path: root/libdino/src/service/file_manager.vala

using Gdk;
using Gee;

using Xmpp;
using Xmpp.Xep;
using Dino.Entities;

namespace Dino {

public class FileManager : StreamInteractionModule, Object {
    public static ModuleIdentity<FileManager> IDENTITY = new ModuleIdentity<FileManager>("file");
    public string id { get { return IDENTITY.id; } }

    public signal void upload_available(Account account);
    public signal void received_file(FileTransfer file_transfer, Conversation conversation);

    private StreamInteractor stream_interactor;
    private Database db;
    private Gee.List<FileSender> file_senders = new ArrayList<FileSender>();
    private Gee.List<FileEncryptor> file_encryptors = new ArrayList<FileEncryptor>();
    private Gee.List<FileDecryptor> file_decryptors = new ArrayList<FileDecryptor>();
    private Gee.List<FileProvider> file_providers = new ArrayList<FileProvider>();
    private Gee.List<FileMetadataProvider> file_metadata_providers = new ArrayList<FileMetadataProvider>();

    public static void start(StreamInteractor stream_interactor, Database db) {
        FileManager m = new FileManager(stream_interactor, db);
        stream_interactor.add_module(m);
    }

    public static string get_storage_dir() {
        return Path.build_filename(Dino.get_storage_dir(), "files");
    }

    private FileManager(StreamInteractor stream_interactor, Database db) {
        this.stream_interactor = stream_interactor;
        this.db = db;
        DirUtils.create_with_parents(get_storage_dir(), 0700);

        this.add_provider(new JingleFileProvider(stream_interactor));
        this.add_sender(new JingleFileSender(stream_interactor));
        this.add_metadata_provider(new GenericFileMetadataProvider());
        this.add_metadata_provider(new ImageFileMetadataProvider());
        this.stream_interactor.account_added.connect((account) => {
            on_account_added(account);
        });
    }

    public const int HTTP_PROVIDER_ID = 0;
    public const int SFS_PROVIDER_ID = 2;

    private FileProvider? select_file_provider(FileTransfer file_transfer) {
        bool http_usable = file_transfer.provider == SFS_PROVIDER_ID;
        foreach (FileProvider file_provider in this.file_providers) {
            if (file_transfer.provider == file_provider.get_id()) {
                return file_provider;
            }
            if (http_usable && file_provider.get_id() == HTTP_PROVIDER_ID) {
                return file_provider;
            }
        }
        return null;
    }

    // For receiving out of band data as sfs
    private async void on_backwards_compatible_sfs(FileProvider file_provider, Jid from, DateTime time, DateTime local_time, Conversation conversation, FileReceiveData receive_data, FileMeta file_meta) {
        Xep.StatelessFileSharing.SfsElement sfs_element = new Xep.StatelessFileSharing.SfsElement();

        Xep.StatelessFileSharing.HttpSource source = new Xep.StatelessFileSharing.HttpSource();
        HttpFileReceiveData http_receive_data = receive_data as HttpFileReceiveData;
        source.url = http_receive_data.url;
        sfs_element.sources.add(source);

        FileTransfer file_transfer = new FileTransfer();

        if (is_jid_trustworthy(from, conversation)) {
            try {
                file_meta = yield file_provider.get_meta_info(file_transfer, http_receive_data, file_meta);
            } catch (Error e) {
                warning("Can't accept oob data as stateless file sharing due to failed http request\n");
            }
        }

        sfs_element.metadata.size = file_meta.size;
        sfs_element.metadata.name = file_meta.file_name;
        sfs_element.metadata.mime_type = file_meta.mime_type;
        // Encryption unused in http file transfers

