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feat: 티켓팅 사이트 서버 시간
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‎src/main/java/com/back/web7_9_codecrete_be/domain/serverTime/controller/TicketServerTimeController.java‎

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package com.back.web7_9_codecrete_be.domain.serverTime.controller;
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import org.springframework.web.bind.annotation.GetMapping;
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import org.springframework.web.bind.annotation.PathVariable;
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import org.springframework.web.bind.annotation.RequestMapping;
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import org.springframework.web.bind.annotation.RestController;
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import com.back.web7_9_codecrete_be.domain.serverTime.dto.ServerTimeResponse;
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import com.back.web7_9_codecrete_be.domain.serverTime.entity.TicketProvider;
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import com.back.web7_9_codecrete_be.domain.serverTime.service.TicketServerTimeService;
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import com.back.web7_9_codecrete_be.global.rsData.RsData;
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import io.swagger.v3.oas.annotations.Operation;
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import io.swagger.v3.oas.annotations.Parameter;
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import io.swagger.v3.oas.annotations.tags.Tag;
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import lombok.RequiredArgsConstructor;
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@Tag(
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name = "Server Time",
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description = """
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외부 티켓 사이트의 서버 시간과
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우리 서버 시간 간의 **차이(offset)** 를 제공하는 API
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지원 티켓사(provider):
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- NOL
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- YES24
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- MELON
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- TICKETLINK
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"""
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)
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@RestController
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@RequiredArgsConstructor
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@RequestMapping("/api/v1/server-time")
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public class TicketServerTimeController {
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private final TicketServerTimeService ticketServerTimeService;
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@Operation(
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summary = "티켓 서버 시간 offset 조회",
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description = """
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외부 티켓 사이트의 HTTP Date 헤더를 기반으로
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우리 서버와의 **시간 차이(offsetMillis)** 를 **밀리초** 단위로 계산해 반환합니다.
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- offsetMillis는 60초간 캐싱됩니다.
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"""
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)
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@GetMapping("/{provider}")
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public RsData<ServerTimeResponse> getServerTime(
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@Parameter(
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description = "티켓 사이트 제공자",
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example = "NOL",
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required = true
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)
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@PathVariable String provider
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) {
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TicketProvider ticketProvider = TicketProvider.valueOf(provider.toUpperCase());
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ServerTimeResponse response = ticketServerTimeService.fetchServerTime(ticketProvider);
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return RsData.success(response);
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}
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}

‎src/main/java/com/back/web7_9_codecrete_be/domain/serverTime/dto/ServerTimeMeasureResult.java‎

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package com.back.web7_9_codecrete_be.domain.serverTime.dto;
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public record ServerTimeMeasureResult(
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long offsetMillis,
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long rttMillis
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) {}
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‎src/main/java/com/back/web7_9_codecrete_be/domain/serverTime/dto/ServerTimeResponse.java‎

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package com.back.web7_9_codecrete_be.domain.serverTime.dto;
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import io.swagger.v3.oas.annotations.media.Schema;
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public record ServerTimeResponse(
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@Schema(
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description = "티켓 사이트 제공자 이름",
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example = "NOL"
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)
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String provider,
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@Schema(
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description = """
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외부 티켓 서버 시간 - 우리 서버 시간 (밀리초 단위)
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예)
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- offsetMillis = -500
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→ 티켓 서버 시간이 우리 서버보다 0.5초 느림
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- offsetMillis = 1200
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→ 티켓 서버 시간이 우리 서버보다 1.2초 빠름
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""",
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example = "-691"
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)
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long offsetMillis
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) {}

‎src/main/java/com/back/web7_9_codecrete_be/domain/serverTime/entity/TicketProvider.java‎

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package com.back.web7_9_codecrete_be.domain.serverTime.entity;
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public enum TicketProvider {
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NOL("https://nol.interpark.com/ticket"),
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YES24("https://ticket.yes24.com"),
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MELON("https://ticket.melon.com"),
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TICKETLINK("https://www.ticketlink.co.kr");
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private final String url;
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TicketProvider(String url) {
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this.url = url;
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}
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public String getUrl() {
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return url;
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}
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}

‎src/main/java/com/back/web7_9_codecrete_be/domain/serverTime/service/TicketServerTimeService.java‎

