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Fix HTML capture race conditions #580

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merged 10 commits into from
Mar 25, 2020
Merged

Fix HTML capture race conditions #580

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e931efd
Change html capture flow
Jan 14, 2020
d2adc59
Rework width setup and size tracking to try improving stability
Jan 21, 2020
e87041a
Eliminate any arbitrary sleep and pause times on captures
Jan 23, 2020
891e6b3
Replace reflective zoom with snapshot param
Feb 11, 2020
a50b835
Make use of the snapshot callback to avoid explicit pulse listening
Feb 11, 2020
8aa4e21
Hide stage after use got lost in a previous refactor
Feb 11, 2020
8d8ee82
Wrap snapshot in animation timer to ensure more stable render
Mar 12, 2020
f0a0a9b
Add test class for webapp captures
Mar 12, 2020
33f6e2d
Bring back zoom through reflection
tresf Mar 12, 2020
d55ee8e
Correct starting timeout
Mar 18, 2020
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1 change: 1 addition & 0 deletions .idea/tray.iml
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178 changes: 96 additions & 82 deletions src/qz/printer/action/WebApp.java
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Original file line number Diff line number Diff line change
@@ -1,20 +1,17 @@
package qz.printer.action;

import javafx.animation.PauseTransition;
import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.concurrent.Worker;
import javafx.embed.swing.SwingFXUtils;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.SnapshotParameters;
import javafx.scene.image.WritableImage;
import javafx.scene.SnapshotResult;
import javafx.scene.web.WebView;
import javafx.stage.Stage;
import javafx.util.Duration;
import javafx.util.Callback;
import org.joor.Reflect;
import org.joor.ReflectException;
import org.slf4j.Logger;
Expand All @@ -26,7 +23,8 @@

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

/**
Expand All @@ -39,9 +37,6 @@ public class WebApp extends Application {

private static final Logger log = LoggerFactory.getLogger(WebApp.class);

private static final int SLEEP = 250;
private static final int TIMEOUT = 60; //total paused seconds before failing

private static WebApp instance = null;

private static Stage stage;
Expand All @@ -50,11 +45,12 @@ public class WebApp extends Application {
private static double pageHeight;
private static double pageZoom;

private static final AtomicBoolean started = new AtomicBoolean(false);
private static final AtomicBoolean complete = new AtomicBoolean(false);
private static CountDownLatch startupLatch;
private static CountDownLatch captureLatch;

private static final AtomicReference<BufferedImage> capture = new AtomicReference<>();
private static final AtomicReference<Throwable> thrown = new AtomicReference<>();

private static PauseTransition snap;

//listens for a Succeeded state to activate image capture
private static ChangeListener<Worker.State> stateListener = new ChangeListener<Worker.State>() {
Expand All @@ -76,40 +72,48 @@ public void changed(ObservableValue<? extends Worker.State> ov, Worker.State old
base.getAttributes().setNamedItem(applied);
}

try {
Reflect.on(webView).call("setZoom", pageZoom);
log.trace("Zooming in by x{} for increased quality", pageZoom);
}
catch(ReflectException e) {
log.warn("Unable zoom, using default quality");
pageZoom = 1; //only zoom affects webView scaling
//width was resized earlier (for responsive html), then calculate the best fit height
if (pageHeight <= 0) {
String heightText = webView.getEngine().executeScript("Math.max(document.body.offsetHeight, document.body.scrollHeight)").toString();
pageHeight = Double.parseDouble(heightText);
}

log.trace("Setting HTML page width to {}", (pageWidth * pageZoom));
webView.setMinWidth(pageWidth * pageZoom);
webView.setPrefWidth(pageWidth * pageZoom);
log.trace("Setting HTML page height to {}", pageHeight * pageZoom);
webView.setMinHeight(pageHeight * pageZoom);
webView.setPrefHeight(pageHeight * pageZoom);
webView.autosize();

//we have to resize the width first, for responsive html, then calculate the best fit height
final PauseTransition resize = new PauseTransition(Duration.millis(100));
resize.setOnFinished(new EventHandler<ActionEvent>() {
//without this runlater, the first capture is missed and all following captures are offset
Platform.runLater(new Runnable() {
@Override
public void handle(ActionEvent actionEvent) {
if (pageHeight <= 0) {
String heightText = webView.getEngine().executeScript("Math.max(document.body.offsetHeight, document.body.scrollHeight)").toString();
pageHeight = Double.parseDouble(heightText);
}

log.trace("Setting HTML page height to {}", (pageHeight * pageZoom));
webView.setMinHeight(pageHeight * pageZoom);
webView.setPrefHeight(pageHeight * pageZoom);
webView.autosize();

snap.playFromStart();
public void run() {
new AnimationTimer() {
int frames = 0;

@Override
public void handle(long l) {
if (++frames == 2) {
log.debug("Attempting image capture");



webView.snapshot(new Callback<SnapshotResult,Void>() {
@Override
public Void call(SnapshotResult snapshotResult) {
capture.set(SwingFXUtils.fromFXImage(snapshotResult.getImage(), null));
unlatch();

return null;
}
}, null, null);

