(), enc("*"));
let test = accept_encoding!("br;q=0");
assert_eq!(test.preference().unwrap(), enc("identity"));
let test = accept_encoding!("br;q=0.900", "gzip;q=1.0", "*;q=0.500");
assert_eq!(test.preference().unwrap(), enc("gzip"));
let test = accept_encoding!("br", "gzip", "*");
assert_eq!(test.preference().unwrap(), enc("br"));
let test = accept_encoding!("gzip", "br", "*");
assert_eq!(test.preference().unwrap(), enc("br"));
}
}