Networking interview questions

URLSession structure

You've inherited an app that does all its networking through URLSession.shared. Can you walk me through the objects involved when URLSession handles one reques…

#urlsession #urlsessionconfiguration #task #shared

Background transfers

In an app that uses URLSession, you want a large file download to keep going after the user sends the app to the Home screen, and to be handled correctly when …

#background-session #downloadtask #uploadtask

Codable JSON decoding

The server responds with something like {"user_id": 3, "created_at": "2026-09-11T02:00:00Z"}. Can you walk me through how that response gets mapped onto a Swif…

#codable #decodable #jsondecoder #serialization

URLComponents and URL encoding

You want to send the search term "café & bar" as the query parameter q to https://api.example.com/search. Select all the correct statements about building the …

#urlcomponents #percent-encoding #query #url

HTTP methods and idempotency

In a REST API, select all the methods that are idempotent, meaning sending the same request several times leaves the server in the same state as sending it onc…

#rest #http-method #idempotent

NetworkingMultiple choiceIntro카카오

HTTP status codes

Select all the correct statements about HTTP response status codes.

#http #status-code #401 #403

NetworkingMultiple choiceIntroSAP

Transport protocols and data link basics

In a first-round iOS interview you get a networking fundamentals question: "What protocols are in the transport layer, and what are frames and ARP in the data …

#tcp #udp #arp #osi

Unstable response schemas

You're decoding responses into the model below with Codable, but the server includes the nickname field in some responses and leaves it out of others entirely.…

#codable #optional #decodeifpresent #schema

Predicting a Codable decode

What happens when you run this Codable decoding code? …

#codable #decodable #optional #null

API error design

You've found network-layer code that collapses every failure into completion(nil). As a senior engineer, how would you model API errors and carry them all the …

#error-handling #result #typed-throws #http-status

Retry strategy

A payment confirmation API times out now and then. A junior engineer opened a PR that says "if it fails, send it three more times." What would you point out?

#retry #exponential-backoff #jitter #idempotency

What to retry

An idempotent GET request failed. Select all the failures where an automatic retry (with backoff) is appropriate.

#retry #http-status #transient-error

Response caching and memory cache

An image-heavy feed app keeps getting memory warnings. How should the response cache have been set up?

#urlcache #nscache #http-cache #memory-warning

NSCache traits

Select all the statements that correctly describe how NSCache differs from Dictionary.

#nscache #dictionary #cache

HTTP/1.1 vs HTTP/2

Select all the statements that correctly describe HTTP/2 compared with HTTP/1.1.

#http2 #multiplexing #hpack #urlsession

Handling connectivity state

There's code that checks Reachability at launch so it can show a "No internet connection" popup. What's the problem with that approach?

#nwpathmonitor #waitsforconnectivity #reachability #connectivity

Synchronous requests and moving to async/await

The legacy code has a function that waits on a URLSession response with DispatchSemaphore to make it "synchronous," and older spots still use NSURLConnection.s…

#async-await #urlsession #nsurlconnection #main-thread

NetworkingMultiple choiceBasicsGoogle

Image download without third parties

At an onsite whiteboard you're asked to download images from a list of URLs and show them in list cells, without a library like Kingfisher. Select all the corr…

#urlsession #datatask #downloadtask #main-thread

NetworkingShort answerBasicsDoorDash

Provided completion code and choosing an async style

In a coding screen the company hands you completion-handler-based networking code and a JSON file, asks for a list screen, and says you can use async/await, Co…

#async-await #continuation #combine #dependency-injection

How HTTPS capture works and defending against it

How can tools like Charles and Proxyman show app traffic that's encrypted with HTTPS in plain text?

#https #mitm #proxy #certificate-pinning

NetworkingShort answerBasicsTencent

URLSession redirect handling

After login, a request sent with an Authorization header gets a 302 from the server to a different host, and then a 401 comes back. Why did that 401 happen?

#redirect #urlsession-delegate #authorization-header #302

NetworkingShort answerBasicsAlibaba Group

What HTTPDNS is for and its side effects

There are reports that API access is slow, or lands on the wrong server, only for users on certain carriers and in certain regions, and a senior teammate says …

#dns #httpdns #sni #cdn

NetworkingMultiple choiceBasics토스

Sending JSON POST with URLRequest

For a take-home assignment you wrote this code that POSTs JSON with URLRequest. Select all the statements that correctly describe problems with it. …

#urlrequest #post #content-type #status-code

NetworkingShort answerBasics지마켓글로벌

REST from the client's side

The interviewer says "explain what a RESTful API is." Going beyond the textbook definition, from the point of view of someone building an iOS client, how does …

#rest #http-method #idempotent #api-design

NetworkingShort answerBasicsCitiinterview report

Designing a networking layer on URLSession

In a phone screen you're asked to design a simple networking layer in Swift. Without third parties, what types would you put on top of URLSession, and what is …

#networking-layer #endpoint #generic #error-handling

NetworkingShort answerBasicsCalm

Fetching, sorting, and showing a JSON list (live coding)

This is a senior iOS virtual onsite, live coding. You have to build, without searching, an app that fetches a list of content from a public JSON API, parses it…

#json #codable #sorting #live-coding

NetworkingShort answerBasicsThe New York Timesinterview report

Parsing XML and a display transform layer

A take-home assignment asks you to download an XML feed from the company's API, show it as a list, and add a feature that swaps the English strings for made-up…

#xml #xmlparser #parsing #take-home

HTTPS and TLS

When the app sends a request to https://api.example.com, what happens at the TLS level before the first byte comes back?

