networking - UDP API in Rust -


1) api send here returns result<usize>. why ? in head, udp send or none. return value seems suggest sending can succeed entire data may not written makes me code like:

let mut bytes_written = 0; while bytes_written < data.len() {     bytes_written += match udp_socket.send_to(&data[bytes_written..]) {          ok(bytes_tx) => bytes_tx,          err(_) => break,     } }

recently told me unnecessary. don't understand. if true why return not result<()> instead, expecting ?

2) for reads though understand. give buffer of size 100 bytes datagram might 50 bytes long. should utilise read_buf[..size_read]. here question happens if buffer size 100 datagram size 150 bytes ? recv_from fill in 100 bytes , return ok(100, some_peer_addr) ? if re-read fill in remaining of datagram ? if datagram of 50 bytes arrived before second read ? remaining 50 bytes second time , 50 bytes of new datagram 3rd time or complete 100 bytes 2nd time contains new datagram ? or error , lose 1st datagram on initial read , never able recover ?

the answer both of these questions lies in documentation of respective bsd sockets functions, sendto() , recvfrom(). if use *nix system (os x or linux, example), can use man sendto , man recvfrom find it.

1) sendto() man page rather vague on this; windows api page explicitly says possible return value less len argument. see this question. looks particular moment under-documented. think safe assume return value equal either len or error code. problems may happen if length of data sent through sendto() exceeds internal buffer size inside os kernel, seems @ least windows return error in case.

2) recvfrom() man page unambiguously states part of datagram not fit buffer discarded:

the recvfrom() function shall return length of message written buffer pointed buffer argument. message-based sockets, such sock_raw, sock_dgram, , sock_seqpacket, entire message shall read in single operation. if message long fit in supplied buffer, , msg_peek not set in flags argument, excess bytes shall discarded.

so yes, recv_from() fill 100 bytes, rest discarded, , further calls recv_from() return new datagrams.


Comments

Post a Comment

Popular posts from this blog

authentication - Mongodb revoke acccess to connect test database -

i have ec2 instance mongodb 3.2.0 installed. have user admin access. can connect user , perform operation remotely. 1 can connect database test remote if knows ip mongo 11.11.11.11. although not able make operations, want restrict access user credentials can connect server. first need create users , grant roles users, example: use admin db.createuser( { user: "myuseradmin", pwd: "abc123", roles: [ { role: "useradminanydatabase", db: "admin" } ] } ) then need start server --auth parameter mongod --auth more information here
Read more

r - Update two sets of radiobuttons reactively - shiny -

i have read ( how make choices in radiobuttons reactive in shiny? ) shows me how update radiobutton s in reactive way. however, when try , update 2 sets of buttons same data, 1 set renders. example: server: # create example data wafer <- rep(c(1:3), each=3) length <- c(1,1,2,1,1,1,3,5,1) width <- c(3,1,6,1,1,1,1,1,6) dd <- data.frame(wafer, length, width) shinyserver(function(input, output, session){ # create reactive dataframe store data values <- reactivevalues() values$df <- data.frame() # lengths , widths of wafer user input <- eventreactive(input$do, { subset(dd, wafer %in% input$wafer, select = length:width) }) # update reactive data frame lengths , widths have been selected user input observe({ if(!is.null(a())) { values$df <- rbind(isolate(values$df), a()) } }) output$wl <- renderdatatable({ a() }) # update radio buttons unique length , widths stored in values$df # ever "observe" put first in co...
Read more

ios - Realm over CoreData should I use NSFetchedResultController or a Dictionary? -

i'm working on app using core data , nsfetchedresultcontroller many reasons switch use realm. saw there "realm version" of nsfetchedresultcontroller on github wouldn't compatible current code using core data. the view controller displaying list of people same school, address book. list sublist of people studied in same city. so thinking make 1 unique request database retrieve list of people , filter locally list within 1 dictionary per school [string: anyobject] string section name within tableview , anyobject array of people. first solution, make nsfetchedresultcontroller each school predicate filtering location. delete actions etc.. handled delegates -> not compatible realm create dictionaries , update them each actions... -> works realm it's annoying code. any better solution? edit: i need clarify request: i'd write class inherit uitableviewcontroller. this class has list of people sorted in alphabetical order the tableview has ...
Read more