linux - Would it be possible to read out physical keyboard strokes in node.js? -

i have node application runs on raspberry pi keeps track of bunch of upnp-players (sonos), able control through physical remote. have couple of airmouses, has small keyboards volume buttons use.

i have tried grip on how read out physical key strokes on linux machine, , come conclusion need read events input device, in case be:

/dev/input/by-id/usb-dell_dell_quietkey_keyboard-event-kbd 

how find device , stuff not problem, real issue how interpret data read it.

i know receive c struct, this:

struct input_event {     struct timeval time;     unsigned short type;     unsigned short code;     unsigned int value; }; 

but i'm not sure how go reading node. if run external app triggered pre-defined keystrokes, , invoke http-request against node, second option, python script or native daemon. have looked @ hotkey-daemons, none of them worked.

if of course nice if contain within node somehow.

edit: did testing, , made simple snippet:

var fs = require('fs');  var buffer = new buffer(16);  fs.open('/dev/input/by-id/usb-hjt_air_mouse-event-kbd', 'r', function (err, fd) {     while (true) {         fs.readsync(fd, buffer, 0, 16, null);         console.log(buffer)     } }); 

this outputs (for space):

<buffer a4 3e 5b 51 ab cf 03 00 04 00 04 00 2c 00 07 00> <buffer a4 3e 5b 51 c3 cf 03 00 01 00 39 00 01 00 00 00> <buffer a4 3e 5b 51 cb cf 03 00 00 00 00 00 00 00 00 00> <buffer a4 3e 5b 51 ba 40 06 00 04 00 04 00 2c 00 07 00> <buffer a4 3e 5b 51 cd 40 06 00 01 00 39 00 00 00 00 00> <buffer a4 3e 5b 51 d2 40 06 00 00 00 00 00 00 00 00 00> 

i realize first 4 bytes sort of timestamp, , following 3 bytes micro/millisecond thing.

another odd thing not keypresses produces output, subsequent press might sent twice data, , of time starts blasting out data stop after subsequent keypresses (or after 20 seconds or so). i'm not sure how interpret that. have tried read source daemon https://github.com/baskerville/shkd/blob/master c not strongest language , can't identify how handles (or if should handled). , daemon didn't work me (compiled on raspberry pi).

well, let's have @ struct.

struct input_event {     struct timeval time;     unsigned short type;     unsigned short code;     unsigned int value; }; 

a struct timeval has structure:

struct timeval   {     __time_t tv_sec;            /* seconds.  */     __suseconds_t tv_usec;      /* microseconds.  */   }; 

the definition of time types are

typedef signed long time_t; typedef signed long suseconds_t; 

a signed long 4 bytes (well, not if follow spec, in practice, is), first 8 bytes typestamp. next, have type , code. both short, in practice, they're 2 bytes each. there's value left, , that's int again, 4 bytes. also, compiler theoretically add padding between fields here, i'm pretty sure won't.

so, first chop bytes you've read chunks of 4+4+2+2+4=16 bytes. each of chunks event. fits sample data. next, extract values buffer (as little endian values because you're on arm system – on normal pc, you'd need big endian) , interpret values. instructions on how that, read http://www.mjmwired.net/kernel/documentation/input/event-codes.txt. values of constants aren't written down there, can find using grep -r name_of_constant /usr/include.

let's chop up

<buffer a4 3e 5b 51 ab cf 03 00 04 00 04 00 2c 00 07 00> 

as example.

<buffer a4 3e 5b 51 ab cf 03 00 04 00 04 00 2c 00 07 00>        |   tv_sec  |  tv_usec  |type |code |   value   | 

tv_sec in hex 0x515b3ea4 (reversed order because it's little endian), 1364934308 in decimal. simple unix time converter reports means 02.04.2013 - 22:25:08. looks good!

tv_usec 0x0003cfab=249771, actually, event happened 249771 microseconds after time.

type 0x0004=4. /usr/include/linux/input.h tells ev_msc.

given type, can see the code, 0x0004=4, means msc_scan.

the value 0x0007002c. turns in input.h. hmm.