How does one 'read' a file from a Dart program ?
http://api.dartlang.org/index.html
Dart would be running on the client-side and so taking files as input should be allowed.
You can find a usage of files in Dart's testing framework:
status_file_parser.dart (search for 'File').
In short:
File file = new File(path);
if (!file.existsSync()) <handle missing file>;
InputStream file_stream = file.openInputStream();
StringInputStream lines = new StringInputStream(file_stream);
lines.lineHandler = () {
String line;
while ((line = lines.readLine()) != null) {
...
};
lines.closeHandler = () {
...
};
Note that the API is not yet finalized and could change at any moment.
Edit: API has changed. See Introduction to new IO
Your question implies you want to do this from the client-side, that is, the browser. The dart:io library only works in the stand-alone VM on the command line.
If you do want to read a file from within the VM, there's now an easier way:
import 'dart:io';
main() {
var filename = new Options().script;
var file = new File(filename);
if (!file.existsSync()) {
print("File $filename does not exist");
return;
}
var contents = file.readAsStringSync();
print(contents);
}
If you do not want to block while the whole file is read, you can use the async version of readAsString which returns a Future:
file.readAsString().then((contents) {
print(contents);
});
Related
I am creating an azure function application to validate xml files using a zip folder of schematron files.
I have run into a compatibility issue with how the URI's for the files are being created between mac and windows.
The files are downloaded from a zip on azure blob storage and then extracted to the functions local storage.
When the a colleague runs the transform method of the saxon cs api on a windows machine the method is able to run the first transformation and produce the stage 1.out file, however on the second transformation the transform method throws an exception stating that it cannot find the file even though it is present on the temp directory.
On mac the URI is /var/folders/6_/3x594vpn6z1fjclc0vx4v89m0000gn/T and on windows it is trying to find it at file:///C:/Users/44741/AppData/Local/Temp/ but the library is unable to find the file on the windows machine even if it is moved out of temp storage.
Unable to retrieve URI file:///C:/Users/44741/Desktop/files/stage1.out
The file is present at this location but for some reason the library cannot pick it up on the windows machine but it works fine on my mac. I am using Path.Combine to build the URI.
Has anyone else ran into this issue before?
The code being used for the transformations is below.
{
try
{
var transform = new Transform();
transform.doTransform(GetTransformArguments(arguments[Constants.InStage1File],
arguments[Constants.SourceDir] + "/" + schematronFile, arguments[Constants.Stage1Out]));
transform.doTransform(GetTransformArguments(arguments[Constants.InStage2File], arguments[Constants.Stage1Out],
arguments[Constants.Stage2Out]));
transform.doTransform(GetFinalTransformArguments(arguments[Constants.InStage3File], arguments[Constants.Stage2Out],
arguments[Constants.Stage3Out]));
Log.Information("Stage 3 out file written to : " + arguments[Constants.Stage3Out]);;
return true;
}
catch (FileNotFoundException ex)
{
Log.Warning("Cannot find files" + ex);
return false;
}
}
private static string[] GetTransformArguments(string xslFile, string inputFile, string outputFile)
{
return new[]
{
"-xsl:" + xslFile,
"-s:" + inputFile,
"-o:" + outputFile
};
}
private static string[] GetFinalTransformArguments(string xslFile, string inputFile, string outputFile)
{
return new[]
{
"-xsl:" + xslFile,
"-s:" + inputFile,
"-o:" + outputFile,
"allow-foreign=true",
"generate-fired-rule=true"
};
}```
So assuming the intermediary results are not needed as files but you just want the result (I assume that is the Schematron schema compiled to XSLT) you could try to run XSLT 3.0 using the API of SaxonCS (using Saxon.Api) by compiling and chaining your three stylesheets with e.g.
using Saxon.Api;
string isoSchematronDir = #"C:\SomePath\SomeDir\iso-schematron-xslt2";
string[] isoSchematronXslts = { "iso_dsdl_include.xsl", "iso_abstract_expand.xsl", "iso_svrl_for_xslt2.xsl" };
Processor processor = new(true);
var xsltCompiler = processor.NewXsltCompiler();
var baseUri = new Uri(Path.Combine(isoSchematronDir, isoSchematronXslts[2]));
xsltCompiler.BaseUri = baseUri;
var isoSchematronStages = isoSchematronXslts.Select(xslt => xsltCompiler.Compile(new Uri(baseUri, xslt)).Load30()).ToList();
isoSchematronStages[2].SetStylesheetParameters(new Dictionary<QName, XdmValue>() { { new QName("allow-foreign"), new XdmAtomicValue(true) } });
using (var schematronIs = File.OpenRead("price.sch"))
{
using (var compiledOs = File.OpenWrite("price.sch.xsl"))
{
isoSchematronStages[0].ApplyTemplates(
schematronIs,
isoSchematronStages[1].AsDocumentDestination(
isoSchematronStages[2].AsDocumentDestination(processor.NewSerializer(compiledOs)
)
);
}
}
If you only need the compiled Schematron to apply it further to validate an XML instance document against that Schematron you could even store the Schematron as an XdmDestination whose XdmNode you feed to XsltCompiler e.g.
