[router]: Add Embedding routing logic (#10129)

Signed-off-by: Jintao Zhang <zhangjintao9020@gmail.com>
Co-authored-by: Waël Boukhobza <wawa_wael@live.fr>

sgl-router/src/protocols/spec.rs

@@ -41,7 +41,10 @@ use std::collections::HashMap;
 // 6. **SGLANG SPEC - RERANK API**
 //    - Request/Response structures
 //
-// 7. **COMMON**
+// 7. **OPENAI SPEC - Embeddings API**
+//    - Request structures
+//
+// 8. **COMMON**
 //    - GenerationRequest trait
 //    - StringOrArray & LoRAPath types
 //    - Helper functions
@@ -2013,6 +2016,61 @@ impl RerankResponse {
     }
 }
 
+// ==================================================================
+// =            OPENAI SPEC - Embeddings API                        =
+// ==================================================================
+
+/// Embeddings request compatible with OpenAI API
+/// We intentionally keep fields flexible to pass through to workers.
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct EmbeddingRequest {
+    /// ID of the model to use
+    pub model: String,
+
+    /// Input can be a string, array of strings, tokens, or batch inputs
+    pub input: serde_json::Value,
+
+    /// Optional encoding format (e.g., "float", "base64")
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub encoding_format: Option<String>,
+
+    /// Optional user identifier
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub user: Option<String>,
+
+    /// Optional number of dimensions for the embedding
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub dimensions: Option<u32>,
+
+    /// SGLang extension: request id for tracking
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub rid: Option<String>,
+}
+
+impl GenerationRequest for EmbeddingRequest {
+    fn is_stream(&self) -> bool {
+        // Embeddings are non-streaming
+        false
+    }
+
+    fn get_model(&self) -> Option<&str> {
+        Some(&self.model)
+    }
+
+    fn extract_text_for_routing(&self) -> String {
+        // Best effort: extract text content for routing decisions
+        match &self.input {
+            serde_json::Value::String(s) => s.clone(),
+            serde_json::Value::Array(arr) => arr
+                .iter()
+                .filter_map(|v| v.as_str())
+                .collect::<Vec<_>>()
+                .join(" "),
+            _ => String::new(),
+        }
+    }
+}
+
 // ==================================================================
 // =            COMMON                                              =
 // ==================================================================
@@ -2715,4 +2773,102 @@ mod tests {
         assert_eq!(deserialized.results.len(), 2);
         assert_eq!(deserialized.model, response.model);
     }
+
+    // ==================================================================
+    // =            EMBEDDINGS REQUEST TESTS                             =
+    // ==================================================================
+
+    #[test]
+    fn test_embedding_request_serialization_string_input() {
+        let req = EmbeddingRequest {
+            model: "test-emb".to_string(),
+            input: serde_json::Value::String("hello".to_string()),
+            encoding_format: Some("float".to_string()),
+            user: Some("user-1".to_string()),
+            dimensions: Some(128),
+            rid: Some("rid-123".to_string()),
+        };
+
+        let serialized = serde_json::to_string(&req).unwrap();
+        let deserialized: EmbeddingRequest = serde_json::from_str(&serialized).unwrap();
+
+        assert_eq!(deserialized.model, req.model);
+        assert_eq!(deserialized.input, req.input);
+        assert_eq!(deserialized.encoding_format, req.encoding_format);
+        assert_eq!(deserialized.user, req.user);
+        assert_eq!(deserialized.dimensions, req.dimensions);
+        assert_eq!(deserialized.rid, req.rid);
+    }
+
+    #[test]
+    fn test_embedding_request_serialization_array_input() {
+        let req = EmbeddingRequest {
+            model: "test-emb".to_string(),
+            input: serde_json::json!(["a", "b", "c"]),
+            encoding_format: None,
+            user: None,
+            dimensions: None,
+            rid: None,
+        };
+
+        let serialized = serde_json::to_string(&req).unwrap();
+        let de: EmbeddingRequest = serde_json::from_str(&serialized).unwrap();
+        assert_eq!(de.model, req.model);
+        assert_eq!(de.input, req.input);
+    }
+
+    #[test]
+    fn test_embedding_generation_request_trait_string() {
+        let req = EmbeddingRequest {
+            model: "emb-model".to_string(),
+            input: serde_json::Value::String("hello".to_string()),
+            encoding_format: None,
+            user: None,
+            dimensions: None,
+            rid: None,
+        };
+        assert!(!req.is_stream());
+        assert_eq!(req.get_model(), Some("emb-model"));
+        assert_eq!(req.extract_text_for_routing(), "hello");
+    }
+
+    #[test]
+    fn test_embedding_generation_request_trait_array() {
+        let req = EmbeddingRequest {
+            model: "emb-model".to_string(),
+            input: serde_json::json!(["hello", "world"]),
+            encoding_format: None,
+            user: None,
+            dimensions: None,
+            rid: None,
+        };
+        assert_eq!(req.extract_text_for_routing(), "hello world");
+    }
+
+    #[test]
+    fn test_embedding_generation_request_trait_non_text() {
+        let req = EmbeddingRequest {
+            model: "emb-model".to_string(),
+            input: serde_json::json!({"tokens": [1, 2, 3]}),
+            encoding_format: None,
+            user: None,
+            dimensions: None,
+            rid: None,
+        };
+        assert_eq!(req.extract_text_for_routing(), "");
+    }
+
+    #[test]
+    fn test_embedding_generation_request_trait_mixed_array_ignores_nested() {
+        let req = EmbeddingRequest {
+            model: "emb-model".to_string(),
+            input: serde_json::json!(["a", ["b", "c"], 123, {"k": "v"}]),
+            encoding_format: None,
+            user: None,
+            dimensions: None,
+            rid: None,
+        };
+        // Only top-level string elements are extracted
+        assert_eq!(req.extract_text_for_routing(), "a");
+    }
 }