Struct ETag 

pub struct ETag(/* private fields */);

An entity tag naming the version of what a page shows: weak (W/"<hash>", the default) or strong ("<hash>").

Build it from everything the page displays, so it changes when the page would: the records, plus the locale, the signed-in user and the flash when the page shows them. The value is the first 128 bits of a SHA-256, as 32 hex characters. It implements [IntoResponseParts] (sets ETag); pass it to Conditional::fresh_when to answer 304s. Like Rails, tags are weak unless built with strong.

Examples

use ocre::cache::ETag;

let a = ETag::new("post-42-1767225600");
assert_eq!(a, ETag::new("post-42-1767225600"));
assert_ne!(a, ETag::new("post-42-1767225601"));
assert!(a.as_str().starts_with("W/\""));

Implementations

impl ETag

pub fn new(version: impl AsRef<[u8]>) -> Self

A tag for a version string you build, e.g. format!("{}-{}", post.id, post.updated_at).

Cheaper than of for large data: only version is hashed.

Examples

let etag = ocre::cache::ETag::new("v1");
assert_eq!(etag.as_str().len(), 36); // W/" + 32 hex + "

pub fn strong(version: impl AsRef<[u8]>) -> Self

A strong tag ("<hash>", Rails’ strong_etag:) for a version string you build.

A strong tag promises that two responses with the same tag are byte-for-byte identical, which caches and range requests rely on; use it for a file or an exact body, not for a page whose HTML may vary (nonces, CSRF tokens). If-None-Match compares weakly, so a strong tag also answers 304s through Conditional.

Examples

use ocre::cache::ETag;

let etag = ETag::strong("report-2026-09.csv");
assert!(etag.as_str().starts_with('"'));
assert_eq!(etag.as_str().len(), 34); // " + 32 hex + "
assert!(etag.is_strong() && !ETag::new("x").is_strong());

pub fn is_strong(&self) -> bool

Whether the tag is strong (built with strong).

Examples

assert!(!ocre::cache::ETag::new("v1").is_strong());

pub fn of<T: Serialize + ?Sized>(data: &T) -> Result<Self>

A tag for any serializable data, hashed as its JSON: ETag::of(&(&posts, i18n.locale()))?.

Errors

Error::Internal (500) when data does not serialize to JSON (e.g. a map with non-string keys).

Examples

use ocre::cache::ETag;
assert_eq!(ETag::of(&("Ada", 1))?, ETag::of(&("Ada", 1))?);
assert_ne!(ETag::of(&("Ada", 1))?, ETag::of(&("Ada", 2))?);

pub fn as_str(&self) -> &str

The header value, W/"<32 hex characters>" (weak) or "<32 hex characters>" (strong).

Examples

let etag = ocre::cache::ETag::new("v1");
assert!(etag.as_str().starts_with("W/\"") && etag.as_str().ends_with('"'));

Trait Implementations

impl Clone for ETag

fn clone(&self) -> ETag

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ETag

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for ETag

impl IntoResponseParts for ETag

type Error = Infallible

The type returned in the event of an error.

fn into_response_parts( self, res: ResponseParts, ) -> Result<ResponseParts, Self::Error>

Set parts of the response

impl PartialEq for ETag

fn eq(&self, other: &ETag) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for ETag