using Saxon.Api;
string isoSchematronDir = #"C:\SomePath\SomeDir\iso-schematron-xslt2";
string[] isoSchematronXslts = { "iso_dsdl_include.xsl", "iso_abstract_expand.xsl", "iso_svrl_for_xslt2.xsl" };
Processor processor = new(true);
var xsltCompiler = processor.NewXsltCompiler();
var baseUri = new Uri(Path.Combine(isoSchematronDir, isoSchematronXslts[2]));
xsltCompiler.BaseUri = baseUri;
var isoSchematronStages = isoSchematronXslts.Select(xslt => xsltCompiler.Compile(new Uri(baseUri, xslt)).Load30()).ToList();
isoSchematronStages[2].SetStylesheetParameters(new Dictionary<QName, XdmValue>() { { new QName("allow-foreign"), new XdmAtomicValue(true) } });
var compiledSchematronXslt = new XdmDestination();
using (var schematronIs = File.OpenRead("price.sch"))
{
isoSchematronStages[0].ApplyTemplates(
schematronIs,
isoSchematronStages[1].AsDocumentDestination(
isoSchematronStages[2].AsDocumentDestination(compiledSchematronXslt)
)
);
}
var schematronValidator = xsltCompiler.Compile(compiledSchematronXslt.XdmNode).Load30();
using (var sampleIs = File.OpenRead("books.xml"))
{
schematronValidator.ApplyTemplates(sampleIs, processor.NewSerializer(Console.Out));
}
The last example writes the XSLT/Schematron validation SVRL output to the console but could of course also write it to a file.
I want to add files to a list and then access them in a for loop. This is how I try to do it:
private get_app_list () {
var file = new File.new_for_path (/usr/share/applications);
List<File> app_list = new List<File> ();
foreach (File desktop_file in app_list) {
// other code here
}
}
What is the right way to access files stored in a directory and then add them to a list??
using Posix;
...
List<File> app_list = new List<File> ();
//Open directory. Returns null on error
var dirHandle = Posix.opendir("/usr/share/applications");
unowned DirEnt entry;
//While there is an entry to read in the directory
while((entry = readdir(dir)) != null) {
//Get the name
var name = (string) entry.d_name;
//And add a new file to the app_list
app_list.add(new File.new_for_path("/usr/share/applications"+name);
}
If you want to merely display the available apps on system, you could use the utilities supplied by the Gio-2.0 lib. After adding dependency ('gio-2.0'), to your meson.build file you could use code similar to the following:
/* We use a `GListStore` here, which is a simple array-like list implementation
* for manual management.
* List models need to know what type of data they provide, so we need to
* provide the type here. As we want to do a list of applications, `GAppInfo`
* is the object we provide.
*/
var app_list = new GLib.ListStore (typeof (GLib.AppInfo));
var apps = GLib.AppInfo.get_all ();
foreach (var app in apps) {
app_list.append (app);
}
If however you need to list files inside a directory, it's possible also to use the higher level API provided by the same gio-2.0 library. Here is a sample code to enumerate files inside "/usr/share/applications/"
void main () {
var app_dir = GLib.File.new_for_path ("/usr/share/applications");
try {
var cancellable = new Cancellable ();
GLib.FileEnumerator enumerator = app_dir.enumerate_children (
GLib.FileAttribute.STANDARD_DISPLAY_NAME,
GLib.FileQueryInfoFlags.NOFOLLOW_SYMLINKS,
cancellable
);
FileInfo ? file_info = null;
while (!cancellable.is_cancelled () &&
((file_info = enumerator.next_file (cancellable)) != null)) {
// Ignore directories
if (file_info.get_file_type () == GLib.FileType.DIRECTORY) {
continue;
}
// files could be added to a list_store here.