#https #tls #certificate #ats

Image upload pipeline

Say you're building a feature that uploads several profile photos. What does the multipart request that a library builds for you actually look like?

#multipart #upload #heic #photokit

WebSocket connection management

You've got a bug report that the chat app's WebSocket connection drops often and the app is slow to notice. How would you detect a dropped connection promptly …

#websocket #urlsessionwebsockettask #reconnect #ping

Diagnosing one network environment

A report says image uploads work on cellular but fail only on the office Wi-Fi. What causes would you suspect?

#debugging #wifi #captive-portal #proxy

Canceling an async URLSession request

In this Swift Concurrency code that sends a URLSession request, task.cancel() runs before the network response arrives. What happens? …

#async-await #cancellation #task #urlerror

Token refresh concurrency

Five API calls go out at once when a screen appears, the access token has expired, and all five get a 401. Right now each request calls refresh on its own, so …

#auth #token-refresh #actor #401

URLSessionConfiguration options

In an app that uses URLSession, a user on the subway loses the connection for a moment. Instead of failing immediately, you want the request to wait until the …

#urlsessionconfiguration #waitsforconnectivity #timeout

NetworkingShort answerAdvancedApple

Image downloader and cache (request coalescing)

In a coding interview you're asked to build, in 30 minutes, an ImageManager that fetches an image by URL and returns it from cache if it's been fetched before.…

#image-cache #nscache #actor #in-flight

NetworkingShort answerAdvancedDoorDash

Search debounce, cancellation, and out-of-order responses

You're asked to build, without third parties, a screen that calls a server search API on every keystroke in a search bar and refreshes the results list. How wo…

#search #debounce #task-cancellation #race-condition

NetworkingShort answerAdvancedPayPal

Idempotency keys for transfers

The user taps the send money button, and the signal drops right after the request goes out. What should the app do?

#idempotency #retry #payments #reliability

NetworkingMultiple choiceAdvancedRevolutinterview report

Handling a payment request timeout

A payment confirmation request, POST /payments, failed with URLError.timedOut. Select all the correct statements.

#timeout #idempotency #retry #urlsessionconfiguration

NetworkingShort answerAdvancedNetEase

Resuming large downloads and integrity

You're downloading an audio file of several hundred MB, and the app gets terminated or the network drops. You want to resume instead of starting over. Which HT…

#range-request #resume-data #download-task #integrity

NetworkingMultiple choiceAdvancedMeituan

TLS 1.3 vs 1.2

The server team moved to TLS 1.3 and says app connections got faster. Select all the statements that correctly describe what changed from TLS 1.2 to 1.3.

#tls #tls13 #handshake #forward-secrecy

NetworkingMultiple choiceAdvancedSonyinterview report

Downloading large media

You're building a feature that downloads video and audio files (hundreds of MB to GB) for offline playback. Select all the correct statements about a URLSessio…

#download-task #background-session #media #resume-data

NetworkingShort answerAdvanced코인원interview report

REST snapshot plus WebSocket delta consistency

This is an exchange app's order book and ticker screen. The design fetches the current snapshot over REST first and then applies only the changes (deltas) that…

#websocket #snapshot #sequence-number #orderbook

NetworkingMultiple choiceAdvanced스푼라디오interview report

Live broadcast: HLS and WebSocket roles

In a live audio broadcast app, the broadcast audio plays over HLS and chat goes over WebSocket. Select all the correct statements about the two protocols' char…

#hls #websocket #streaming #live

NetworkingShort answerAdvanced카카오엔터테인먼트interview report

FairPlay key exchange on HLS

A music and video streaming app plays paid content over HLS and has to add FairPlay Streaming (DRM) for copyright protection. On top of the HLS playback flow, …

#hls #fairplay #drm #avcontentkeysession

Network metrics and request priority

A report says the app is slow only for users in one region, but the server metrics look normal. What would you measure in the app's network layer to split the …

#urlsessiontaskmetrics #priority #http2 #connection-coalescing

NetworkingShort answerExpertPayPalinterview report

Priorities in an API-to-list exercise

In a one-hour exercise you're asked to build an app that calls a public API and shows the results in a list, and you'll be graded on architecture, error handli…

#live-coding #architecture #error-handling #pagination

Background session completion

A large file is downloading through a background URLSession and the app gets terminated completely (by the system, not a swipe up). When the download finishes,…

#background-session #handleeventsforbackgroundurlsession #downloadtask #delegate

HTTP cache revalidation

A server response came with Cache-Control: max-age=60 and ETag: "abc" and was stored in URLCache. With the default cache policy (.useProtocolCachePolicy), if y…

#urlcache #etag #cache-control #304