Merge pull request #90 from ajaishankar/feature/expression-eval

Compiled and cached expressions

packages/bruno-js/package.json

@@ -9,6 +9,9 @@
   "peerDependencies": {
     "vm2": "^3.9.13"
   },
+  "scripts": {
+    "test": "jest --testPathIgnorePatterns test.js"
+  },
   "dependencies": {
     "atob": "^2.1.2",
     "ajv": "^8.12.0",

packages/bruno-js/src/utils.js

@@ -1,15 +1,69 @@
 const jsonQuery = require('json-query');
 
+const JS_KEYWORDS = `
+  break case catch class const continue debugger default delete do
+  else export extends false finally for function if import in instanceof
+  new null return super switch this throw true try typeof var void while with
+  undefined let static yield arguments of
+`.split(/\s+/).filter(word => word.length > 0);
+
+/**
+ * Creates a function from a Javascript expression
+ * 
+ * When the function is called, the variables used in this expression are picked up from the context
+ * 
+ * ```js
+ * res.data.pets.map(pet => pet.name.toUpperCase())
+ * 
+ * function(context) {
+ *   const { res, pet } = context;
+ *   return res.data.pets.map(pet => pet.name.toUpperCase())
+ * }
+ * ```
+ */
+const compileJsExpression = (expr) => {
+  // get all dotted identifiers (foo, bar.baz, .baz)
+  const matches = expr.match(/([\w\.$]+)/g) ?? [];
+
+  // get valid js identifiers (foo, bar)
+  const vars = new Set(
+    matches
+      .filter(match => /^[a-zA-Z$_]/.test(match))   // starts with valid js identifier (foo.bar)
+      .map(match => match.split('.')[0])            // top level identifier (foo)
+      .filter(name => !JS_KEYWORDS.includes(name))  // exclude js keywords
+  );
+
+  // globals such as Math
+  const globals = [...vars].filter(name => name in globalThis);
+
+  const code = {
+    vars: [...vars].join(", "),
+    // pick global from context or globalThis
+    globals: globals
+      .map(name => ` ${name} = ${name} ?? globalThis.${name};`)
+      .join('')
+  };
+
+  const body = `let { ${code.vars} } = context; ${code.globals}; return ${expr}`;
+
+  return new Function("context", body);
+};
+
+const internalExpressionCache = new Map();
+
 const evaluateJsExpression = (expression, context) => {
-  const fn = new Function(...Object.keys(context), `return ${expression}`);
+  let fn = internalExpressionCache.get(expression);
-  return fn(...Object.values(context));
+  if (fn == null) {
+    internalExpressionCache.set(expression, fn = compileJsExpression(expression));
+  }
+  return fn(context);
 };
 
 const createResponseParser = (response = {}) => {
-  const res = (expr)  => {
+  const res = (expr) => {
     const output = jsonQuery(expr, { data: response.data });
     return output ? output.value : null;
-  }
+  };
 
   res.status = response.status;
   res.statusText = response.statusText;
@@ -21,5 +75,6 @@ const createResponseParser = (response = {}) => {
 
 module.exports = {
   evaluateJsExpression,
-  createResponseParser
+  createResponseParser,
+  internalExpressionCache
 };

packages/bruno-js/tests/utils.spec.js

@@ -0,0 +1,115 @@
+const { evaluateJsExpression, internalExpressionCache: cache } = require("../src/utils");
+
+describe("utils", () => {
+  describe("expression evaluation", () => {
+    const context = {
+      res: {
+        data: { pets: ["bruno", "max"] }
+      }
+    };
+
+    beforeEach(() => cache.clear());
+    afterEach(() => cache.clear());
+
+    it("should evaluate expression", () => {
+      let result;
+
+      result = evaluateJsExpression("res.data.pets", context);
+      expect(result).toEqual(["bruno", "max"]);
+
+      result = evaluateJsExpression("res.data.pets[0].toUpperCase()", context);
+      expect(result).toEqual("BRUNO");
+    });
+
+    it("should cache expression", () => {
+      expect(cache.size).toBe(0);
+      evaluateJsExpression("res.data.pets", context);
+      expect(cache.size).toBe(1);
+    });
+
+    it("should use cached expression", () => {
+      const expr = "res.data.pets";
+
+      evaluateJsExpression(expr, context);
+
+      const fn = cache.get(expr);
+      expect(fn).toBeDefined();
+
+      evaluateJsExpression(expr, context);
+
+      // cache should not be overwritten
+      expect(cache.get(expr)).toBe(fn);
+    });
+
+    it("should identify top level variables", () => {
+      const expr = "res.data.pets[0].toUpperCase()";
+      evaluateJsExpression(expr, context);
+      expect(cache.get(expr).toString()).toContain("let { res } = context;");
+    });
+
+    it("should not duplicate variables", () => {
+      const expr = "res.data.pets[0] + res.data.pets[1]";
+      evaluateJsExpression(expr, context);
+      expect(cache.get(expr).toString()).toContain("let { res } = context;");
+    });
+
+    it("should exclude js keywords like true false from vars", () => {
+      const expr = "res.data.pets.length > 0 ? true : false";
+      evaluateJsExpression(expr, context);
+      expect(cache.get(expr).toString()).toContain("let { res } = context;");
+    });
+
+    it("should exclude numbers from vars", () => {
+      const expr = "res.data.pets.length + 10";
+      evaluateJsExpression(expr, context);
+      expect(cache.get(expr).toString()).toContain("let { res } = context;");
+    });
+
+    it("should pick variables from complex expressions", () => {
+      const expr = "res.data.pets.map(pet => pet.length)";
+      const result = evaluateJsExpression(expr, context);
+      expect(result).toEqual([5, 3]);
+      expect(cache.get(expr).toString()).toContain("let { res, pet } = context;");
+    });
+
+    it("should be ok picking extra vars from strings", () => {
+      const expr = "'hello' + ' ' + res.data.pets[0]";
+      const result = evaluateJsExpression(expr, context);
+      expect(result).toBe("hello bruno");
+      // extra var hello is harmless
+      expect(cache.get(expr).toString()).toContain("let { hello, res } = context;");
+    });
+
+    it("should evaluate expressions referencing globals", () => {
+      const startTime = new Date("2022-02-01").getTime();
+      const currentTime = new Date("2022-02-02").getTime();
+
+      jest.useFakeTimers({ now: currentTime });
+
+      const expr = "Math.max(Date.now(), startTime)";
+      const result = evaluateJsExpression(expr, { startTime });
+
+      expect(result).toBe(currentTime);
+
+      expect(cache.get(expr).toString()).toContain("Math = Math ?? globalThis.Math;");
+      expect(cache.get(expr).toString()).toContain("Date = Date ?? globalThis.Date;");
+    });
+
+    it("should use global overridden in context", () => {
+      const startTime = new Date("2022-02-01").getTime();
+      const currentTime = new Date("2022-02-02").getTime();
+
+      jest.useFakeTimers({ now: currentTime });
+
+      const context = {
+        Date: { now: () => new Date("2022-01-31").getTime() },
+        startTime
+      };
+
+      const expr = "Math.max(Date.now(), startTime)";
+      const result = evaluateJsExpression(expr, context);
+
+      expect(result).toBe(startTime);
+    });
+  });
+});