--- title: ReplaceBuilder summary: A builder-style API for configuring a non-transactional replace. url: https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.ReplaceBuilder/ --- **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#65 ```rust pub struct ReplaceBuilder { /* private fields */ } ``` A builder-style API for configuring a non-transactional replace. ## Methods ### always_use_requested_range **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#186 ```rust fn always_use_requested_range(self) -> Self ``` Respect the range in `to_stream_with_range` even when the body length is not yet known. When a cache item is `Found`, the length of the cached item may or may not be known: - the item may be fully cached; - the item may be streaming in, but have a known length; or - the item may be streaming in progressively, **without a known length**. By default (legacy behavior), if a range is specified but the length is not known, the contents of the entire item will be provided instead of the requested range. `always_use_requested_range` indicates any cached item returned by this lookup should provide only the requested range, regardless of whether the length is known. An invalid range will eventually return a read error, possibly after providing some data. **NOTE:** In the future, the `always_use_requested_range` behavior will be the default, and this method will be removed. **Parameters** - `self`: `Self` **Returns** `Self` ### begin **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#132 ```rust fn begin(self) -> Result ``` Begin the replace, returning a [`Replace`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Replace/) for reading the object to be replaced (if it exists) which is also used to provide the new replacement object. A [`Replace`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Replace/) gives access to the existing object, if one is stored, that may be used to construct the replacement object. Use [`Replace::execute()`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Replace/#method-execute) to get a [`StreamingBody`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/body/struct.StreamingBody/) to write the replacement object into. The existing object cannot be accessed after calling [`Replace::execute()`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/struct.Replace/#method-execute). For the replace to complete successfully, the object must be written into the [`StreamingBody`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/body/struct.StreamingBody/), and then [`StreamingBody::finish()`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/body/struct.StreamingBody/#method-finish) must be called. If the [`StreamingBody`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/body/struct.StreamingBody/) is dropped before calling [`StreamingBody::finish()`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/body/struct.StreamingBody/#method-finish), the replacement is considered incomplete, and any concurrent lookups that may be reading from the object as it is streamed into the cache may encounter a streaming error. **Parameters** - `self`: `Self` **Returns** `Result` ### header **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#157 ```rust fn header(self, name: impl ToHeaderName, value: impl ToHeaderValue) -> Self ``` Sets a single-value header for looking up an existing object to replace, 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#165 ```rust fn header_values<'a>(self, name: impl ToHeaderName, values: impl IntoIterator) -> Self ``` Sets a multi-value header for looking up an existing object to replace, 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` ### replace_strategy **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/cache/core/replace.rs#180 ```rust fn replace_strategy(self, strategy: ReplaceStrategy) -> Self ``` Sets the strategy for performing the replace. See [`ReplaceStrategy`](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/cache/core/enum.ReplaceStrategy/) for details. **Parameters** - `self`: `Self` - `strategy`: `ReplaceStrategy` **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`