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Use Server-Sent Events in the Couch DB adapter (#4427)

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* Use SSE instead of chunked HTTP response.

Co-authored-by: Joshi <simplyrender@gmail.com>
This commit is contained in:
Scott Bell
2021-12-06 22:22:30 +01:00
committed by GitHub
parent 7b53cad2c5
commit 84e82d3bda
5 changed files with 147 additions and 171 deletions
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148
src/plugins/persistence/couch/CouchObjectProvider.js
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@@ -38,6 +38,8 @@ class CouchObjectProvider {
this.objectQueue = {};
this.observers = {};
this.batchIds = [];
this.onEventMessage = this.onEventMessage.bind(this);
this.onEventError = this.onEventError.bind(this);
}
/**
@@ -50,7 +52,7 @@ class CouchObjectProvider {
// eslint-disable-next-line no-undef
const sharedWorkerURL = `${this.openmct.getAssetPath()}${__OPENMCT_ROOT_RELATIVE__}couchDBChangesFeed.js`;
sharedWorker = new SharedWorker(sharedWorkerURL);
sharedWorker = new SharedWorker(sharedWorkerURL, 'CouchDB SSE Shared Worker');
sharedWorker.port.onmessage = provider.onSharedWorkerMessage.bind(this);
sharedWorker.port.onmessageerror = provider.onSharedWorkerMessageError.bind(this);
sharedWorker.port.start();
@@ -70,6 +72,13 @@ class CouchObjectProvider {
console.log('Error', event);
}
isSynchronizedObject(object) {
return (object && object.type
&& this.openmct.objects.SYNCHRONIZED_OBJECT_TYPES
&& this.openmct.objects.SYNCHRONIZED_OBJECT_TYPES.includes(object.type));
}
onSharedWorkerMessage(event) {
if (event.data.type === 'connection') {
this.changesFeedSharedWorkerConnectionId = event.data.connectionId;
@@ -86,7 +95,9 @@ class CouchObjectProvider {
if (observersForObject) {
observersForObject.forEach(async (observer) => {
const updatedObject = await this.get(objectChanges.identifier);
observer(updatedObject);
if (this.isSynchronizedObject(updatedObject)) {
observer(updatedObject);
}
});
}
}
@@ -390,38 +401,16 @@ class CouchObjectProvider {
* @private
*/
observeObjectChanges() {
let filter = {selector: {}};
if (this.openmct.objects.SYNCHRONIZED_OBJECT_TYPES.length > 1) {
filter.selector.$or = this.openmct.objects.SYNCHRONIZED_OBJECT_TYPES
.map(type => {
return {
'model': {
type
}
};
});
} else {
filter.selector.model = {
type: this.openmct.objects.SYNCHRONIZED_OBJECT_TYPES[0]
};
}
// feed=continuous maintains an indefinitely open connection with a keep-alive of HEARTBEAT milliseconds until this client closes the connection
// style=main_only returns only the current winning revision of the document
let url = `${this.url}/_changes?feed=continuous&style=main_only&heartbeat=${HEARTBEAT}`;
let body = {};
if (filter) {
url = `${url}&filter=_selector`;
body = JSON.stringify(filter);
}
const sseChangesPath = `${this.url}/_changes`;
const sseURL = new URL(sseChangesPath);
sseURL.searchParams.append('feed', 'eventsource');
sseURL.searchParams.append('style', 'main_only');
sseURL.searchParams.append('heartbeat', HEARTBEAT);
if (typeof SharedWorker === 'undefined') {
this.fetchChanges(url, body);
this.fetchChanges(sseURL.toString());
} else {
this.initiateSharedWorkerFetchChanges(url, body);
this.initiateSharedWorkerFetchChanges(sseURL.toString());
}
}
@@ -429,7 +418,7 @@ class CouchObjectProvider {
/**
* @private
*/
initiateSharedWorkerFetchChanges(url, body) {
initiateSharedWorkerFetchChanges(url) {
if (!this.changesFeedSharedWorker) {
this.changesFeedSharedWorker = this.startSharedWorker();
@@ -443,17 +432,40 @@ class CouchObjectProvider {
this.changesFeedSharedWorker.port.postMessage({
request: 'changes',
body,
url
});
}
}
async fetchChanges(url, body) {
const controller = new AbortController();
const signal = controller.signal;
onEventError(error) {
console.error('Error on feed', error);
if (Object.keys(this.observers).length > 0) {
this.observeObjectChanges();
}
}
let error = false;
onEventMessage(event) {
const object = JSON.parse(event.data);
object.identifier = {
namespace: this.namespace,
key: object.id
};
let keyString = this.openmct.objects.makeKeyString(object.identifier);
let observersForObject = this.observers[keyString];
if (observersForObject) {
observersForObject.forEach(async (observer) => {
const updatedObject = await this.get(object.identifier);
if (this.isSynchronizedObject(updatedObject)) {
observer(updatedObject);
}
});
}
}
fetchChanges(url) {
const controller = new AbortController();
let couchEventSource;
if (this.isObservingObjectChanges()) {
this.stopObservingObjectChanges();
@@ -461,66 +473,18 @@ class CouchObjectProvider {
this.stopObservingObjectChanges = () => {
controller.abort();
couchEventSource.removeEventListener('message', this.onEventMessage);
delete this.stopObservingObjectChanges;
};
const response = await fetch(url, {
method: 'POST',
signal,
headers: {
"Content-Type": 'application/json'
},
body
});
console.debug('⇿ Opening CouchDB change feed connection ⇿');
let reader;
couchEventSource = new EventSource(url);
couchEventSource.onerror = this.onEventError;
if (response.body === undefined) {
error = true;
} else {
reader = response.body.getReader();
}
while (!error) {
const {done, value} = await reader.read();
//done is true when we lose connection with the provider
if (done) {
error = true;
}
if (value) {
let chunk = new Uint8Array(value.length);
chunk.set(value, 0);
const decodedChunk = new TextDecoder("utf-8").decode(chunk).split('\n');
if (decodedChunk.length && decodedChunk[decodedChunk.length - 1] === '') {
decodedChunk.forEach((doc, index) => {
try {
const object = JSON.parse(doc);
object.identifier = {
namespace: this.namespace,
key: object.id
};
let keyString = this.openmct.objects.makeKeyString(object.identifier);
let observersForObject = this.observers[keyString];
if (observersForObject) {
observersForObject.forEach(async (observer) => {
const updatedObject = await this.get(object.identifier);
observer(updatedObject);
});
}
} catch (e) {
//do nothing;
}
});
}
}
}
if (error && Object.keys(this.observers).length > 0) {
this.observeObjectChanges();
}
// start listening for events
couchEventSource.addEventListener('message', this.onEventMessage);
console.debug('⇿ Opened connection ⇿');
}
/**