mongo/jstests/change_streams/pipeline_cannot_modify_id_field.js

/**
 * Tests that stages which modify or remove the _id field are not permitted to run in a
 * $changeStream pipeline.
 */
import {assertDropAndRecreateCollection} from "jstests/libs/collection_drop_recreate.js";

const coll = assertDropAndRecreateCollection(db, jsTestName());

// Bare-bones $changeStream pipeline which will be augmented during tests.
const changeStream = [{$changeStream: {}}];

// Test-cases of transformations that modify or remove _id, and are thus disallowed.
const idModifyingTransformations = [
    {$project: {_id: 0}},
    {$project: {_id: "newValue"}},
    {$project: {_id: "$otherField"}},
    {$project: {_id: 0, otherField: 0}},
    {$project: {_id: 0, otherField: 1}},
    {$project: {"_id._data": 0}},
    {$project: {"_id._data": 1}},
    {$project: {"_id._data": "newValue"}},
    {$project: {"_id._data": "$_id._data"}}, // Disallowed because it discards _typeBits.
    {$project: {"_id._data": "$otherField"}},
    {$project: {"_id.otherField": 1}},
    {$project: {"_id._typeBits": 0}},
    [{$project: {otherField: "$_id"}}, {$project: {otherField: 0}}, {$project: {_id: "$otherField"}}],
    {$project: {_id: {data: "$_id._data", typeBits: "$_id._typeBits"}}}, // Fields renamed.
    {$project: {_id: {_typeBits: "$_id._typeBits", _data: "$_id._data"}}}, // Fields reordered.
    {$project: {_id: {_data: "$_id._typeBits", _typeBits: "$_id._data"}}}, // Fields swapped.
    {$set: {_id: "newValue"}},
    {$set: {_id: "$otherField"}},
    {$set: {"_id._data": "newValue"}},
    {$set: {"_id._data": "$otherField"}},
    {$set: {"_id.otherField": "newValue"}}, // New subfield added to _id.
    [{$addFields: {otherField: "$_id"}}, {$set: {otherField: "newValue"}}, {$set: {_id: "$otherField"}}],
    [
        // Fields renamed.
        {$addFields: {newId: {data: "$_id._data", typeBits: "$_id._typeBits"}}},
        {$set: {_id: "$newId"}},
    ],
    [
        // Fields reordered.
        {$addFields: {newId: {_typeBits: "$_id._typeBits", _data: "$_id._data"}}},
        {$set: {_id: "$newId"}},
    ],
    [
        // Fields swapped.
        {$addFields: {newId: {_data: "$_id._typeBits", _typeBits: "$_id._data"}}},
        {$set: {_id: "$newId"}},
    ],
    {$replaceRoot: {newRoot: {otherField: "$_id"}}},
    {$replaceWith: {otherField: "$_id"}},
    {$redact: {$cond: {if: {$gt: ["$_id", {}]}, then: "$$DESCEND", else: "$$PRUNE"}}}, // _id:0
];

// Test-cases of projections which are allowed: explicit inclusion of _id, implicit inclusion of
// _id, renames which retain the full _id field, exclusion of unrelated fields, addition of and
// modifications to unrelated fields, sequential renames which ultimately preserve _id, etc.
const idPreservingTransformations = [
    {$project: {_id: 1}},
    {$project: {_id: 1, otherField: 0}},
    {$project: {_id: 1, otherField: 1}},
    {$project: {_id: "$_id", otherField: 1}},
    {$project: {"_id.otherField": 0}},
    {$project: {otherField: 1}},
    {$project: {otherField: 0}},
    {$project: {otherField: "$_id"}},
    [{$project: {otherField: "$_id"}}, {$project: {otherField: 1}}, {$project: {_id: "$otherField"}}],
    {$project: {"_id._data": 1, "_id._typeBits": 1}},
    {$project: {_id: {_data: "$_id._data", _typeBits: "$_id._typeBits"}}},
    {$set: {_id: "$_id"}},
    {$addFields: {otherField: "newValue"}},
    {$set: {_id: {_data: "$_id._data", _typeBits: "$_id._typeBits"}}},
    [{$addFields: {otherField: "$_id"}}, {$set: {_id: "$otherField"}}],
    [{$addFields: {newId: {_data: "$_id._data", _typeBits: "$_id._typeBits"}}}, {$set: {_id: "$newId"}}],
    {$replaceRoot: {newRoot: {_id: "$_id"}}},
    {$replaceWith: {_id: "$_id"}},
    {
        $redact: {
            $cond: {
                if: {
                    $or: [
                        // Keeps _id, descends into fullDocument.
                        {$not: {$isArray: "$tags"}},
                        {$gt: [{$size: {$setIntersection: ["$tags", ["USA"]]}}, 0]},
                    ],
                },
                then: "$$DESCEND",
                else: "$$PRUNE",
            },
        },
    },
    {$redact: "$$DESCEND"}, // Descends through entire document, retaining all of it.
    {$redact: "$$KEEP"}, // Keeps entire document.
];

let docId = 0;

// Verify that each of the allowlisted transformations above succeeds.
for (let transform of idPreservingTransformations) {
    const cmdRes = assert.commandWorked(
        db.runCommand({aggregate: coll.getName(), pipeline: changeStream.concat(transform), cursor: {}}),
        transform,
    );
    assert.commandWorked(coll.insert({_id: docId++}));
    assert.soon(() => {
        const getMoreRes = assert.commandWorked(
            db.runCommand({getMore: cmdRes.cursor.id, collection: coll.getName()}),
            transform,
        );
        return getMoreRes.cursor.nextBatch.length > 0;
    }, transform);
}

// Verify that each of the denylisted transformations above are rejected.
for (let transform of idModifyingTransformations) {
    const cmdRes = assert.commandWorked(
        db.runCommand({aggregate: coll.getName(), pipeline: changeStream.concat(transform), cursor: {}}),
        transform,
    );
    assert.commandWorked(coll.insert({_id: docId++}));
    assert.soon(() => {
        const getMoreRes = db.runCommand({getMore: cmdRes.cursor.id, collection: coll.getName()});
        return (
            !getMoreRes.ok &&
            assert.commandFailedWithCode(
                getMoreRes,
                [ErrorCodes.IllegalOperation, ErrorCodes.ChangeStreamFatalError],
                transform,
            )
        );
    }, transform);
}