Generate JS and CSS bundle with fixed buffer size (#6573)

#### What type of PR is this?

/kind improvement
/area core
/milestone 2.20.x

#### What this PR does / why we need it:

If we are running Halo instance in machine with small memory available, the JS/CSS bundle might  not be accessible.

This RP refactors generation of JS and CSS bundle with fixed buffer size rather than length of original resources.

```java
2024-09-02T15:01:27.667+08:00  WARN 62039 --- [boundedElastic-3] reactor.core.Exceptions                  : throwIfFatal detected a jvm fatal exception, which is thrown and logged below:

java.lang.OutOfMemoryError: Java heap space
        at java.base/java.nio.HeapByteBuffer.<init>(HeapByteBuffer.java:64) ~[na:na]
        at java.base/java.nio.ByteBuffer.allocate(ByteBuffer.java:363) ~[na:na]
        at org.springframework.core.io.buffer.DefaultDataBuffer.allocate(DefaultDataBuffer.java:234) ~[spring-core-6.1.12.jar:6.1.12]
        at org.springframework.core.io.buffer.DefaultDataBuffer.setCapacity(DefaultDataBuffer.java:196) ~[spring-core-6.1.12.jar:6.1.12]
        at org.springframework.core.io.buffer.DefaultDataBuffer.ensureWritable(DefaultDataBuffer.java:228) ~[spring-core-6.1.12.jar:6.1.12]
        at org.springframework.core.io.buffer.DefaultDataBuffer.write(DefaultDataBuffer.java:296) ~[spring-core-6.1.12.jar:6.1.12]
        at org.springframework.core.io.buffer.DefaultDataBuffer.write(DefaultDataBuffer.java:289) ~[spring-core-6.1.12.jar:6.1.12]
        at org.springframework.core.io.buffer.DefaultDataBuffer.write(DefaultDataBuffer.java:43) ~[spring-core-6.1.12.jar:6.1.12]
        at run.halo.app.core.extension.service.impl.PluginServiceImpl.lambda$uglifyJsBundle$17(PluginServiceImpl.java:257) ~[classes/:na]
        at run.halo.app.core.extension.service.impl.PluginServiceImpl$$Lambda$4661/0x000000c80214e298.accept(Unknown Source) ~[na:na]
        at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:196) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxUsing$UsingFuseableSubscriber.onNext(FluxUsing.java:353) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxGenerate$GenerateSubscription.next(FluxGenerate.java:178) ~[reactor-core-3.6.9.jar:3.6.9]
        at org.springframework.core.io.buffer.DataBufferUtils$ReadableByteChannelGenerator.accept(DataBufferUtils.java:1002) ~[spring-core-6.1.12.jar:6.1.12]
        at org.springframework.core.io.buffer.DataBufferUtils$ReadableByteChannelGenerator.accept(DataBufferUtils.java:974) ~[spring-core-6.1.12.jar:6.1.12]
        at reactor.core.publisher.FluxGenerate.lambda$new$1(FluxGenerate.java:58) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxGenerate$$Lambda$4155/0x000000c802069228.apply(Unknown Source) ~[na:na]
        at reactor.core.publisher.FluxGenerate$GenerateSubscription.slowPath(FluxGenerate.java:271) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxGenerate$GenerateSubscription.request(FluxGenerate.java:213) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxUsing$UsingFuseableSubscriber.request(FluxUsing.java:320) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.request(FluxPeekFuseable.java:144) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxFlatMap$FlatMapInner.onSubscribe(FluxFlatMap.java:968) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onSubscribe(FluxPeekFuseable.java:178) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxUsing$UsingFuseableSubscriber.onSubscribe(FluxUsing.java:347) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxGenerate.subscribe(FluxGenerate.java:85) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxUsing.subscribe(FluxUsing.java:102) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.Flux.subscribe(Flux.java:8848) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.onNext(FluxFlatMap.java:430) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.tryOnNext(FluxHandleFuseable.java:135) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxIterable$IterableSubscriptionConditional.slowPath(FluxIterable.java:664) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxIterable$IterableSubscriptionConditional.request(FluxIterable.java:623) ~[reactor-core-3.6.9.jar:3.6.9]
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.request(FluxHandleFuseable.java:260) ~[reactor-core-3.6.9.jar:3.6.9]

2024-09-02T15:01:27.681+08:00 DEBUG 62039 --- [boundedElastic-3] a.w.r.e.AbstractErrorWebExceptionHandler : [131a559b-102] Resolved [OutOfMemoryError: Java heap space] for HTTP GET /apis/api.console.halo.run/v1alpha1/plugins/-/bundle.js
2024-09-02T15:01:27.681+08:00 ERROR 62039 --- [boundedElastic-3] a.w.r.e.AbstractErrorWebExceptionHandler : [131a559b-102]  500 Server Error for HTTP GET "/apis/api.console.halo.run/v1alpha1/plugins/-/bundle.js?v=1725260408176"

java.lang.OutOfMemoryError: Java heap space
        at java.base/java.nio.HeapByteBuffer.<init>(HeapByteBuffer.java:64) ~[na:na]
```

#### Does this PR introduce a user-facing change?

```release-note
优化在内存紧张时 Console 端无法加载插件资源的问题
```

application/src/main/java/run/halo/app/core/extension/service/impl/PluginServiceImpl.java

