--- title: SendErrorCause summary: The reason that a request sent to a backend failed. url: https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/request/enum.SendErrorCause/ --- **Kind:** Enum **Module:** [request](https://www.fastly.com/documentation/reference/compute/sdks/rust/fastly/http/request/) **Package:** fastly 0.13.1 **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/http/request.rs#3215 ```rust #[non_exhaustive] pub enum SendErrorCause { DnsTimeout, DnsError { rcode: Option, info_code: Option, }, DestinationNotFound, DestinationUnavailable, DestinationIpUnroutable, ConnectionRefused, ConnectionTerminated, ConnectionTimeout, ConnectionLimitReached, TlsProtocolError, TlsCertificateError, TlsAlertReceived { alert_id: Option, }, TlsConfigurationError, HttpIncompleteResponse, HttpResponseHeaderSectionTooLarge, HttpResponseBodyTooLarge, HttpResponseTimeout, HttpResponseStatusInvalid, HttpUpgradeFailed, Http2StreamError { frame_type: u8, error_code: u32, }, HttpProtocolError, HttpRequestCacheKeyInvalid, HttpRequestUriInvalid, HttpCacheLimitExceeded, HttpCacheApiUnsupported, IoError(Error), FanoutNotEnabled, ImageOptimizerUnsupported, InternalError(Option), RequestCollapse, Custom(Error), } ``` The reason that a request sent to a backend failed. ## Variants ### DnsTimeout The system encountered a timeout when trying to find an IP address for the backend hostname. ### DnsError - `rcode`: `Option` - `info_code`: `Option` The system encountered a DNS error when trying to find an IP address for the backend hostname. The `rcode` and `info_code` fields may be set with more detail. ### DestinationNotFound The system cannot determine which backend to use, or the specified backend was invalid. ### DestinationUnavailable The system considers the backend to be unavailable; e.g., recent attempts to communicate with it may have failed, or a health check may indicate that it is down. ### DestinationIpUnroutable The system cannot find a route to the next-hop IP address. ### ConnectionRefused The system's connection to the backend was refused. ### ConnectionTerminated The system's connection to the backend was closed before a complete response was received. ### ConnectionTimeout The system's attempt to open a connection to the backend timed out. ### ConnectionLimitReached The system is configured to limit the number of connections it has to the backend, and that limit has been exceeded. ### TlsProtocolError The system encountered a TLS error when communicating with the backend, either during the handshake or afterwards. ### TlsCertificateError The system encountered an error when verifying the certificate presented by the backend. ### TlsAlertReceived - `alert_id`: `Option` The system received a TLS alert from the backend. The `alert_id` field will specific which alert occurred. ### TlsConfigurationError The system encountered an error with the backend TLS configuration. ### HttpIncompleteResponse The system received an incomplete response to the request from the backend. ### HttpResponseHeaderSectionTooLarge The system received a response to the request whose header section was considered too large. ### HttpResponseBodyTooLarge The system received a response to the request whose body was considered too large. ### HttpResponseTimeout The system reached a configured time limit waiting for the complete response. ### HttpResponseStatusInvalid The system received a response to the request whose status code or reason phrase was invalid. ### HttpUpgradeFailed The process of negotiating an upgrade of the HTTP version between the system and backend failed. ### Http2StreamError - `frame_type`: `u8` - `error_code`: `u32` The system received an unexpected HTTP/2 error response from the backend. ### HttpProtocolError The system encountered an HTTP protocol error when communicating with the backend. This error will only be used when a more specific one is not defined. ### HttpRequestCacheKeyInvalid An invalid cache key was provided for the request. ### HttpRequestUriInvalid An invalid URI was provided for the request. ### HttpCacheLimitExceeded A caching limit was reached. ### HttpCacheApiUnsupported A caching limit was reached. ### IoError - `0`: `std::io::Error` An I/O error was encountered. ### FanoutNotEnabled Fanout/WebSocket features are not enabled on this service. ### ImageOptimizerUnsupported Image Optimizer is not supported on this service. ### InternalError - `0`: `Option` The system encountered an unexpected internal error. ### RequestCollapse This should only occur for "followers" of a request collapse; the leader sees the original error. ### Custom - `0`: `anyhow::Error` A custom error occurred while processing the request. ## Trait implementations ### impl Debug for SendErrorCause #### fmt **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/http/request.rs#3214 ```rust fn fmt(&self, f: &mut Formatter<'_>) -> Result ``` **Parameters** - `self`: `&Self` - `f`: `&mut $crate::fmt::Formatter` **Returns** `$crate::fmt::Result` ### impl Display for SendErrorCause #### fmt **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/http/request.rs#3214 ```rust fn fmt(&self, __formatter: &mut Formatter<'_>) -> Result ``` **Parameters** - `self`: `&Self` - `__formatter`: `&mut ::core::fmt::Formatter` **Returns** `::core::fmt::Result` ### impl Error for SendErrorCause #### source **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/http/request.rs#3214 ```rust fn source(&self) -> Option<&(dyn Error + 'static)> ``` **Parameters** - `self`: `&Self` **Returns** `::core::option::Option<&(dyn Error + 'static)>` ### impl From for SendErrorCause #### from **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/http/request.rs#3214 ```rust fn from(source: Error) -> Self ``` **Parameters** - `source`: `std::io::Error` **Returns** `Self` ### impl From for SendErrorCause #### from **Source:** https://docs.rs/crate/fastly/0.13.1/source/src/http/request.rs#3580 ```rust fn from(err: SendError) -> Self ``` **Parameters** - `err`: `SendError` **Returns** `Self` ## Auto trait implementations - `Freeze` - `RefUnwindSafe` - `Send` - `Sync` - `Unpin` - `UnsafeUnpin` - `UnwindSafe` ## Blanket implementations - `Any` - `Borrow` - `BorrowMut` - `Downcast` - `DowncastSync` - `ErasedDestructor` - `From` - `Into` - `IntoEither` - `Same` - `ToString` - `TryFrom` - `TryInto`