From a61893f2ed9535ce070b51e2ffceee9fc64285ee Mon Sep 17 00:00:00 2001
From: Frederik Baldauf <f.baldauf@conterra.de>
Date: Tue, 23 Jun 2026 16:16:08 +0200
Subject: [PATCH] Add CSP to dev server

---
 csp.middleware.js | 138 ++++++++++++++++++++++++++++++++++++++++++++++
 gulpfile.js       |  15 ++++-
 2 files changed, 152 insertions(+), 1 deletion(-)
 create mode 100644 csp.middleware.js

diff --git a/csp.middleware.js b/csp.middleware.js
new file mode 100644
index 0000000..a862e00
--- /dev/null
+++ b/csp.middleware.js
@@ -0,0 +1,138 @@
+// Sets a Content-Security-Policy header in the DevServer analogous to the deployment.
+// Override per developer via gulpfile.overrides.js (csp: false) or env CSP_POLICY.
+
+const fs = require("fs");
+const path = require("path");
+const crypto = require("crypto");
+
+// Fixed nonce per DevServer start (the header stays static, no per-request
+// coordination needed). Sufficient for locally catching CSP violations.
+const NONCE = crypto.randomBytes(16).toString("base64");
+
+// CSP as a directive map, so origins/nonce can be added selectively.
+const DIRECTIVES = {
+    "default-src": ["'self'"],
+    "object-src": ["'none'"],
+    "script-src": ["'self'", `'nonce-${NONCE}'`, "'unsafe-eval'", "'wasm-unsafe-eval'"],
+    "worker-src": ["'self'", "blob:"],
+    "child-src": ["'self'"],
+    "connect-src": ["'self'", "https:", "http:", "wss:", "ws:"],
+    "frame-src": ["'self'", "https:", "http:"],
+    "img-src": ["'self'", "data:", "blob:", "https://cdn.arcgis.com", "https:", "http:"],
+    "style-src": ["'self'", "'unsafe-inline'"],
+    "base-uri": ["'none'"],
+    "font-src": ["'self'", "data:"],
+    "form-action": ["'self'"],
+};
+
+// Directives the remote origin is added to when mapapps.remote.base is an
+// absolute URL.
+const REMOTE_DIRECTIVES = ["script-src", "style-src", "font-src", "img-src", "connect-src"];
+
+// Default server dirs of the DevServer
+const PROPERTY_DIRS = ["./target/webapp", "./target/test-classes"];
+
+function readRemoteBaseFromProperties() {
+    let value;
+    for (const dir of PROPERTY_DIRS) {
+        const file = path.resolve(process.cwd(), dir, "application.properties");
+        let content;
+        try {
+            content = fs.readFileSync(file, "utf-8");
+        } catch (e) {
+            continue;
+        }
+        for (const line of content.split(/\r?\n/)) {
+            const m = line.match(/^\s*mapapps\.remote\.base\s*[=:]\s*(.+?)\s*$/);
+            if (m && !/^\s*[#!]/.test(line)) {
+                value = m[1];
+            }
+        }
+    }
+    return value;
+}
+
+function resolveRemoteOrigin() {
+    const raw = process.env.MAPAPPS_REMOTE_BASE ?? readRemoteBaseFromProperties() ?? ".";
+    if (!/^https?:\/\//i.test(raw)) {
+        return undefined; // "." or relative -> same-origin, covered by 'self'
+    }
+    try {
+        return new URL(raw).origin; // scheme://host[:port], path discarded
+    } catch (e) {
+        return undefined;
+    }
+}
+
+function buildPolicy() {
+    const directives = {};
+    for (const [name, sources] of Object.entries(DIRECTIVES)) {
+        directives[name] = sources.slice();
+    }
+    const remoteOrigin = resolveRemoteOrigin();
+    if (remoteOrigin) {
+        for (const name of REMOTE_DIRECTIVES) {
+            if (!directives[name].includes(remoteOrigin)) {
+                directives[name].push(remoteOrigin);
+            }
+        }
+    }
+    return `${Object.entries(directives)
+        .map(([name, sources]) => `${name} ${sources.join(" ")}`)
+        .join("; ")};`;
+}
+
+// Determined once on load (remote.base does not change at runtime; restart the
+// DevServer when it does). CSP_POLICY overrides completely.
+const POLICY = process.env.CSP_POLICY || buildPolicy();
+
+// Inserts the nonce attribute into all <script> tags that don't have one yet.
+// The propertiesfilter's token replacement (@@...@@) runs afterwards and does not
+// touch the attribute.
+function injectNonce(html) {
+    return html.replace(/<script(?![^>]*\snonce=)(\s|>)/gi, `<script nonce="${NONCE}"$1`);
+}
+
+function isHtmlRequest(req) {
+    const pathname = (req.url || "").split("?")[0];
+    return pathname === "/" || /\.html?$/i.test(pathname);
+}
+
+module.exports = function devCspMiddleware(req, res, next) {
+    res.setHeader("Content-Security-Policy", POLICY);
+
+    if (!isHtmlRequest(req)) {
+        next();
+        return;
+    }
+
+    // Buffer the HTML and inject the nonce into the <script> tags. This middleware
+    // is registered last -> our wrapper runs BEFORE the propertiesfilter's, which
+    // then still replaces the @@...@@ tokens and sends.
+    const orgWrite = res.write;
+    const orgEnd = res.end;
+    let buffer = "";
+
+    res.write = function (chunk, encoding, callback) {
+        if (!this.headersSent) {
+            this.removeHeader("content-length");
+        }
+        if (!chunk || callback) {
+            return orgWrite.call(this, chunk, encoding, callback);
+        }
+        buffer += chunk instanceof Buffer ? chunk.toString(encoding) : chunk;
+        return true;
+    };
+
+    res.end = function (chunk, encoding, callback) {
+        if (!this.headersSent) {
+            this.removeHeader("content-length");
+        }
+        if (chunk) {
+            buffer += chunk instanceof Buffer ? chunk.toString(encoding) : chunk;
+        }
+        return orgEnd.call(this, injectNonce(buffer), encoding, callback);
+    };
+
+    next();
+};
diff --git a/gulpfile.js b/gulpfile.js
index 04170bb..cd3e7ca 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -1,4 +1,5 @@
 const gulp = require("gulp");
+const path = require("path");
 const mapapps = require('ct-mapapps-gulp-js');
 const mapappsBrowserSync = require("ct-mapapps-browser-sync");
 const dotEnv = require("dotenv");
@@ -103,7 +104,19 @@ mapappsBrowserSync.registerTask({
         ]
     },
     // prevent reload by browser sync (reload triggered on watch end)
-    externalReloadTrigger: true
+    externalReloadTrigger: true,
+    // Set Content-Security-Policy header in dev server to mirror deployment.
+    // Disable locally via gulpfile.overrides.js (csp: false) or override the
+    // policy string via env CSP_POLICY. See csp.middleware.js.
+    middleware: (localOverrides?.csp ?? true)
+        ? [path.resolve(__dirname, "csp.middleware.js")]
+        : [],
+    // Make browsersync inject its live-reload client as an EXTERNAL script
+    // (.../browser-sync/browser-sync-client.js) instead of an inline snippet, so
+    // it is covered by CSP script-src 'self' and no 'unsafe-inline' is needed.
+    rawOptions: {
+        localOnly: true,
+    },
 }, gulp);
 
 gulp.task("build",