@@ -40,6 +40,7 @@ import org.springframework.stereotype.Component;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.FileSystemUtils;
+import org.springframework.util.StreamUtils;
 import org.springframework.web.server.ServerWebInputException;
 import reactor.core.Exceptions;
 import reactor.core.publisher.Flux;
@@ -229,61 +230,73 @@ public class PluginServiceImpl implements PluginService, InitializingBean, Dispo
     @Override
     public Flux<DataBuffer> uglifyJsBundle() {
         var startedPlugins = List.copyOf(pluginManager.getStartedPlugins());
-        String plugins = """
-            this.enabledPlugins = [%s]
-            """.formatted(startedPlugins.stream()
-            .map(plugin -> """
-                {
-                  "name": "%s",
-                  "version": "%s"
+        var dataBufferFactory = DefaultDataBufferFactory.sharedInstance;
+        var end = Mono.fromSupplier(
+            () -> {
+                var sb = new StringBuilder("this.enabledPlugins = [");
+                var iterator = startedPlugins.iterator();
+                while (iterator.hasNext()) {
+                    var plugin = iterator.next();
+                    sb.append("""
+                        {"name":"%s","version":"%s"}\
+                        """
+                        .formatted(
+                            plugin.getPluginId(),
+                            plugin.getDescriptor().getVersion()
+                        )
+                    );
+                    if (iterator.hasNext()) {
+                        sb.append(',');
+                    }
                 }
-                """.formatted(plugin.getPluginId(), plugin.getDescriptor().getVersion())
-            )
-            .collect(Collectors.joining(", ")));
-        return Flux.fromIterable(startedPlugins)
-            .mapNotNull(pluginWrapper -> {
-                var pluginName = pluginWrapper.getPluginId();
-                return BundleResourceUtils.getJsBundleResource(pluginManager, pluginName,
-                    BundleResourceUtils.JS_BUNDLE);
-            })
-            .flatMap(resource -> {
-                try {
-                    // Specifying bufferSize as resource content length is
-                    // to append line breaks at the end of each plugin
-                    return DataBufferUtils.read(resource, DefaultDataBufferFactory.sharedInstance,
-                            (int) resource.contentLength())
-                        .doOnNext(dataBuffer -> {
-                            // add a new line after each plugin bundle to avoid syntax error
-                            dataBuffer.write("\n".getBytes(StandardCharsets.UTF_8));
-                        });
-                } catch (IOException e) {
-                    log.error("Failed to read plugin bundle resource", e);
-                    return Flux.empty();
-                }
-            })
-            .concatWith(Flux.defer(() -> {
-                var dataBuffer = DefaultDataBufferFactory.sharedInstance
-                    .wrap(plugins.getBytes(StandardCharsets.UTF_8));
-                return Flux.just(dataBuffer);
-            }));
+                sb.append(']');
+                return dataBufferFactory.wrap(sb.toString().getBytes(StandardCharsets.UTF_8));
+            });
+        var body = Flux.fromIterable(startedPlugins)
+            .sort(Comparator.comparing(PluginWrapper::getPluginId))
+            .concatMap(pluginWrapper -> {
+                var pluginId = pluginWrapper.getPluginId();
+                return Mono.<Resource>fromSupplier(
+                        () -> BundleResourceUtils.getJsBundleResource(
+                            pluginManager, pluginId, BundleResourceUtils.JS_BUNDLE
+                        )
+                    )
+                    .filter(Resource::isReadable)
+                    .flatMapMany(resource -> {
+                        var head = Mono.<DataBuffer>fromSupplier(
+                            () -> dataBufferFactory.wrap(
+                                ("// Generated from plugin " + pluginId + "\n").getBytes()
+                            ));
+                        var content = DataBufferUtils.read(
+                            resource, dataBufferFactory, StreamUtils.BUFFER_SIZE
+                        );
+                        var tail = Mono.fromSupplier(() -> dataBufferFactory.wrap("\n".getBytes()));
+                        return Flux.concat(head, content, tail);
+                    });
+            });
+        return Flux.concat(body, end);
     }
 
     @Override
     public Flux<DataBuffer> uglifyCssBundle() {
         return Flux.fromIterable(pluginManager.getStartedPlugins())
-            .mapNotNull(pluginWrapper -> {
-                String pluginName = pluginWrapper.getPluginId();
-                return BundleResourceUtils.getJsBundleResource(pluginManager, pluginName,
-                    BundleResourceUtils.CSS_BUNDLE);
-            })
-            .flatMap(resource -> {
-                try {
-                    return DataBufferUtils.read(resource, DefaultDataBufferFactory.sharedInstance,
-                        (int) resource.contentLength());
-                } catch (IOException e) {
-                    log.error("Failed to read plugin css bundle resource", e);
-                    return Flux.empty();
-                }
+            .sort(Comparator.comparing(PluginWrapper::getPluginId))
+            .concatMap(pluginWrapper -> {
+                var pluginId = pluginWrapper.getPluginId();
+                var dataBufferFactory = DefaultDataBufferFactory.sharedInstance;
+                return Mono.<Resource>fromSupplier(() -> BundleResourceUtils.getJsBundleResource(
+                        pluginManager, pluginId, BundleResourceUtils.CSS_BUNDLE
+                    ))
+                    .filter(Resource::isReadable)
+                    .flatMapMany(resource -> {
+                        var head = Mono.<DataBuffer>fromSupplier(() -> dataBufferFactory.wrap(
+                            ("/* Generated from plugin " + pluginId + " */\n").getBytes()
+                        ));
+                        var content = DataBufferUtils.read(
+                            resource, dataBufferFactory, StreamUtils.BUFFER_SIZE);
+                        var tail = Mono.fromSupplier(() -> dataBufferFactory.wrap("\n".getBytes()));
+                        return Flux.concat(head, content, tail);
+                    });
             });
     }