Add offset and size parameters to read_file tool

app/tools/read_file.py

@@ -8,13 +8,21 @@ def spec():
             "type": "function",
             "function": {
                 "name": "read_file",
-                "description": "Read and return the contents of a file",
+                "description": "Read and return the contents of a file. Supports optional offset and size parameters for partial reads.",
                 "parameters": {
                     "type": "object",
                     "properties": {
                         "file_path": {
                             "type": "string",
                             "description": "The path to the file to read"
+                        },
+                        "offset": {
+                            "type": "integer",
+                            "description": "Byte offset to start reading from (default: 0)"
+                        },
+                        "size": {
+                            "type": "integer",
+                            "description": "Maximum number of bytes to read (default: read to end of file)"
                         }
                     },
                     "required": ["file_path"]
@@ -23,12 +31,20 @@ def spec():
         }
 
     @staticmethod
-    def call(file_path: str) -> str:
-        log.info(f"read_file, file_path: {file_path}")
+    def call(file_path: str, offset: int = 0, size: int | None = None) -> str:
+        log.info(f"read_file, file_path: {file_path}, offset: {offset}, size: {size}")
+
+        if offset < 0:
+            return "Error: offset must be non-negative"
+        if size is not None and size < 0:
+            return "Error: size must be non-negative"
 
         try:
-            with open(file_path, encoding="utf-8") as f:
-                return f.read()
+            with open(file_path, "rb") as f:
+                if offset:
+                    f.seek(offset)
+                data = f.read(size) if size is not None else f.read()
+            return data.decode("utf-8", errors="replace")
         except FileNotFoundError:
             return f"Error: file {file_path} does not exist"
         except Exception as e:

tests/test_read_file.py

@@ -25,3 +25,46 @@ def test_read_file_multiline(tmp_path):
     f = tmp_path / "multi.txt"
     f.write_text(content, encoding="utf-8")
     assert read_file(str(f)) == content
+
+
+def test_read_file_with_offset(tmp_path):
+    f = tmp_path / "offset.txt"
+    f.write_text("hello world", encoding="utf-8")
+    assert read_file(str(f), offset=6) == "world"
+
+
+def test_read_file_with_size(tmp_path):
+    f = tmp_path / "size.txt"
+    f.write_text("hello world", encoding="utf-8")
+    assert read_file(str(f), size=5) == "hello"
+
+
+def test_read_file_with_offset_and_size(tmp_path):
+    f = tmp_path / "both.txt"
+    f.write_text("hello world", encoding="utf-8")
+    assert read_file(str(f), offset=3, size=4) == "lo w"
+
+
+def test_read_file_offset_beyond_end(tmp_path):
+    f = tmp_path / "short.txt"
+    f.write_text("hi", encoding="utf-8")
+    assert read_file(str(f), offset=100) == ""
+
+
+def test_read_file_size_larger_than_remaining(tmp_path):
+    f = tmp_path / "small.txt"
+    f.write_text("hello", encoding="utf-8")
+    assert read_file(str(f), offset=3, size=100) == "lo"
+
+
+def test_read_file_negative_offset_or_size(tmp_path):
+    f = tmp_path / "test.txt"
+    f.write_text("hello", encoding="utf-8")
+    assert "Error" in read_file(str(f), offset=-1)
+    assert "Error" in read_file(str(f), size=-1)
+
+
+def test_read_file_utf8_split(tmp_path):
+    f = tmp_path / "utf8.txt"
+    f.write_bytes(b"abc\xf0\x9f\x9a\x80def")
+    assert read_file(str(f), offset=3, size=2) == "\ufffd"