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package com.back.web7_9_codecrete_be.domain.serverTime.service;
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import java.time.Duration;
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import java.time.Instant;
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import java.time.ZoneId;
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import java.time.format.DateTimeFormatter;
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import java.util.ArrayList;
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import java.util.Comparator;
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import java.util.List;
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import org.springframework.data.redis.core.RedisTemplate;
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import org.springframework.http.HttpHeaders;
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import org.springframework.http.HttpMethod;
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import org.springframework.http.ResponseEntity;
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import org.springframework.stereotype.Service;
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import org.springframework.web.client.RestTemplate;
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import com.back.web7_9_codecrete_be.domain.serverTime.dto.ServerTimeMeasureResult;
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import com.back.web7_9_codecrete_be.domain.serverTime.dto.ServerTimeResponse;
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import com.back.web7_9_codecrete_be.domain.serverTime.entity.TicketProvider;
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import lombok.RequiredArgsConstructor;
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import lombok.extern.slf4j.Slf4j;
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@Service
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@RequiredArgsConstructor
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@Slf4j
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public class TicketServerTimeService {
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private final RestTemplate restTemplate;
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private final RedisTemplate<String, Object> redisTemplate;
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private static final int MEASURE_COUNT = 5;
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private static final int MIN_VALID_SAMPLE = 3;
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private static final ZoneId KST = ZoneId.of("Asia/Seoul");
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private static final Duration OFFSET_TTL = Duration.ofSeconds(60);
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private static final String REDIS_KEY_PREFIX = "serverTime:offset:";
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/**
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* 외부 티켓 서버 시간 조회
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*/
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public ServerTimeResponse fetchServerTime(TicketProvider provider) {
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String redisKey = REDIS_KEY_PREFIX + provider.name();
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Number cached = (Number) redisTemplate.opsForValue().get(redisKey);
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Long offsetMillis = cached != null ? cached.longValue() : null;
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// 캐시 HIT
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if (offsetMillis != null) {
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log.info("[SERVER TIME][CACHE HIT] provider={}, offset={}ms",
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provider.name(), offsetMillis);
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return new ServerTimeResponse(
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provider.name(),
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offsetMillis
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);
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}
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// 캐시 MISS
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long medianOffset = measureMedianOffset(provider);
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redisTemplate.opsForValue()
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.set(redisKey, medianOffset, OFFSET_TTL);
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log.info("[SERVER TIME][CACHE MISS] provider={}, offset={}ms",
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provider.name(), medianOffset);
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return new ServerTimeResponse(
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provider.name(),
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medianOffset
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);
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}
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/**
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* 여러 번 측정 후 RTT 기준 필터링 + 중앙값(offset)
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*/
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private long measureMedianOffset(TicketProvider provider) {
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List<ServerTimeMeasureResult> results = new ArrayList<>();
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for (int i = 0; i < MEASURE_COUNT; i++) {
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try {
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results.add(measureOnce(provider));
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} catch (Exception e) {
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log.warn("[SERVER TIME] measure failed: {}", e.getMessage());
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}
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}
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if (results.size() < MIN_VALID_SAMPLE) {
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throw new IllegalStateException("Not enough valid server time samples");
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}
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results.sort(Comparator.comparingLong(ServerTimeMeasureResult::rttMillis));
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List<Long> offsets = results.stream()
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.limit(results.size() - 1)
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.map(ServerTimeMeasureResult::offsetMillis)
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.sorted()
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.toList();
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return offsets.get(offsets.size() / 2);
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}
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/**
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* 서버 시간 측정
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*/
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private ServerTimeMeasureResult measureOnce(TicketProvider provider) {
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long t1Nano = System.nanoTime();
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long t1Millis = System.currentTimeMillis();
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ResponseEntity<Void> response = restTemplate.exchange(
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provider.getUrl(),
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HttpMethod.HEAD,
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null,
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Void.class
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);
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long t2Nano = System.nanoTime();
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long rttMillis = (t2Nano - t1Nano) / 1_000_000;
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long tMidMillis = t1Millis + (rttMillis / 2);
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String dateHeader = response.getHeaders().getFirst(HttpHeaders.DATE);
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if (dateHeader == null) {
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throw new IllegalStateException("Date header missing");
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}
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Instant serverInstant = DateTimeFormatter.RFC_1123_DATE_TIME
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.parse(dateHeader, Instant::from);
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long offset = serverInstant.toEpochMilli() - tMidMillis;
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return new ServerTimeMeasureResult(offset, rttMillis);
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}
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}

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