Converts all the non printable characters of bin->data into the "\xyz" representation where "xyz" is the octal representation of the byte, and the '\' (backslash) character is converted to "\\".
Printable characters (defined by isprint) as well as newline character are not converted.
Note that the backslash and newline characters are considered as printable characters and will not be represented by the "\xyz" representation.
Use this function to get a representation as much readable by humans as possible of a binary chunk. Note that this function is internally called when transforming a binary value to a string for example when using transform or value_stringify.
a correctly filled
a maximum len used to truncate, or
a new string from this