sharedb/lib/submit-request.js

JSON OT database backend

var ot = require('./ot');
var projections = require('./projections');

function SubmitRequest(backend, agent, index, id, op) {
  this.backend = backend;
  this.agent = agent;
  // If a projection, rewrite the call into a call against the collection
  var projection = backend.projections[index];
  this.index = index;
  this.projection = projection;
  this.collection = (projection) ? projection.target : index;
  this.id = id;
  this.op = op;

  this.start = Date.now();
  this._addOpMeta();

  // Set as this request is sent through middleware
  this.action = null;
  // For custom use in middleware
  this.custom = {};

  this.suppressPublish = backend.suppressPublish;
  this.maxRetries = backend.maxSubmitRetries;
  this.retries = 0;

  // return values
  this.snapshot = null;
  this.ops = [];
  this.channels = null;
}
module.exports = SubmitRequest;

SubmitRequest.prototype.submit = function(callback) {
  var request = this;
  var backend = this.backend;
  var collection = this.collection;
  var id = this.id;
  var op = this.op;
  // Send a special projection so that getSnapshot knows to return all fields.
  // With a null projection, it strips document metadata
  var fields = {$submit: true};

  backend.db.getSnapshot(collection, id, fields, function(err, snapshot) {
    if (err) return callback(err);

    request.snapshot = snapshot;
    request._addSnapshotMeta();

    if (op.v == null) {

      if (op.create && snapshot.type && op.src) {
        // If the document was already created by another op, we will return a
        // 'Document already exists' error in response and fail to submit this
        // op. However, this could also happen in the case that the op was
        // already committed and the create op was simply resent. In that
        // case, we should return a non-fatal 'Op already submitted' error. We
        // must get the past ops and check their src and seq values to
        // differentiate.
        backend.db.getCommittedOpVersion(collection, id, snapshot, op, function(err, version) {
          if (err) return callback(err);
          if (version == null) {
            callback(request.alreadyCreatedError());
          } else {
            op.v = version;
            callback(request.alreadySubmittedError());
          }
        });
        return;
      }

      // Submitting an op with a null version means that it should get the
      // version from the latest snapshot. Generally this will mean the op
      // won't be transformed, though transform could be called on it in the
      // case of a retry from a simultaneous submit
      op.v = snapshot.v;
    }

    if (op.v === snapshot.v) {
      // The snapshot hasn't changed since the op's base version. Apply
      // without transforming the op
      return request.apply(callback);
    }

    if (op.v > snapshot.v) {
      // The op version should be from a previous snapshot, so it should never
      // never exceed the current snapshot's version
      return callback(request.newerVersionError());
    }

    // Transform the op up to the current snapshot version, then apply
    var from = op.v;
    backend.db.getOpsToSnapshot(collection, id, from, snapshot, function(err, ops) {
      if (err) return callback(err);

      if (ops.length !== snapshot.v - from) {
        return callback(request.missingOpsError());
      }

      err = request._transformOp(ops);
      if (err) return callback(err);

      if (op.v !== snapshot.v) {
        // This shouldn't happen, but is just a final sanity check to make
        // sure we have transformed the op to the current snapshot version
        return callback(request.versionAfterTransformError());
      }

      request.apply(callback);
    });
  });
};

SubmitRequest.prototype.apply = function(callback) {
  // If we're being projected, verify that the op is allowed
  var projection = this.projection;
  if (projection && !projections.isOpAllowed(this.snapshot.type, projection.fields, this.op)) {
    return callback(this.projectionError());
  }

  // Always set the channels before each attempt to apply. If the channels are
  // modified in a middleware and we retry, we want to reset to a new array
  this.channels = this.backend.getChannels(this.collection, this.id);

  var request = this;
  this.backend.trigger('apply', this.agent, this, function(err) {
    if (err) return callback(err);

    // Apply the submitted op to the snapshot
    err = ot.apply(request.snapshot, request.op);
    if (err) return callback(err);

    request.commit(callback);
  });
};

