switchyard_protocol/
client.rs

1// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
2// SPDX-License-Identifier: Apache-2.0
3
4//! The routed-call server trait and its shared error types.
5//!
6//! [`RoutedLlmClient`] is the one piece of I/O the protocol does not own: a host
7//! implements it to actually perform a model call. It lives here — rather than in
8//! libsy's orchestration crate — so a client crate that depends only on the protocol
9//! can serve routed calls without pulling in the orchestrator.
10
11use async_trait::async_trait;
12use thiserror::Error;
13
14use crate::{ModelId, Request, Response};
15
16/// A boxed client-specific error preserved as the source of a routed call failure.
17pub type BoxError = Box<dyn std::error::Error + Send + Sync + 'static>;
18
19/// Failures a routed LLM client can surface to its caller.
20///
21/// The variants classify failures that routing hosts commonly need to handle,
22/// while boxed sources preserve implementation-specific detail. `General` is the
23/// escape hatch for failures that do not fit a shared category.
24#[non_exhaustive]
25#[derive(Debug, Error)]
26pub enum LlmClientError {
27    /// The request cannot be served as supplied.
28    #[error("invalid request: {message}")]
29    InvalidRequest {
30        /// Human-readable request validation failure.
31        message: String,
32    },
33
34    /// Decoding the inbound request failed in the translation engine.
35    #[error("request translation failed: {0}")]
36    RequestTranslation(String),
37
38    /// Encoding the request for the upstream failed in the translation engine.
39    #[error("outbound request encoding failed: {0}")]
40    RequestEncoding(String),
41
42    /// Decoding or encoding the response failed in the translation engine.
43    #[error("response translation failed: {0}")]
44    ResponseTranslation(String),
45
46    /// The client is not configured to serve the selected target.
47    #[error("client configuration error: {message}")]
48    Configuration {
49        /// Human-readable configuration failure.
50        message: String,
51    },
52
53    /// The upstream could not be reached or the request could not be sent.
54    #[error("upstream transport error: {source}")]
55    Transport {
56        /// Client-specific transport failure.
57        #[source]
58        source: BoxError,
59    },
60
61    /// The upstream request exceeded its timeout.
62    #[error("upstream request timed out: {source}")]
63    Timeout {
64        /// Client-specific timeout failure.
65        #[source]
66        source: BoxError,
67    },
68
69    /// The upstream rejected the request because it exceeds the model's context window.
70    #[error("context window exceeded for model {model}: {message}")]
71    ContextWindowExceeded {
72        /// Model whose context window was exceeded.
73        model: ModelId,
74        /// Upstream error message.
75        message: String,
76    },
77
78    /// The upstream returned a non-success HTTP response.
79    #[error("upstream returned HTTP {status}: {body}")]
80    UpstreamHttp {
81        /// Upstream HTTP status code.
82        status: http::StatusCode,
83        /// Raw upstream error body.
84        body: String,
85    },
86
87    /// The upstream returned a response the client could not decode.
88    #[error("invalid upstream response: {source}")]
89    InvalidResponse {
90        /// Client-specific decoding or validation failure.
91        #[source]
92        source: BoxError,
93    },
94
95    /// A call across a foreign-function boundary (e.g. a Python-implemented client)
96    /// failed. The boxed source is the foreign error itself.
97    #[error("foreign function interface error: {source}")]
98    Ffi {
99        /// Foreign-language failure, preserved verbatim.
100        #[source]
101        source: BoxError,
102    },
103
104    /// A string message. Useful in testing, but prefer adding variants over using this.
105    #[error("{0}")]
106    General(String),
107}
108
109/// Why routing replaced a selected target with another eligible target.
110#[derive(Clone, Copy, Debug, Eq, PartialEq)]
111pub enum RoutingFallbackReason {
112    /// The selected target rejected the request because its context window was too small.
113    ContextWindow,
114    /// The selected target was unavailable after its client retries finished.
115    Unavailable,
116}
117
118impl RoutingFallbackReason {
119    /// Stable value used when logging a routing fallback.
120    pub const fn as_str(self) -> &'static str {
121        match self {
122            Self::ContextWindow => "context_window",
123            Self::Unavailable => "unavailable",
124        }
125    }
126}
127
128/// Performs the actual model call for a target. This is the one piece of I/O the
129/// library does not own — a host implements it over its own transport (HTTP SDK,
130/// in-process model, mock). It serves a call the stream consumer chose not to
131/// override, reached as a routed request's `default_client`.
132///
133/// # Concurrency
134///
135/// A client may be shared by many targets and concurrent algorithm runs. Calls may
136/// overlap, so implementations must synchronize mutable state internally and should
137/// not serialize requests unless their transport requires it.
138#[async_trait]
139pub trait RoutedLlmClient: Send + Sync {
140    /// Make a request
141    async fn call(&self, request: Request) -> Result<Response, LlmClientError>;
142}
switchyard_protocol/client.rs

switchyard_protocol/
client.rs
