[router] add worker abstraction (#7960)

sgl-router/src/core/error.rs

@@ -0,0 +1,57 @@
+//! Error types for the SGLang router core
+//!
+//! This module defines error types used throughout the router for worker operations.
+
+use std::fmt;
+
+/// Worker-related errors
+#[derive(Debug)]
+pub enum WorkerError {
+    /// Health check failed
+    HealthCheckFailed { url: String, reason: String },
+    /// Worker not found
+    WorkerNotFound { url: String },
+    /// Invalid worker configuration
+    InvalidConfiguration { message: String },
+    /// Network error
+    NetworkError { url: String, error: String },
+    /// Worker is at capacity
+    WorkerAtCapacity { url: String },
+}
+
+impl fmt::Display for WorkerError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            WorkerError::HealthCheckFailed { url, reason } => {
+                write!(f, "Health check failed for worker {}: {}", url, reason)
+            }
+            WorkerError::WorkerNotFound { url } => {
+                write!(f, "Worker not found: {}", url)
+            }
+            WorkerError::InvalidConfiguration { message } => {
+                write!(f, "Invalid worker configuration: {}", message)
+            }
+            WorkerError::NetworkError { url, error } => {
+                write!(f, "Network error for worker {}: {}", url, error)
+            }
+            WorkerError::WorkerAtCapacity { url } => {
+                write!(f, "Worker at capacity: {}", url)
+            }
+        }
+    }
+}
+
+impl std::error::Error for WorkerError {}
+
+/// Result type for worker operations
+pub type WorkerResult<T> = Result<T, WorkerError>;
+
+/// Convert from reqwest errors to worker errors
+impl From<reqwest::Error> for WorkerError {
+    fn from(err: reqwest::Error) -> Self {
+        WorkerError::NetworkError {
+            url: err.url().map(|u| u.to_string()).unwrap_or_default(),
+            error: err.to_string(),
+        }
+    }
+}