/*
* var files_list = new GLib.ListStore (typeof (GLib.FileInfo));
* files_list.append (file_info);
*/
print (file_info.get_display_name () + "\n");
}
} catch (GLib.Error err) {
info ("%s\n", err.message);
}
}
I hope this could be of any help.
Is there an easy way to open a file and continously read from it without the stream getting closed on EOF? Like the Unix command tail -f.
Just reading until EOF is described in the API docs. But I can't see an obvious/simple way to block or pause the stream for more input.
One solution would be to repeatedly reopen the file and continue reading from the last known length when I detect that the file size has changed.
Somethink like this
import 'dart:io';
void main(List<String> args ) {
var file = new File("test.txt");
print(file.absolute);
var openFuture = file.open(mode: FileMode.READ);
openFuture.then((raf) => raf.length().then((len) => raf.setPosition(len)
.then((raf) => raf.readXxx...
}
You can also use Directory.watch to get notified about changes and then reopen and read from the last known position.
(even though this questions is a bunch of years old now, I stumbled across the same issue today and couldn't find a viable solution and therefore had to roll my own and wanted to share my findings with future generations of Dart programmers. ;-))
The dart:io package in conjunction with a bit of stream and async-await magic should offer everything that is needed to achieve a "tail -f"-like functionality:
import 'dart:typed_data';
import 'dart:io';
Stream<List<int>> tail(final File file) async* {
final randomAccess = await file.open(mode: FileMode.read);
var pos = await randomAccess.position();
var len = await randomAccess.length();
// Increase/decrease buffer size as needed.
var buf = Uint8List(8192);
Stream<Uint8List> _read() async* {
while (pos < len) {
final bytesRead = await randomAccess.readInto(buf);
pos += bytesRead;
yield buf.sublist(0, bytesRead);
}
}
// Step 1: read whole file
yield* _read();
// Step 2: wait for modify events and read more bytes from file
await for (final event in file.watch(events: FileSystemEvent.modify)) {
if ((event as FileSystemModifyEvent).contentChanged) {
len = await (randomAccess.length());
yield* _read();
}
}
}
This function (tail) might then be used like that:
import 'dart:convert';
import 'dart:io';
void main() {
final file = File('/var/log/messages');
tail(file).transform(utf8.decoder).transform(LineSplitter()).forEach((line) {
// Do something with the line that has been read, e.g. print it out...
print(line);
});
}
I'm just new in this PCL libraries, I'm developing an iPhone app with Xamarin and I can't find the way to save it on the phone. The closest I get is with PCLStorage but he only saves text.
There is another way that I can save binary files with other procedure.
Thank you.
foreach (images element in json_object)
{
//var nameFile = Path.Combine (directoryname, element.name);
try{
IFile file = await folder_new.GetFileAsync(element.name);
}catch(FileNotFoundException ex ){
RestClient _Client = new RestClient(element.root);
RestRequest request_file = new RestRequest("/images/{FileName}");
request_file.AddParameter("FileName", element.name, ParameterType.UrlSegment);
_Client.ExecuteAsync<MemoryStream>(
request_file,
async Response =>
{
if (Response != null)
{
IFolder rootFolder_new = FileSystem.Current.LocalStorage;
IFile file_new = await rootFolder_new.CreateFileAsync(element.name,CreationCollisionOption.ReplaceExisting);
await file_new.WriteAllTextAsync(Response.Data);
}
});
}
}
Use the IFile.OpenAsync method to get a stream which you can use to read/write binary data. Here's how you would read a file:
IFile file = await folder_new.GetFileAsync(element.name);
using (Stream stream = await file.OpenAsync(FileAccess.Read))
{
// Read stream and process binary data from it...
}
This code is trying to open an existing file, then add text to it via openWrite.
import 'dart:io';
main() {
File inFile = new File('/tmp/foo.txt');
String currentText = inFile.readAsStringSync();
var writer = inFile.openWrite();
writer.write(currentText);
writer.write("\nOne more line");
writer.close();
exit(0);
}
After completion the file is empty. If the exit(0) is not there it works fine.
What call(s) should be done to ensure all writes are written before exit?
Since the writer is async, you will want to use the done property of the writer to be notified when the writing and closing of the stream is done. For instance:
import 'dart:io';
main() {
File inFile = new File('/tmp/foo.txt');
String currentText = inFile.readAsStringSync();
var writer = inFile.openWrite();
writer.write(currentText);
writer.write("\nOne more line");
writer.close();
writer.done.then((_) {
exit(0);
});
}
According to the document, data may be buffered, you shoud await writer.flush(); to make sure data is written to file.