--- title: Replace summary: An in-progress Replace operation. url: https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Replace/ --- **Kind:** Struct **Module:** [core](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/) **Package:** fastly 0.13.1 **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#193 ```rust pub struct Replace { /* private fields */ } ``` An in-progress Replace operation. ## Methods ### deliver_node_max_age **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#226 ```rust fn deliver_node_max_age(self, duration: Duration) -> Self ``` Sets the maximum time the cached item may live on a deliver node in a POP. **Parameters** - `self`: `Self` - `duration`: `Duration` **Returns** `Self` ### execute **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#205 ```rust fn execute(self, max_age: Duration) -> Result ``` Finish using the existing object and start writing a replacement object to the [`StreamingBody`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/body/struct.StreamingBody/). The required `max_age` argument is the "time to live" for the replacement cache item: the time for which the item will be considered fresh, starting from the start of its history (now, unless `initial_age` was provided). **Parameters** - `self`: `Self` - `max_age`: `Duration` **Returns** `Result` ### existing_object **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#234 ```rust fn existing_object(&self) -> Option<&Found> ``` The existing object, if one exists. The existing object may be stale. **Parameters** - `self`: `&Self` **Returns** `Option<&Found>` ### header **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#242 ```rust fn header(self, name: impl ToHeaderName, value: impl ToHeaderValue) -> Self ``` Sets a single-value header for the replacement object, discarding any previous values associated with the header `name`. **Note**: These headers are narrowly useful for implementing cache lookups incorporating the semantics of the [HTTP `Vary` header](https://www.rfc-editor.org/rfc/rfc9110#section-12.5.5), but the APIs in this module are not suitable for HTTP caching out-of-the-box. Future SDK releases will contain an HTTP Cache API. The headers act as additional factors in object selection, and the choice of _which_ headers to factor in is determined during insertion, via e.g. [`crate::cache::core::InsertBuilder::vary_by`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.InsertBuilder/#method-vary_by). A lookup will succeed when there is at least one cached item that matches lookup's cache key, and all of the lookup's headers included in the cache items' `vary_by` list match the corresponding headers in that cached item. A [typical example](https://www.fastly.com/blog/best-practices-using-vary-header) is a cached HTTP response, where the request had an `Accept-Encoding` header. In that case, the origin server may or may not decide on a given encoding, and whether that same response is suitable for a request with a different (or missing) `Accept-Encoding` header is determined by whether `Accept-Encoding` is listed in `Vary` header in the origin's response. **Parameters** - `self`: `Self` - `name`: `impl ToHeaderName` - `value`: `impl ToHeaderValue` **Returns** `Self` ### header_values **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#250 ```rust fn header_values<'a>(self, name: impl ToHeaderName, values: impl IntoIterator) -> Self ``` Sets a multi-value header for the replacement object, discarding any previous values associated with the header `name`. **Note**: These headers are narrowly useful for implementing cache lookups incorporating the semantics of the [HTTP `Vary` header](https://www.rfc-editor.org/rfc/rfc9110#section-12.5.5), but the APIs in this module are not suitable for HTTP caching out-of-the-box. Future SDK releases will contain an HTTP Cache API. The headers act as additional factors in object selection, and the choice of _which_ headers to factor in is determined during insertion, via e.g. [`crate::cache::core::InsertBuilder::vary_by`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.InsertBuilder/#method-vary_by). A lookup will succeed when there is at least one cached item that matches lookup's cache key, and all of the lookup's headers included in the cache items' `vary_by` list match the corresponding headers in that cached item. A [typical example](https://www.fastly.com/blog/best-practices-using-vary-header) is a cached HTTP response, where the request had an `Accept-Encoding` header. In that case, the origin server may or may not decide on a given encoding, and whether that same response is suitable for a request with a different (or missing) `Accept-Encoding` header is determined by whether `Accept-Encoding` is listed in `Vary` header in the origin's response. **Parameters** - `self`: `Self` - `name`: `impl ToHeaderName` - `values`: `impl IntoIterator` **Returns** `Self` ### initial_age **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#265 ```rust fn initial_age(self, age: Duration) -> Self ``` Sets the initial age of the cached item, to be used in freshness calculations. The initial age is `Duration::ZERO` by default. **Parameters** - `self`: `Self` - `age`: `Duration` **Returns** `Self` ### known_length **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#271 ```rust fn known_length(self, length: u64) -> Self ``` Sets the size of the cached item, in bytes, when known prior to actually providing the bytes. It is preferable to provide a length, if possible. Clients that begin streaming the item's contents before it is completely provided will see the promised length which allows them to, for example, use `content-length` instead of `transfer-encoding: chunked` if the item is used as the body of a [`Request`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/request/struct.Request/) or [`Response`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/struct.Response/). **Parameters** - `self`: `Self` - `length`: `u64` **Returns** `Self` ### sensitive_data **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#277 ```rust fn sensitive_data(self, is_sensitive_data: bool) -> Self ``` Enable or disable PCI/HIPAA-compliant non-volatile caching. By default, this is `false` See the [Fastly PCI-Compliant Caching and Delivery documentation](https://docs.fastly.com/products/pci-compliant-caching-and-delivery) for details. **Parameters** - `self`: `Self` - `is_sensitive_data`: `bool` **Returns** `Self` ### stale_while_revalidate **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#283 ```rust fn stale_while_revalidate(self, duration: Duration) -> Self ``` Sets the stale-while-revalidate period for the cached item, which is the time for which the item can be safely used despite being considered stale. Having a stale-while-revalidate period provides a signal that the cache should be updated (or its contents otherwise revalidated for freshness) asynchronously, while the stale cached item continues to be used, rather than blocking on updating the cached item. The methods [`Found::is_usable`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Found/#method-is_usable) and [`Found::is_stale`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Found/#method-is_stale) can be used to determine the current state of a found item. The stale-while-revalidate period is `Duration::ZERO` by default. **Parameters** - `self`: `Self` - `duration`: `Duration` **Returns** `Self` ### surrogate_keys **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#289 ```rust fn surrogate_keys<'a>(self, keys: impl IntoIterator) -> Self ``` Sets the surrogate keys that can be used for purging this cached item. [Surrogate key purges](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/purge/fn.purge_surrogate_key/) are the only means to purge specific items from the cache. At least one surrogate key must be set in order to remove an item without performing a [purge-all](https://developer.fastly.com/learning/concepts/purging/#purge-all), waiting for the item's TTL to elapse, or overwriting the item with [`crate::cache::core::insert()`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/fn.insert/). Surrogate keys must contain only printable ASCII characters (those between 0x21 and 0x7E, inclusive). Any invalid keys will be ignored. See the [Fastly surrogate keys guide](https://docs.fastly.com/en/guides/purging-api-cache-with-surrogate-keys) for details. **Parameters** - `self`: `Self` - `keys`: `impl IntoIterator` **Returns** `Self` ### user_metadata **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#295 ```rust fn user_metadata(self, user_metadata: Bytes) -> Self ``` Sets the user-defined metadata to associate with the cached item. **Parameters** - `self`: `Self` - `user_metadata`: `Bytes` **Returns** `Self` ### vary_by **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#303 ```rust fn vary_by<'a>(self, headers: impl IntoIterator) -> Self ``` Sets the list of headers that must match when looking up this cached item. **Note**: These headers are narrowly useful for implementing cache lookups incorporating the semantics of the [HTTP `Vary` header](https://www.rfc-editor.org/rfc/rfc9110#section-12.5.5), but the APIs in this module are not suitable for HTTP caching out-of-the-box. Future SDK releases will contain an HTTP Cache API. The headers act as additional factors in object selection, and the choice of _which_ headers to factor in is determined during insertion, via e.g. [`crate::cache::core::InsertBuilder::vary_by`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.InsertBuilder/#method-vary_by). A lookup will succeed when there is at least one cached item that matches lookup's cache key, and all of the lookup's headers included in the cache items' `vary_by` list match the corresponding headers in that cached item. A [typical example](https://www.fastly.com/blog/best-practices-using-vary-header) is a cached HTTP response, where the request had an `Accept-Encoding` header. In that case, the origin server may or may not decide on a given encoding, and whether that same response is suitable for a request with a different (or missing) `Accept-Encoding` header is determined by whether `Accept-Encoding` is listed in `Vary` header in the origin's response. **Parameters** - `self`: `Self` - `headers`: `impl IntoIterator` **Returns** `Self` ## Auto trait implementations - `Freeze` - `RefUnwindSafe` - `Send` - `Sync` - `Unpin` - `UnsafeUnpin` - `UnwindSafe` ## Blanket implementations - `Any` - `Borrow` - `BorrowMut` - `Downcast` - `DowncastSync` - `ErasedDestructor` - `From` - `Into` - `IntoEither` - `Same` - `TryFrom` - `TryInto`