next/dist/esm/server/app-render/collect-segment-data.js

The React Framework

import { jsx as _jsx } from "react/jsx-runtime";
// eslint-disable-next-line import/no-extraneous-dependencies
import { createFromReadableStream } from 'react-server-dom-webpack/client.edge';
// eslint-disable-next-line import/no-extraneous-dependencies
import { unstable_prerender as prerender } from 'react-server-dom-webpack/static.edge';
import { streamFromBuffer, streamToBuffer } from '../stream-utils/node-web-streams-helper';
import { waitAtLeastOneReactRenderTask } from '../../lib/scheduler';
import { encodeChildSegmentKey, encodeSegment, ROOT_SEGMENT_KEY } from '../../shared/lib/segment-cache/segment-value-encoding';
import { getDigestForWellKnownError } from './create-error-handler';
function onSegmentPrerenderError(error) {
    const digest = getDigestForWellKnownError(error);
    if (digest) {
        return digest;
    }
// We don't need to log the errors because we would have already done that
// when generating the original Flight stream for the whole page.
}
export async function collectSegmentData(shouldAssumePartialData, fullPageDataBuffer, staleTime, clientModules, serverConsumerManifest, fallbackRouteParams) {
    // Traverse the router tree and generate a prefetch response for each segment.
    // A mutable map to collect the results as we traverse the route tree.
    const resultMap = new Map();
    // Before we start, warm up the module cache by decoding the page data once.
    // Then we can assume that any remaining async tasks that occur the next time
    // are due to hanging promises caused by dynamic data access. Note we only
    // have to do this once per page, not per individual segment.
    //
    try {
        await createFromReadableStream(streamFromBuffer(fullPageDataBuffer), {
            serverConsumerManifest
        });
        await waitAtLeastOneReactRenderTask();
    } catch  {}
    // Create an abort controller that we'll use to stop the stream.
    const abortController = new AbortController();
    const onCompletedProcessingRouteTree = async ()=>{
        // Since all we're doing is decoding and re-encoding a cached prerender, if
        // serializing the stream takes longer than a microtask, it must because of
        // hanging promises caused by dynamic data.
        await waitAtLeastOneReactRenderTask();
        abortController.abort();
    };
    // Generate a stream for the route tree prefetch. While we're walking the
    // tree, we'll also spawn additional tasks to generate the segment prefetches.
    // The promises for these tasks are pushed to a mutable array that we will
    // await once the route tree is fully rendered.
    const segmentTasks = [];
    const { prelude: treeStream } = await prerender(// RootTreePrefetch is not a valid return type for a React component, but
    // we need to use a component so that when we decode the original stream
    // inside of it, the side effects are transferred to the new stream.
    // @ts-expect-error
    /*#__PURE__*/ _jsx(PrefetchTreeData, {
        shouldAssumePartialData: shouldAssumePartialData,
        fullPageDataBuffer: fullPageDataBuffer,
        fallbackRouteParams: fallbackRouteParams,
        serverConsumerManifest: serverConsumerManifest,
        clientModules: clientModules,
        staleTime: staleTime,
        segmentTasks: segmentTasks,
        onCompletedProcessingRouteTree: onCompletedProcessingRouteTree
    }), clientModules, {
        signal: abortController.signal,
        onError: onSegmentPrerenderError
    });
    // Write the route tree to a special `/_tree` segment.
    const treeBuffer = await streamToBuffer(treeStream);
    resultMap.set('/_tree', treeBuffer);
    // Now that we've finished rendering the route tree, all the segment tasks
    // should have been spawned. Await them in parallel and write the segment
    // prefetches to the result map.
    for (const [segmentPath, buffer] of (await Promise.all(segmentTasks))){
        resultMap.set(segmentPath, buffer);
    }
    return resultMap;
}
async function PrefetchTreeData({ shouldAssumePartialData, fullPageDataBuffer, fallbackRouteParams, serverConsumerManifest, clientModules, staleTime, segmentTasks, onCompletedProcessingRouteTree }) {
    // We're currently rendering a Flight response for the route tree prefetch.
