Refactor config regex/log preview into dedicated log_service

Docs/Tasks.md

@@ -109,12 +109,13 @@ Reference: `Docs/Refactoring.md` for full analysis of each issue.
 
 ---
 
-### Task 5 — Extract log-preview / regex-test from `config_service.py`
+### Task 5 — Extract log-preview / regex-test from `config_service.py` (✅ completed)
 
 **Priority**: Medium  
 **Refactoring ref**: Refactoring.md §2  
 **Affected files**:
 - `backend/app/services/config_service.py` (~1845 lines)
+- `backend/app/services/log_service.py` (new)
 - `backend/app/routers/config.py` (routes that call log-preview / regex-test functions)
 
 **What to do**:

backend/app/routers/config.py

@@ -76,7 +76,7 @@ from app.models.config import (
     RollbackResponse,
     ServiceStatusResponse,
 )
-from app.services import config_service, jail_service
+from app.services import config_service, jail_service, log_service
 from app.services import (
     action_config_service,
     config_file_service,
@@ -472,7 +472,7 @@ async def regex_test(
     Returns:
         :class:`~app.models.config.RegexTestResponse` with match result and groups.
     """
-    return config_service.test_regex(body)
+    return log_service.test_regex(body)
 
 
 # ---------------------------------------------------------------------------
@@ -578,7 +578,7 @@ async def preview_log(
     Returns:
         :class:`~app.models.config.LogPreviewResponse` with per-line results.
     """
-    return await config_service.preview_log(body)
+    return await log_service.preview_log(body)
 
 
 # ---------------------------------------------------------------------------

backend/app/services/config_service.py

@@ -35,7 +35,6 @@ from app.models.config import (
     JailConfigListResponse,
     JailConfigResponse,
     JailConfigUpdate,
-    LogPreviewLine,
     LogPreviewRequest,
     LogPreviewResponse,
     MapColorThresholdsResponse,
@@ -45,7 +44,7 @@ from app.models.config import (
     ServiceStatusResponse,
 )
 from app.exceptions import ConfigOperationError, ConfigValidationError, JailNotFoundError
-from app.services import setup_service
+from app.services import log_service, setup_service
 from app.utils.fail2ban_client import Fail2BanClient
 
 log: structlog.stdlib.BoundLogger = structlog.get_logger()
@@ -495,27 +494,8 @@ async def update_global_config(socket_path: str, update: GlobalConfigUpdate) ->
 
 
 def test_regex(request: RegexTestRequest) -> RegexTestResponse:
-    """Test a regex pattern against a sample log line.
+    """Proxy to :func:`app.services.log_service.test_regex`."""
-
+    return log_service.test_regex(request)
-    This is a pure in-process operation — no socket communication occurs.
-
-    Args:
-        request: The :class:`~app.models.config.RegexTestRequest` payload.
-
-    Returns:
-        :class:`~app.models.config.RegexTestResponse` with match result.
-    """
-    try:
-        compiled = re.compile(request.fail_regex)
-    except re.error as exc:
-        return RegexTestResponse(matched=False, groups=[], error=str(exc))
-
-    match = compiled.search(request.log_line)
-    if match is None:
-        return RegexTestResponse(matched=False)
-
-    groups: list[str] = list(match.groups() or [])
-    return RegexTestResponse(matched=True, groups=[str(g) for g in groups if g is not None])
 