SubmitRequest.prototype.commit = function(callback) {
  var request = this;
  var backend = this.backend;
  backend.trigger('commit', this.agent, this, function(err) {
    if (err) return callback(err);

    // Try committing the operation and snapshot to the database atomically
    backend.db.commit(request.collection, request.id, request.op, request.snapshot, function(err, succeeded) {
      if (err) return callback(err);
      if (!succeeded) {
        // Between our fetch and our call to commit, another client committed an
        // operation. We expect this to be relatively infrequent but normal.
        return request.retry(callback);
      }
      if (!request.suppressPublish) {
        var op = request.op;
        op.c = request.collection;
        op.d = request.id;
        op.m = undefined;
        // Needed for agent to detect if it can ignore sending the op back to
        // the client that submitted it in subscriptions
        if (request.collection !== request.index) op.i = request.index;
        backend.pubsub.publish(request.channels, op);
      }
      callback();
    });
  });
};

SubmitRequest.prototype.retry = function(callback) {
  this.retries++;
  if (this.maxRetries != null && this.retries > this.maxRetries) {
    return callback(this.maxRetriesError());
  }
  this.backend.emit('timing', 'submit.retry', Date.now() - this.start, this);
  this.submit(callback);
};

SubmitRequest.prototype._transformOp = function(ops) {
  var type = this.snapshot.type;
  for (var i = 0; i < ops.length; i++) {
    var op = ops[i];

    if (this.op.src && this.op.src === op.src && this.op.seq === op.seq) {
      // The op has already been submitted. There are a variety of ways this
      // can happen in normal operation, such as a client resending an
      // unacknowledged operation at reconnect. It's important we don't apply
      // the same op twice
      return this.alreadySubmittedError();
    }

    if (this.op.v !== op.v) {
      return this.versionDuringTransformError();
    }

    var err = ot.transform(type, this.op, op);
    if (err) return err;
    this.ops.push(op);
  }
};

SubmitRequest.prototype._addOpMeta = function() {
  this.op.m = {
    ts: this.start
  };
  if (this.op.create) {
    // Consistently store the full URI of the type, not just its short name
    this.op.create.type = ot.normalizeType(this.op.create.type);
  }
};

SubmitRequest.prototype._addSnapshotMeta = function() {
  var meta = this.snapshot.m || (this.snapshot.m = {});
  if (this.op.create) {
    meta.ctime = this.start;
  } else if (this.op.del) {
    this.op.m.data = this.snapshot.data;
  }
  meta.mtime = this.start;
};

// Non-fatal client errors:
SubmitRequest.prototype.alreadySubmittedError = function() {
  return {code: 4001, message: 'Op already submitted'};
};
SubmitRequest.prototype.rejectedError = function() {
  return {code: 4002, message: 'Op submit rejected'};
};
// Fatal client errors:
SubmitRequest.prototype.alreadyCreatedError = function() {
  return {code: 4010, message: 'Invalid op submitted. Document already created'};
};
SubmitRequest.prototype.newerVersionError = function() {
  return {code: 4011, message: 'Invalid op submitted. Op version newer than current snapshot'};
};
SubmitRequest.prototype.projectionError = function() {
  return {code: 4012, message: 'Invalid op submitted. Operation invalid in projected collection'};
};
// Fatal internal errors:
SubmitRequest.prototype.missingOpsError = function() {
  return {code: 5001, message: 'Op submit failed. DB missing ops needed to transform it up to the current snapshot version'};
};
SubmitRequest.prototype.versionDuringTransformError = function() {
  return {code: 5002, message: 'Op submit failed. Versions mismatched during op transform'};
};
SubmitRequest.prototype.versionAfterTransformError = function() {
  return {code: 5003, message: 'Op submit failed. Op version mismatches snapshot after op transform'};
};
SubmitRequest.prototype.maxRetriesError = function() {
  return {code: 5004, message: 'Op submit failed. Maximum submit retries exceeded'};
};