    // Inside this component, decode the Flight stream for the whole page. This is
    // a hack to transfer the side effects from the original Flight stream (e.g.
    // Float preloads) onto the Flight stream for the tree prefetch.
    // TODO: React needs a better way to do this. Needed for Server Actions, too.
    const initialRSCPayload = await createFromReadableStream(createUnclosingPrefetchStream(streamFromBuffer(fullPageDataBuffer)), {
        serverConsumerManifest
    });
    const buildId = initialRSCPayload.b;
    // FlightDataPath is an unsound type, hence the additional checks.
    const flightDataPaths = initialRSCPayload.f;
    if (flightDataPaths.length !== 1 && flightDataPaths[0].length !== 3) {
        console.error('Internal Next.js error: InitialRSCPayload does not match the expected ' + 'shape for a prerendered page during segment prefetch generation.');
        return null;
    }
    const flightRouterState = flightDataPaths[0][0];
    const seedData = flightDataPaths[0][1];
    const head = flightDataPaths[0][2];
    // Compute the route metadata tree by traversing the FlightRouterState. As we
    // walk the tree, we will also spawn a task to produce a prefetch response for
    // each segment.
    const tree = collectSegmentDataImpl(shouldAssumePartialData, flightRouterState, buildId, seedData, fallbackRouteParams, fullPageDataBuffer, clientModules, serverConsumerManifest, ROOT_SEGMENT_KEY, segmentTasks);
    const isHeadPartial = shouldAssumePartialData || await isPartialRSCData(head, clientModules);
    // Notify the abort controller that we're done processing the route tree.
    // Anything async that happens after this point must be due to hanging
    // promises in the original stream.
    onCompletedProcessingRouteTree();
    // Render the route tree to a special `/_tree` segment.
    const treePrefetch = {
        buildId,
        tree,
        head,
        isHeadPartial,
        staleTime
    };
    return treePrefetch;
}
function collectSegmentDataImpl(shouldAssumePartialData, route, buildId, seedData, fallbackRouteParams, fullPageDataBuffer, clientModules, serverConsumerManifest, key, segmentTasks) {
    // Metadata about the segment. Sent as part of the tree prefetch. Null if
    // there are no children.
    let slotMetadata = null;
    const children = route[1];
    const seedDataChildren = seedData !== null ? seedData[2] : null;
    for(const parallelRouteKey in children){
        const childRoute = children[parallelRouteKey];
        const childSegment = childRoute[0];
        const childSeedData = seedDataChildren !== null ? seedDataChildren[parallelRouteKey] : null;
        const childKey = encodeChildSegmentKey(key, parallelRouteKey, Array.isArray(childSegment) && fallbackRouteParams !== null ? encodeSegmentWithPossibleFallbackParam(childSegment, fallbackRouteParams) : encodeSegment(childSegment));
        const childTree = collectSegmentDataImpl(shouldAssumePartialData, childRoute, buildId, childSeedData, fallbackRouteParams, fullPageDataBuffer, clientModules, serverConsumerManifest, childKey, segmentTasks);
        if (slotMetadata === null) {
            slotMetadata = {};
        }
        slotMetadata[parallelRouteKey] = childTree;
    }
    if (seedData !== null) {
        // Spawn a task to write the segment data to a new Flight stream.
        segmentTasks.push(// Since we're already in the middle of a render, wait until after the
        // current task to escape the current rendering context.
        waitAtLeastOneReactRenderTask().then(()=>renderSegmentPrefetch(shouldAssumePartialData, buildId, seedData, key, clientModules)));
    } else {
    // This segment does not have any seed data. Skip generating a prefetch
    // response for it. We'll still include it in the route tree, though.
    // TODO: We should encode in the route tree whether a segment is missing
    // so we don't attempt to fetch it for no reason. As of now this shouldn't
    // ever happen in practice, though.
