From a203dc6e46f952911e22e98982546887f64654b8 Mon Sep 17 00:00:00 2001
From: Adam Teichert <adam.teichert@snow.edu>
Date: Wed, 10 Dec 2025 17:44:02 -0700
Subject: [PATCH] mermaid diagrams are rendered as image tags with link to
 mermaid server rendering; uses pako for compression as expected

---
 package.json                                  |  1 +
 pnpm-lock.yaml                                |  8 +++++++
 .../htmlMarkdownUtils.mermaid.test.ts         | 22 +++++++++++++++++++
 src/services/htmlMarkdownUtils.ts             | 17 +++++++++++---
 4 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 src/services/htmlMarkdownUtils.mermaid.test.ts

diff --git a/package.json b/package.json
index 77d4429..c65b636 100644
--- a/package.json
+++ b/package.json
@@ -32,6 +32,7 @@
     "marked-katex-extension": "^5.1.5",
     "mcp-handler": "^1.0.0",
     "next": "^15.3.5",
+    "pako": "^2.1.0",
     "react": "^19.1.0",
     "react-dom": "^19.1.0",
     "socket.io": "^4.8.1",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9ff1c95..d7a48f4 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -65,6 +65,9 @@ importers:
       next:
         specifier: ^15.3.5
         version: 15.3.5(@babel/core@7.28.0)(react-dom@19.1.0(react@19.1.0))(react@19.1.0)
+      pako:
+        specifier: ^2.1.0
+        version: 2.1.0
       react:
         specifier: ^19.1.0
         version: 19.1.0
@@ -2628,6 +2631,9 @@ packages:
     resolution: {integrity: sha512-LaNjtRWUBY++zB5nE/NwcaoMylSPk+S+ZHNB1TzdbMJMny6dynpAGt7X/tl/QYq3TIeE6nxHppbo2LGymrG5Pw==}
     engines: {node: '>=10'}
 
+  pako@2.1.0:
+    resolution: {integrity: sha512-w+eufiZ1WuJYgPXbV/PO3NCMEc3xqylkKHzp8bxp1uW4qaSNQUkwmLLEc3kKsfz8lpV1F8Ht3U1Cm+9Srog2ug==}
+
   parent-module@1.0.1:
     resolution: {integrity: sha512-GQ2EWRpQV8/o+Aw8YqtfZZPfNRWZYkbidE9k5rpl/hC3vtHHBfGm2Ifi6qWV+coDGkrUKZAxE3Lot5kcsRlh+g==}
     engines: {node: '>=6'}
@@ -5853,6 +5859,8 @@ snapshots:
     dependencies:
       p-limit: 3.1.0
 
+  pako@2.1.0: {}
+
   parent-module@1.0.1:
     dependencies:
       callsites: 3.1.0
diff --git a/src/services/htmlMarkdownUtils.mermaid.test.ts b/src/services/htmlMarkdownUtils.mermaid.test.ts
new file mode 100644
index 0000000..0d12f06
--- /dev/null
+++ b/src/services/htmlMarkdownUtils.mermaid.test.ts
@@ -0,0 +1,22 @@
+import { describe, it, expect } from 'vitest';
+import { markdownToHtmlNoImages } from './htmlMarkdownUtils';
+
+describe('markdownToHtmlNoImages', () => {
+  it('renders mermaid diagrams correctly using pako compression', () => {
+    const markdown = `
+\`\`\`mermaid
+graph TD;
+    A-->B;
+    A-->C;
+    B-->D;
+    C-->D;
+\`\`\`
+    `;
+    const html = markdownToHtmlNoImages(markdown);
+    
+    // The expected URL part for the graph above when compressed with pako
+    const expectedUrlPart = "pako:eNqrVkrOT0lVslJKL0osyFAIcbGOyVMAAkddXTsnJLYzlO0EZMPUOIPZSjpKualFuYmZKUpW1UolGam5IONSUtMSS3NKlGprAQJ0Gx4";
+    
+    expect(html).toContain(`https://mermaid.ink/img/${expectedUrlPart}`);
+  });
+});
diff --git a/src/services/htmlMarkdownUtils.ts b/src/services/htmlMarkdownUtils.ts
index 59b48d2..abb905b 100644
--- a/src/services/htmlMarkdownUtils.ts
+++ b/src/services/htmlMarkdownUtils.ts
@@ -2,6 +2,7 @@
 import { marked } from "marked";
 import DOMPurify from "isomorphic-dompurify";
 import markedKatex from "marked-katex-extension";
+import pako from "pako";
 import { LocalCourseSettings } from "@/features/local/course/localCourseSettings";
 
 const mermaidExtension = {
@@ -22,9 +23,17 @@ const mermaidExtension = {
     }
   },
   renderer(token: { text: string }) {
-    const base64 = btoa(token.text);
-    const url = `https://mermaid.ink/img/${base64}?type=svg`;
-    console.log(token.text, url);
+    const data = JSON.stringify({
+      code: token.text,
+      mermaid: { theme: "default" },
+    });
+    const compressed = pako.deflate(data, { level: 9 });
+    const binaryString = Array.from(compressed, (byte) =>
+      String.fromCharCode(byte)
+    ).join("");
+    const base64 = btoa(binaryString).replace(/\+/g, "-").replace(/\//g, "_");
+    const url = `https://mermaid.ink/img/pako:${base64}?type=svg`;
+    // console.log(token.text, url);
     return `<img src="${url}" alt="Mermaid diagram" />`;
   },
 };
@@ -63,6 +72,8 @@ export function convertImagesToCanvasImages(
   }, {} as { [key: string]: string });
 
   for (const imageSrc of imageSources) {
+    if (imageSrc.startsWith("http://") || imageSrc.startsWith("https://"))
+      continue;
     const destinationUrl = imageLookup[imageSrc];
     if (typeof destinationUrl === "undefined") {
       console.log(