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Merged
itssimon merged 2 commits into from
Jan 22, 2026
Merged

Make instance UUIDs stable across restarts #51

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8345d61
Make instance UUIDs stable across restarts
itssimon Jan 22, 2026
5b834b6
Fix
itssimon Jan 22, 2026
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3 changes: 3 additions & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
@@ -1,4 +1,7 @@
target/

# VS Code
.vscode/

# misc
.DS_Store
10 changes: 5 additions & 5 deletions src/main/java/io/apitally/common/ApitallyClient.java
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Expand Up @@ -11,7 +11,6 @@
import java.util.Optional;
import java.util.Queue;
import java.util.Random;
import java.util.UUID;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executors;
Expand Down Expand Up @@ -60,7 +59,7 @@ public enum HubRequestStatus {

private final String clientId;
private final String env;
private final UUID instanceUuid;
private final InstanceLock instanceLock;
private final HttpClient httpClient;
private ScheduledExecutorService scheduler;
private ScheduledFuture<?> syncTask;
Expand All @@ -80,7 +79,7 @@ public enum HubRequestStatus {
public ApitallyClient(String clientId, String env, RequestLoggingConfig requestLoggingConfig) {
this.clientId = clientId;
this.env = env;
this.instanceUuid = java.util.UUID.randomUUID();
this.instanceLock = InstanceLock.create(clientId, env);
this.httpClient = createHttpClient();

this.requestCounter = new RequestCounter();
Expand Down Expand Up @@ -115,7 +114,7 @@ private URI getHubUrl(String endpoint, String query) {
}

public void setStartupData(List<Path> paths, Map<String, String> versions, String client) {
startupData = new StartupData(instanceUuid, paths, versions, client);
startupData = new StartupData(instanceLock.getInstanceUuid(), paths, versions, client);
}

private void sendStartupData() {
Expand All @@ -142,7 +141,7 @@ private void sendStartupData() {

private void sendSyncData() {
SyncData data = new SyncData(
instanceUuid,
instanceLock.getInstanceUuid(),
requestCounter.getAndResetRequests(),
validationErrorCounter.getAndResetValidationErrors(),
serverErrorCounter.getAndResetServerErrors(),
Expand Down Expand Up @@ -314,6 +313,7 @@ public void shutdown() {
scheduler.shutdownNow();
}
}
instanceLock.close();
} catch (InterruptedException e) {
if (scheduler != null) {
scheduler.shutdownNow();
Expand Down
135 changes: 135 additions & 0 deletions src/main/java/io/apitally/common/InstanceLock.java
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@@ -0,0 +1,135 @@
package io.apitally.common;

import java.io.Closeable;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.FileTime;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.time.Duration;
import java.time.Instant;
import java.util.HexFormat;
import java.util.UUID;

public class InstanceLock implements Closeable {
private static final int MAX_SLOTS = 100;
private static final int MAX_LOCK_AGE_SECONDS = 24 * 60 * 60;

private final UUID instanceUuid;
private final FileChannel lockChannel;

private InstanceLock(UUID uuid, FileChannel lockChannel) {
this.instanceUuid = uuid;
this.lockChannel = lockChannel;
}

public UUID getInstanceUuid() {
return instanceUuid;
}

public static InstanceLock create(String clientId, String env) {
return create(clientId, env, Path.of(System.getProperty("java.io.tmpdir"), "apitally"));
}

static InstanceLock create(String clientId, String env, Path lockDir) {
try {
Files.createDirectories(lockDir);
} catch (Exception e) {
return new InstanceLock(UUID.randomUUID(), null);
}

String appEnvHash;
try {
appEnvHash = getAppEnvHash(clientId, env);
} catch (Exception e) {
return new InstanceLock(UUID.randomUUID(), null);
}

for (int slot = 0; slot < MAX_SLOTS; slot++) {
Path lockPath = lockDir.resolve("instance_" + appEnvHash + "_" + slot + ".lock");
FileChannel channel = null;
try {
channel = FileChannel.open(
lockPath,
StandardOpenOption.CREATE,
StandardOpenOption.READ,
StandardOpenOption.WRITE);

FileLock lock = channel.tryLock();
if (lock == null) {
channel.close();
continue;
}

FileTime lastModified = Files.getLastModifiedTime(lockPath);
boolean tooOld = Duration.between(lastModified.toInstant(), Instant.now()).getSeconds() > MAX_LOCK_AGE_SECONDS;

String existingUuid = readChannel(channel);
UUID uuid = parseUuid(existingUuid);

if (uuid != null && !tooOld) {
return new InstanceLock(uuid, channel);
}

UUID newUuid = UUID.randomUUID();
channel.truncate(0);
channel.write(ByteBuffer.wrap(newUuid.toString().getBytes(StandardCharsets.UTF_8)));
channel.force(true);

return new InstanceLock(newUuid, channel);
} catch (Exception e) {
if (channel != null) {
try {
channel.close();
} catch (IOException ignored) {
}
}
}
}

return new InstanceLock(UUID.randomUUID(), null);
}

private static String readChannel(FileChannel channel) throws IOException {
channel.position(0);
ByteBuffer buffer = ByteBuffer.allocate(64);
int bytesRead = channel.read(buffer);
if (bytesRead <= 0) {
return "";
}
return new String(buffer.array(), 0, bytesRead, StandardCharsets.UTF_8).trim();
}

private static UUID parseUuid(String s) {
if (s == null || s.isEmpty()) {
return null;
}
try {
return UUID.fromString(s);
} catch (IllegalArgumentException e) {
return null;
}
}

private static String getAppEnvHash(String clientId, String env) throws NoSuchAlgorithmException {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest((clientId + ":" + env).getBytes(StandardCharsets.UTF_8));
return HexFormat.of().formatHex(hash, 0, 4);
}

