fix: add cls pooling as default for BERT variants (#426)

Author: OlivierDehaene

router/src/lib.rs

@@ -91,13 +91,20 @@ pub async fn run(
         // Optionally download the pooling config.
         if pooling.is_none() {
             // If a pooling config exist, download it
-            let _ = download_pool_config(&api_repo).await;
+            let _ = download_pool_config(&api_repo).await.map_err(|err| {
+                tracing::warn!("Download failed: {err}");
+                err
+            });
         }
 
-        // Download sentence transformers config
+        // Download legacy sentence transformers config
+        // We don't warn on failure as it is a legacy file
         let _ = download_st_config(&api_repo).await;
         // Download new sentence transformers config
-        let _ = download_new_st_config(&api_repo).await;
+        let _ = download_new_st_config(&api_repo).await.map_err(|err| {
+            tracing::warn!("Download failed: {err}");
+            err
+        });
 
         // Download model from the Hub
         download_artifacts(&api_repo)
@@ -387,10 +394,21 @@ fn get_backend_model_type(
         None => {
             // Load pooling config
             let config_path = model_root.join("1_Pooling/config.json");
-            let config = fs::read_to_string(config_path).context("The `--pooling` arg is not set and we could not find a pooling configuration (`1_Pooling/config.json`) for this model.")?;
-            let config: PoolConfig =
-                serde_json::from_str(&config).context("Failed to parse `1_Pooling/config.json`")?;
-            Pool::try_from(config)?
+
+            match fs::read_to_string(config_path) {
+                Ok(config) => {
+                    let config: PoolConfig = serde_json::from_str(&config)
+                        .context("Failed to parse `1_Pooling/config.json`")?;
+                    Pool::try_from(config)?
+                }
+                Err(err) => {
+                    if !config.model_type.to_lowercase().contains("bert") {
+                        return Err(err).context("The `--pooling` arg is not set and we could not find a pooling configuration (`1_Pooling/config.json`) for this model.");
+                    }
+                    tracing::warn!("The `--pooling` arg is not set and we could not find a pooling configuration (`1_Pooling/config.json`) for this model but the model is a BERT variant. Defaulting to `CLS` pooling.");
+                    text_embeddings_backend::Pool::Cls
+                }
+            }
         }
     };
     Ok(text_embeddings_backend::ModelType::Embedding(pool))