feat(esmole): readonly request guard

packages/esmole-mcp/src/es/guard.ts

@@ -0,0 +1,54 @@
+export class EsGuardError extends Error {
+    constructor(message: string) {
+        super(message)
+        this.name = 'EsGuardError'
+    }
+}
+
+// POST is allowed in readonly mode only when the path ends in one of these
+// read-intent suffixes. Matched against the path with its query string and
+// trailing slash stripped.
+const READ_POST_SUFFIXES = [
+    '_search',
+    '_msearch',
+    '_count',
+    '_field_caps',
+    '_mapping',
+    '_search/scroll',
+    '_pit'
+]
+
+// DELETE is allowed in readonly mode only for read-session teardown.
+const READ_DELETE_PATHS = ['_pit', '_search/scroll']
+
+const normalize = (path: string): string => {
+    const noQuery = path.split('?')[0]
+    return noQuery.endsWith('/') ? noQuery.slice(0, -1) : noQuery
+}
+
+const endsWithSegment = (path: string, suffix: string): boolean =>
+    path === '/' + suffix || path.endsWith('/' + suffix)
+
+export const assertReadAllowed = (method: string, path: string): void => {
+    const m = method.toUpperCase()
+    const p = normalize(path)
+    if (m === 'GET' || m === 'HEAD') {
+        return
+    }
+    if (m === 'POST') {
+        if (
+            p.includes('/_cat/') ||
+            p.endsWith('/_cat') ||
+            READ_POST_SUFFIXES.some((s) => endsWithSegment(p, s))
+        ) {
+            return
+        }
+        throw new EsGuardError(
+            "readonly connection: POST to '" + p + "' is not a permitted read operation"
+        )
+    }
+    if (m === 'DELETE' && READ_DELETE_PATHS.some((s) => endsWithSegment(p, s))) {
+        return
+    }
+    throw new EsGuardError('readonly connection: ' + m + ' is not permitted')
+}