        yield on_receive_sfs(from, conversation, sfs_element, null);
    }

    private async void on_receive_sfs(Jid from, Conversation conversation, Xep.StatelessFileSharing.SfsElement sfs_element, string? id) {
        FileTransfer file_transfer = new FileTransfer();
        file_transfer.account = conversation.account;
        file_transfer.counterpart = file_transfer.direction == FileTransfer.DIRECTION_RECEIVED ? from : conversation.counterpart;
        if (conversation.type_.is_muc_semantic()) {
            file_transfer.ourpart = stream_interactor.get_module(MucManager.IDENTITY).get_own_jid(conversation.counterpart, conversation.account) ?? conversation.account.bare_jid;
            file_transfer.direction = from.equals(file_transfer.ourpart) ? FileTransfer.DIRECTION_SENT : FileTransfer.DIRECTION_RECEIVED;
        } else {
            file_transfer.ourpart = conversation.account.full_jid;
            file_transfer.direction = from.equals_bare(file_transfer.ourpart) ? FileTransfer.DIRECTION_SENT : FileTransfer.DIRECTION_RECEIVED;
        }
        file_transfer.time = new DateTime.now_utc();
        // TODO: get time from message
        file_transfer.local_time = new DateTime.now_utc();
        file_transfer.provider = SFS_PROVIDER_ID;
        file_transfer.with_metadata_element(sfs_element.metadata);
        foreach (Xep.StatelessFileSharing.SfsSource source in sfs_element.sources) {
            file_transfer.sfs_sources.append(new FileTransfer.SerializedSfsSource.from_sfs_source(source) as Object);
        }
        // FileTransfer.info stores the id of the MessageStanza for future SfsSourceAttachments
        // Prior to sfs, info stored the id of the Message entity for oob
        file_transfer.info = id;

        stream_interactor.get_module(FileTransferStorage.IDENTITY).add_file(file_transfer);

        if (is_sender_trustworthy(file_transfer, conversation)) {
            if (file_transfer.size >= 0 && file_transfer.size < 500) {
                FileProvider? file_provider = this.select_file_provider(file_transfer);
                download_file_internal.begin(file_provider, file_transfer, conversation, (_, res) => {
                    download_file_internal.end(res);
                });
            }
        }

        conversation.last_active = file_transfer.time;
        received_file(file_transfer, conversation);
    }

    private void on_receive_sfs_attachment(Jid from, Conversation conversation, Xep.StatelessFileSharing.SfsSourceAttachment attachment) {
        foreach (Qlite.Row file_transfer_row in this.db.file_transfer.select()
                .with(db.file_transfer.info, "=", attachment.sfs_id)) {
            FileTransfer file_transfer = new FileTransfer.from_row(this.db, file_transfer_row, FileManager.get_storage_dir());
            if (file_transfer.hashes.supported_hashes().is_empty) {
                return;
            }
            foreach (StatelessFileSharing.SfsSource source in attachment.sources) {
                file_transfer.sfs_sources.append(new FileTransfer.SerializedSfsSource.from_sfs_source(source) as Object);
            }
        }

    }

    private void on_account_added(Account account) {
        Xep.StatelessFileSharing.Module fsf_module = stream_interactor.module_manager.get_module(account, Xep.StatelessFileSharing.Module.IDENTITY);
        fsf_module.received_sfs.connect((from, to, sfs_element, message) => {
            Conversation? conversation = stream_interactor.get_module(ConversationManager.IDENTITY).approx_conversation_for_stanza(from, to, account, message.type_);
            on_receive_sfs(from, conversation, sfs_element, message.id);
        });
        fsf_module.received_sfs_attachment.connect((from, to, sfs_attachment, message) => {
            Conversation? conversation = stream_interactor.get_module(ConversationManager.IDENTITY).approx_conversation_for_stanza(from, to, account, message.type_);
            on_receive_sfs_attachment(from, conversation, sfs_attachment);
        });
    }

        public async HashMap<int, long> get_file_size_limits(Conversation conversation) {
        HashMap<int, long> ret = new HashMap<int, long>();
        foreach (FileSender sender in file_senders) {
            ret[sender.get_id()] = yield sender.get_file_size_limit(conversation);
        }
        return ret;
    }

    public async void send_file(File file, Conversation conversation) {
        FileTransfer file_transfer = new FileTransfer();
        file_transfer.account = conversation.account;
        file_transfer.counterpart = conversation.counterpart;
        if (conversation.type_.is_muc_semantic()) {
            file_transfer.ourpart = stream_interactor.get_module(MucManager.IDENTITY).get_own_jid(conversation.counterpart, conversation.account) ?? conversation.account.bare_jid;
        } else {
            file_transfer.ourpart = conversation.account.full_jid;
        }
        file_transfer.direction = FileTransfer.DIRECTION_SENT;
        file_transfer.time = new DateTime.now_utc();
        file_transfer.local_time = new DateTime.now_utc();
        file_transfer.encryption = conversation.encryption;

