Fix and document console.write()

Added example on using framed data transmission over the console.

components/modules/console.c

@@ -203,13 +203,19 @@ static int console_mode(lua_State *L)
 }
 
 
-// Lua: console.write(string1, [string2], ..., [stringn])
+// Lua: console.write(str_or_num [, str_or_num2 ... ])
 static int console_write(lua_State *L)
 {
   int total = lua_gettop(L);
   for (int s = 1; s <= total; ++s)
   {
-    if (lua_isnumber(L, s))
+    if (lua_type(L, s) == LUA_TSTRING)
+    {
+      size_t len = 0;
+      const char *buf = lua_tolstring(L, s, &len);
+      retrying_write(buf, len);
+    }
+    else if (lua_isnumber(L, s))
     {
       int n = lua_tointeger(L, s);
       if (n < 0 || n > 255)
@@ -217,13 +223,6 @@ static int console_write(lua_State *L)
       char ch = n;
       retrying_write(&ch, 1);
     }
-    else
-    {
-      luaL_checktype(L, s, LUA_TSTRING);
-      size_t len = 0;
-      const char *buf = lua_tolstring(L, s, &len);
-      retrying_write(buf, len);
-    }
   }
   fflush(stdout);
   fsync(fileno(stdout));

docs/modules/console.md

@@ -39,16 +39,14 @@ To unregister the callback, specify `nil` as the function.
 #### Example
 ```lua
 -- when 4 chars is received.
-console.on("data", 4,
-  function(data)
+console.on("data", 4, function(data)
   print("received from console:", data)
   if data=="quit" then
     console.on("data", 0, nil)
   end
 end)
 -- when '\r' is received.
-console.on("data", "\r",
-  function(data)
+console.on("data", "\r", function(data)
   print("received from console:", data)
   if data=="quit\r" then
     console.on("data", 0, nil)
@@ -56,8 +54,7 @@ console.on("data", "\r",
 end)
 
 -- error handler
-console.on("error",
-  function(err)
+console.on("error", function(err)
   print("error on console:", err)
 end)
 ```
@@ -81,8 +78,133 @@ Controls the interactivity of the console.
 `nil`
 
 #### Example
+Implement a REL instead of the usual REPL
 ```lua
--- Implement a REL instead of the usual REPL
 console.on("data", "\r", function(line) node.input(line.."\r\n") end)
 console.mode(console.NONINTERACTIVE)
 ```
+
+Receive potentially binary data on the console, and process it without letting
+it reach the Lua interpreter.
+```lua
+-- Instantiate a stream handling function that processes a classic framing
+-- protocol: <STX><escaped-data><ETX> where <escaped-data> has the
+-- STX, ETX and DLE symbols escaped as <DLE><STX>, <DLE><ETX>, <DLE><DLE>.
+-- The chunk_cb gets called incrementally with partial stream data which is
+-- effectively unescaped. When the end of frame is encountered, the done_cb
+-- gets invoked.
+function transmission_receiver(chunk_cb, done_cb)
+  local inframe = false
+  local escaped = false
+  local done = false
+  local STX = 2
+  local ETX = 3
+  local DLE = 16
+  local function dispatch(data, i, j)
+    if (j - i) < 0 then return end
+    chunk_cb(data:sub(i, j))
+  end
+  return function(data)
+    if done then return end
+    local from
+    local to
+    for i = 1, #data
+    do
+      local b = data:byte(i)
+      if inframe
+      then
+        if not from then from = i end -- first valid byte
+        if escaped
+        then
+          escaped = false
+        else
+          if b == DLE
+          then
+            escaped = true
+            dispatch(data, from, i-1)
+            from = nil
+          elseif b == ETX
+          then
+            done = true
+            to = i-1
+            break
+          end
+        end
+      else -- look for an (unescaped) STX to sync frame start
+        if b == DLE then escaped = true
+        elseif b == STX and not escaped then inframe = true
+        else escaped = false
+        end
+      end
+      -- else ignore byte outside of framing
+    end
+    if from then dispatch(data, from, to or #data) end
+    if done then done_cb() end
+  end
+end
+
+function print_hex(chunk)
+  for i = 1, #chunk
+  do
+    print(string.format("%02x ", chunk:sub(i,i)))
+  end
+end
+
+function resume_interactive()
+  console.on("data", 0, nil)
+  console.mode(console.INTERACTIVE)
+end
+
+-- The 0 may be adjusted upwards for improved efficiency, but be mindful to
+-- always send enough data to reach the ETX marker.
+console.on("data", 0, transmission_receiver(print_hex, resume_interactive))
+console.mode(console.NONINTERACTIVE)
+```
+
+Example C program for encoding data suitable for the above.
+```C
+#include <stdio.h>
+
+#define STX 0x02
+#define ETX 0x03
+#define DLE 0x10
+
+int main(int argc, char *argv[])
+{
+  putchar(STX);
+  int ch;
+  while ((ch = getchar()) != EOF)
+  {
+    switch(ch)
+    {
+      case STX: case ETX: case DLE: putchar(DLE); break;
+      default: break;
+    }
+    putchar(ch);
+  }
+  putchar(ETX);
+  return 0;
+}
+```
+
+## console.write()
+
+Provides ability to write raw, unformatted data to the console.
+
+#### Syntax
+`console.write(str_or_num [, str2_or_num ...])`
+
+#### Parameters
+- `str_or_num` Either
+    - A string to write to the console. May contain binary data.
+    - A number representing the character code to write the console.
+  Multiple parameters may be given, and they will be written in sequence.
+
+#### Returns
+`nil`
+
+#### Example
+Write "Hello world!\n" to the console, in a roundabout manner
+```lua
+console.write("Hello", 0x20, "world", 0x21, "\n")
+```