androidApp/app/src/main/java/com/localtransfer/UploadFile.java

package com.localtransfer;

import android.database.Cursor;
import android.net.Uri;
import android.provider.OpenableColumns;
import android.util.Log;
import android.view.View;

import androidx.core.content.FileProvider;

import com.google.android.material.snackbar.Snackbar;

import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.sql.Timestamp;
import java.text.SimpleDateFormat;
import java.util.ConcurrentModificationException;
import java.util.Date;

public class UploadFile extends Transfer {

    public Uri uri;

    public UploadFile() {
        this.id = View.generateViewId();
        instances.add(this);
        info = "Upload complete";
        state = STATE_NOT_REQUESTED;
        drawable = R.drawable.ic_upload_24;
    }

    public static void handleSendFile(Uri uri) {
        if (uri != null) {
            UploadFile file = new UploadFile();
            file.uri = uri;

            Cursor cursor = activity.getContentResolver().query(uri, null, null, null, null);
            cursor.moveToFirst();

            file.name = cursor.getString(cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME));
            file.size = cursor.getLong(cursor.getColumnIndex(OpenableColumns.SIZE));
            file.sizeSI = Transfer.humanReadableByteCountBin(file.size);

            file.AddTransfer();
        }
    }

    public static void handleSendText(String sharedText) {
        if (sharedText != null) {
            SimpleDateFormat sdfDate = new SimpleDateFormat("yyyyMMdd_HHmmss");
            Date now = new Date();
            String strDate = sdfDate.format(now);
            Uri uri = null;

            try {
                File outputFile = new File(activity.getCacheDir(), strDate + ".txt");
                FileOutputStream fileOut = new FileOutputStream(outputFile);
                OutputStreamWriter OutWriter = new OutputStreamWriter(fileOut);
                OutWriter.append(sharedText);
                OutWriter.close();

                fileOut.flush();
                fileOut.close();

                uri = FileProvider.getUriForFile(activity, activity.getPackageName(), outputFile);

            } catch (IOException e) {
                e.printStackTrace();
            }
            handleSendFile(uri);
        }
    }

    @Override
    public void startTransfer() {
        super.startTransfer();

        startedTime = new Timestamp(System.currentTimeMillis());

        state = STATE_RUNNING;

        try {
            uploadFile();
        } catch (IOException e) {
            final String ExceptionName = e.getClass().getSimpleName();
            final String ExceptionMess = e.getMessage();

            state = Transfer.STATE_FAILED;
            error = ExceptionName + ": " + ExceptionMess;
            progressEnd();

            if(ExceptionName != null && ExceptionMess != null) {
                errorSnackbar(ExceptionMess);
            }

        }
    }

    private String uploadFile() throws IOException {
        String message = null;
        URL url = null;
        HttpURLConnection conn = null;
        DataOutputStream request = null;
        String boundary = "*****";
        final int maxBufferSize = 1 * 1024 * 1024;
        byte[] buffer = new byte[maxBufferSize];
        int bufferLength;
        loaded = 0;

        Cursor cursor = activity.getContentResolver().query(uri, null, null, null, null);
        cursor.moveToFirst();

        String type = activity.getContentResolver().getType(uri);

        String fileName = null;
        int col_name = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
        if (col_name != -1)
            fileName = cursor.getString(col_name);
        if(fileName == null)
            fileName = type.split("/")[0] + "_" + new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date()) + "." + type.split("/")[1];
        String fileNameUTF8 = new String(fileName.getBytes(), StandardCharsets.ISO_8859_1);

        url = new URL(protocol, host, port, root + "/upload.php");

        url = checkRedirection(url);

        Log.d("URL", url.toString());

        conn = (HttpURLConnection) url.openConnection();
        conn.setDoInput(true); // Allow Inputs
        conn.setDoOutput(true); // Allow Outputs
        conn.setUseCaches(false); // Don't use a Cached Copy
        conn.setChunkedStreamingMode(maxBufferSize);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Connection", "keep-alive");
        conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

        conn.connect();

        request = new DataOutputStream(conn.getOutputStream());

        request.writeBytes("--" + boundary + "\r\n");
        request.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\"" + fileNameUTF8 + "\"\r\n");
        request.writeBytes("Content-Type: " + type + "\r\n\r\n");

        InputStream in = activity.getContentResolver().openInputStream(uri);

        size = in.available();

        while ((bufferLength = in.read(buffer)) > 0) {
            request.write(buffer, 0, bufferLength);
            loaded+= bufferLength;
            percent = ((loaded * 100) / size);
            progressUpdateDelay();
        }

        request.writeBytes("\r\n");
        request.writeBytes("--" + boundary + "--\r\n");

        in.close();

        int responseCode = conn.getResponseCode();

        if (responseCode == HttpURLConnection.HTTP_OK) {
            message = "File " + fileName + " successful upload";
            state = Transfer.STATE_SUCCESS;
            progressEnd();
        }
        else {
            String s = conn.getResponseMessage();
            throw new HttpErrorException("error code: " + responseCode + " " + s);
        }

        request.flush();

        request.close();

        conn.disconnect();

        System.out.println(message);
        if (activity != null) {
            String finalMessage = message;
            activity.runOnUiThread(() ->
                    Snackbar.make(activity.findViewById(R.id.view_pager), finalMessage, Snackbar.LENGTH_LONG)
                            .setAction("Action", null).show());
        }

        return message;
    }
}