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diff --git a/IBRAHIM_MKUSA.md b/IBRAHIM_MKUSA.md index a24560c..48a7ed1 100644 --- a/IBRAHIM_MKUSA.md +++ b/IBRAHIM_MKUSA.md @@ -1,36 +1,39 @@ -# Interface to Google Drive in Racket +# Hermes - A chat server and client written in Racket -## Fred Martin -### April 22, 2017 +## Ibrahim Mkusa +### April 30, 2017 # Overview -This set of code provides an interface to searching through one's Google Drive account. -Its most important feature is that it provides a *folder-delimited search*. +Hermes is a chat server and client written in Racket. One can run the Hermes +server on any machine that is internet accessible. The Hermes clients then +connect to the server from anywhere on the internet. It's inspired by chat +systems and clients like irc. -The essential model of files in Google Drive is that they are in one big “pile.” So you can't directly find a file in a -given folder. +The goal in building Hermes was to expose myself to several concepts integral to +systems like networking, synchronization, and multitasking. -This code recursively collects all folders found within a given folder, and then -construct a search query that includes a list of all the subfolders (flattened into a single list). - -This then allows you to perform a folder-delimited search. **Authorship note:** All of the code described here was written by myself. # Libraries Used -The code uses four libraries: +Most libraries and utilities used are part of base Drracket installation and +therefore do not need to be imported. + +The date and time modules were used for various time related queries. +The tcp module was used for communication via Transmission Control Protocol. +Concurrency and synchronization modules that provide threads, and semaphores +were also used. + +Below are libraries that were not part of base system: ``` -(require net/url) -(require (planet ryanc/webapi:1:=1/oauth2)) -(require json) -(require net/uri-codec) +(require racket/gui/base) +(require math/base) ``` -* The ```net/url``` library provides the ability to make REST-style https queries to the Google Drive API. -* Ryan Culpepper's ```webapi``` library is used to provide the ```oauth2``` interface required for authentication. -* The ```json``` library is used to parse the replies from the Google Drive API. -* The ```net/uri-codec``` library is used to format parameters provided in API calls into an ASCII encoding used by Google Drive. +* The ```racket/gui/base``` library used to build graphical user interface. +* The ```math/base``` library was used for testing purposes. It was used to +generated random numbers. # Key Code Excerpts @@ -39,116 +42,187 @@ UMass Lowell's COMP.3010 Organization of Programming languages course. Five examples are shown and they are individually numbered. -## 1. Initialization using a Global Object +## 1. Tracking client connections using an object and closures. -The following code creates a global object, ```drive-client``` that is used in each of the subsequent API calls: +The following code defines and creates a global object, ```make-connections``` +that abstracts client connections. It also creates a semaphore to control access +to ```make-connections``` object. ``` -(define drive-client - (oauth2-client - #:id "548798434144-6s8abp8aiqh99bthfptv1cc4qotlllj6.apps.googleusercontent.com" - #:secret "<email me for secret if you want to use my API>")) +(define (make-connections connections) + (define (null-cons?) + (null? connections)) + (define (add username in out) + (set! connections (append connections (list (list username in out)))) + connections) + (define (cons-list) + connections) + (define (remove-ports in out) + (set! connections + (filter + (lambda (ports) + (if (and (eq? in (get-input-port ports)) + (eq? out (get-output-port ports))) + #f + #t)) + connections))) + (define (dispatch m) + (cond [(eq? m 'null-cons) null-cons?] + [(eq? m 'cons-list) cons-list] + [(eq? m 'remove-ports) remove-ports] + [(eq? m 'add) add])) + dispatch) + +(define c-connections (make-connections '())) + +(define connections-s (make-semaphore 1)) ;; control access to connections ``` + When the tcp-listener accepts a connection from a client, the associated input + output ports along with username are added as an entry in ```make-connections``` via ```add``` function. + External functions can operate on the connections by securing the semaphore, + and then calling ```cons-list``` to expose the underlying list of connections. + ```remove-ports``` method is also available to remove input output ports from + managed connections. + + - While using global objects is not a central theme in the course, it's necessary to show this code to understand - the later examples. -## 2. Selectors and Predicates using Procedural Abstraction - -A set of procedures was created to operate on the core ```drive-file``` object. Drive-files may be either -actual file objects or folder objects. In Racket, they are represented as a hash table. +## 2. Tracking received messages via objects and closures. -```folder?