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+;; Utility module for coprocesses in newlisp
+;;
+;; This is a convenience implementation for running a sub process with
+;; its stdio via pipes. It is somewhat similar to the standard
+;; <process> function but the <coproc> utility combines the process
+;; PID together with its stdin/stdout into a FOOP object for onwards
+;; interactions. The <coproc> command is passed as a command line to
+;; /bin/sh and allows passing in environment. Further, the startup
+;; includes closing the unused file descriptors.
+;;
+;; @syntax: (coproc cmd [ env ] )
+;; Start a coprocess and returns its representation which is a FOOP
+;; object: ([coproc] PID outfd infd)
+;;
+;; The given <cmd> command is passed to "sh -c 'cmd'" sub process
+;; through a fork+execve scheme. The <env> argument should be a
+;; pointer to a null-terminated array of pointers to environment
+;; NUL-terminated strings of format "NAME=VALUE". (The caller must
+;; take care of providing existing pointers.
+;;
+;; @syntax: (:put0 coproc str )
+;; Write <str> to the given <coproc>. Returns the number of bytes
+;; written.
+;;
+;; @syntax: (:puts coproc str )
+;; Write <str> followed by newline to the given <coproc>. Returns the
+;; number of bytes written.
+;;
+;; @syntax: (:gets coproc [ limit [ waitms ]] )
+;; Read one line from the given <coproc> or up to <limit> bytes
+;; (default 100000) with up to <waitms> millisceonds delay (default
+;; 100) before reading. 
+;;
+;; @syntax: (:pug coproc str [ limit [ waitms ]] )
+;; Write <str> with :puts, then read once with :gets and return that.
+;;
+;; @syntax: (:pugs coproc str [ limit [ waitms ]] )
+;; Write <str> with :puts, then read repeatedly with :gets collating
+;; its returned lines into a list until :gets retuns nil. Returns the
+;; list of lines.
+;;
+;; @syntax: (:running? coproc [ timeout ])
+;; Check if coproc is running, i.e., that its stdin is still open.
+
+(context 'coproc)
+
+(constant 'LIBC6 "/lib/x86_64-linux-gnu/libc.so.6")
+(import LIBC6 "execve" "int"
+        "void*" ; pathname
+        "void*" ; argv[]
+        "void*" ; env[]
+        )
+(import LIBC6 "dup2" "int"
+        "int" ; oldfd
+        "int" ; newfd
+        )
+(import LIBC6 "poll" "int"
+        "void*" ; struct pollfd *fds
+        "int" ; nfds_t nfds
+        "int" ; timeout
+        )
+
+(constant 'F_GETFD 1)
+
+; <environ> is a 64-bit char** variable, rather than a function
+(import LIBC6 "environ")
+
+; Return the 64-bit value of environ
+(define (environ@) ((unpack "Lu" (address environ)) 0))
+
+; Pack a list of void* pointers into an array with a final null
+; pointer added.
+(define (pack-ptrs PTRS)
+  (pack (dup "Lu" (+ 1 (length PTRS))) (append PTRS (list 0))))
+
+; Prepare the binary data setup for calling execve to execute <cmd>
+; via "sh -c 'exec <cmd>'" and the given environment <ENV>. If <ENV>
+; is <true>, then the current process environment is used, otherwise
+; it should be a list of name-value pairs (strings).
+(define (wrapper cmd IO ENV)
+  (letn ((ARGS (list "/bin/sh" "-c" (string "exec " cmd)))
+         (ARGV (pack-ptrs (find-all nil ARGS (address $it) !=)))
+         (EV (if (list? ENV) (map (curry format "%s=%s") ENV)))
+         (ENVP (if (= true ENV) (environ@)
+                 EV (pack-ptrs (find-all nil EV (address $it) !=))))
+         )
+    (map dup2 (list (IO 0 0) (IO 1 1) (IO 1 1)) '(0 1 2))
+    (map close (flat IO))
+    (execve "/bin/sh" ARGV (or ENVP 0))
+    (exit 1)))
+
+; Create a coproc FOOP object which holds PID and pipe ends.
+(define (coproc:coproc cmd ENV)
+  (let ((IO (list (pipe) (pipe))))
+    (list (context)
+          (fork (wrapper cmd IO ENV))
+          (begin (close (IO 0 0)) (close (IO 1 1)) (IO 0 1))
+          (IO 1 0))))
+
+; Wait up to <waitms> for input from the coproc, then read one line of
+; up to <limit> bytes and return. The final newline, if any, is
+; chopped off.
+(define (gets limit waitms)
+  (let ((buffer "")
+        (delay (if (number? waitms) (* waitms 1000) 100000))
+        (maxsize (if (number? limit) limit 1000000))
+        )
+    (and (net-select (self 3) "r" delay)
+         (read (self 3) buffer maxsize "\n")
+         (if (empty? buffer) buffer
+           (!= "\n" (buffer -1)) buffer
+           (chop buffer))
+         )))
+
+; Write <str> to the coproc.
+(define (put0 str)
+  (write (self 2) str (length str)))
+
+; Write <str> to the coproc plus a newline.
+(define (puts str)
+  (write-line (self 2) str (length str)))
+
+; First :puts, then :gets
+(define (pug str limit waitms) (puts str) (gets limit waitms))
+
+; First :puts, then collect :gets until nil
+(define (pugs str limit waitms) (puts str) (collect (gets limit waitms)))
+
+; Poll the stdin pipe
+(define (running? (timeout 1))
+  (let ((FDS (pack "Lu" (self 2))))
+    (>= 0 (poll FDS 1 timeout))))