katex_server: Add Prometheus metrics.

package.json

@@ -69,6 +69,7 @@
     "postcss-prefixwrap": "^1.24.0",
     "postcss-preset-env": "^9.0.0",
     "postcss-simple-vars": "^7.0.0",
+    "prom-client": "^15.1.0",
     "regenerator-runtime": "^0.14.0",
     "shebang-loader": "^0.0.1",
     "simplebar": "^6.2.0",

pnpm-lock.yaml

@@ -214,6 +214,9 @@ dependencies:
   postcss-simple-vars:
     specifier: ^7.0.0
     version: 7.0.1(postcss@8.4.35)
+  prom-client:
+    specifier: ^15.1.0
+    version: 15.1.0
   regenerator-runtime:
     specifier: ^0.14.0
     version: 0.14.1
@@ -2727,6 +2730,11 @@ packages:
       rimraf: 3.0.2
     dev: false
 
+  /@opentelemetry/api@1.8.0:
+    resolution: {integrity: sha512-I/s6F7yKUDdtMsoBWXJe8Qz40Tui5vsuKCWJEWVL+5q9sSWRzzx6v2KeNsOBEwd94j0eWkpWCH4yB6rZg9Mf0w==}
+    engines: {node: '>=8.0.0'}
+    dev: false
+
   /@pkgjs/parseargs@0.11.0:
     resolution: {integrity: sha512-+1VkjdD0QBLPodGrJUeqarH8VAIvQODIbwh9XpP5Syisf7YoQgsJKPNFoqqLQlu+VQ/tVSshMR6loPMn8U+dPg==}
     engines: {node: '>=14'}
@@ -4360,6 +4368,10 @@ packages:
       file-uri-to-path: 1.0.0
     dev: false
 
+  /bintrees@1.0.2:
+    resolution: {integrity: sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw==}
+    dev: false
+
   /bit-twiddle@1.0.2:
     resolution: {integrity: sha512-B9UhK0DKFZhoTFcfvAzhqsjStvGJp9vYWf3+6SNTtdSQnvIgfkHbgHrg/e4+TH71N2GDu8tpmCVoyfrL1d7ntA==}
     dev: false
@@ -10573,6 +10585,14 @@ packages:
     engines: {node: '>=0.4.0'}
     dev: true
 
+  /prom-client@15.1.0:
+    resolution: {integrity: sha512-cCD7jLTqyPdjEPBo/Xk4Iu8jxjuZgZJ3e/oET3L+ZwOuap/7Cw3dH/TJSsZKs1TQLZ2IHpIlRAKw82ef06kmMw==}
+    engines: {node: ^16 || ^18 || >=20}
+    dependencies:
+      '@opentelemetry/api': 1.8.0
+      tdigest: 0.1.2
+    dev: false
+
   /promise-inflight@1.0.1:
     resolution: {integrity: sha512-6zWPyEOFaQBJYcGMHBKTKJ3u6TBsnMFOIZSa6ce1e/ZrrsOlnHRHbabMjLiBYKp+n44X9eUI6VUPaukCXHuG4g==}
     peerDependencies:
@@ -12002,6 +12022,12 @@ packages:
       yallist: 4.0.0
     dev: false
 
+  /tdigest@0.1.2:
+    resolution: {integrity: sha512-+G0LLgjjo9BZX2MfdvPfH+MKLCrxlXSYec5DaPYP1fe6Iyhf0/fSmJ0bFiZ1F8BT6cGXl2LpltQptzjXKWEkKA==}
+    dependencies:
+      bintrees: 1.0.2
+    dev: false
+
   /terser-webpack-plugin@5.3.10(webpack@5.90.3):
     resolution: {integrity: sha512-BKFPWlPDndPs+NGGCr1U59t0XScL5317Y0UReNrHaw9/FwhPENlq6bfgs+4yPfyP51vqC1bQ4rp1EfXW5ZSH9w==}
     engines: {node: '>= 10.13.0'}

web/server/katex_server.ts

@@ -3,6 +3,7 @@ import crypto from "node:crypto";
 import bodyParser from "@koa/bodyparser";
 import katex from "katex";
 import Koa from "koa";
+import Prometheus from "prom-client";
 
 const host = "localhost";
 const port = Number(process.argv[2] ?? "9700");
@@ -30,6 +31,43 @@ const compare_secret = (given_secret: string): boolean => {
 const app = new Koa();
 app.use(bodyParser());
 
+Prometheus.collectDefaultMetrics();
+const httpRequestDurationSeconds = new Prometheus.Histogram({
+    name: "katex_http_request_duration_seconds",
+    help: "Duration of HTTP requests in seconds",
+    labelNames: ["method", "path", "status"] as const,
+    buckets: [
+        0.00001, 0.00002, 0.00005, 0.0001, 0.0002, 0.0005, 0.001, 0.002, 0.005, 0.01, 0.02, 0.05,
+        0.1,
+    ],
+});
+
+const httpRequestSizeBytes = new Prometheus.Histogram({
+    name: "katex_request_size_bytes",
+    help: "Size of successful KaTeX input in bytes",
+    labelNames: ["display_mode"] as const,
+    buckets: [1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000],
+});
+
+const httpResponseSizeBytes = new Prometheus.Histogram({
+    name: "katex_response_size_bytes",
+    help: "Size of successful KaTeX output in bytes",
+    labelNames: ["display_mode"] as const,
+    buckets: [100, 200, 500, 1000, 2000, 5000, 10000, 20000, 50000, 100000, 200000, 500000],
+});
+
+app.use(async (ctx, next) => {
+    if (ctx.request.method === "GET" && ctx.request.path === "/metrics") {
+        ctx.body = await Prometheus.register.metrics();
+        return;
+    }
+    const endTimer = httpRequestDurationSeconds.startTimer();
+    await next();
+    const {method, path} = ctx.request;
+    const {status} = ctx.response;
+    httpRequestDurationSeconds.labels({method, path, status: String(status)}).observe(endTimer());
+});
+
 app.use((ctx, _next) => {
     if (ctx.request.method !== "POST" || ctx.request.path !== "/") {
         ctx.status = 404;
@@ -59,8 +97,12 @@ app.use((ctx, _next) => {
         return;
     }
 
+    httpRequestSizeBytes.labels(String(is_display)).observe(Buffer.byteLength(content, "utf8"));
     try {
         ctx.body = katex.renderToString(content, {displayMode: is_display});
+        httpResponseSizeBytes
+            .labels(String(is_display))
+            .observe(Buffer.byteLength(ctx.body, "utf8"));
     } catch (error) {
         if (error instanceof katex.ParseError) {
             ctx.status = 400;