Add a renderer for log files that can render ansi colours

Convert the text of the log file to HTML using ansi2html, which
converts ANSI colour codes to css classes so we get the colour
formatting from the original log.

It produces a full HTML file, which isn't what we want to display.
We just extract the <pre></pre> tag which contains the log content,
and the <style> which contains the relevant inline css.

airlock/renderers.py

@@ -2,16 +2,19 @@
 
 import csv
 import mimetypes
+import re
 from dataclasses import dataclass
 from email.utils import formatdate
 from functools import cached_property
 from io import BytesIO, StringIO
 from pathlib import Path
 from typing import IO, Any, ClassVar, Self, cast
 
+from ansi2html import Ansi2HTMLConverter
 from django.http import FileResponse, HttpResponseBase
 from django.template import Template, loader
 from django.template.response import SimpleTemplateResponse
+from django.utils.safestring import mark_safe
 
 from airlock.types import UrlPath
 from airlock.utils import is_valid_file_type
@@ -158,9 +161,35 @@ def context(self):
         }
 
 
+class LogRenderer(TextRenderer):
+    def context(self):
+        # Convert the text of the log file to HTML, converting ANSI colour codes to css classes
+        # so we get the colour formatting from the original log.
+        # We don't need the full HTML file that's produced, so just extract the <pre></pre>
+        # tag which contains the log content and the inline styles.
+        conv = Ansi2HTMLConverter()
+        text = conv.convert(self.stream.read())
+        match = re.match(
+            r".*(?P<style_tag><style.*</style>).*(?P<pre_tag><pre.*</pre>).*",
+            text,
+            flags=re.S,
+        )
+        if match:  # pragma: no branch
+            # After conversion, we should always find a match. As a precaution, check
+            # and render the plain text if we don't.
+            style_tag = match.group("style")
+            pre_tag = match.group("pre_tag")
+            text = mark_safe(f"{style_tag}{pre_tag}")
+
+        return {
+            "text": text,
+            "class": Path(self.filename).suffix.lstrip("."),
+        }
+
+
 FILE_RENDERERS = {
     ".csv": CSVRenderer,
-    ".log": TextRenderer,
+    ".log": LogRenderer,
     ".txt": TextRenderer,
     ".json": TextRenderer,
     ".md": TextRenderer,

requirements.prod.in

@@ -1,3 +1,4 @@
+ansi2html
 Django
 django-vite
 slippers

requirements.prod.txt

@@ -4,6 +4,10 @@
 #
 #    pip-compile --allow-unsafe --generate-hashes --strip-extras requirements.prod.in
 #
+ansi2html==1.9.2 \
+    --hash=sha256:3453bf87535d37b827b05245faaa756dbab4ec3d69925e352b6319c3c955c0a5 \
+    --hash=sha256:dccb75aa95fb018e5d299be2b45f802952377abfdce0504c17a6ee6ef0a420c5
+    # via -r requirements.prod.in
 asgiref==3.8.1 \
     --hash=sha256:3e1e3ecc849832fe52ccf2cb6686b7a55f82bb1d6aee72a58826471390335e47 \
     --hash=sha256:c343bd80a0bec947a9860adb4c432ffa7db769836c64238fc34bdc3fec84d590

tests/unit/test_renderers.py

@@ -12,10 +12,12 @@
     (".png", "image/png", False, None),
     (".csv", "text/html", False, "airlock/templates/file_browser/csv.html"),
     (".txt", "text/html", False, "airlock/templates/file_browser/text.html"),
+    (".log", "text/html", False, "airlock/templates/file_browser/text.html"),
     (".html", "text/html", True, "airlock/templates/file_browser/plaintext.html"),
     (".png", "text/html", True, "airlock/templates/file_browser/plaintext.html"),
     (".csv", "text/html", True, "airlock/templates/file_browser/plaintext.html"),
     (".txt", "text/html", True, "airlock/templates/file_browser/plaintext.html"),
+    (".log", "text/html", True, "airlock/templates/file_browser/plaintext.html"),
 ]
 
 
@@ -145,3 +147,27 @@ def test_plaintext_renderer_handles_invalid_utf8(tmp_path):
     response.render()
     assert response.status_code == 200
     assert "invalid � continuation byte" in response.rendered_content
+
+
+def test_log_renderer_handles_ansi_colors(tmp_path):
+    log_file = tmp_path / "test.log"
+    # in ansi codes:
+    # \x1B[32m = foregrouund green
+    # \x1b[1m bold
+    # \x1b[0m resets formatting
+    log_file.write_bytes(
+        b"No ansi here \x1b[32m\x1b[1mThis is green and bold.\x1b[0m This is not."
+    )
+    relpath = log_file.relative_to(tmp_path)
+    Renderer = renderers.get_renderer(relpath)
+    renderer = Renderer.from_file(log_file, relpath)
+    response = renderer.get_response()
+    response.render()
+    assert response.status_code == 200
+
+    assert "ansi1 { font-weight: bold; }" in response.rendered_content
+    assert "ansi32 { color: #00aa00; }" in response.rendered_content
+    assert (
+        '<span class="ansi1 ansi32">This is green and bold.</span>'
+        in response.rendered_content
+    )