convert : ability to lazy-load safetensors remotely without downloading to disk (#12820)

* gguf util : add SafetensorRemote

* fix style

* convert: add --remote option

* convert : allow using lazy remote tensors

It's a bit slow for now since everything is blocking and single-threaded.

* correct metadata.name

* small style fix

* support HF_TOKEN

* convert : use writeable buffer for remote lazy tensors

* convert : fix flake8 lint regarding lamdba assigment

* multithreaded download

* multithread: print debug

* fix style

* Revert "multithreaded download"

This reverts commit 42fc895ace.

* bring back _get_request_headers

---------

Co-authored-by: Francis Couture-Harpin <git@compilade.net>

gguf-py/gguf/utility.py

@@ -1,7 +1,11 @@
 from __future__ import annotations
 
+from dataclasses import dataclass
 from typing import Literal
 
+import os
+import json
+
 
 def fill_templated_filename(filename: str, output_type: str | None) -> str:
     # Given a file name fill in any type templates e.g. 'some-model-name.{ftype}.gguf'
@@ -67,3 +71,194 @@ def naming_convention(model_name: str | None, base_name: str | None, finetune_st
     kind = f"-{model_type.strip().replace(' ', '-')}" if model_type is not None else ""
 
     return f"{name}{parameters}{finetune}{version}{encoding}{kind}"
+
+
+@dataclass
+class RemoteTensor:
+    dtype: str
+    shape: tuple[int, ...]
+    offset_start: int
+    size: int
+    url: str
+
+    def data(self) -> bytearray:
+        # TODO: handle request errors (maybe with limited retries?)
+        # NOTE: using a bytearray, otherwise PyTorch complains the buffer is not writeable
+        data = bytearray(SafetensorRemote.get_data_by_range(url=self.url, start=self.offset_start, size=self.size))
+        return data
+
+
+class SafetensorRemote:
+    """
+    Uility class to handle remote safetensor files.
+    This class is designed to work with Hugging Face model repositories.
+
+    Example (one model has single safetensor file, the other has multiple):
+        for model_id in ["ngxson/TEST-Tiny-Llama4", "Qwen/Qwen2.5-7B-Instruct"]:
+            tensors = SafetensorRemote.get_list_tensors_hf_model(model_id)
+            print(tensors)
+
+    Example reading tensor data:
+        tensors = SafetensorRemote.get_list_tensors_hf_model(model_id)
+        for name, meta in tensors.items():
+            dtype, shape, offset_start, size, remote_safetensor_url = meta
+            # read the tensor data
+            data = SafetensorRemote.get_data_by_range(remote_safetensor_url, offset_start, size)
+            print(data)
+    """
+
+    BASE_DOMAIN = "https://huggingface.co"
+    ALIGNMENT = 8 # bytes
+
+    @classmethod
+    def get_list_tensors_hf_model(cls, model_id: str) -> dict[str, RemoteTensor]:
+        """
+        Get list of tensors from a Hugging Face model repository.
+
+        Returns a dictionary of tensor names and their metadata.
+        Each tensor is represented as a tuple of (dtype, shape, offset_start, size, remote_safetensor_url)
+        """
+        # case 1: model has only one single model.safetensor file
+        is_single_file = cls.check_file_exist(f"{cls.BASE_DOMAIN}/{model_id}/resolve/main/model.safetensors")
+        if is_single_file:
+            url = f"{cls.BASE_DOMAIN}/{model_id}/resolve/main/model.safetensors"
+            return cls.get_list_tensors(url)
+
+        # case 2: model has multiple files
+        index_url = f"{cls.BASE_DOMAIN}/{model_id}/resolve/main/model.safetensors.index.json"
+        is_multiple_files = cls.check_file_exist(index_url)
+        if is_multiple_files:
+            # read the index file
+            index_data = cls.get_data_by_range(index_url, 0)
+            index_str = index_data.decode('utf-8')
+            index_json = json.loads(index_str)
+            assert index_json.get("weight_map") is not None, "weight_map not found in index file"
+            weight_map = index_json["weight_map"]
+            # get the list of files
+            all_files = list(set(weight_map.values()))
+            all_files.sort() # make sure we load shard files in order
+            # get the list of tensors
+            tensors: dict[str, RemoteTensor] = {}
+            for file in all_files:
+                url = f"{cls.BASE_DOMAIN}/{model_id}/resolve/main/{file}"
+                for key, val in cls.get_list_tensors(url).items():
+                    tensors[key] = val
+            return tensors
+
+        raise ValueError(f"Model {model_id} does not have any safetensor files")
+
+    @classmethod
+    def get_list_tensors(cls, url: str) -> dict[str, RemoteTensor]:
+        """