    }
    // Metadata about the segment. Sent to the client as part of the
    // tree prefetch.
    return {
        segment: route[0],
        slots: slotMetadata,
        isRootLayout: route[4] === true
    };
}
function encodeSegmentWithPossibleFallbackParam(segment, fallbackRouteParams) {
    const name = segment[0];
    if (!fallbackRouteParams.has(name)) {
        // Normal case. No matching fallback parameter.
        return encodeSegment(segment);
    }
    // This segment includes a fallback parameter. During prerendering, a random
    // placeholder value was used; however, for segment prefetches, we need the
    // segment path to be predictable so the server can create a rewrite for it.
    // So, replace the placeholder segment value with a "template" string,
    // e.g. `[name]`.
    // TODO: This will become a bit cleaner once remove route parameters from the
    // server response, and instead add them to the segment keys on the client.
    // Instead of a string replacement, like we do here, route params will always
    // be encoded in separate step from the rest of the segment, not just in the
    // case of fallback params.
    const encodedSegment = encodeSegment(segment);
    const lastIndex = encodedSegment.lastIndexOf('$');
    const encodedFallbackSegment = // NOTE: This is guaranteed not to clash with the rest of the segment
    // because non-simple characters (including [ and ]) trigger a base
    // 64 encoding.
    encodedSegment.substring(0, lastIndex + 1) + `[${name}]`;
    return encodedFallbackSegment;
}
async function renderSegmentPrefetch(shouldAssumePartialData, buildId, seedData, key, clientModules) {
    // Render the segment data to a stream.
    // In the future, this is where we can include additional metadata, like the
    // stale time and cache tags.
    const rsc = seedData[1];
    const loading = seedData[3];
    const segmentPrefetch = {
        buildId,
        rsc,
        loading,
        isPartial: shouldAssumePartialData || await isPartialRSCData(rsc, clientModules)
    };
    // Since all we're doing is decoding and re-encoding a cached prerender, if
    // it takes longer than a microtask, it must because of hanging promises
    // caused by dynamic data. Abort the stream at the end of the current task.
    const abortController = new AbortController();
    waitAtLeastOneReactRenderTask().then(()=>abortController.abort());
    const { prelude: segmentStream } = await prerender(segmentPrefetch, clientModules, {
        signal: abortController.signal,
        onError: onSegmentPrerenderError
    });
    const segmentBuffer = await streamToBuffer(segmentStream);
    if (key === ROOT_SEGMENT_KEY) {
        return [
            '/_index',
            segmentBuffer
        ];
    } else {
        return [
            key,
            segmentBuffer
        ];
    }
}
async function isPartialRSCData(rsc, clientModules) {
    // We can determine if a segment contains only partial data if it takes longer
    // than a task to encode, because dynamic data is encoded as an infinite
    // promise. We must do this in a separate Flight prerender from the one that
    // actually generates the prefetch stream because we need to include
    // `isPartial` in the stream itself.
    let isPartial = false;
    const abortController = new AbortController();
    waitAtLeastOneReactRenderTask().then(()=>{
        // If we haven't yet finished the outer task, then it must be because we
        // accessed dynamic data.
        isPartial = true;
        abortController.abort();
    });
    await prerender(rsc, clientModules, {
        signal: abortController.signal,
        onError () {}
    });
    return isPartial;
}
function createUnclosingPrefetchStream(originalFlightStream) {
    // When PPR is enabled, prefetch streams may contain references that never
    // resolve, because that's how we encode dynamic data access. In the decoded
    // object returned by the Flight client, these are reified into hanging
    // promises that suspend during render, which is effectively what we want.
    // The UI resolves when it switches to the dynamic data stream
    // (via useDeferredValue(dynamic, static)).
    //
    // However, the Flight implementation currently errors if the server closes
    // the response before all the references are resolved. As a cheat to work
    // around this, we wrap the original stream in a new stream that never closes,
    // and therefore doesn't error.
    const reader = originalFlightStream.getReader();
    return new ReadableStream({
        async pull (controller) {
            while(true){
                const { done, value } = await reader.read();
                if (!done) {
                    // Pass to the target stream and keep consuming the Flight response
                    // from the server.
                    controller.enqueue(value);
                    continue;
                }
                // The server stream has closed. Exit, but intentionally do not close
                // the target stream.
                return;
            }
        }
    });
}

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