fix(emulator): display localhost in function initialization URLs (Fix issue 3728)

[aanyabharti101]

Description

Fixes #3728.

Function initialization messages can display local URLs using 0.0.0.0 or 127.0.0.1, which is inconvenient because developers generally expect a browser-friendly localhost URL.

This change adds display-only URL formatting that replaces those local IPv4 addresses with localhost. Non-loopback hosts remain unchanged, and the emulator's internal binding and networking behavior are not affected.

Before:

http://0.0.0.0:9002/...
http://127.0.0.1:9002/...

After:

http://localhost:9002/...

Scenarios Tested

• Confirmed that 0.0.0.0 is displayed as localhost.
• Confirmed that 127.0.0.1 is displayed as localhost.
• Confirmed that non-loopback hosts remain unchanged.
• Ran the complete related utility test file with all 28 tests passing.
• Ran the changed-file lint check with 0 errors.
• Built the complete Firebase Tools CLI successfully.
• Launched the Functions Emulator and confirmed that initialization URLs display http://localhost:9002/....

Acceptance Criteria

• Tests added for the new behavior
• All directly related tests passing
• Follows the project style requirements
• No unrelated or breaking changes introduced
• Documentation changes are not required

Sample Commands

node lib/bin/firebase.js emulators:start \
  --config scripts/triggers-end-to-end-tests/firebase.json \
  --only functions:v1 \
  --project demo-test

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[gemini-code-assist]

Code Review

This pull request introduces a utility function formatFunctionUrlForDisplay to format function URLs for display by replacing IPv4 wildcard (0.0.0.0) and loopback (127.0.0.1) hostnames with localhost, and integrates it into the functions emulator logs along with corresponding unit tests. The feedback suggests enhancing this utility's robustness by wrapping the URL parsing in a try...catch block to handle invalid URLs gracefully, extending support to IPv6 loopback addresses (::1 and [::1]), and adding unit tests to cover these scenarios.

[gemini-code-assist]

To make this utility more robust and complete, consider the following improvements:\n\n1. Defensive Programming: new URL(url) throws a TypeError if the input is not a valid absolute URL. Wrapping this in a try...catch block and falling back to the original url prevents potential runtime crashes.\n2. IPv6 Support: The current check only covers IPv4 (127.0.0.1 and 0.0.0.0). Adding support for IPv6 loopback ([::1] and ::1) ensures consistency with other localhost utilities in this file (like isLocalHost).

Suggested change

	export function formatFunctionUrlForDisplay(url: string): string {
	const parsedUrl = new URL(url);
	if (parsedUrl.hostname === "0.0.0.0" || parsedUrl.hostname === "127.0.0.1") {
	parsedUrl.hostname = "localhost";
	}
	return parsedUrl.toString();
	}
	export function formatFunctionUrlForDisplay(url: string): string {
	try {
	const parsedUrl = new URL(url);
	if (
	parsedUrl.hostname === "0.0.0.0" ||
	parsedUrl.hostname === "127.0.0.1" ||
	parsedUrl.hostname === "::1" ||
	parsedUrl.hostname === "[::1]"
	) {
	parsedUrl.hostname = "localhost";
	}
	return parsedUrl.toString();
	} catch {
	return url;
	}
	}

[gemini-code-assist]

Add unit tests to verify the behavior of formatFunctionUrlForDisplay with IPv6 loopback addresses and invalid URL strings, matching the defensive programming and IPv6 improvements.

    it("should preserve non-loopback hosts", () => {
      const url = "http://192.168.1.10:5001/demo-project/us-central1/testFunction";

      expect(formatFunctionUrlForDisplay(url)).to.equal(url);
    });

    it("should display localhost instead of the IPv6 loopback address", () => {
      const url = "http://[::1]:5001/demo-project/us-central1/testFunction";

      expect(formatFunctionUrlForDisplay(url)).to.equal(
        "http://localhost:5001/demo-project/us-central1/testFunction",
      );
    });

    it("should gracefully handle and return invalid URLs", () => {
      const url = "invalid-url-string";

      expect(formatFunctionUrlForDisplay(url)).to.equal(url);
    });

[aanyabharti101]

Hi @yuchenshi and @joehan, I’ve opened this PR to address #3728. When you have a chance, I’d appreciate your review. Thank you!