@ydbjs/topic/dist/writer/_init_reponse.js

YDB Topics client for publish-subscribe messaging. Provides at-least-once delivery, exactly-once publishing, FIFO guarantees, and scalable message processing for unstructured data.

import { _flush } from './_flush.js';
export const _on_init_response = function on_init_response(ctx, input) {
    let serverLastSeqNo = input.lastSeqNo || 0n;
    let currentLastSeqNo = ctx.lastSeqNo;
    let isFirstInit = currentLastSeqNo === undefined;
    let lastSeqNoChanged = isFirstInit || currentLastSeqNo !== serverLastSeqNo;
    // Return inflight messages to buffer
    while (ctx.inflight.length > 0) {
        const message = ctx.inflight.pop();
        if (!message) {
            continue;
        }
        ctx.buffer.unshift(message);
        ctx.updateBufferSize(BigInt(message.data.length));
    }
    // If this is the first initialization or server provided a new lastSeqNo, and we're in auto seqNo mode,
    // renumber all messages in buffer to continue from serverLastSeqNo + 1
    // Always renumber on first init, even if currentLastSeqNo === serverLastSeqNo (messages written before init)
    // Also renumber if there are messages in buffer that were written before init (their seqNo start from 1, not serverLastSeqNo + 1)
    let finalLastSeqNo = serverLastSeqNo;
    let shouldRenumber = false;
    // Only renumber in auto mode (when user didn't provide seqNo)
    if (!ctx.isSeqNoProvided && ctx.buffer.length > 0) {
        if (isFirstInit) {
            // First initialization: always renumber messages written before init
            shouldRenumber = true;
        }
        else if (lastSeqNoChanged) {
            // Reconnection: renumber if server's lastSeqNo changed
            shouldRenumber = true;
        }
        else if (ctx.buffer.length > 0) {
            // Check if messages in buffer were written before init (seqNo start from 1, not serverLastSeqNo + 1)
            // If first message's seqNo is <= serverLastSeqNo, it was written before init and needs renumbering
            let firstMessageSeqNo = ctx.buffer[0]?.seqNo;
            if (firstMessageSeqNo !== undefined &&
                firstMessageSeqNo <= serverLastSeqNo) {
                shouldRenumber = true;
            }
        }
    }
    if (shouldRenumber) {
        let nextSeqNo = serverLastSeqNo + 1n;
        // Renumber all messages in buffer sequentially starting from serverLastSeqNo + 1
        for (let message of ctx.buffer) {
            message.seqNo = nextSeqNo;
            nextSeqNo++;
        }
        // Update lastSeqNo to the last renumbered seqNo so flush() returns correct value
        finalLastSeqNo = nextSeqNo - 1n;
        ctx.updateLastSeqNo(finalLastSeqNo);
    }
    else if (lastSeqNoChanged) {
        // Store the last sequence number from the server if we didn't renumber
        ctx.updateLastSeqNo(serverLastSeqNo);
    }
    // Flush the buffer to send any pending messages
    _flush(ctx);
};
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