Add method for retrieving contact list from own mailbox

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApi.java

@@ -6,6 +6,7 @@ import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.mailbox.MailboxProperties;
 
 import java.io.IOException;
+import java.util.Collection;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -46,6 +47,13 @@ interface MailboxApi {
 	void deleteContact(MailboxProperties properties, ContactId contactId)
 			throws IOException, ApiException;
 
+	/**
+	 * Gets a list of {@link ContactId}s from the mailbox.
+	 * These are the contacts that the mailbox already knows about.
+	 */
+	Collection<ContactId> getContacts(MailboxProperties properties)
+			throws IOException, ApiException;
+
 	@Immutable
 	@JsonSerialize
 	class MailboxContact {

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApiImpl.java

@@ -10,6 +10,9 @@ import org.briarproject.bramble.api.mailbox.MailboxProperties;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
 
 import javax.inject.Inject;
 
@@ -127,6 +130,38 @@ class MailboxApiImpl implements MailboxApi {
 		if (response.code() != 200) throw new ApiException();
 	}
 
+	@Override
+	public Collection<ContactId> getContacts(MailboxProperties properties)
+			throws IOException, ApiException {
+		if (!properties.isOwner()) throw new IllegalArgumentException();
+		Request request = getRequestBuilder(properties.getAuthToken())
+				.url(properties.getOnionAddress() + "/contacts")
+				.build();
+		OkHttpClient client = httpClientProvider.get();
+		Response response = client.newCall(request).execute();
+		if (response.code() != 200) throw new ApiException();
+
+		ResponseBody body = response.body();
+		if (body == null) throw new ApiException();
+		try {
+			JsonNode node = mapper.readTree(body.string());
+			JsonNode contactsNode = node.get("contacts");
+			if (contactsNode == null || !contactsNode.isArray()) {
+				throw new ApiException();
+			}
+			List<ContactId> list = new ArrayList<>();
+			for (JsonNode contactNode : contactsNode) {
+				if (!contactNode.isNumber()) throw new ApiException();
+				int id = contactNode.intValue();
+				if (id < 1) throw new ApiException();
+				list.add(new ContactId(id));
+			}
+			return list;
+		} catch (JacksonException e) {
+			throw new ApiException();
+		}
+	}
+
 	private Request.Builder getRequestBuilder(String token) {
 		return new Request.Builder()
 				.addHeader("Authorization", "Bearer " + token);