Fix reading special character issue for tool resolver (#778)

# Description

For LLM/Prompt/CUSTOM_LLM tool, we need to read file to resolve the
tool.
If there is special character, will introduce unexpected error.
So, we set encoding as "uts-8".

This is continuing PR for
#759

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- [X] **The pull request does not introduce [breaking changes].**
- [ ] **CHANGELOG is updated for new features, bug fixes or other
significant changes.**
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- [ ] **Create an issue and link to the pull request to get dedicated
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workflow](../CONTRIBUTING.md#suggested-workflow).**

## General Guidelines and Best Practices
- [X] Title of the pull request is clear and informative.
- [X] There are a small number of commits, each of which have an
informative message. This means that previously merged commits do not
appear in the history of the PR. For more information on cleaning up the
commits in your PR, [see this
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### Testing Guidelines
- [X] Pull request includes test coverage for the included changes.

---------

Co-authored-by: Robben Wang <[email protected]>

src/promptflow/promptflow/executor/_tool_resolver.py

@@ -146,15 +146,16 @@ def resolve_tool_by_node(self, node: Node, convert_input_types=True) -> Resolved
 
     def _load_source_content(self, node: Node) -> str:
         source = node.source
-        if source is None or source.path is None or not Path(self._working_dir / source.path).exists():
+        # If is_file returns True, the path points to a existing file, so we don't need to check if exists.
+        if source is None or source.path is None or not (self._working_dir / source.path).is_file():
             raise InvalidSource(
                 target=ErrorTarget.EXECUTOR,
                 message_format="Node source path '{source_path}' is invalid on node '{node_name}'.",
                 source_path=source.path if source is not None else None,
                 node_name=node.name,
             )
-        with open(self._working_dir / source.path) as fin:
-            return fin.read()
+        file = self._working_dir / source.path
+        return file.read_text(encoding="utf-8")
 
     def _validate_duplicated_inputs(self, prompt_tpl_inputs: list, tool_params: list, msg: str):
         duplicated_inputs = set(prompt_tpl_inputs) & set(tool_params)

src/promptflow/tests/executor/unittests/_utils/test_generate_tool_meta_utils.py

@@ -75,6 +75,7 @@ class TestToolMetaUtils:
             ("prompt_tools", "summarize_text_content_prompt.jinja2", "llm"),
             ("script_with_import", "dummy_utils/main.py", "python"),
             ("script_with___file__", "script_with___file__.py", "python"),
+            ("script_with_special_character", "script_with_special_character.py", "python"),
         ],
     )
     def test_generate_tool_meta_dict_by_file(self, flow_dir, tool_path, tool_type):

src/promptflow/tests/executor/unittests/executor/test_tool_resolver.py

@@ -6,7 +6,7 @@
 from promptflow._core.tools_manager import ToolLoader
 from promptflow._sdk.entities import CustomConnection, CustomStrongTypeConnection
 from promptflow.connections import AzureOpenAIConnection
-from promptflow.contracts.flow import InputAssignment, InputValueType, Node, ToolSourceType
+from promptflow.contracts.flow import InputAssignment, InputValueType, Node, ToolSource, ToolSourceType
 from promptflow.contracts.tool import InputDefinition, Secret, Tool, ToolType, ValueType
 from promptflow.contracts.types import PromptTemplate
 from promptflow.exceptions import UserErrorException
@@ -20,6 +20,8 @@
 )
 from promptflow.executor._tool_resolver import ResolvedTool, ToolResolver
 
+from ...utils import FLOW_ROOT
+
 TEST_ROOT = Path(__file__).parent.parent.parent
 REQUESTS_PATH = TEST_ROOT / "test_configs/executor_api_requests"
 WRONG_REQUESTS_PATH = TEST_ROOT / "test_configs/executor_wrong_requests"
@@ -416,3 +418,30 @@ def test_convert_to_custom_strong_type_connection_value(self, conn_types: list[s
         actual = tool_resolver._convert_to_custom_strong_type_connection_value("conn_name", v, node, conn_types, m)
         assert isinstance(actual, expected_type)
         assert actual.api_base == "mock"
+
+    def test_load_source(self):
+        # Create a mock Node object with a valid source path
+        node = Node(name="mock", tool=None, inputs={}, source=ToolSource())
+        node.source.path = "./script_with_special_character/script_with_special_character.py"
+
+        resolver = ToolResolver(FLOW_ROOT)
+
+        result = resolver._load_source_content(node)
+        assert "https://www.bing.com/\ue000\ue001/" in result
+
+    @pytest.mark.parametrize(
+        "source",
+        [
+            None,
+            ToolSource(path=None),  # Then will try to read one directory.
+            ToolSource(path=""),  # Then will try to read one directory.
+            ToolSource(path="NotExistPath.py"),
+        ],
+    )
+    def test_load_source_error(self, source):
+        # Create a mock Node object with a valid source path
+        node = Node(name="mock", tool=None, inputs={}, source=source)
+        resolver = ToolResolver(FLOW_ROOT)
+
+        with pytest.raises(InvalidSource) as _:
+            resolver._load_source_content(node)

src/promptflow/tests/test_configs/flows/script_with___file__/script_with___file__.py

@@ -2,9 +2,6 @@
 
 from promptflow import tool
 
-# Add special character to test if file read is working.
-print("https://www.bing.com/")
-
 print(f"The script is {__file__}")
 assert Path(__file__).is_absolute(), f"__file__ should be absolute path, got {__file__}"
 

src/promptflow/tests/test_configs/flows/script_with_special_character/script_with_special_character.meta.json

@@ -0,0 +1,13 @@
+{
+  "name": "script_with_special_character",
+  "type": "python",
+  "inputs": {
+    "input1": {
+      "type": [
+        "string"
+      ]
+    }
+  },
+  "source": "script_with_special_character.py",
+  "function": "print_special_character"
+}

src/promptflow/tests/test_configs/flows/script_with_special_character/script_with_special_character.py

@@ -0,0 +1,6 @@
+from promptflow import tool
+
+@tool
+def print_special_character(input1: str) -> str:
+    # Add special character to test if file read is working.
+    return "https://www.bing.com//"