Implement FR #3364: Add --download-file feature

* Add feature request --download-file to download a single file based on the online path

src/config.d

@@ -1132,6 +1132,7 @@ class ApplicationConfig {
 		stringValues["auth_files"] = "";
 		stringValues["auth_response"] = "";
 		stringValues["share_password"] = "";
+		stringValues["download_single_file"] = "";
 		boolValues["display_config"] = false;
 		boolValues["display_sync_status"] = false;
 		boolValues["display_quota"] = false;
@@ -1214,6 +1215,9 @@ class ApplicationConfig {
 				"download-only",
 					"Replicate the OneDrive online state locally, by only downloading changes from OneDrive. Do not upload local changes to OneDrive",
 					&boolValues["download_only"],
+				"download-file",
+					"Download a single file from Microsoft OneDrive",
+					&stringValues["download_single_file"],
 				"dry-run",
 					"Perform a trial sync with no changes made",
 					&boolValues["dry_run"],
@@ -2641,6 +2645,7 @@ class ApplicationConfig {
 		// - Are we just deleting a directory online, without any sync being performed?
 		// - Are we renaming or moving a directory?
 		// - Are we displaying the quota information?
+		// - Are we downloading a single file?
 		bool noSyncOperation = false;
 		
 		// Return a true|false if any of these have been set, so that we use the 'dry-run' DB copy, to execute these tasks, in case the client is currently operational
@@ -2718,6 +2723,12 @@ class ApplicationConfig {
 			noSyncOperation = true;
 		}
 		
+		// Are we downloading a single file?
+		if ((getValueString("download_single_file") != "")) {
+			// flag that a no sync operation has been requested
+			noSyncOperation = true;
+		}
+		
 		// Return result
 		return noSyncOperation;
 	}
@@ -2801,6 +2812,7 @@ void outputLongHelp(Option[] opt) {
 			"--classify-as-big-delete",
 			"--create-share-link",
 			"--destination-directory",
+			"--download-file",
 			"--get-file-link",
 			"--get-O365-drive-id",
 			"--get-sharepoint-drive-id",
@@ -2842,7 +2854,9 @@ void outputLongHelp(Option[] opt) {
 			writefln("  %s%s%s%s\n      %s",
 					it.optLong,
 					it.optShort == "" ? "" : " " ~ it.optShort,
-					argsNeedingOptions.canFind(it.optLong) ? " ARG" : "",
+					argsNeedingOptions.canFind(it.optLong) ? " '<path or required value>'" : "",
 					it.required ? " (required)" : "", it.help);
 		}
+		// end with a blank line
+		writeln();
 }

src/main.d

@@ -745,6 +745,15 @@ int main(string[] cliArgs) {
 					return EXIT_SUCCESS;
 				}
 				
+				// --download-file - Are we downloading a single file from Microsoft OneDrive
+				if ((appConfig.getValueString("download_single_file") != "")) {
+					// Handle downloading the single file
+					syncEngineInstance.downloadSingleFile(appConfig.getValueString("download_single_file"));
+					// Exit application
+					// Use exit scopes to shutdown API
+					return EXIT_SUCCESS;
+				}
+				
 				// If we get to this point, we have not performed a 'no-sync' task ..
 				
 				// Did we just authorise the client?

src/sync.d

@@ -14753,4 +14753,89 @@ class SyncEngine {
 		// Return sanitised JSON string for logging output
 		return sanitisedJSONString;
 	}
+	
+	// Download a single file via --download-file <path/to/file>
+	void downloadSingleFile(string pathToQuery) {
+		// Function Start Time
+		SysTime functionStartTime;
+		string logKey;
+		string thisFunctionName = format("%s.%s", strip(__MODULE__) , strip(getFunctionName!({})));
+		// Only set this if we are generating performance processing times
+		if (appConfig.getValueBool("display_processing_time") && debugLogging) {
+			functionStartTime = Clock.currTime();
+			logKey = generateAlphanumericString();
+			displayFunctionProcessingStart(thisFunctionName, logKey);
+		}
+		
+		OneDriveApi queryPathDetailsOnline;
+		JSONValue onlinePathData;
+		
+		// Was a path to query passed in?
+		if (pathToQuery.empty) {
+			// Nothing to query
+			addLogEntry("No path to query");
+			return;
+		}
+		
+		// Create new OneDrive API Instance
+		queryPathDetailsOnline = new OneDriveApi(appConfig);
+		queryPathDetailsOnline.initialise();
+		
+		try {
+			// Query the OneDrive API, using the path, which will query 'our' OneDrive Account
+			onlinePathData = queryPathDetailsOnline.getPathDetails(pathToQuery);
+			
+			
+		} catch (OneDriveException exception) {
+			
+			if (exception.httpStatusCode == 404) {
+				// Path does not exist online ...
+				addLogEntry("ERROR: The requested path does not exist online. Please check for your file online.");
+			} else {
+				// Display error message
+				displayOneDriveErrorMessage(exception.msg, thisFunctionName);
+			}
+			
+			// OneDrive API Instance Cleanup - Shutdown API, free curl object and memory
+			queryPathDetailsOnline.releaseCurlEngine();
+			queryPathDetailsOnline = null;
+			// Perform Garbage Collection
+			GC.collect();
+			
+			// Return .. nothing to do
+			return;
+		}
+		
+		// Was a valid JSON response provided?
+		if (onlinePathData.type() == JSONType.object) {
+			// Valid JSON item was returned
+			// Is the item a file ?
+			if (isFileItem(onlinePathData)) {
+				// JSON item is a file
+				// Download the file based on the data returned
+				downloadFileItem(onlinePathData);
+			} else {
+				// The provided path is not a file
+				addLogEntry();
+				addLogEntry("ERROR: The requested path to download is not a file. Please correct this error and try again.");
+				addLogEntry();
+			}
+		} else {
+			addLogEntry();
+			addLogEntry("ERROR: The requested file to download has generated an error. Please correct this error and try again.");
+			addLogEntry();
+		}
+		
+		// OneDrive API Instance Cleanup - Shutdown API, free curl object and memory
+		queryPathDetailsOnline.releaseCurlEngine();
+		queryPathDetailsOnline = null;
+		// Perform Garbage Collection
+		GC.collect();
+		
+		// Display function processing time if configured to do so
+		if (appConfig.getValueBool("display_processing_time") && debugLogging) {
+			// Combine module name & running Function
+			displayFunctionProcessingTime(thisFunctionName, functionStartTime, Clock.currTime(), logKey);
+		}
+	}
 }