+        Get list of tensors from a remote safetensor file.
+
+        Returns a dictionary of tensor names and their metadata.
+        Each tensor is represented as a tuple of (dtype, shape, offset_start, size)
+        """
+        metadata, data_start_offset = cls.get_metadata(url)
+        res: dict[str, RemoteTensor] = {}
+
+        for name, meta in metadata.items():
+            if name == "__metadata__":
+                continue
+            if not isinstance(meta, dict):
+                raise ValueError(f"Invalid metadata for tensor '{name}': {meta}")
+            try:
+                dtype = meta["dtype"]
+                shape = meta["shape"]
+                offset_start_relative, offset_end_relative = meta["data_offsets"]
+                size = offset_end_relative - offset_start_relative
+                offset_start = data_start_offset + offset_start_relative
+                res[name] = RemoteTensor(dtype=dtype, shape=tuple(shape), offset_start=offset_start, size=size, url=url)
+            except KeyError as e:
+                raise ValueError(f"Missing key in metadata for tensor '{name}': {e}, meta = {meta}")
+
+        return res
+
+    @classmethod
+    def get_metadata(cls, url: str) -> tuple[dict, int]:
+        """
+        Get JSON metadata from a remote safetensor file.
+
+        Returns tuple of (metadata, data_start_offset)
+        """
+        # Request first 5MB of the file (hopefully enough for metadata)
+        read_size = 5 * 1024 * 1024
+        raw_data = cls.get_data_by_range(url, 0, read_size)
+
+        # Parse header
+        # First 8 bytes contain the metadata length as u64 little-endian
+        if len(raw_data) < 8:
+            raise ValueError("Not enough data to read metadata size")
+        metadata_length = int.from_bytes(raw_data[:8], byteorder='little')
+
+        # Calculate the data start offset
+        data_start_offset = 8 + metadata_length
+        alignment = SafetensorRemote.ALIGNMENT
+        if data_start_offset % alignment != 0:
+            data_start_offset += alignment - (data_start_offset % alignment)
+
+        # Check if we have enough data to read the metadata
+        if len(raw_data) < 8 + metadata_length:
+            raise ValueError(f"Could not read complete metadata. Need {8 + metadata_length} bytes, got {len(raw_data)}")
+
+        # Extract metadata bytes and parse as JSON
+        metadata_bytes = raw_data[8:8 + metadata_length]
+        metadata_str = metadata_bytes.decode('utf-8')
+        try:
+            metadata = json.loads(metadata_str)
+            return metadata, data_start_offset
+        except json.JSONDecodeError as e:
+            raise ValueError(f"Failed to parse safetensor metadata as JSON: {e}")
+
+    @classmethod
+    def get_data_by_range(cls, url: str, start: int, size: int = -1) -> bytes:
+        """
+        Get raw byte data from a remote file by range.
+        If size is not specified, it will read the entire file.
+        """
+        import requests
+        from urllib.parse import urlparse
+
+        parsed_url = urlparse(url)
+        if not parsed_url.scheme or not parsed_url.netloc:
+            raise ValueError(f"Invalid URL: {url}")
+
+        headers = cls._get_request_headers()
+        if size > -1:
+            headers["Range"] = f"bytes={start}-{start + size}"
+        response = requests.get(url, allow_redirects=True, headers=headers)
+        response.raise_for_status()
+
+        # Get raw byte data
+        return response.content[:size]
+
+    @classmethod
+    def check_file_exist(cls, url: str) -> bool:
+        """
+        Check if a file exists at the given URL.
+        Returns True if the file exists, False otherwise.
+        """
+        import requests
+        from urllib.parse import urlparse
+
+        parsed_url = urlparse(url)
+        if not parsed_url.scheme or not parsed_url.netloc:
+            raise ValueError(f"Invalid URL: {url}")
+
+        try:
+            headers = cls._get_request_headers()
+            headers["Range"] = "bytes=0-0"
+            response = requests.head(url, allow_redirects=True, headers=headers)
+            # Success (2xx) or redirect (3xx)
+            return 200 <= response.status_code < 400
+        except requests.RequestException:
+            return False
+
+    @classmethod
+    def _get_request_headers(cls) -> dict[str, str]:
+        """Prepare common headers for requests."""
+        headers = {"User-Agent": "convert_hf_to_gguf"}
+        if os.environ.get("HF_TOKEN"):
+            headers["Authorization"] = f"Bearer {os.environ['HF_TOKEN']}"
+        return headers