@Override
public void close() {
if (lockChannel != null) {
try {
lockChannel.close();
} catch (IOException ignored) {
}
}
}
}
152 changes: 152 additions & 0 deletions src/test/java/io/apitally/common/InstanceLockTest.java
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package io.apitally.common;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.Comparator;
import java.util.HexFormat;
import java.util.UUID;

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

class InstanceLockTest {
private Path tempDir;

@BeforeEach
void setUp() throws IOException {
tempDir = Files.createTempDirectory("apitally_test_");
}

@AfterEach
void tearDown() throws IOException {
if (tempDir != null && Files.exists(tempDir)) {
try (var paths = Files.walk(tempDir)) {
paths.sorted(Comparator.reverseOrder())
.forEach(path -> {
try {
Files.deleteIfExists(path);
} catch (IOException ignored) {
}
});
}
}
}

@Test
void createsNewUUID() throws IOException {
String clientId = UUID.randomUUID().toString();
String env = "test";

try (InstanceLock lock = InstanceLock.create(clientId, env, tempDir)) {
assertNotNull(lock.getInstanceUuid());

String hash = getAppEnvHash(clientId, env);
Path lockFile = tempDir.resolve("instance_" + hash + "_0.lock");
assertTrue(Files.exists(lockFile));
}
}

@Test
void reusesExistingUUID() throws IOException {
String clientId = UUID.randomUUID().toString();
String env = "test";

UUID firstUuid;
try (InstanceLock lock1 = InstanceLock.create(clientId, env, tempDir)) {
firstUuid = lock1.getInstanceUuid();
}

try (InstanceLock lock2 = InstanceLock.create(clientId, env, tempDir)) {
assertEquals(firstUuid, lock2.getInstanceUuid());
}
}

@Test
void differentEnvsGetDifferentUUIDs() throws IOException {
String clientId = UUID.randomUUID().toString();

try (InstanceLock lock1 = InstanceLock.create(clientId, "env1", tempDir);
InstanceLock lock2 = InstanceLock.create(clientId, "env2", tempDir)) {
assertNotEquals(lock1.getInstanceUuid(), lock2.getInstanceUuid());
}
}

@Test
void multipleSlots() throws IOException {
String clientId = UUID.randomUUID().toString();
String env = "test";

try (InstanceLock lock1 = InstanceLock.create(clientId, env, tempDir);
InstanceLock lock2 = InstanceLock.create(clientId, env, tempDir);
InstanceLock lock3 = InstanceLock.create(clientId, env, tempDir)) {

assertNotEquals(lock1.getInstanceUuid(), lock2.getInstanceUuid());
assertNotEquals(lock2.getInstanceUuid(), lock3.getInstanceUuid());
assertNotEquals(lock1.getInstanceUuid(), lock3.getInstanceUuid());

String hash = getAppEnvHash(clientId, env);
assertTrue(Files.exists(tempDir.resolve("instance_" + hash + "_0.lock")));
assertTrue(Files.exists(tempDir.resolve("instance_" + hash + "_1.lock")));
assertTrue(Files.exists(tempDir.resolve("instance_" + hash + "_2.lock")));
}
}

@Test
void overwritesOldUUID() throws IOException {
String clientId = UUID.randomUUID().toString();
String env = "test";
String hash = getAppEnvHash(clientId, env);

String oldUuid = "550e8400-e29b-41d4-a716-446655440000";
Path lockFile = tempDir.resolve("instance_" + hash + "_0.lock");
Files.writeString(lockFile, oldUuid);
Instant oldTime = Instant.now().minus(25, ChronoUnit.HOURS);
Files.setLastModifiedTime(lockFile, java.nio.file.attribute.FileTime.from(oldTime));

try (InstanceLock lock = InstanceLock.create(clientId, env, tempDir)) {
assertNotEquals(UUID.fromString(oldUuid), lock.getInstanceUuid());
assertNotNull(lock.getInstanceUuid());
}
}

@Test
void overwritesInvalidUUID() throws IOException {
String clientId = UUID.randomUUID().toString();
String env = "test";
String hash = getAppEnvHash(clientId, env);

Path lockFile = tempDir.resolve("instance_" + hash + "_0.lock");
Files.writeString(lockFile, "not-a-valid-uuid");

UUID uuid;
try (InstanceLock lock = InstanceLock.create(clientId, env, tempDir)) {
uuid = lock.getInstanceUuid();
assertNotNull(uuid);
}

String content = Files.readString(lockFile).trim();
assertEquals(uuid.toString(), content);
}

private static String getAppEnvHash(String clientId, String env) {
try {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest((clientId + ":" + env).getBytes(StandardCharsets.UTF_8));
return HexFormat.of().formatHex(hash, 0, 4);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException("SHA-256 not available", e);
}
}
}