I ran into this issue with rsound. I'm not sure how standard output can be directly captured from a lower-level language in a Racket context when that language can freely ignore the Racket printer and write directly to STDOUT within the same operating system process.
I'd hate to just add a "me too", but the only way quick way I could think to handle that was to add another subprocess. If I were wanting to solve the problem in one process, I'd probably extend Racket at the C level and integrate my output with ports. https://docs.racket-lang.org/inside/Ports_and_the_Filesystem.html?q=c%20api On 5/12/21 3:48 AM, Paulo Matos wrote: > Hi, > > I have a shared library for which I am creating some bindings: > https://github.com/pmatos/racket-binaryen > > There's a function BinaryenModulePrint that prints a WebAssembly module > to stdout. > > When I wrap it in racket, if I do something like: > (define mod ...) > (with-output-to-string (lambda () (BinaryenModulePrint mod))) > > The return value will be "" and it will still print the module to > stdout. I understand! However, I don't know how to solve it in Racket. > > In C, things seem easier because I have access to dup2 and pipe in case > I need to redirect things, however in Racket all my attempts have > failed. > > I have created the simple example: > ```hello.c > #include <stdio.h> > > void hello(void) { > printf("hello world!\n"); > } > ``` > > Compile with `gcc -shared -o hello.so hello.c`. > > Then: > ```hello.rkt > #lang racket/base > > (require racket/port > ffi/unsafe > ffi/unsafe/define) > > (define libhello (ffi-lib "/home/pmatos/dev/tmp/ffi-hello-world/hello.so")) > (define-ffi-definer define-hello libhello) > (define-hello hello (_fun -> _void)) > (with-output-to-string hello) > ``` > > Here's the issue! In C, I can do something like: > ```hello-fix.c > #include <stdio.h> > #include <unistd.h> > #include <sys/stat.h> > #include <fcntl.h> > > extern void hello(void); > > int main(void) { > int filefd = open("test.txt", O_WRONLY|O_CREAT, 0666); > dup2(filefd, fileno(stdout)); > hello(); > > return 0; > } > ``` > Compile with `gcc -o hello hello.c hello-fix.c` > > This will, send the output of hello() to a file. Now, in racket > preferably I want to connect what is sent to raw stdout, fd 1, to > current-output-port. > > My thought was that I could create a dup2 ffi binding, and use > unsafe-port->file-descriptor to install the racket pipe file descriptor > in stdout using the dup2 ffi binding but it doesn't work. > > And it doesn't work because the unsafe-port->file-descriptor returns #f, > even though port-waiting-peer? return #f as well (which sort of hints > that maybe the documentation of unsafe-port->file-descriptor is > incomplete. > > The start of my attempt would look like this: > > ```hello.rkt > #lang racket/base > > (require racket/port > ffi/unsafe > ffi/unsafe/define > ffi/unsafe/port) > > (define libhello (ffi-lib "/home/pmatos/dev/tmp/ffi-hello-world/hello.so")) > > (define-ffi-definer define-libc (ffi-lib #f)) > (define-ffi-definer define-hello libhello) > > (define-libc dup2 (_fun _int _int -> _int)) > (define-hello hello (_fun -> _void)) > > (define-values (in out) (make-pipe)) > > ;; FAILS because (unsafe-port-> ...) return #f > (dup2 (unsafe-port->file-descriptor out) 1) > > ;;... > ;; connect the other end of the port to current-output-port > ;; and use a thread to copy-port > ``` > > Surely there must be a better way than this and I would be surprised if > there isn't already something out there in a library but I haven't found > anything yet. Any help here would be great. > > Thanks, > > -- > Paulo Matos > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/87r1icxuhi.fsf%40linki.tools. -- ~slg -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/1abd8d17-a53c-b7fa-8983-57deec760e96%40sagegerard.com.
