/**
 * Test that transactions are only allowed on primaries, and prohibited from running on secondaries.
 *
 * @tags: [uses_transactions]
 */
(function() {
"use strict";

// In 4.0, we allow read-only transactions on secondaries when test commands are enabled, so we
// disable them in this test, to test that transactions on secondaries will be disallowed
// for production users.

TestData.enableTestCommands = false;
TestData.roleGraphInvalidationIsFatal = false;
TestData.authenticationDatabase = "local";

const dbName = "test";
const collName = "transactions_only_allowed_on_primaries";

// Start up the replica set. We want a stable topology, so make the secondary unelectable.
const replTest = new ReplSetTest({name: collName, nodes: 2});
replTest.startSet();
let config = replTest.getReplSetConfig();
config.members[1].priority = 0;
replTest.initiate(config);

const primary = replTest.getPrimary();
const secondary = replTest.getSecondary();

// Set secondaryOk=true so that normal read commands would be allowed on the secondary.
secondary.setSecondaryOk();

// Create a test collection that we can run commands against.
const primaryDB = primary.getDB(dbName);
assert.commandWorked(primary.getDB(dbName).createCollection(collName));
assert.commandWorked(
    primaryDB.runCommand({createIndexes: collName, indexes: [{name: "geo_2d", key: {geo: "2d"}}]}));
replTest.awaitLastOpCommitted();

/**
 * Verify that all given commands are disallowed from starting a transaction on a secondary by
 * checking that each command fails with the expected error code.
 */
function testCommands(session, commands, expectedErrorCode, readPref) {
    const sessionDb = session.getDatabase(dbName);
    for (let i = 0; i < commands.length; i++) {
        session.startTransaction();
        // Use a read preference that would normally allow read commands to run on secondaries.
        if (readPref !== null) {
            session.getOptions().setReadPreference(readPref);
        }
        const cmdObject = commands[i];

        jsTestLog("Trying to start transaction on secondary with command: " + tojson(cmdObject));
        assert.commandFailedWithCode(sessionDb.runCommand(cmdObject), expectedErrorCode);

        // Call abort for good measure, even though the transaction should have already been
        // aborted on the server.
        assert.commandFailedWithCode(session.abortTransaction_forTesting(),
                                     ErrorCodes.NotWritablePrimary);
    }
}

//
// Make sure transactions are disallowed on secondaries.
//

// Initiate a session on the secondary.
const sessionOptions = {
    causalConsistency: false
};
const secondarySession = secondary.getDB(dbName).getMongo().startSession(sessionOptions);

// Test read commands that are supported in transactions.
let readCommands = [
    {find: collName},
    {aggregate: collName, pipeline: [{$project: {_id: 1}}], cursor: {}},
    {distinct: collName, key: "_id"},
];

jsTestLog("Testing read commands.");
// Make sure read commands can not start transactions with any supported read preference.
testCommands(secondarySession, readCommands, ErrorCodes.NotWritablePrimary, "secondary");
testCommands(secondarySession, readCommands, ErrorCodes.NotWritablePrimary, "secondaryPreferred");
testCommands(secondarySession, readCommands, ErrorCodes.NotWritablePrimary, "primaryPreferred");
testCommands(secondarySession, readCommands, ErrorCodes.NotWritablePrimary, null);

// Test one write command. Normal write commands should already be
// disallowed on secondaries so we don't test them exhaustively here.
let writeCommands = [{insert: collName, documents: [{_id: 0}]}];

jsTestLog("Testing write commands.");
testCommands(secondarySession, writeCommands, ErrorCodes.NotWritablePrimary, "secondary");

secondarySession.endSession();

//
// Make sure transactions are allowed on primaries with any valid read preference.
//

const primarySession = primary.getDB(dbName).getMongo().startSession(sessionOptions);
const primarySessionDb = primarySession.getDatabase(dbName);

primarySession.startTransaction();
assert.commandWorked(
    primarySessionDb.runCommand({find: collName, $readPreference: {mode: "primary"}}));
assert.commandWorked(primarySession.commitTransaction_forTesting());

primarySession.startTransaction();
assert.commandWorked(
    primarySessionDb.runCommand({find: collName, $readPreference: {mode: "primaryPreferred"}}));
assert.commandWorked(primarySession.commitTransaction_forTesting());

primarySession.startTransaction();
assert.commandWorked(
    primarySessionDb.runCommand({find: collName, $readPreference: {mode: "secondaryPreferred"}}));
assert.commandWorked(primarySession.commitTransaction_forTesting());

primarySession.startTransaction();
assert.commandWorked(
    primarySessionDb.runCommand({find: collName, $readPreference: {mode: "nearest"}}));
assert.commandWorked(primarySession.commitTransaction_forTesting());

primarySession.endSession();

replTest.stopSet();
}());