 
 # ---------------------------------------------------------------------------
@@ -594,100 +574,8 @@ async def delete_log_path(
 
 
 async def preview_log(req: LogPreviewRequest) -> LogPreviewResponse:
-    """Read the last *num_lines* of a log file and test *fail_regex* against each.
+    """Proxy to :func:`app.services.log_service.preview_log`."""
-
+    return await log_service.preview_log(req)
-    This operation reads from the local filesystem — no socket is used.
-
-    Args:
-        req: :class:`~app.models.config.LogPreviewRequest`.
-
-    Returns:
-        :class:`~app.models.config.LogPreviewResponse` with line-by-line results.
-    """
-    # Validate the regex first.
-    try:
-        compiled = re.compile(req.fail_regex)
-    except re.error as exc:
-        return LogPreviewResponse(
-            lines=[],
-            total_lines=0,
-            matched_count=0,
-            regex_error=str(exc),
-        )
-
-    path = Path(req.log_path)
-    if not path.is_file():
-        return LogPreviewResponse(
-            lines=[],
-            total_lines=0,
-            matched_count=0,
-            regex_error=f"File not found: {req.log_path!r}",
-        )
-
-    # Read the last num_lines lines efficiently.
-    try:
-        raw_lines = await asyncio.get_event_loop().run_in_executor(
-            None,
-            _read_tail_lines,
-            str(path),
-            req.num_lines,
-        )
-    except OSError as exc:
-        return LogPreviewResponse(
-            lines=[],
-            total_lines=0,
-            matched_count=0,
-            regex_error=f"Cannot read file: {exc}",
-        )
-
-    result_lines: list[LogPreviewLine] = []
-    matched_count = 0
-    for line in raw_lines:
-        m = compiled.search(line)
-        groups = [str(g) for g in (m.groups() or []) if g is not None] if m else []
-        result_lines.append(LogPreviewLine(line=line, matched=(m is not None), groups=groups))
-        if m:
-            matched_count += 1
-
-    return LogPreviewResponse(
-        lines=result_lines,
-        total_lines=len(result_lines),
-        matched_count=matched_count,
-    )
-
-
-def _read_tail_lines(file_path: str, num_lines: int) -> list[str]:
-    """Read the last *num_lines* from *file_path* synchronously.
-
-    Uses a memory-efficient approach that seeks from the end of the file.
-
-    Args:
-        file_path: Absolute path to the log file.
-        num_lines: Number of lines to return.
-
-    Returns:
-        A list of stripped line strings.
-    """
-    chunk_size = 8192
-    raw_lines: list[bytes] = []
-    with open(file_path, "rb") as fh:
-        fh.seek(0, 2)  # seek to end
-        end_pos = fh.tell()
-        if end_pos == 0:
-            return []
-        buf = b""
-        pos = end_pos
-        while len(raw_lines) <= num_lines and pos > 0:
-            read_size = min(chunk_size, pos)
-            pos -= read_size
-            fh.seek(pos)
-            chunk = fh.read(read_size)
-            buf = chunk + buf
-            raw_lines = buf.split(b"\n")
-        # Strip incomplete leading line unless we've read the whole file.
-        if pos > 0 and len(raw_lines) > 1:
-            raw_lines = raw_lines[1:]
-    return [ln.decode("utf-8", errors="replace").rstrip() for ln in raw_lines[-num_lines:] if ln.strip()]
 
