Talk given at the London Ajax Users Group, June 14 2011

1. Developing node-mdb SimpleDB emulation using Node.js and GT.M Rob Tweed M/Gateway Developments Ltd http://www.mgateway.com Twitter: @rtweed

10. How does SimpleDB work? HTTP Server Authenticate Request (HMacSHA) Security Key Id Secret Key Execute API Action Generate HTTP Response SimpleDB Database Copy 1 SimpleDB Database Copy 2 SimpleDB Database Copy n SimpleDB Database Copy 2 SimpleDB Database Copy 2 Incoming SDB HTTP Request Outgoing SDB HTTP Response Error Success and/or data/results

11. Node.js can emulate all this HTTP Server Authenticate Request (HMacSHA) Security Key Id Secret Key Execute API Action Generate HTTP Response SimpleDB Database Copy 1 SimpleDB Database Copy 2 SimpleDB Database Copy n SimpleDB Database Copy 2 SimpleDB Database Copy 2 Incoming SDB HTTP Request Outgoing SDB HTTP Response Error Success and/or data/results

12. GT.M can emulate this HTTP Server Authenticate Request Security Key Id Secret Key Execute API Action Generate HTTP Response SimpleDB Database Copy 1 Incoming SDB HTTP Request Outgoing SDB HTTP Response Error Success and/or data/results

14. Result: deeply nested call-backs HTTP Server Authenticate Request Security Key Id Secret Key Execute API Action Generate HTTP Response Error Success and/or data/results

15. Flattening the call-back nesting processSDBRequest() http server executeAPI() sendResponse() http.createServer(function(req,res) {..} var processSDBRequest = function() {…}; var executeAPI = function() {…};

16. Node.js HTTP Server http.createServer(function(request, response) { request.content = ''; request.on("data", function(chunk) { request.content += chunk; }); request.on("end", function(){ var SDB = {startTime: new Date().getTime(), request: request, response: response }; var urlObj = url.parse(request.url, true); if (request.method === 'POST') { SDB.nvps = parseContent(request.content); } else { SDB.nvps = urlObj.query; } var uri = urlObj.pathname; if ((uri.indexOf(sdbURLPattern) !== -1)||(uri.indexOf(mdbURLPattern) !== -1)) { processSDBRequest(SDB); } else { var uriString = 'http://' + request.headers.host + request.url; var error = {code:'InvalidURI', message: 'The URI ' + uriString + ' is not valid',status:400}; returnError(SDB ,error); } }); }).listen(httpPort);

17. processSDBRequest() var processSDBRequest = function(SDB) { var accessKeyId = SDB.nvps.AWSAccessKeyId; if (!accessKeyId) { var error = {code:'AuthMissingFailure', message: 'AWS was not able to authenticate the request: access credentials are missing',status:403}; returnError(SDB, error); } else { MDB.getGlobal('MDBUAF', ['keys', accessKeyId], function (error, results) { if (!error) { if (results.value !== '') { accessKey[accessKeyId] = results.value; validateSDBRequest(SDB, results.value); } else { var error = {code:'AuthMissingFailure', message: 'AWS was not able to authenticate the request: access credentials are missing',status:403}; returnError(SDB, error); } } }); } };

18. validateSDBRequest() var validateSDBRequest = function(SDB, secretKey) { var type = ‘HmacSHA256’; var stringToSign = createStringToSign(SDB, true); var hash = digest(stringToSign, secretKey, type); if (hash === SDB.nvps.Signature) { processSDBAction(SDB); } else { errorResponse('SignatureDoesNotMatch', SDB) } };

19. stringToSign() POST {lf} 192.168.1.134:8081 {lf} / {lf} AWSAccessKeyId= rob &Action=ListDomains& MaxNumberOfDomains=100&SignatureMethod=HmacSHA1& SignatureVersion=2& Timestamp=2011-06-06T22%3A39%3A30%2 B00%3A00& Version=2009-04-15 ie: reconstruct the same string that the SDB client used to sign the request then use rob ’s secret key to sign it:

20. digest() var crypto = require("crypto"); var digest = function(string, secretKey, type) { var hmac = crypto.createHmac(type, secretKey); hmac.update(string); return hmac.digest('base64'); };

