feat(exp): add zone format txt record helper (#578)

Add a helper function to format a TXT record before sending it to the
API.

Author: jooola

hcloud/exp/__init__.py

@@ -0,0 +1,4 @@
+"""
+The `exp` module is a namespace that holds experimental features for the `hcloud-python`
+library, breaking changes may occur within minor releases.
+"""

hcloud/exp/zone.py

@@ -0,0 +1,35 @@
+"""
+The `exp.zone` module is a namespace that holds experimental features for the `hcloud-python`
+library, breaking changes may occur within minor releases.
+"""
+
+from __future__ import annotations
+
+
+def is_txt_record_quoted(value: str) -> bool:
+    """
+    Check whether a TXT record is already quoted.
+
+    - hello world	=> false
+    - "hello world"	=> true
+    """
+    return value.startswith('"') and value.endswith('"')
+
+
+def format_txt_record(value: str) -> str:
+    """
+    Format a TXT record by splitting it in quoted strings of 255 characters.
+    Existing quotes will be escaped.
+
+    - hello world	=> "hello world"
+    - hello "world"	=> "hello \"world\""
+    """
+    value = value.replace('"', '\\"')
+
+    parts = []
+    for start in range(0, len(value), 255):
+        end = min(start + 255, len(value))
+        parts.append('"' + value[start:end] + '"')
+    value = " ".join(parts)
+
+    return value

tests/unit/exp/__init__.py

@@ -0,0 +1,37 @@
+from __future__ import annotations
+
+import pytest
+
+from hcloud.exp.zone import format_txt_record, is_txt_record_quoted
+
+
+@pytest.mark.parametrize(
+    ("value", "expected"),
+    [
+        ("hello world", False),
+        ('"hello world', False),
+        ('"hello world"', True),
+    ],
+)
+def test_is_txt_record_quoted(value: str, expected: bool):
+    assert is_txt_record_quoted(value) == expected
+
+
+manyA = "a" * 255
+someB = "b" * 10
+
+
+@pytest.mark.parametrize(
+    ("value", "expected"),
+    [
+        ("", ""),
+        ('""', '"\\"\\""'),
+        ("hello world", '"hello world"'),
+        ("hello\nworld", '"hello\nworld"'),
+        ('hello "world"', '"hello \\"world\\""'),
+        ('hello "world', '"hello \\"world"'),
+        (manyA + someB, f'"{manyA}" "{someB}"'),
+    ],
+)
+def test_format_txt_record(value: str, expected: str):
+    assert format_txt_record(value) == expected