Establish some rules for handling InputStreams

* Methods shouldn't place any special requirements on the streams
  passed into them
* This implies that if a stream's going to be marked and reset,
  that should all happen within one method
* This also implies that if a method needs to mark and reset a stream,
  it should wrap the stream in a BufferedInputStream before doing so,
  rather than requiring a markable stream to be passed in

briar-android/src/main/java/org/briarproject/briar/android/conversation/AttachmentController.java

@@ -16,6 +16,7 @@ import org.briarproject.briar.api.messaging.Attachment;
 import org.briarproject.briar.api.messaging.AttachmentHeader;
 import org.briarproject.briar.api.messaging.MessagingManager;
 
+import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
@@ -92,14 +93,13 @@ class AttachmentController {
 
 	/**
 	 * Creates {@link AttachmentItem}s from the passed headers and Attachments.
-	 * Note: This marks the {@link Attachment}'s {@link InputStream}
+	 *
-	 * and closes the streams.
+	 * Note: This closes the {@link Attachment}'s {@link InputStream}.
 	 */
 	List<AttachmentItem> getAttachmentItems(
 			List<Pair<AttachmentHeader, Attachment>> attachments) {
 		List<AttachmentItem> items = new ArrayList<>(attachments.size());
 		for (Pair<AttachmentHeader, Attachment> a : attachments) {
-			a.getSecond().getStream().mark(Integer.MAX_VALUE);
 			AttachmentItem item =
 					getAttachmentItem(a.getFirst(), a.getSecond());
 			items.add(item);
@@ -109,16 +109,14 @@ class AttachmentController {
 
 	/**
 	 * Creates an {@link AttachmentItem} from the {@link Attachment}'s
-	 * {@link InputStream}.
+	 * {@link InputStream} which will be closed when this method returns.
-	 * Note: Requires a resettable InputStream
-	 *       with the beginning already marked.
-	 *       The stream will be closed when this method returns.
 	 */
 	AttachmentItem getAttachmentItem(AttachmentHeader h, Attachment a) {
 		MessageId messageId = h.getMessageId();
 		Size size = new Size();
 
-		InputStream is = a.getStream();
+		InputStream is = new BufferedInputStream(a.getStream());
+		is.mark(Integer.MAX_VALUE);
 		try {
 			// use exif to get size
 			if (h.getContentType().equals("image/jpeg")) {
@@ -190,13 +188,6 @@ class AttachmentController {
 				options.outMimeType);
 	}
 
-	static String getContentTypeFromBitmap(InputStream is) {
-		BitmapFactory.Options options = new BitmapFactory.Options();
-		options.inJustDecodeBounds = true;
-		BitmapFactory.decodeStream(is, null, options);
-		return options.outMimeType;
-	}
-
 	private Size getThumbnailSize(int width, int height, String mimeType) {
 		float widthPercentage = maxWidth / (float) width;
 		float heightPercentage = maxHeight / (float) height;

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationViewModel.java

@@ -31,7 +31,6 @@ import org.briarproject.briar.api.messaging.PrivateMessage;
 import org.briarproject.briar.api.messaging.PrivateMessageFactory;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 
-import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
@@ -48,7 +47,6 @@ import static org.briarproject.bramble.util.IoUtils.tryToClose;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
-import static org.briarproject.briar.android.conversation.AttachmentController.getContentTypeFromBitmap;
 import static org.briarproject.briar.android.util.UiUtils.observeForeverOnce;
 
 @NotNullByDefault
@@ -140,7 +138,6 @@ public class ConversationViewModel extends AndroidViewModel {
 		observeForeverOnce(messagingGroupId, groupId -> {
 			if (groupId == null) return;
 			// calls through to creating and storing the message
-			// (wouldn't Kotlin's co-routines be nice here?)
 			storeAttachments(groupId, text, uris, timestamp);
 		});
 	}
@@ -185,12 +182,14 @@ public class ConversationViewModel extends AndroidViewModel {
 					getApplication().getContentResolver();
 			is = contentResolver.openInputStream(uri);
 			if (is == null) throw new IOException();
-			is = new BufferedInputStream(is);  // adds support for reset()
-			is.mark(Integer.MAX_VALUE);
 			String contentType = contentResolver.getType(uri);
-			if (contentType == null) contentType = getContentTypeFromBitmap(is);
+			if (contentType == null) throw new IOException("null content type");
 			AttachmentHeader h = messagingManager
 					.addLocalAttachment(groupId, timestamp, contentType, is);
+			is.close();
+			// re-open stream to get AttachmentItem
+			is = contentResolver.openInputStream(uri);
+			if (is == null) throw new IOException();
 			AttachmentItem item = attachmentController
 					.getAttachmentItem(h, new Attachment(is));
 			return new Pair<>(h, item);

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

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.api.conversation.ConversationManager.ConversationClient;
 
+import java.io.IOException;
 import java.io.InputStream;
 
 @NotNullByDefault
@@ -37,7 +38,7 @@ public interface MessagingManager extends ConversationClient {
 	 * Stores a local attachment message.
 	 */
 	AttachmentHeader addLocalAttachment(GroupId groupId, long timestamp,
-			String contentType, InputStream is) throws DbException;
+			String contentType, InputStream is) throws DbException, IOException;
 
 	/**
 	 * Returns the ID of the contact with the given private conversation.

briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java

@@ -33,6 +33,7 @@ import org.briarproject.briar.api.messaging.event.PrivateMessageReceivedEvent;
 import org.briarproject.briar.client.ConversationClientImpl;
 
 import java.io.ByteArrayInputStream;
+import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -154,8 +155,9 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	@Override
 	public AttachmentHeader addLocalAttachment(GroupId groupId, long timestamp,
-			String contentType, InputStream is) {
+			String contentType, InputStream is) throws IOException {
 		// TODO add real implementation
+		if (is.available() == 0) throw new IOException();
 		byte[] b = new byte[MessageId.LENGTH];
 		new Random().nextBytes(b);
 		return new AttachmentHeader(new MessageId(b), "image/png");