21. Ready to execute an API! HTTP Server Authenticate Request Security Key Id Secret Key Execute API Action Generate HTTP Response SimpleDB Database Copy 1 SimpleDB Database Copy 2 SimpleDB Database Copy n SimpleDB Database Copy 2 SimpleDB Database Copy 2 Incoming SDB HTTP Request Outgoing SDB HTTP Response Error Success and/or data/results

26. SDB Domain in Globals CreateDomain AWSAccessKeyId = ‘rob’ DomainName = ‘books’

27. Multiple Domains in Globals MDB ‘rob’ ‘domains’ ‘name’ ‘domainIndex’ ‘created’ 1304956337618 ‘books’ ‘modified’ 1304956337618 ‘books’ 1 1 ‘’ ‘name’ ‘created’ 1304956337423 ‘accounts’ ‘modified’ 1304956337423 2 ‘accounts’ 2 ‘’

28. Creating a new domain (1) MDB ‘rob’ ‘domains’ ‘name’ ‘domainIndex’ ‘created’ 1304956337618 ‘books’ ‘modified’ 1304956337618 ‘books’ 1 1 ‘’ 2 increment()

29. Creating a new domain (2) MDB ‘rob’ ‘domains’ ‘name’ ‘domainIndex’ ‘created’ 1304956337618 ‘books’ ‘modified’ 1304956337618 ‘books’ 1 1 ‘’ ‘name’ ‘created’ 1304956337423 ‘accounts’ ‘modified’ 1304956337423 2 ‘accounts’ 2 ‘’ setGlobal()

31. Dependent pattern MDB ‘rob’ ‘domains’ ‘name’ ‘created’ 1304956337618 ‘books’ ‘modified’ 1304956337618 1 2 MDB.increment([accessKeyId, 'domains'], 1, function (error, results) { var id = results.value; //….now create the other global nodes inside callback }); IncrBy

32. Dependent pattern MDB ‘rob’ ‘domains’ ‘name’ ‘created’ 1304956337618 ‘books’ ‘modified’ 1304956337618 1 2 MDB.increment([accessKeyId, 'domains'], 1, function (error, results) { var id = results.value; //….now create the other global nodes inside callback });

33. Parallel Pattern (semaphore) var count = 0; MDB.setGlobal([accessKeyId, 'domains', id, 'name'], domainName, function (error, results) { count++; if (count === 4) sendCreateDomainResponse(count, SDB); }); MDB.setGlobal([accessKeyId, 'domains', id, 'created'], now, function (error, results) { count++; if (count === 4) sendCreateDomainResponse(count, SDB); }); MDB.setGlobal([accessKeyId, 'domains', id, 'modified'], now, function (error, results) { count++; if (count === 4) sendCreateDomainResponse(count, SDB); }); MDB.setGlobal([accessKeyId, 'domainIndex', nameIndex, id], '', function (error, results) { count++; if (count === 4) sendCreateDomainResponse(count, SDB); });

34. New domain nodes created MDB ‘rob’ ‘domains’ ‘name’ ‘domainIndex’ ‘created’ 1304956337618 ‘books’ ‘modified’ 1304956337618 ‘books’ 1 1 ‘’ ‘name’ ‘created’ 1304956337423 ‘accounts’ ‘modified’ 1304956337423 2 ‘accounts’ 2 ‘’

35. Send CreateDomain Response HTTP Server Authenticate Request Security Key Id Secret Key Execute API Action Generate HTTP Response SimpleDB Database Copy 1 SimpleDB Database Copy 2 SimpleDB Database Copy n SimpleDB Database Copy 2 SimpleDB Database Copy 2 Incoming SDB HTTP Request Outgoing SDB HTTP Response Error Success and/or data/results

36. CreateDomain Response <?xml version=&quot;1.0&quot;?> <CreateDomainResponse xmlns=&quot;http://sdb.amazonaws.com/doc/2009-04-15/&quot;> <ResponseMetadata> <RequestID>e4e9fa45-f9dc-4e5b-8f0a-777acce6505e</RequestID> <BoxUsage>0.0020000000</BoxUsage> </ResponseMetadata> </CreateDomainResponse> var okResponse = function(SDB) { var nvps = SDB.nvps; var xml = responseStart({action: nvps.Action, version: nvps.Version}); xml = xml + responseEnd(nvps.Action, SDB.startTime, false); responseHeader(200, SDB.response); SDB.response.write(xml); SDB.response.end(); };