Added "async" and "attempts" parameters to GET /arbitrary/{service}/{name}* endpoints.

async = fail immediately with 404 if missing, and request in the background
attempts = the number of times to request the data (synchronous mode only for now)

src/main/java/org/qortal/api/resource/ArbitraryResource.java

@@ -576,14 +576,16 @@ public class ArbitraryResource {
 								   @PathParam("service") Service service,
 								   @PathParam("name") String name,
 								   @QueryParam("filepath") String filepath,
-								   @QueryParam("rebuild") boolean rebuild) {
+								   @QueryParam("rebuild") boolean rebuild,
+								   @QueryParam("async") boolean async,
+								   @QueryParam("attempts") Integer attempts) {
 
 		// Authentication can be bypassed in the settings, for those running public QDN nodes
 		if (!Settings.getInstance().isQDNAuthBypassEnabled()) {
 			Security.checkApiCallAllowed(request);
 		}
 
-		return this.download(service, name, null, filepath, rebuild);
+		return this.download(service, name, null, filepath, rebuild, async, attempts);
 	}
 
 	@GET
@@ -609,14 +611,16 @@ public class ArbitraryResource {
 								   @PathParam("name") String name,
 								   @PathParam("identifier") String identifier,
 								   @QueryParam("filepath") String filepath,
-								   @QueryParam("rebuild") boolean rebuild) {
+								   @QueryParam("rebuild") boolean rebuild,
+								   @QueryParam("async") boolean async,
+								   @QueryParam("attempts") Integer attempts) {
 
 		// Authentication can be bypassed in the settings, for those running public QDN nodes
 		if (!Settings.getInstance().isQDNAuthBypassEnabled()) {
 			Security.checkApiCallAllowed(request);
 		}
 
-		return this.download(service, name, identifier, filepath, rebuild);
+		return this.download(service, name, identifier, filepath, rebuild, async, attempts);
 	}
 
 
@@ -1027,30 +1031,45 @@ public class ArbitraryResource {
 		}
 	}
 
-	private HttpServletResponse download(Service service, String name, String identifier, String filepath, boolean rebuild) {
+	private HttpServletResponse download(Service service, String name, String identifier, String filepath, boolean rebuild, boolean async, Integer maxAttempts) {
 
 		ArbitraryDataReader arbitraryDataReader = new ArbitraryDataReader(name, ArbitraryDataFile.ResourceIdType.NAME, service, identifier);
 		try {
 
 			int attempts = 0;
+			if (maxAttempts == null) {
+				maxAttempts = 5;
+			}
 
 			// Loop until we have data
-			while (!Controller.isStopping()) {
-				attempts++;
-				if (!arbitraryDataReader.isBuilding()) {
-					try {
-						arbitraryDataReader.loadSynchronously(rebuild);
-						break;
-					} catch (MissingDataException e) {
-						if (attempts > 5) {
-							// Give up after 5 attempts
-							throw ApiExceptionFactory.INSTANCE.createCustomException(request, ApiError.INVALID_CRITERIA, "Data unavailable. Please try again later.");
+			if (async) {
+				// Asynchronous
+				arbitraryDataReader.loadAsynchronously(false);
+			}
+			else {
+				// Synchronous
+				while (!Controller.isStopping()) {
+					attempts++;
+					if (!arbitraryDataReader.isBuilding()) {
+						try {
+							arbitraryDataReader.loadSynchronously(rebuild);
+							break;
+						} catch (MissingDataException e) {
+							if (attempts > maxAttempts) {
+								// Give up after 5 attempts
+								throw ApiExceptionFactory.INSTANCE.createCustomException(request, ApiError.INVALID_CRITERIA, "Data unavailable. Please try again later.");
+							}
 						}
 					}
+					Thread.sleep(3000L);
 				}
-				Thread.sleep(3000L);
 			}
+
 			java.nio.file.Path outputPath = arbitraryDataReader.getFilePath();
+			if (outputPath == null) {
+				// Assume the resource doesn't exist
+				throw ApiExceptionFactory.INSTANCE.createCustomException(request, ApiError.FILE_NOT_FOUND, "File not found");
+			}
 
 			if (filepath == null || filepath.isEmpty()) {
 				// No file path supplied - so check if this is a single file resource

src/main/java/org/qortal/arbitrary/ArbitraryDataReader.java

@@ -122,9 +122,19 @@ public class ArbitraryDataReader {
      * This adds the build task to a queue, and the result will be cached when complete
      * To check the status of the build, periodically call isCachedDataAvailable()
      * Once it returns true, you can then use getFilePath() to access the data itself.
+     *
+     * @param overwrite - set to true to force rebuild an existing cache
      * @return true if added or already present in queue; false if not
      */
-    public boolean loadAsynchronously() {
+    public boolean loadAsynchronously(boolean overwrite) {
+        ArbitraryDataCache cache = new ArbitraryDataCache(this.uncompressedPath, overwrite,
+                this.resourceId, this.resourceIdType, this.service, this.identifier);
+        if (cache.isCachedDataAvailable()) {
+            // Use cached data
+            this.filePath = this.uncompressedPath;
+            return true;
+        }
+
         return ArbitraryDataBuildManager.getInstance().addToBuildQueue(this.createQueueItem());
     }
 

src/main/java/org/qortal/arbitrary/ArbitraryDataRenderer.java

@@ -76,7 +76,7 @@ public class ArbitraryDataRenderer {
             if (!arbitraryDataReader.isCachedDataAvailable()) {
                 // If async is requested, show a loading screen whilst build is in progress
                 if (async) {
-                    arbitraryDataReader.loadAsynchronously();
+                    arbitraryDataReader.loadAsynchronously(false);
                     return this.getLoadingResponse(service, resourceId);
                 }