esc-printer-driver: async device file

src/esc_printer_driver.nim

@@ -4,12 +4,15 @@
 ## ESC/P printer control actor.
 
 import
-  std/[cmdline, oserrors, posix, sets],
+  std/[cmdline, oserrors, posix, sequtils, sets],
+  pkg/sys/[files, ioqueue],
   preserves, preserves/sugar,
   syndicate, syndicate/relays,
   syndicate/protocols/[gatekeeper, sturdy],
   ./private/esc_p
 
+from pkg/sys/handles import FD
+
 proc echo(args: varargs[string, `$`]) {.used.} =
   stderr.writeLine(args)
 
@@ -17,12 +20,26 @@ type
   HandleSet = HashSet[Handle]
 
   Printer = ref object of Entity
-    device: cint
+    device: AsyncFile
     boldHandles, italicHandles, superscriptHandles, subscriptHandles: HandleSet
+    buffer: seq[byte]
+    isBusy: bool
+
+proc flush(printer: Printer) {.asyncio.} =
+  printer.isBusy = true
+  while printer.buffer.len > 0:
+    let n = printer.device.write(printer.buffer)
+    if n > 0:
+      printer.buffer.delete(0, n)
+    elif n < 0:
+      osLastError().osErrorMsg().quit()
+  printer.isBusy = false
 
 proc write(printer: Printer; s: string) {.inline.} =
-  if posix.write(printer.device, s[0].addr, s.len) < 0:
-    osLastError().osErrorMsg().quit()
+  printer.buffer.add cast[seq[byte]](s)
+  if not printer.isBusy:
+    discard trampoline:
+      whelp printer.flush()
 
 proc writeLine(printer: Printer; s: string) {.inline.} =
   printer.write(s)
@@ -73,7 +90,9 @@ let devicePath = paramStr(1)
 proc openPrinter(turn: Turn): Printer =
   new result
   result.facet = turn.facet
-  result.device = posix.open(devicePath, O_WRONLY, 0)
+  let fd = posix.open(devicePath, O_WRONLY or O_NONBLOCK, 0)
+  if fd < 0: osLastError().osErrorMsg().quit()
+  result.device = newAsyncFile(FD fd)
   result.write(InitializePrinter)
 
 runActor(devicePath) do (turn: Turn):