//stop timer after snapshot
stop();
}
}
}.start();
}
});

resize.playFromStart();
}
}
};
Expand All @@ -122,6 +126,17 @@ public void changed(ObservableValue<? extends Number> ov, Number oldWork, Number
}
};

//listens for failures
private static ChangeListener<Throwable> exceptListener = new ChangeListener<Throwable>() {
@Override
public void changed(ObservableValue<? extends Throwable> obs, Throwable oldExc, Throwable newExc) {
if (newExc != null) {
thrown.set(newExc);
unlatch();
}
}
};


/** Called by JavaFX thread */
public WebApp() {
Expand All @@ -131,28 +146,30 @@ public WebApp() {
/** Starts JavaFX thread if not already running */
public static synchronized void initialize() throws IOException {
if (instance == null) {
startupLatch = new CountDownLatch(1);

new Thread() {
public void run() {
Application.launch(WebApp.class);
}
}.start();
}

for(int i = 0; i < (TIMEOUT * 1000); i += SLEEP) {
if (started.get()) { break; }
if (startupLatch.getCount() > 0) {
try {
log.trace("Waiting for JavaFX..");

log.trace("Waiting for JavaFX..");
try { Thread.sleep(SLEEP); } catch(Exception ignore) {}
}

if (!started.get()) {
throw new IOException("JavaFX did not start");
if (!startupLatch.await(60, TimeUnit.SECONDS)) {
throw new IOException("JavaFX did not start");
}
}
catch(InterruptedException ignore) {}
}
}

@Override
public void start(Stage st) throws Exception {
started.set(true);
startupLatch.countDown();
log.debug("Started JavaFX");

webView = new WebView();
Expand All @@ -164,6 +181,7 @@ public void start(Stage st) throws Exception {
Worker<Void> worker = webView.getEngine().getLoadWorker();
worker.stateProperty().addListener(stateListener);
worker.workDoneProperty().addListener(workDoneListener);
worker.exceptionProperty().addListener(exceptListener);

//prevents JavaFX from shutting down when hiding window
Platform.setImplicitExit(false);
Expand All @@ -177,12 +195,13 @@ public void start(Stage st) throws Exception {
* @return BufferedImage of the rendered html
*/
public static synchronized BufferedImage capture(final WebAppModel model) throws Throwable {
final AtomicReference<BufferedImage> capture = new AtomicReference<>();
complete.set(false);
captureLatch = new CountDownLatch(1);

capture.set(null);
thrown.set(null);

//ensure JavaFX has started before we run
if (!started.get()) {
if (startupLatch.getCount() > 0) {
throw new IOException("JavaFX has not been started");
}

Expand All @@ -194,35 +213,27 @@ public void run() {
pageHeight = model.getWebHeight();
pageZoom = model.getZoom();

webView.setMinSize(100, 100);
webView.setPrefSize(100, 100);
try {
Reflect.on(webView).call("setZoom", pageZoom);
log.trace("Zooming in by x{} for increased quality", pageZoom);
}
catch(ReflectException e) {
log.warn("Unable zoom, using default quality");
pageZoom = 1; //only zoom affects webView scaling
}

webView.setMinSize(pageWidth * pageZoom, pageHeight * pageZoom);
webView.setPrefSize(pageWidth * pageZoom, pageHeight * pageZoom);
if (pageHeight == 0) {
//jfx8 uses a default of 600 if height is exactly 0, set it to 1 here to avoid that behavior
webView.setMinHeight(1);
webView.setPrefHeight(1);
}
webView.autosize();

stage.show(); //FIXME - will not capture without showing stage
stage.toBack();

//ran when engine reaches SUCCEEDED state, takes snapshot of loaded html
snap = new PauseTransition(Duration.millis(100));
snap.setOnFinished(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent actionEvent) {
try {
log.debug("Attempting image capture");

WritableImage snapshot = webView.snapshot(new SnapshotParameters(), null);
capture.set(SwingFXUtils.fromFXImage(snapshot, null));

complete.set(true);
}
catch(Throwable t) {
thrown.set(t);
}
finally {
stage.hide(); //hide stage so users won't have to manually close it
}
}
});

//actually begin loading the html
if (model.isPlainText()) {
webView.getEngine().loadContent(model.getSource(), "text/html");
Expand All @@ -232,19 +243,22 @@ public void handle(ActionEvent actionEvent) {
}
catch(Throwable t) {
thrown.set(t);
unlatch();
}
}
});

Throwable t = null;
while(!complete.get() && (t = thrown.get()) == null) {
log.trace("Waiting on capture..");
try { Thread.sleep(1000); } catch(Exception ignore) {}
}
log.trace("Waiting on capture..");
captureLatch.await(); //should be released when either the capture or thrown variables are set

if (t != null) { throw t; }
if (thrown.get() != null) { throw thrown.get(); }

return capture.get();
}

private static void unlatch() {
captureLatch.countDown();
stage.hide(); //hide stage so users won't have to manually close it
}

}
16 changes: 16 additions & 0 deletions test/log4j.xml
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="[%p] %d{ISO8601} @ %c:%L%n\t%m%n" />
</layout>
</appender>

<root>
<priority value="trace" />
<appender-ref ref="console" />
</root>
</log4j:configuration>
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