From 1bbbb7903caf010231bec7888b8bf2c4ee38927a Mon Sep 17 00:00:00 2001
From: Quentin Fuxa <quentin.fuxa@gmail.com>
Date: Sun, 16 Nov 2025 18:44:35 +0100
Subject: [PATCH] lora loader in shared whisper core

---
 whisperlivekit/whisper/__init__.py | 94 +++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 3 deletions(-)

diff --git a/whisperlivekit/whisper/__init__.py b/whisperlivekit/whisper/__init__.py
index 751020a..8ae68c9 100644
--- a/whisperlivekit/whisper/__init__.py
+++ b/whisperlivekit/whisper/__init__.py
@@ -4,11 +4,12 @@ import json
 import os
 import urllib
 import warnings
-from typing import List, Optional, Union, Dict
+from typing import Dict, List, Optional, Union
 
 import torch
 from tqdm import tqdm
 from pathlib import Path
+from torch import Tensor
 
 from .audio import load_audio, log_mel_spectrogram, pad_or_trim
 from .decoding import DecodingOptions, DecodingResult, decode, detect_language
@@ -233,13 +234,97 @@ def _convert_hf_state_dict(state_dict: Dict[str, torch.Tensor]) -> Dict[str, tor
     return converted if converted else state_dict
 
 
+def _load_lora_state(lora_path: str):
+    safe_path = os.path.join(lora_path, "adapter_model.safetensors")
+    bin_path = os.path.join(lora_path, "adapter_model.bin")
+    if os.path.isfile(safe_path):
+        try:
+            from safetensors.torch import load_file
+        except ImportError as exc:
+            raise ImportError(
+                "Loading LoRA adapters stored as .safetensors requires the `safetensors` package."
+            ) from exc
+        return load_file(safe_path)
+    if os.path.isfile(bin_path):
+        return torch.load(bin_path, map_location="cpu")
+    raise FileNotFoundError(
+        f"No adapter weights found under {lora_path}. Expected adapter_model.safetensors or adapter_model.bin."
+    )
+
+
+def _collapse_hf_module_name(module: str):
+    if module.startswith("base_model."):
+        module = module[len("base_model.") :]
+    if module.startswith("model.model."):
+        module = module[len("model.") :]
+    if not module.startswith("model."):
+        module = f"model.{module}"
+    return module
+
+
+def _apply_lora_adapter(state_dict: Dict[str, Tensor], lora_path: Optional[str]):
+    if not lora_path:
+        return
+
+    config_path = os.path.join(lora_path, "adapter_config.json")
+    if not os.path.isfile(config_path):
+        raise FileNotFoundError(f"Missing adapter_config.json inside {lora_path}")
+    with open(config_path, "r", encoding="utf-8") as handle:
+        config = json.load(handle)
+    if config.get("peft_type") != "LORA":
+        raise ValueError("Only LoRA adapters are supported.")
+
+    r = config.get("r")
+    alpha = config.get("lora_alpha") or config.get("alpha")
+    if not r or not alpha:
+        raise ValueError("LoRA config must include `r` and `lora_alpha`.")
+    scaling = alpha / r
+
+    adapter_state = _load_lora_state(lora_path)
+    lora_layers: Dict[str, Dict[str, Tensor]] = {}
+    for key, tensor in adapter_state.items():
+        if key.endswith("lora_A.weight"):
+            module = key[: -len(".lora_A.weight")]
+            lora_layers.setdefault(module, {})["A"] = tensor
+        elif key.endswith("lora_B.weight"):
+            module = key[: -len(".lora_B.weight")]
+            lora_layers.setdefault(module, {})["B"] = tensor
+
+    if not lora_layers:
+        raise ValueError(f"No LoRA tensors found in {lora_path}")
+
+    for module, parts in lora_layers.items():
+        if "A" not in parts or "B" not in parts:
+            raise ValueError(f"Incomplete LoRA tensors for module '{module}'")
+
+        hf_module = _collapse_hf_module_name(module)
+        hf_weight_key = f"{hf_module}.weight"
+
+        delta = parts["B"] @ parts["A"]
+        delta = delta * scaling
+
+        converted = _convert_hf_state_dict({hf_weight_key: delta})
+        if not converted:
+            raise KeyError(f"Failed to map LoRA module '{module}' into Whisper state dict.")
+        target_name, delta_tensor = next(iter(converted.items()))
+        if target_name not in state_dict:
+            raise KeyError(
+                f"LoRA module '{module}' mapped to '{target_name}', but the base model has no such parameter."
+            )
+
+        state_dict[target_name] = state_dict[target_name] + delta_tensor.to(
+            dtype=state_dict[target_name].dtype, device=state_dict[target_name].device
+        )
+
+
 def load_model(
     name: str,
     device: Optional[Union[str, torch.device]] = None,
     download_root: str = None,
     in_memory: bool = False,
-    decoder_only=False,
-    custom_alignment_heads=None
+    decoder_only: bool = False,
+    custom_alignment_heads: Optional[str] = None,
+    lora_path: Optional[str] = None,
 ) -> Whisper:
     """
     Load a Whisper ASR model
@@ -255,6 +340,8 @@ def load_model(
         path to download the model files; by default, it uses "~/.cache/whisper"
     in_memory: bool
         whether to preload the model weights into host memory
+    lora_path: str
+        optional directory containing PEFT LoRA adapter weights (adapter_config + adapter_model)
 
     Returns
     -------
@@ -302,6 +389,7 @@ def load_model(
     else:
         state_dict = checkpoint
     state_dict = _convert_hf_state_dict(state_dict)
+    _apply_lora_adapter(state_dict, lora_path)
 
     if dims_cfg is not None:
         dims = ModelDimensions(**dims_cfg)