        Xep.FileMetadataElement.FileMetadata metadata = new Xep.FileMetadataElement.FileMetadata();
        foreach (FileMetadataProvider file_metadata_provider in this.file_metadata_providers) {
            if (file_metadata_provider.supports_file(file)) {
                yield file_metadata_provider.fill_metadata(file, metadata);
            }
        }
        file_transfer.with_metadata_element(metadata);

        try {
            file_transfer.input_stream = yield file.read_async();

            yield save_file(file_transfer);

            stream_interactor.get_module(FileTransferStorage.IDENTITY).add_file(file_transfer);
            conversation.last_active = file_transfer.time;
            received_file(file_transfer, conversation);
        } catch (Error e) {
            file_transfer.state = FileTransfer.State.FAILED;
            warning("Error saving outgoing file: %s", e.message);
            return;
        }

        try {
            var file_meta = new FileMeta();
            file_meta.size = file_transfer.size;
            file_meta.mime_type = file_transfer.mime_type;

            FileSender file_sender = null;
            FileEncryptor file_encryptor = null;
            foreach (FileSender sender in file_senders) {
                if (yield sender.can_send(conversation, file_transfer)) {
                    if (file_transfer.encryption == Encryption.NONE || yield sender.can_encrypt(conversation, file_transfer)) {
                        file_sender = sender;
                        break;
                    } else {
                        foreach (FileEncryptor encryptor in file_encryptors) {
                            if (encryptor.can_encrypt_file(conversation, file_transfer)) {
                                file_encryptor = encryptor;
                                break;
                            }
                        }
                        if (file_encryptor != null) {
                            file_sender = sender;
                            break;
                        }
                    }
                }
            }

            if (file_sender == null) {
                throw new FileSendError.UPLOAD_FAILED("No sender/encryptor combination available");
            }

            if (file_encryptor != null) {
                file_meta = file_encryptor.encrypt_file(conversation, file_transfer);
            }

            FileSendData file_send_data = yield file_sender.prepare_send_file(conversation, file_transfer, file_meta);

            if (file_encryptor != null) {
                file_send_data = file_encryptor.preprocess_send_file(conversation, file_transfer, file_send_data, file_meta);
            }

            yield file_sender.send_file(conversation, file_transfer, file_send_data, file_meta);

        } catch (Error e) {
            warning("Send file error: %s", e.message);
            file_transfer.state = FileTransfer.State.FAILED;
        }
    }

    public async void download_file(FileTransfer file_transfer) {
        Conversation conversation = stream_interactor.get_module(ConversationManager.IDENTITY).get_conversation(file_transfer.counterpart.bare_jid, file_transfer.account);

        FileProvider? file_provider = this.select_file_provider(file_transfer);

        yield download_file_internal(file_provider, file_transfer, conversation);
    }

    public async bool is_upload_available(Conversation? conversation) {
        if (conversation == null) return false;

        foreach (FileSender file_sender in file_senders) {
            if (yield file_sender.is_upload_available(conversation)) return true;
        }
        return false;
    }

    public void add_provider(FileProvider file_provider) {
        file_providers.add(file_provider);
        file_provider.file_incoming.connect((info, from, time, local_time, conversation, receive_data, file_meta) => {
            if (receive_data is HttpFileReceiveData) {
                printerr("Handling oob data as stateless file sharing");
                this.on_backwards_compatible_sfs.begin(file_provider, from, time, local_time, conversation, receive_data, file_meta);
            } else {
                handle_incoming_file.begin(file_provider, info, from, time, local_time, conversation, receive_data, file_meta);
            }
        });
    }

