fix(shared-ini-file-loader): cache value returned by os.homedir() (#903)

Author: trivikr

.changeset/unlucky-tigers-raise.md

@@ -0,0 +1,5 @@
+---
+"@smithy/shared-ini-file-loader": patch
+---
+
+Cache value returned by os.homedir()

packages/shared-ini-file-loader/src/getHomeDir.spec.ts

@@ -6,6 +6,7 @@ import { getHomeDir } from "./getHomeDir";
 jest.mock("os");
 
 describe(getHomeDir.name, () => {
+  const mockUid = 1;
   const mockHOME = "mockHOME";
   const mockUSERPROFILE = "mockUSERPROFILE";
   const mockHOMEPATH = "mockHOMEPATH";
@@ -28,23 +29,28 @@ describe(getHomeDir.name, () => {
   afterEach(() => {
     process.env = OLD_ENV;
     jest.clearAllMocks();
-    jest.resetModules();
   });
 
   it("returns value in process.env.HOME first", () => {
     expect(getHomeDir()).toEqual(mockHOME);
+    expect(homedir).not.toHaveBeenCalled();
   });
 
   it("returns value in process.env.USERPROFILE second", () => {
     process.env = { ...process.env, HOME: undefined };
     expect(getHomeDir()).toEqual(mockUSERPROFILE);
+    expect(homedir).not.toHaveBeenCalled();
   });
 
   describe("returns value in HOMEPATH third", () => {
     beforeEach(() => {
       process.env = { ...process.env, HOME: undefined, USERPROFILE: undefined };
     });
 
+    afterEach(() => {
+      expect(homedir).not.toHaveBeenCalled();
+    });
+
     it("uses value in process.env.HOMEDRIVE if it's set", () => {
       expect(getHomeDir()).toEqual(`${mockHOMEDRIVE}${mockHOMEPATH}`);
     });
@@ -56,7 +62,84 @@ describe(getHomeDir.name, () => {
   });
 
   it("returns value from homedir fourth", () => {
+    const processGeteuidSpy = jest.spyOn(process, "geteuid").mockReturnValue(mockUid);
     process.env = { ...process.env, HOME: undefined, USERPROFILE: undefined, HOMEPATH: undefined };
     expect(getHomeDir()).toEqual(mockHomeDir);
+    expect(homedir).toHaveBeenCalledTimes(1);
+    expect(processGeteuidSpy).toHaveBeenCalledTimes(1);
+  });
+
+  describe("makes one homedir call irrespective of getHomeDir calls", () => {
+    const testSingleHomeDirCall = (num: number) => {
+      jest.isolateModules(() => {
+        const { getHomeDir } = require("./getHomeDir");
+        process.env = { ...process.env, HOME: undefined, USERPROFILE: undefined, HOMEPATH: undefined };
+
+        expect(homedir).not.toHaveBeenCalled();
+        const homeDirArr = Array(num)
+          .fill(num)
+          .map(() => getHomeDir());
+        expect(homeDirArr).toStrictEqual(Array(num).fill(mockHomeDir));
+
+        // There is one homedir call even through getHomeDir is called num times.
+        expect(homedir).toHaveBeenCalledTimes(1);
+      });
+    };
+
+    describe("when geteuid is available", () => {
+      it.each([10, 100, 1000, 10000])("calls: %d ", (num: number) => {
+        const processGeteuidSpy = jest.spyOn(process, "geteuid").mockReturnValue(mockUid);
+        expect(processGeteuidSpy).not.toHaveBeenCalled();
+        testSingleHomeDirCall(num);
+        expect(processGeteuidSpy).toHaveBeenCalledTimes(num);
+      });
+    });
+
+    describe("when geteuid is not available", () => {
+      const OLD_GETEUID = process.geteuid;
+
+      beforeAll(() => {
+        // @ts-ignore Type 'undefined' is not assignable to type '() => number'.
+        process.geteuid = undefined;
+      });
+
+      afterAll(() => {
+        process.geteuid = OLD_GETEUID;
+      });
+
+      it.each([10, 100, 1000, 10000])("calls: %d ", testSingleHomeDirCall);
+    });
+  });
+
+  describe("makes multiple homedir calls with based on UIDs", () => {
+    it.each([2, 10, 100])("calls: %d ", (num: number) => {
+      jest.isolateModules(() => {
+        const { getHomeDir } = require("./getHomeDir");
+        const processGeteuidSpy = jest.spyOn(process, "geteuid").mockReturnValue(mockUid);
+        for (let i = 0; i < num; i++) {
+          jest.spyOn(process, "geteuid").mockReturnValueOnce(mockUid + i);
+        }
+        process.env = { ...process.env, HOME: undefined, USERPROFILE: undefined, HOMEPATH: undefined };
+
+        expect(homedir).not.toHaveBeenCalled();
+        expect(processGeteuidSpy).not.toHaveBeenCalled();
+        const homeDirArr = Array(num)
+          .fill(num)
+          .map(() => getHomeDir());
+        expect(homeDirArr).toStrictEqual(Array(num).fill(mockHomeDir));
+
+        // There is num homedir calls as each call returns different UID
+        expect(homedir).toHaveBeenCalledTimes(num);
+        expect(processGeteuidSpy).toHaveBeenCalledTimes(num);
+
+        const homeDir = getHomeDir();
+        expect(homeDir).toStrictEqual(mockHomeDir);
+
+        // No extra calls made to homedir, as mockUid is same as the first call.
+        expect(homedir).toHaveBeenCalledTimes(num);
+        // Extra call was made to geteuid to get the same UID as the first call.
+        expect(processGeteuidSpy).toHaveBeenCalledTimes(num + 1);
+      });
+    });
   });
 });

packages/shared-ini-file-loader/src/getHomeDir.ts

@@ -1,5 +1,16 @@
 import { homedir } from "os";
 import { sep } from "path";
+import { geteuid } from "process";
+
+const homeDirCache: Record<string, string> = {};
+
+const getHomeDirCacheKey = (): string => {
+  // geteuid is only available on POSIX platforms (i.e. not Windows or Android).
+  if (geteuid) {
+    return `${geteuid()}`;
+  }
+  return "DEFAULT";
+};
 
 /**
  * Get the HOME directory for the current runtime.
@@ -13,5 +24,8 @@ export const getHomeDir = (): string => {
   if (USERPROFILE) return USERPROFILE;
   if (HOMEPATH) return `${HOMEDRIVE}${HOMEPATH}`;
 
-  return homedir();
+  const homeDirCacheKey = getHomeDirCacheKey();
+  if (!homeDirCache[homeDirCacheKey]) homeDirCache[homeDirCacheKey] = homedir();
+
+  return homeDirCache[homeDirCacheKey];
 };