ascii() and unascii() to help with broken utf-8 or binary data

README.md

@@ -262,6 +262,27 @@ You can still resume it by typing `/eval_resume <text>` - the argument
 text will be passed instead of the context of text area of the formspec.
 
 
+### More utilities
+
+#### Binary data
+
+##### `ascii()` and `unascii()`
+
+Have you ever encountered "<invalid UTF-8 string>" somewhere with no
+easy way to display it?
+
+`ascii()` will allow you to inspect these strings (which may be just
+some broken unicode or arbitrary binary data).
+
+`ascii(str)` will escape all control sequences and unprintable
+characters so you can output it normally. It works well with broken
+strings, because printable ASCII characters will be kept unchanged.
+
+The reverse of this is `unascii(str)`, which will take the escaped
+sequence and turn it back into raw bytes. This supports only `\xFF`
+hex escapes, but it works well enough in pair with `ascii()`.
+
+
 ### Resetting your personal environment
 
 If your environment gets messed up, or you just want to get rid of the

init.lua

@@ -222,7 +222,9 @@ fsinput(label, text) -- show a form that will return the text you entered
                 core.show_formspec(player_name, "cmd_eval:input", table.concat(fs, ""))
                 local result = coroutine.yield(WAIT_FOR_FORMSPEC)
                 return result
-            end
+            end,
+            ascii = util.ascii,
+            unascii = util.unascii,
         },
         {
             __index = function(_self, key)

util.lua

@@ -1,3 +1,5 @@
+local fmt = string.format
+
 
 -- get actual eye_pos of the player (including eye_offset)
 local function player_get_eye_pos(player)
@@ -69,11 +71,74 @@ local function get_pointed_position(player, range, point_to_objects, point_to_li
     return pointed_pos, pointed_thing
 end
 
+local escapes = {
+    ['\a'] = '\\a',
+    ['\b'] = '\\b',
+    ['\f'] = '\\f',
+    ['\n'] = '\\n',
+    ['\r'] = '\\r',
+    ['\t'] = '\\t',
+    ['\v'] = '\\v',
+    ['\\'] = '\\\\',
+    ['"'] = '\\"',
+}
+
+local unescapes = {
+    ['\\a'] = '\a',
+    ['\\b'] = '\b',
+    ['\\f'] = '\f',
+    ['\\n'] = '\n',
+    ['\\r'] = '\r',
+    ['\\t'] = '\t',
+    ['\\v'] = '\v',
+    ['\\\\'] = '\\',
+    ['\\"'] = '"',
+}
+
+local function escape_nonascii(c)
+    return escapes[c] or string.format('\\x%02x', string.byte(c))
+end
+
+
+local function ascii(str)
+    str = str:gsub('[%c\r\n\\"\128-\255]', escape_nonascii)
+    return str
+end
+
+
+local function unescape_hex(backslashes, hex)
+    if #backslashes % 2 == 0 then
+        -- Even number of backslashes, they escape each other, not the digits.
+        -- Return them so that next step can treat them.
+        return backslashes .. 'x' .. hex
+    else
+        -- Remove the odd backslash, which escapes the hex code.
+        -- The rest will be processed by the next step.
+        backslashes = backslashes:sub(1, -2)
+    end
+    local c = string.char(tonumber(hex, 16))
+    if c == '\\' then
+        -- will be unsecaped by the next step ("\x5cb" --> "\\b")
+        c = '\\\\'
+    end
+    return backslashes .. c
+end
+
+
+local function unascii(str)
+    --str = str:gsub('(\\+)(%d%d%d)', unescape_digits)
+    str = str:gsub('(\\+)x(%x%x)', unescape_hex)
+    str = str:gsub('\\[abfnrtv\\"]', unescapes)
+    return str
+end
+
 
 local util = {
     player_get_eye_pos = player_get_eye_pos,
     raycast_crosshair = raycast_crosshair,
     raycast_crosshair_to_object = raycast_crosshair_to_object,
     get_pointed_position = get_pointed_position,
+    ascii = ascii,
+    unascii = unascii,
 }
 return util