snapshot of https://github.com/zulip/zulip.git @ 48c69911c7dd4e03b20552eb3bd77ad8151c1357 (2026-09-15)

zerver/lib/tex.py

@@ -0,0 +1,99 @@
+import logging
+import os
+import subprocess
+from typing import Any
+
+import lxml.html
+import requests
+from django.conf import settings
+
+from zerver.lib.outgoing_http import OutgoingSession
+from zerver.lib.storage import static_path
+
+
+class KatexSession(OutgoingSession):
+    def __init__(self, **kwargs: Any) -> None:
+        # We set a very short timeout because these requests are
+        # expected to be quite fast (milliseconds) and blocking on
+        # this affects message rendering performance.
+        super().__init__(role="katex", timeout=0.5, **kwargs)
+
+
+def render_tex(tex: str, is_inline: bool = True) -> str | None:
+    r"""Render a TeX string into HTML using KaTeX
+
+    Returns the HTML string, or None if there was some error in the TeX syntax
+
+    Keyword arguments:
+    tex -- Text string with the TeX to render
+           Don't include delimiters ('$$', '\[ \]', etc.)
+    is_inline -- Boolean setting that indicates whether the render should be
+                 inline (i.e. for embedding it in text) or not. The latter
+                 will show the content centered, and in the "expanded" form
+                 (default True)
+    """
+
+    if settings.KATEX_SERVER:
+        try:
+            resp = KatexSession().post(
+                # We explicitly disable the Smokescreen proxy for this
+                # call, since it intentionally connects to localhost.
+                # This is safe because the host is explicitly fixed, and
+                # the port is pulled from our own configuration.
+                f"http://localhost:{settings.KATEX_SERVER_PORT}/",
+                data={
+                    "content": tex,
+                    "is_display": "false" if is_inline else "true",
+                    "shared_secret": settings.SHARED_SECRET,
+                },
+                proxies={"http": ""},
+            )
+        except requests.exceptions.Timeout:
+            logging.warning("KaTeX rendering service timed out with %d byte long input", len(tex))
+            return None
+        except requests.exceptions.RequestException as e:
+            logging.warning("KaTeX rendering service failed: %s", type(e).__name__)
+            return None
+
+        if resp.status_code == 200:
+            return resp.content.decode().strip()
+        elif resp.status_code == 400:
+            return None
+        else:
+            logging.warning(
+                "KaTeX rendering service failed: (%s) %s", resp.status_code, resp.content.decode()
+            )
+            return None
+
+    katex_path = (
+        static_path("webpack-bundles/katex-cli.js")
+        if settings.PRODUCTION
+        else os.path.join(settings.DEPLOY_ROOT, "node_modules/katex/cli.js")
+    )
+    if not os.path.isfile(katex_path):
+        logging.error("Cannot find KaTeX for latex rendering!")
+        return None
+    command = ["node", katex_path]
+    if not is_inline:
+        command.extend(["--display-mode"])
+    try:
+        stdout = subprocess.check_output(command, input=tex, stderr=subprocess.DEVNULL, text=True)
+        # stdout contains a newline at the end
+        return stdout.strip()
+    except subprocess.CalledProcessError:
+        return None
+
+
+def change_katex_to_raw_latex(fragment: lxml.html.HtmlElement) -> None:
+    # Selecting the <span> elements with class 'katex'
+    katex_spans = fragment.xpath("//span[@class='katex']")
+
+    # Iterate through 'katex_spans' and replace with a new <span> having LaTeX text.
+    for katex_span in katex_spans:
+        latex_text = katex_span.xpath(".//annotation[@encoding='application/x-tex']")[0].text
+        # We store 'tail' to insert them back as the replace operation removes it.
+        tail = katex_span.tail
+        latex_span = lxml.html.Element("span")
+        latex_span.text = f"$${latex_text}$$"
+        katex_span.getparent().replace(katex_span, latex_span)
+        latex_span.tail = tail