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* @file resource.js
* @description Recording and replay of `<resource>` requests.
*
* Resources are Avenx's declarative async boundary, which makes them the one
* place the framework can see network work happening. Recording their
* settlements — and feeding those settlements back during replay — is what
* lets a recorded session be reproduced without a server.
*
* This deliberately does not intercept `fetch` or `XMLHttpRequest` globally. A
* trace that silently swallowed every request in the page would be recording
* work Avenx has no model of, and would report success for reproductions that
* only appeared to work. Requests made outside a `<resource>` are not
* reproduced, and a trace whose state depends on them diverges visibly during
* replay rather than passing by accident.
* @module lib/core/trace/resource
*/
import { tracer } from './tracer.js';
import { TraceNodeType, NonDeterminismReason } from './schema.js';
/**
* Recorded settlements queued per resource name, oldest first.
*
* Empty outside replay, so {@link takeRecordedResponse} is a `Map.size` check
* on the recording path.
* @type {Map<string, object[]>}
*/
const recordedResponses = new Map();
/**
* Called when replay asks for a response that was never recorded.
* @type {function(string): void|null}
*/
let onMissingResponse = null;
/**
* Loads a trace's resource settlements so replay can serve them.
* @param {object} trace - The trace to replay.
* @param {function(string): void} [onMissing] - Called when a resource asks for a response the trace does not have.
*/
export function installResourceResponses(trace, onMissing) {
recordedResponses.clear();
onMissingResponse = onMissing || null;
for (const node of trace.nodes || []) {
if (node.type !== TraceNodeType.RESOURCE || node.phase !== 'settled') {
continue;
}
let queue = recordedResponses.get(node.name);
if (!queue) {
queue = [];
recordedResponses.set(node.name, queue);
}
queue.push({ status: node.status, value: node.value, error: node.error });
}
}
/**
* Discards any loaded responses, restoring live resource behaviour.
*/
export function clearResourceResponses() {
recordedResponses.clear();
onMissingResponse = null;
}
/**
* Whether replay has responses loaded.
* @returns {boolean}
*/
export function hasRecordedResponses() {
return recordedResponses.size > 0;
}
/**
* Takes the next recorded settlement for a resource.
*
* A resource that asks for more settlements than were recorded is reported
* rather than served a repeat: replay has gone further than the recording did,
* which is divergence, and inventing a response would hide it.
* @param {string} name - The resource name.
* @returns {object|null} `{status, value, error}`, or null when nothing is queued.
*/
export function takeRecordedResponse(name) {
if (recordedResponses.size === 0) {
return null;
}
const queue = recordedResponses.get(name);
if (!queue || queue.length === 0) {
if (onMissingResponse) {
onMissingResponse(name);
}
return null;
}
return queue.shift();
}
/**
* Opens a node for a resource that has started work.
* @param {string} name - The resource name.
* @param {object|null} component - The owning component instance.
* @param {number} pollInterval - The configured poll interval, if any.
* @returns {object|null} The opened node, for later settlement.
*/
export function traceResourceStart(name, component, pollInterval) {
const recorder = tracer.sink;
if (!recorder) {
return null;
}
if (pollInterval > 0) {
// How many times a polling resource settled depends on wall-clock time, so
// the sequence cannot be reproduced by replaying inputs.
recorder.markNonDeterministic(
NonDeterminismReason.POLLING_RESOURCE,
`<resource name="${name}"> polls every ${pollInterval}ms`,
);
}
return tracer.record(TraceNodeType.RESOURCE, {
name,
phase: 'pending',
component: component && component.constructor && component.constructor.name,
});
}
/**
* Records how a resource settled.
*
* Settlements are recorded as their own node rather than by annotating the
* pending one: a resource settles asynchronously, and a trace that mutated an
* older node in place would lose the ordering that replay depends on.
* @param {object|null} pending - The node returned by {@link traceResourceStart}.
* @param {string} name - The resource name.
* @param {'resolved'|'rejected'} status - How it settled.
* @param {any} payload - The value, or the error.
*/
export function traceResourceSettle(pending, name, status, payload) {
const recorder = tracer.sink;
if (!recorder) {
return;
}
const node = {
name,
phase: 'settled',
status,
// Parented to the request rather than to whatever happened to be running
// when the promise settled, which is a microtask with no causal relation.
request: pending ? pending.id : undefined,
};
if (status === 'rejected') {
node.error = {
name: (payload && payload.name) || 'Error',
message: String((payload && payload.message) || payload),
};
} else {
node.value = recorder.capture(payload, `resource.${name}`);
}
tracer.record(TraceNodeType.RESOURCE, node);
}
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