feat: add file upload support and utility functions to client library

This update adds file uploading support to the Dioptra client library through a new DioptraFile
class, supporting utility functions, and extending the client's post method to accept `data` and
`files` arguments. The changes enable users to upload single files, multiple files, or all files
within a directory while enforcing strict path validation in the associated filenames to prevent
server-side directory traversal attacks.

The new functionality includes:

- A DioptraFile class that validates filenames to ensure they are normalized, POSIX-compliant
  relative paths without traversal components (e.g., "..").
- File selection utility functions:
  - select_files_in_directory: Recursively selects files from a directory with optional regex
    pattern filtering
  - select_one_or_more_files: Selects individual files with optional renaming support to handle
    filename collisions
- Extended POST request in the client to handle multipart form data that contains regular form
  fields and file uploads. All file uploads, whether they're single file or multiple files, are
  streamed to the server.

The DioptraSession implementation for the requests-based client and the Flask test client have both
been updated to support the new functionality.

src/dioptra/client/__init__.py

@@ -14,14 +14,19 @@
 #
 # ACCESS THE FULL CC BY 4.0 LICENSE HERE:
 # https://creativecommons.org/licenses/by/4.0/legalcode
+from .base import DioptraFile
 from .client import (
     DioptraClient,
     connect_json_dioptra_client,
     connect_response_dioptra_client,
 )
+from .utils import select_files_in_directory, select_one_or_more_files
 
 __all__ = [
     "connect_response_dioptra_client",
     "connect_json_dioptra_client",
+    "select_files_in_directory",
+    "select_one_or_more_files",
     "DioptraClient",
+    "DioptraFile",
 ]

src/dioptra/client/base.py

@@ -14,13 +14,19 @@
 #
 # ACCESS THE FULL CC BY 4.0 LICENSE HERE:
 # https://creativecommons.org/licenses/by/4.0/legalcode
+import posixpath
+import re
 from abc import ABC, abstractmethod
-from pathlib import Path
+from dataclasses import dataclass
+from io import BufferedReader
+from pathlib import Path, PurePosixPath, PureWindowsPath
 from posixpath import join as urljoin
 from typing import Any, ClassVar, Generic, Protocol, TypeVar
 
 T = TypeVar("T")
 
+DOTS_REGEX = re.compile(r"^\.\.\.+$")
+
 
 class DioptraClientError(Exception):
     """Base class for client errors"""
@@ -91,6 +97,52 @@ def json(self) -> dict[str, Any]:
         ...  # fmt: skip
 
 
+@dataclass
+class DioptraFile(object):
+    """A file to be uploaded to the Dioptra API.
+
+    Attributes:
+        filename: The name of the file.
+        stream: The file stream.
+        content_type: The content type of the file.
+    """
+
+    filename: str
+    stream: BufferedReader
+    content_type: str | None
+
+    def __post_init__(self) -> None:
+        if PureWindowsPath(self.filename).as_posix() != str(PurePosixPath(self.filename)):  # noqa: B950; fmt: skip
+            raise ValueError(
+                "Invalid filename (reason: filename is a Windows path): "
+                f"{self.filename}"
+            )
+
+        if posixpath.normpath(self.filename) != self.filename:
+            raise ValueError(
+                "Invalid filename (reason: filename is not normalized): "
+                f"{self.filename}"
+            )
+
+        if not PurePosixPath(self.filename).is_relative_to("."):
+            raise ValueError(
+                "Invalid filename (reason: filename is not relative to ./): "
+                f"{self.filename}"
+            )
+
+        if PurePosixPath("..") in PurePosixPath(posixpath.normpath(self.filename)).parents:  # noqa: B950; fmt: skip
+            raise ValueError(
+                "Invalid filename (reason: filename is not a sub-directory of ./): "
+                f"{self.filename}"
+            )
+
+        if any([DOTS_REGEX.match(str(x)) for x in PurePosixPath(posixpath.normpath(self.filename)).parts]):  # noqa: B950; fmt: skip
+            raise ValueError(
+                "Invalid filename (reason: filename contains a sub-directory name that "
+                f"is all dots): {self.filename}"
+            )
+
+
 class DioptraSession(ABC, Generic[T]):
     """The interface for communicating with the Dioptra API."""
 
@@ -117,6 +169,8 @@ def make_request(
         url: str,
         params: dict[str, Any] | None = None,
         json_: dict[str, Any] | None = None,
+        data: dict[str, Any] | None = None,
+        files: dict[str, DioptraFile | list[DioptraFile]] | None = None,
     ) -> DioptraResponseProtocol:
         """Make a request to the API.
 
@@ -129,6 +183,10 @@ def make_request(
             params: The query parameters to include in the request. Optional, defaults
                 to None.
             json_: The JSON data to include in the request. Optional, defaults to None.
+            data: A dictionary to send in the body of the request as part of a
+                multipart form. Optional, defaults to None.
+            files: Dictionary of "name": DioptraFile or lists of DioptraFile pairs to be
+                uploaded. Optional, defaults to None.
 
         Returns:
             The response from the API.
@@ -179,6 +237,8 @@ def post(
         *parts,
         params: dict[str, Any] | None = None,
         json_: dict[str, Any] | None = None,
+        data: dict[str, Any] | None = None,
+        files: dict[str, DioptraFile | list[DioptraFile]] | None = None,
     ) -> T:
         """Make a POST request to the API.
 
@@ -188,6 +248,10 @@ def post(
             params: The query parameters to include in the request. Optional, defaults
                 to None.
             json_: The JSON data to include in the request. Optional, defaults to None.
+            data: A dictionary to send in the body of the request as part of a
+                multipart form. Optional, defaults to None.
+            files: Dictionary of "name": DioptraFile or lists of DioptraFile pairs to be
+                uploaded. Optional, defaults to None.
 
         Returns:
             The response from the API.
@@ -311,6 +375,8 @@ def _post(
         *parts,
         params: dict[str, Any] | None = None,
         json_: dict[str, Any] | None = None,
+        data: dict[str, Any] | None = None,
+        files: dict[str, DioptraFile | list[DioptraFile]] | None = None,
     ) -> DioptraResponseProtocol:
         """Make a POST request to the API.
 
@@ -323,12 +389,21 @@ def _post(
             params: The query parameters to include in the request. Optional, defaults
                 to None.
             json_: The JSON data to include in the request. Optional, defaults to None.
+            data: A dictionary to send in the body of the request as part of a
+                multipart form. Optional, defaults to None.
+            files: Dictionary of "name": DioptraFile or lists of DioptraFile pairs to be
+                uploaded. Optional, defaults to None.
 
         Returns:
             A response object that implements the DioptraResponseProtocol interface.
         """
         return self.make_request(
-            "post", self.build_url(endpoint, *parts), params=params, json_=json_
+            "post",
+            self.build_url(endpoint, *parts),
+            params=params,
+            json_=json_,
+            data=data,
+            files=files,
         )
 
     def _delete(