Functional Scope (In-Scope)
- Strict Server-Side Comment Sequencing: Assigns monotonic sequence IDs to prevent out-of-order comments.
- Synchronous Word Filtering: Moderates content using quick, lock-free keyword matching algorithms.
- In-Memory Catch-Up buffers: Keeps circular caches of the last 50 approved comments to bootstrap joining viewers.
- Historical VOD replay aggregates: Archives approved content to support indexed replays at specific stream times.
Explicit Boundaries (Out-of-Scope)
- Web Socket Framing Protocol: Mocks socket connections and protocol upgrades (Socket.io or raw ws).
- Machine Learning Moderation Models: Simplifies image classification and complex deep-learning NLP pipelines.
Production reference implementations demonstrating sequence generators, circular buffers, moderation filters, and VOD query engines in Java and Python:
// ─── JAVA BLUEPRINT ──────────────────────────────────────────────────────────
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicLong;
import java.util.stream.Collectors;
enum ModerationStatus {
PENDING, APPROVED, REJECTED
}
class Comment {
private final String id;
private final String streamId;
private final String authorId;
private final String text;
private final long timestampMs;
private final long sequenceNumber;
private final ModerationStatus status;
public Comment(String id, String streamId, String authorId, String text, long sequenceNumber, ModerationStatus status) {
this.id = id;
this.streamId = streamId;
this.authorId = authorId;
this.text = text;
this.timestampMs = System.currentTimeMillis();
this.sequenceNumber = sequenceNumber;
this.status = status;
}
public String getId() { return id; }
public String getStreamId() { return streamId; }
public String getAuthorId() { return authorId; }
public String getText() { return text; }
public long getTimestampMs() { return timestampMs; }
public long getSequenceNumber() { return sequenceNumber; }
public ModerationStatus getStatus() { return status; }
}
class LiveCommentsService {
private final ConcurrentHashMap<String, ConcurrentLinkedQueue<Comment>> commentsStore = new ConcurrentHashMap<>(); // VOD Replay store
private final ConcurrentHashMap<String, ConcurrentLinkedDeque<Comment>> catchUpBuffers = new ConcurrentHashMap<>(); // Circular memory buffers for catch-up
private final ConcurrentHashMap<String, AtomicLong> sequenceGenerators = new ConcurrentHashMap<>();
private final Set<String> moderationBlacklist = ConcurrentHashMap.newKeySet();
private final int catchUpBufferSize = 50;
public void addBlacklistWord(String word) {
moderationBlacklist.add(word.toLowerCase());
}
// Ingestion pipeline: fast-path moderation -> sequencing -> buffer -> broadcast
public Comment ingestComment(String authorId, String streamId, String text) {
// 1. Moderation filter block
ModerationStatus status = runModerationFilter(text);
if (status == ModerationStatus.REJECTED) {
return new Comment(UUID.randomUUID().toString(), streamId, authorId, text, -1, ModerationStatus.REJECTED);
}
// 2. Server-side atomic sequencing
long sequence = sequenceGenerators.computeIfAbsent(streamId, k -> new AtomicLong(0)).incrementAndGet();
String commentId = UUID.randomUUID().toString();
Comment comment = new Comment(commentId, streamId, authorId, text, sequence, ModerationStatus.APPROVED);
// 3. Persist to VOD archive list
commentsStore.computeIfAbsent(streamId, k -> new ConcurrentLinkedQueue<>()).add(comment);
// 4. Update circular catch-up buffer
ConcurrentLinkedDeque<Comment> buffer = catchUpBuffers.computeIfAbsent(streamId, k -> new ConcurrentLinkedDeque<>());
buffer.addLast(comment);
while (buffer.size() > catchUpBufferSize) {
buffer.pollFirst(); // evict oldest
}
// 5. Broadcast to online viewers
broadcastComment(comment);
return comment;
}
// Catch-up path for users joining stream
public List<Comment> getJoinerCatchUpSnapshot(String streamId) {
ConcurrentLinkedDeque<Comment> buffer = catchUpBuffers.get(streamId);
if (buffer == null) {
return Collections.emptyList();
}
return new ArrayList<>(buffer);
}
// VOD replay: retrieve all comments in a specific stream and time window
public List<Comment> getVODReplayRange(String streamId, long startTimestampMs, long endTimestampMs) {
ConcurrentLinkedQueue<Comment> store = commentsStore.get(streamId);
if (store == null) {
return Collections.emptyList();
}
return store.stream()
.filter(c -> c.getTimestampMs() >= startTimestampMs && c.getTimestampMs() <= endTimestampMs)
.sorted(Comparator.comparingLong(Comment::getSequenceNumber))
.collect(Collectors.toList());
}
private ModerationStatus runModerationFilter(String text) {
String lowerContent = text.toLowerCase();
for (String badWord : moderationBlacklist) {
if (lowerContent.contains(badWord)) {
return ModerationStatus.REJECTED;
}
}
return ModerationStatus.APPROVED;
}
private void broadcastComment(Comment comment) {
System.out.println("BROADCAST COMMENT -> Stream: " + comment.getStreamId() + " [" + comment.getSequenceNumber() + "] " + comment.getAuthorId() + ": " + comment.getText());
}
}
public class Main {
public static void main(String[] args) {
System.out.println("=== JAVA LIVE COMMENTS SIMULATION ===");
LiveCommentsService service = new LiveCommentsService();
service.addBlacklistWord("spam");
service.ingestComment("user1", "streamA", "Hello world!");
service.ingestComment("user2", "streamA", "This is spam content");
service.ingestComment("user3", "streamA", "Great stream!");
List<Comment> recent = service.getJoinerCatchUpSnapshot("streamA");
System.out.println("Catch-up size: " + recent.size());
for (Comment c : recent) {
System.out.println("Catch-up Comment: " + c.getText());
}
System.out.println("=== END OF JAVA SIMULATION ===");
}
}