    public void add_sender(FileSender file_sender) {
        file_senders.add(file_sender);
        file_sender.upload_available.connect((account) => {
            upload_available(account);
        });
        file_senders.sort((a, b) => {
            return (int) (b.get_priority() - a.get_priority());
        });
    }

    public void add_file_encryptor(FileEncryptor encryptor) {
        file_encryptors.add(encryptor);
    }

    public void add_file_decryptor(FileDecryptor decryptor) {
        file_decryptors.add(decryptor);
    }

    public void add_metadata_provider(FileMetadataProvider file_metadata_provider) {
        file_metadata_providers.add(file_metadata_provider);
    }

    private bool is_jid_trustworthy(Jid from, Conversation conversation) {
        Jid relevant_jid = conversation.counterpart;
        if (conversation.type_ == Conversation.Type.GROUPCHAT) {
            relevant_jid = stream_interactor.get_module(MucManager.IDENTITY).get_real_jid(from, conversation.account);
        }
        if (relevant_jid == null) return false;

        bool in_roster = stream_interactor.get_module(RosterManager.IDENTITY).get_roster_item(conversation.account, relevant_jid) != null;
        return in_roster;
    }

    public bool is_sender_trustworthy(FileTransfer file_transfer, Conversation conversation) {
        if (file_transfer.direction == FileTransfer.DIRECTION_SENT) return true;

        return is_jid_trustworthy(file_transfer.from, conversation);
    }

    private async FileMeta get_file_meta(FileProvider file_provider, FileTransfer file_transfer, Conversation conversation, FileReceiveData receive_data_) throws FileReceiveError {
        FileReceiveData receive_data = receive_data_;
        FileMeta file_meta = file_provider.get_file_meta(file_transfer);

        if (file_meta.size == -1) {
            foreach (FileDecryptor file_decryptor in file_decryptors) {
                if (file_decryptor.can_decrypt_file(conversation, file_transfer, receive_data)) {
                    receive_data = file_decryptor.prepare_get_meta_info(conversation, file_transfer, receive_data);
                    break;
                }
            }

            file_meta = yield file_provider.get_meta_info(file_transfer, receive_data, file_meta);

            file_transfer.size = (int)file_meta.size;
            file_transfer.file_name = file_meta.file_name;
            file_transfer.mime_type = file_meta.mime_type;
        }
        return file_meta;
    }

    private async void download_file_internal(FileProvider file_provider, FileTransfer file_transfer, Conversation conversation) {
        try {
            // Get meta info
            FileReceiveData receive_data = yield file_provider.get_file_receive_data(file_transfer);
            FileDecryptor? file_decryptor = null;
            foreach (FileDecryptor decryptor in file_decryptors) {
                if (decryptor.can_decrypt_file(conversation, file_transfer, receive_data)) {
                    file_decryptor = decryptor;
                    break;
                }
            }

            if (file_decryptor != null) {
                receive_data = file_decryptor.prepare_get_meta_info(conversation, file_transfer, receive_data);
            }

            FileMeta file_meta = yield get_file_meta(file_provider, file_transfer, conversation, receive_data);


            InputStream? input_stream = null;

            // Download and decrypt file
            file_transfer.state = FileTransfer.State.IN_PROGRESS;

            if (file_decryptor != null) {
                file_meta = file_decryptor.prepare_download_file(conversation, file_transfer, receive_data, file_meta);
            }

            input_stream = yield file_provider.download(file_transfer, receive_data, file_meta);
            if (file_decryptor != null) {
                input_stream = yield file_decryptor.decrypt_file(input_stream, conversation, file_transfer, receive_data);
            }

            // Save file
            string filename = Random.next_int().to_string("%x") + "_" + file_transfer.file_name;
            File file = File.new_for_path(Path.build_filename(get_storage_dir(), filename));

