Ghost/core/server/middleware/api/version-match.js

var semver = require('semver'),
    errors = require('../../errors'),
    i18n = require('../../i18n');

function checkVersionMatch(req, res, next) {
    var clientVersion = req.get('X-Ghost-Version'),
        serverVersion = res.locals.version,
        constraint = '^' + clientVersion + '.0';

    // no error when client is on an earlier minor version than server
    // error when client is on a later minor version than server
    // always error when the major version is different

    if (clientVersion && !semver.satisfies(serverVersion, constraint)) {
        return next(new errors.VersionMismatchError({
            message: i18n.t('errors.middleware.api.versionMismatch', {clientVersion: clientVersion, serverVersion: serverVersion})
        }));
    }

    next();
}

module.exports = checkVersionMatch;