``` accepts a ```drive-file```, inspects its ```mimeType```, and returns ```#t``` or ```#f```: +The code below manages broadcast messages from one client to the rest. It wraps +a list of strings inside an object that has functions similar to ```make-connections``` for +exposing and manipulating the list from external functions. The code creates +```make-messages``` global object and a semaphore to control access to it from +various threads of execution. ``` -(define (folder? drive-file) - (string=? (hash-ref drive-file 'mimeType "nope") "application/vnd.google-apps.folder")) +(define (make-messages messages) + (define (add message) + (set! messages (append messages (list message))) + messages) + (define (mes-list) + messages) + (define (remove-top) + (set! messages (rest messages)) + messages) + (define (dispatch m) + (cond [(eq? m 'add) add] + [(eq? m 'mes-list) mes-list] + [(eq? m 'remove-top) remove-top])) + dispatch) + +(define c-messages (make-messages '())) + +(define messages-s (make-semaphore 1)) ;; control access to messages ``` -Another object produced by the Google Drive API is a list of drive-file objects ("```drive#fileList```"). -When converted by the JSON library, -this list appears as hash map. +## 3. Using map to broadcast messages from client to clients -```get-files``` retrieves a list of the files themselves, and ```get-id``` retrieves the unique ID -associated with a ```drive#fileList``` object: +The ```broadcast``` function is called repeatedly in a loop to extract a message +from ```make-messages``` object, and send it to every other client. It uses the +```make-connections``` objects to extract output port of a client. The ```map``` +routine is called on every client in the connections object to send it +a message. ``` -(define (get-files obj) - (hash-ref obj 'files)) - -(define (get-id obj) - (hash-ref obj 'id)) +(define broadcast + (lambda () + (semaphore-wait messages-s) + (cond [(not (null? ((c-messages 'mes-list)))) + (map + (lambda (ports) + (if (not (port-closed? (get-output-port ports))) + (begin + (displayln (first ((c-messages 'mes-list))) (get-output-port ports)) + (flush-output (get-output-port ports))) + (displayln-safe "Failed to broadcast. Port not open." error-out-s error-out))) + ((c-connections 'cons-list))) + (displayln-safe (first ((c-messages 'mes-list))) convs-out-s convs-out) + ;; remove top message from "queue" after broadcasting + ((c-messages 'remove-top)) + ; debugging displayln below + ; (displayln "Message broadcasted") + ]) ; end of cond + (semaphore-post messages-s))) ``` -## 3. Using Recursion to Accumulate Results +After the message is send, the message is removed from the "queue" via the +```remove-top```. -The low-level routine for interacting with Google Drive is named ```list-children```. This accepts an ID of a -folder object, and optionally, a token for which page of results to produce. +The code snippet below creates a thread that iteratively calls ```broadcast``` +every interval, where interval(in secs) is defined by ```sleep-t```. -A lot of the work here has to do with pagination. Because it's a web interface, one can only obtain a page of -results at a time. So it's necessary to step through each page. When a page is returned, it includes a token -for getting the next page. The ```list-children``` just gets one page: +** note ** : ```sleep``` is very important for making Hermes behave gracefully +in a system. Without it, it would be called at the rate derived from cpu clock +rate. This raises cpu temperatures substantially, and make cause a pre-mature +system shutdown. ``` -(define (list-children folder-id . next-page-token) - (read-json - (get-pure-port - (string->url (string-append "https://www.googleapis.com/drive/v3/files?" - "q='" folder-id "'+in+parents" - "&key=" (send drive-client get-id) - (if (= 1 (length next-page-token)) - (string-append "&pageToken=" (car next-page-token)) - "") -; "&pageSize=5" - )) - token))) +(thread (lambda () + (displayln-safe "Broadcast thread started!") + (let loopb [] + (sleep sleep-t) ;; wait 0.2 ~ 0.5 secs before beginning to broadcast + (broadcast) + (loopb)))) ``` -The interesting routine is ```list-all-children```. This routine is directly invoked by the user. -It optionally accepts a page token; when it's used at top level this parameter will be null. -The routine uses ```let*``` to retrieve one page of results (using the above ```list-children``` procedure) -and also possibly obtain a token for the next page. +## 4. Filtering a List of connections to find recipient of a whisper -If there is a need to get more pages, the routine uses ```append``` to pre-pend the current results with -a recursive call to get the next page (and possibly more pages). +I implemented a whisper functionality, where a user can whisper to any user in +the chat room. The whisper message is only sent to specified user. To implement +this i used ```filter``` over the connections, where the predicate tested whether the +current list item matched that of a specific user. -Ultimately, when there are no more pages to be had, the routine terminates and returns the current page. +''' +(define whisper (regexp-match #px"(.*)/whisper\\s+(\\w+)\\s+(.*)" evt-t0)) -This then generates a recursive process from the recursive definition. +[whisper + (semaphore-wait connections-s) + ; get output port for user + ; this might be null + (define that-user-ports + (filter + (lambda (ports) + (if (string=? (whisper-to whisper) (get-username ports)) + #t + #f)) + ((c-connections 'cons-list)))) + ; try to send that user the whisper + (if (and (null? that-user-ports) + #t) ; #t is placeholder for further checks + (begin + (displayln "User is unavailable. /color blue" out) + (flush-output out)) + (begin + (displayln (string-append "(whisper) " + (whisper-info whisper) (whisper-message whisper)) + (get-output-port (car that-user-ports))) + (flush-output (get-output-port (car that-user-ports))))) + (semaphore-post connections-s)] +''' -``` -(define (list-all-children folder-id . next-page-token) - (let* ((this-page (if (= 0 (length next-page-token)) - (list-children folder-id) - (list-children folder-id (car next-page-token)))) - (page-token (hash-ref this-page 'nextPageToken #f))) - (if page-token - (append (get-files this-page) - (list-all-children folder-id page-token)) - (get-files this-page)))) -``` - -## 4. Filtering a List of File Objects for Only Those of Folder Type +The snippet above is part of cond statement that tests contents of input from +clients to determine what the client is trying wants/trying to do. The top-line +is using regexes to determine whether the received message is a whisper or not. -The ```list-all-children``` procedure creates a list of all objects contained within a given folder. -These objects include the files themselves and other folders. -The ```filter``` abstraction is then used with the ```folder?``` predicate to make a list of subfolders -contained in a given folder: -``` -(define (list-folders folder-id) - (filter folder? (list-all-children folder-id))) -``` +## 5. Selectors for dealing with content of a whisper from clients -## 5. Recursive Descent on a Folder Hierarchy +Below are are three selectors that help abstract the contents of a whisper +message. -These procedures are used together in ```list-all-folders```, which accepts a folder ID and recursively -obtains the folders at the current level and then recursively calls itself to descend completely into the folder -hierarchy. -```map``` and ```flatten``` are used to accomplish the recursive descent: ``` +; whisper selector for the username and message +(define (whisper-info exp) + (cadr exp)) + +(define (whisper-to exp) + (caddr exp)) + +(define (whisper-message exp) + (cadddr exp)) (define (list-all-folders folder-id) (let ((this-level (list-folders folder-id))) (begin @@ -156,3 +230,7 @@ hierarchy. (append this-level (flatten (map list-all-folders (map get-id this-level))))))) ``` + +```whisper-info``` retrieves the date-time and username info. +```whisper-to``` retrieves the username of the intented recipient of a whisper. +```whisper-message``` retrieves the actual whisper. |