            OutputStream os = file.create(FileCreateFlags.REPLACE_DESTINATION);
            uint8[] buffer = new uint8[1024];
            ssize_t read;
            while ((read = yield input_stream.read_async(buffer, Priority.LOW, file_transfer.cancellable)) > 0) {
                buffer.length = (int) read;
                yield os.write_async(buffer, Priority.LOW, file_transfer.cancellable);
                buffer.length = 1024;
            }
            yield input_stream.close_async(Priority.LOW, file_transfer.cancellable);
            yield os.close_async(Priority.LOW, file_transfer.cancellable);
            file_transfer.path = file.get_basename();
            file_transfer.input_stream = yield file.read_async();

            FileInfo file_info = file_transfer.get_file().query_info("*", FileQueryInfoFlags.NONE);
            file_transfer.mime_type = file_info.get_content_type();

            file_transfer.state = FileTransfer.State.COMPLETE;
        } catch (Error e) {
            warning("Error downloading file: %s", e.message);
            file_transfer.state = FileTransfer.State.FAILED;
        }
    }

    private async void handle_incoming_file(FileProvider file_provider, string info, Jid from, DateTime time, DateTime local_time, Conversation conversation, FileReceiveData receive_data, FileMeta file_meta) {
        FileTransfer file_transfer = new FileTransfer();
        file_transfer.account = conversation.account;
        file_transfer.counterpart = file_transfer.direction == FileTransfer.DIRECTION_RECEIVED ? from : conversation.counterpart;
        if (conversation.type_.is_muc_semantic()) {
            file_transfer.ourpart = stream_interactor.get_module(MucManager.IDENTITY).get_own_jid(conversation.counterpart, conversation.account) ?? conversation.account.bare_jid;
            file_transfer.direction = from.equals(file_transfer.ourpart) ? FileTransfer.DIRECTION_SENT : FileTransfer.DIRECTION_RECEIVED;
        } else {
            if (from.equals_bare(conversation.account.bare_jid)) {
                file_transfer.ourpart = from;
                file_transfer.direction = FileTransfer.DIRECTION_SENT;
            } else {
                file_transfer.ourpart = conversation.account.full_jid;
                file_transfer.direction = FileTransfer.DIRECTION_RECEIVED;
            }
        }
        file_transfer.time = time;
        file_transfer.local_time = local_time;
        file_transfer.provider = file_provider.get_id();
        file_transfer.file_name = file_meta.file_name;
        file_transfer.size = (int)file_meta.size;
        file_transfer.info = info;

        var encryption = file_provider.get_encryption(file_transfer, receive_data, file_meta);
        if (encryption != Encryption.NONE) file_transfer.encryption = encryption;

        foreach (FileDecryptor decryptor in file_decryptors) {
            if (decryptor.can_decrypt_file(conversation, file_transfer, receive_data)) {
                file_transfer.encryption = decryptor.get_encryption();
            }
        }

        stream_interactor.get_module(FileTransferStorage.IDENTITY).add_file(file_transfer);

        if (is_sender_trustworthy(file_transfer, conversation)) {
            try {
                yield get_file_meta(file_provider, file_transfer, conversation, receive_data);
            } catch (Error e) {
                warning("Error downloading file: %s", e.message);
                file_transfer.state = FileTransfer.State.FAILED;
            }
            if (file_transfer.size >= 0 && file_transfer.size < 5000000) {
                download_file_internal.begin(file_provider, file_transfer, conversation, (_, res) => {
                    download_file_internal.end(res);
                });
            }
        }

        conversation.last_active = file_transfer.time;
        received_file(file_transfer, conversation);
    }

    private async void save_file(FileTransfer file_transfer) throws FileSendError {
        try {
            string filename = Random.next_int().to_string("%x") + "_" + file_transfer.file_name;
            File file = File.new_for_path(Path.build_filename(get_storage_dir(), filename));
            OutputStream os = file.create(FileCreateFlags.REPLACE_DESTINATION);
            yield os.splice_async(file_transfer.input_stream, OutputStreamSpliceFlags.CLOSE_SOURCE|OutputStreamSpliceFlags.CLOSE_TARGET);
            file_transfer.state = FileTransfer.State.COMPLETE;
            file_transfer.path = filename;
            file_transfer.input_stream = yield file.read_async();
        } catch (Error e) {
            throw new FileSendError.SAVE_FAILED("Saving file error: %s".printf(e.message));
        }
    }
}