 
 # ---------------------------------------------------------------------------

backend/app/services/log_service.py

@@ -0,0 +1,128 @@
+"""Log helper service.
+
+Contains regex test and log preview helpers that are independent of
+fail2ban socket operations.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import re
+from pathlib import Path
+
+from app.models.config import (
+    LogPreviewLine,
+    LogPreviewRequest,
+    LogPreviewResponse,
+    RegexTestRequest,
+    RegexTestResponse,
+)
+
+
+def test_regex(request: RegexTestRequest) -> RegexTestResponse:
+    """Test a regex pattern against a sample log line.
+
+    Args:
+        request: The regex test payload.
+
+    Returns:
+        RegexTestResponse with match result, groups and optional error.
+    """
+    try:
+        compiled = re.compile(request.fail_regex)
+    except re.error as exc:
+        return RegexTestResponse(matched=False, groups=[], error=str(exc))
+
+    match = compiled.search(request.log_line)
+    if match is None:
+        return RegexTestResponse(matched=False)
+
+    groups: list[str] = list(match.groups() or [])
+    return RegexTestResponse(matched=True, groups=[str(g) for g in groups if g is not None])
+
+
+async def preview_log(req: LogPreviewRequest) -> LogPreviewResponse:
+    """Inspect the last lines of a log file and evaluate regex matches.
+
+    Args:
+        req: Log preview request.
+
+    Returns:
+        LogPreviewResponse with lines, total_lines and matched_count, or error.
+    """
+    try:
+        compiled = re.compile(req.fail_regex)
+    except re.error as exc:
+        return LogPreviewResponse(
+            lines=[],
+            total_lines=0,
+            matched_count=0,
+            regex_error=str(exc),
+        )
+
+    path = Path(req.log_path)
+    if not path.is_file():
+        return LogPreviewResponse(
+            lines=[],
+            total_lines=0,
+            matched_count=0,
+            regex_error=f"File not found: {req.log_path!r}",
+        )
+
+    try:
+        raw_lines = await asyncio.get_event_loop().run_in_executor(
+            None,
+            _read_tail_lines,
+            str(path),
+            req.num_lines,
+        )
+    except OSError as exc:
+        return LogPreviewResponse(
+            lines=[],
+            total_lines=0,
+            matched_count=0,
+            regex_error=f"Cannot read file: {exc}",
+        )
+
+    result_lines: list[LogPreviewLine] = []
+    matched_count = 0
+    for line in raw_lines:
+        m = compiled.search(line)
+        groups = [str(g) for g in (m.groups() or []) if g is not None] if m else []
+        result_lines.append(
+            LogPreviewLine(line=line, matched=(m is not None), groups=groups),
+        )
+        if m:
+            matched_count += 1
+
+    return LogPreviewResponse(
+        lines=result_lines,
+        total_lines=len(result_lines),
+        matched_count=matched_count,
+    )
+
+
+def _read_tail_lines(file_path: str, num_lines: int) -> list[str]:
+    """Read the last *num_lines* from *file_path* in a memory-efficient way."""
+    chunk_size = 8192
+    raw_lines: list[bytes] = []
+    with open(file_path, "rb") as fh:
+        fh.seek(0, 2)
+        end_pos = fh.tell()
+        if end_pos == 0:
+            return []
+
+        buf = b""
+        pos = end_pos
+        while len(raw_lines) <= num_lines and pos > 0:
+            read_size = min(chunk_size, pos)
+            pos -= read_size
+            fh.seek(pos)
+            chunk = fh.read(read_size)
+            buf = chunk + buf
+            raw_lines = buf.split(b"\n")
+
+        if pos > 0 and len(raw_lines) > 1:
+            raw_lines = raw_lines[1:]
+
+    return [ln.decode("utf-8", errors="replace").rstrip() for ln in raw_lines[-num_lines:] if ln.strip()]

backend/tests/test_routers/test_config.py

@@ -503,7 +503,7 @@ class TestRegexTest:
         """POST /api/config/regex-test returns matched=true for a valid match."""
         mock_response = RegexTestResponse(matched=True, groups=["1.2.3.4"], error=None)
         with patch(
-            "app.routers.config.config_service.test_regex",
+            "app.routers.config.log_service.test_regex",
             return_value=mock_response,
         ):
             resp = await config_client.post(
@@ -521,7 +521,7 @@ class TestRegexTest:
         """POST /api/config/regex-test returns matched=false for no match."""
         mock_response = RegexTestResponse(matched=False, groups=[], error=None)
         with patch(
-            "app.routers.config.config_service.test_regex",
+            "app.routers.config.log_service.test_regex",
             return_value=mock_response,
         ):
             resp = await config_client.post(
@@ -599,7 +599,7 @@ class TestPreviewLog:
             matched_count=1,
         )
         with patch(
-            "app.routers.config.config_service.preview_log",
+            "app.routers.config.log_service.preview_log",
             AsyncMock(return_value=mock_response),
         ):
             resp = await config_client.post(