elisp: lay out subprocess standard i/o library

Implementation of stdio-read-line is working.

elisp/jx.el

@@ -0,0 +1,15 @@
+;;; jx.el -- JsonInteractiveExperience for emacs  -*- lexical-binding: t; -*-
+;;; Commentary:
+;;; Code:
+
+(require 'stdio)
+
+(defun jx-test ()
+  "Test the jx stuff."
+  (interactive)
+  (let ((process (stdio-call (list "cat" "testfile"))))
+    (while-let ((line (stdio-read-line process)))
+      (message (format "jx-test: %s" line)))))
+
+(provide 'jx)
+;;; jx.el ends here

elisp/stdio.el

@@ -0,0 +1,58 @@
+;;; stdio.el -- stdio routines for emacs lisp  -*- lexical-binding: t; -*-
+;;; Commentary:
+;;; Code:
+
+(require 'cl-lib)
+
+(cl-defstruct (stdio-process (:constructor stdio-process-create)
+                             (:copier nil))
+  emacs-process buffer)
+
+(defun stdio-make-filter (process)
+  "Return a filter function for PROCESS."
+  (lambda (_ input)
+    (setf (stdio-process-buffer process)
+          (concat (stdio-process-buffer process)
+                  input))))
+
+(defvar stdio--process-counter 0)
+(defun stdio--make-process-name ()
+  "Generate a new uniqe process name."
+  (let* ((num stdio--process-counter)
+        (name (format "stdio-subp-%d" num)))
+    (setq stdio--process-counter (+ stdio--process-counter 1))
+    name))
+
+(defun stdio-call (command)
+  "Call COMMAND, return stdio-process."
+  (let* ((process (stdio-process-create))
+         (emacs-process (make-process
+                         :name (stdio--make-process-name)
+                         :command command
+                         :coding 'utf-8-unix
+                         :noquery nil
+                         :connection-type 'pipe
+                         :filter (stdio-make-filter process)
+                         )))
+    (setf (stdio-process-emacs-process process) emacs-process)
+    process))
+
+(defun stdio-read-line (process)
+  "Read next line from PROCESS."
+  (if-let ((stdin-buf (stdio-process-buffer process))
+           (newline-pos (string-search "\n" stdin-buf))
+           (line (substring stdin-buf 0 newline-pos))
+           (rest (substring stdin-buf (+ 1 newline-pos))))
+      (progn
+        (setf (stdio-process-buffer process) rest)
+        line)
+    ;; no newline character found
+    (if (accept-process-output (stdio-process-emacs-process process))
+        (stdio-read-line process)
+      ;; no more output from process
+      (when (> (length stdin-buf) 0)
+          (progn (setf (stdio-process-buffer process) "")
+                 stdin-buf)))))
+
+(provide 'stdio)
+;;; stdio.el ends here

elisp/testfile

@@ -0,0 +1,3 @@
+eins
+zwei
+drei