public errordomain FileSendError {
    ENCRYPTION_FAILED,
    UPLOAD_FAILED,
    SAVE_FAILED
}

public errordomain FileReceiveError {
    GET_METADATA_FAILED,
    DECRYPTION_FAILED,
    DOWNLOAD_FAILED
}

public class FileMeta {
    public int64 size = -1;
    public string? mime_type = null;
    public string? file_name = null;
    public Encryption encryption = Encryption.NONE;
}

public class HttpFileMeta : FileMeta {
    public Message message;
}

public class FileSendData { }

public class HttpFileSendData : FileSendData {
    public string url_down { get; set; }
    public string url_up { get; set; }
    public HashMap<string, string> headers { get; set; }

    public bool encrypt_message { get; set; default=true; }
}

public class FileReceiveData { }

public class HttpFileReceiveData : FileReceiveData {
    public string url { get; set; }
}

public interface FileProvider : Object {
    public signal void file_incoming(string info, Jid from, DateTime time, DateTime local_time, Conversation conversation, FileReceiveData receive_data, FileMeta file_meta);

    public abstract Encryption get_encryption(FileTransfer file_transfer, FileReceiveData receive_data, FileMeta file_meta);
    public abstract FileMeta get_file_meta(FileTransfer file_transfer) throws FileReceiveError;
    public abstract async FileReceiveData? get_file_receive_data(FileTransfer file_transfer);

    public abstract async FileMeta get_meta_info(FileTransfer file_transfer, FileReceiveData receive_data, FileMeta file_meta) throws FileReceiveError;
    public abstract async InputStream download(FileTransfer file_transfer, FileReceiveData receive_data, FileMeta file_meta) throws FileReceiveError;

    public abstract int get_id();
}

public interface FileSender : Object {
    public signal void upload_available(Account account);

    public abstract async bool is_upload_available(Conversation conversation);
    public abstract async long get_file_size_limit(Conversation conversation);
    public abstract async bool can_send(Conversation conversation, FileTransfer file_transfer);
    public abstract async FileSendData? prepare_send_file(Conversation conversation, FileTransfer file_transfer, FileMeta file_meta) throws FileSendError;
    public abstract async void send_file(Conversation conversation, FileTransfer file_transfer, FileSendData file_send_data, FileMeta file_meta) throws FileSendError;
    public abstract async bool can_encrypt(Conversation conversation, FileTransfer file_transfer);

    public abstract int get_id();
    public abstract float get_priority();
}

public interface FileEncryptor : Object {
    public abstract bool can_encrypt_file(Conversation conversation, FileTransfer file_transfer);
    public abstract FileMeta encrypt_file(Conversation conversation, FileTransfer file_transfer) throws FileSendError;
    public abstract FileSendData? preprocess_send_file(Conversation conversation, FileTransfer file_transfer, FileSendData file_send_data, FileMeta file_meta) throws FileSendError;
}

public interface FileDecryptor : Object {
    public abstract Encryption get_encryption();
    public abstract FileReceiveData prepare_get_meta_info(Conversation conversation, FileTransfer file_transfer, FileReceiveData receive_data);
    public abstract FileMeta prepare_download_file(Conversation conversation, FileTransfer file_transfer, FileReceiveData receive_data, FileMeta file_meta);
    public abstract bool can_decrypt_file(Conversation conversation, FileTransfer file_transfer, FileReceiveData receive_data);
    public abstract async InputStream decrypt_file(InputStream encrypted_stream, Conversation conversation, FileTransfer file_transfer, FileReceiveData receive_data) throws FileReceiveError;
}

public interface FileMetadataProvider : Object {
    public abstract bool supports_file(File file);

    public abstract async void fill_metadata(File file, Xep.FileMetadataElement.FileMetadata metadata);
}

class GenericFileMetadataProvider: Dino.FileMetadataProvider, Object {
    public bool supports_file(File file) {
        return true;
    }

    public async void fill_metadata(File file, Xep.FileMetadataElement.FileMetadata metadata) {
        FileInfo info = file.query_info("*", FileQueryInfoFlags.NONE);

        metadata.name = info.get_display_name();
        metadata.mime_type = info.get_content_type();
        metadata.size = info.get_size();
        metadata.date = info.get_modification_date_time();

