[android] Create attachments before showing previews

briar-api/src/main/java/org/briarproject/briar/api/messaging/AttachmentHeader.java

@@ -25,4 +25,15 @@ public class AttachmentHeader {
 		return contentType;
 	}
 
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof AttachmentHeader &&
+				messageId.equals(((AttachmentHeader) o).messageId);
+	}
+
+	@Override
+	public int hashCode() {
+		return messageId.hashCode();
+	}
+
 }

briar-api/src/main/java/org/briarproject/briar/api/messaging/MessagingConstants.java

@@ -8,4 +8,19 @@ public interface MessagingConstants {
 	 * The maximum length of a private message's text in UTF-8 bytes.
 	 */
 	int MAX_PRIVATE_MESSAGE_TEXT_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+	/**
+	 * The supported mime types for image attachments.
+	 */
+	String[] IMAGE_MIME_TYPES = {
+			"image/jpeg",
+			"image/png",
+			"image/gif",
+	};
+
+	/**
+	 * The maximum allowed size of image attachments.
+	 */
+	int MAX_IMAGE_SIZE = 6 * 1024 * 1024;
+
 }

briar-api/src/main/java/org/briarproject/briar/api/messaging/MessagingManager.java

@@ -41,6 +41,11 @@ public interface MessagingManager extends ConversationClient {
 	AttachmentHeader addLocalAttachment(GroupId groupId, long timestamp,
 			String contentType, InputStream is) throws DbException, IOException;
 
+	/**
+	 * Removes an unsent attachment.
+	 */
+	void removeAttachment(AttachmentHeader header) throws DbException;
+
 	/**
 	 * Returns the ID of the contact with the given private conversation.
 	 */