fix: function:serve shows undefined port in url

src/lib/functions/netlify-function.js

@@ -131,7 +131,13 @@ class NetlifyFunction {
   }
 
   get url() {
-    return `http://localhost:${this.settings.port}/.netlify/functions/${this.name}`
+    // This line fixes the issue here https://github.com/netlify/cli/issues/4116
+    // Not sure why `settings.port` was used here nor does a valid reference exist.
+    // However, it remains here to serve whatever purpose for which it was added.
+    const port = this.settings.port || this.settings.functionsPort
+
+    const url = new URL(`/.netlify/functions/${this.name}`, `http://localhost:${port}`)
+    return url.href
   }
 }
 

tests/integration/20.command.functions.test.js

@@ -8,6 +8,7 @@ const getPort = require('get-port')
 const waitPort = require('wait-port')
 
 const fs = require('../../src/lib/fs')
+const { NetlifyFunction } = require('../../src/lib/functions/netlify-function')
 
 const callCli = require('./utils/call-cli')
 const cliPath = require('./utils/cli-path')
@@ -21,6 +22,20 @@ const { withSiteBuilder } = require('./utils/site-builder')
 
 const test = isCI ? avaTest.serial.bind(avaTest) : avaTest
 
+test('should return the correct function url for a NetlifyFunction object', (t) => {
+  const port = 7331
+  const functionName = 'test-function'
+
+  const functionUrl = `http://localhost:${port}/.netlify/functions/${functionName}`
+
+  const ntlFunction = new NetlifyFunction({
+    name: functionName,
+    settings: { functionsPort: port },
+  })
+
+  t.is(ntlFunction.url, functionUrl)
+})
+
 test('should return function response when invoked with no identity argument', async (t) => {
   await withSiteBuilder('function-invoke-with-no-identity-argument', async (builder) => {
     builder.withNetlifyToml({ config: { functions: { directory: 'functions' } } }).withFunction({