        Bytes file_data = file.load_bytes();
        metadata.hashes.hashes.add(new CryptographicHashes.Hash.from_data(GLib.ChecksumType.SHA256, file_data.get_data()));
        metadata.hashes.hashes.add(new CryptographicHashes.Hash.from_data(GLib.ChecksumType.SHA512, file_data.get_data()));
    }
}

public class ImageFileMetadataProvider: Dino.FileMetadataProvider, Object {
    public bool supports_file(File file) {
        return file.query_info("*", FileQueryInfoFlags.NONE).get_content_type().has_prefix("image");
    }

    private const int[] THUMBNAIL_DIMS = { 1, 2, 3, 4, 8 };
    private const string IMAGE_TYPE = "png";
    private const string MIME_TYPE = "image/png";

    public async void fill_metadata(File file, Xep.FileMetadataElement.FileMetadata metadata) {
        Pixbuf pixbuf = new Pixbuf.from_stream(yield file.read_async());
        metadata.width = pixbuf.get_width();
        metadata.height = pixbuf.get_height();
        float ratio = (float)metadata.width / (float) metadata.height;

        int thumbnail_width = -1;
        int thumbnail_height = -1;
        float diff = float.INFINITY;
        for (int i = 0; i < THUMBNAIL_DIMS.length; i++) {
            int test_width = THUMBNAIL_DIMS[i];
            int test_height = THUMBNAIL_DIMS[THUMBNAIL_DIMS.length - 1 - i];
            float test_ratio = (float)test_width / (float)test_height;
            float test_diff = (test_ratio - ratio).abs();
            if (test_diff < diff) {
                thumbnail_width = test_width;
                thumbnail_height = test_height;
                diff = test_diff;
            }
        }

        Pixbuf thumbnail_pixbuf = pixbuf.scale_simple(thumbnail_width, thumbnail_height, InterpType.BILINEAR);
        uint8[] buffer;
        thumbnail_pixbuf.save_to_buffer(out buffer, IMAGE_TYPE);
        string base_64 = GLib.Base64.encode(buffer);
        string uri = @"data:$MIME_TYPE;base64,$base_64";
        Xep.JingleContentThumbnails.Thumbnail thumbnail = new Xep.JingleContentThumbnails.Thumbnail();
        thumbnail.uri = uri;
        thumbnail.media_type = MIME_TYPE;
        thumbnail.width = thumbnail_width;
        thumbnail.height = thumbnail_height;
        metadata.thumbnails.add(thumbnail);
    }

    public static Pixbuf? parse_thumbnail(Xep.JingleContentThumbnails.Thumbnail thumbnail) {
        string[] splits = thumbnail.uri.split(":", 2);
        if (splits.length != 2) {
            printerr("Thumbnail parsing error: ':' not found");
            return null;
        }
        if (splits[0] != "data") {
            printerr("Unsupported thumbnail: unimplemented uri type\n");
            return null;
        }
        splits = splits[1].split(";", 2);
        if (splits.length != 2) {
            printerr("Thumbnail parsing error: ';' not found");
            return null;
        }
        if (splits[0] != MIME_TYPE) {
            printerr("Unsupported thumbnail: unsupported mime-type\n");
            return null;
        }
        splits = splits[1].split(",", 2);
        if (splits.length != 2) {
            printerr("Thumbnail parsing error: ',' not found");
            return null;
        }
        if (splits[0] != "base64") {
            printerr("Unsupported thumbnail: data is not base64 encoded\n");
            return null;
        }
        uint8[] data = Base64.decode(splits[1]);
        MemoryInputStream input_stream = new MemoryInputStream.from_data(data);
        Pixbuf pixbuf = new Pixbuf.from_stream(input_stream);
        return pixbuf;
    }
}

}