Add get_txt function (#2639)

### What problem does this PR solve?

Add get_txt function to reduce duplicate code

### Type of change

- [x] Refactoring

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

rag/app/one.py

@@ -13,6 +13,8 @@
 from tika import parser
 from io import BytesIO
 import re
+
+from deepdoc.parser.utils import get_txt
 from rag.app import laws
 from rag.nlp import rag_tokenizer, tokenize, find_codec
 from deepdoc.parser import PdfParser, ExcelParser, PlainParser, HtmlParser
@@ -82,17 +84,7 @@ def chunk(filename, binary=None, from_page=0, to_page=100000,
 
     elif re.search(r"\.(txt|md|markdown)$", filename, re.IGNORECASE):
         callback(0.1, "Start to parse.")
-        txt = ""
-        if binary:
-            encoding = find_codec(binary)
-            txt = binary.decode(encoding, errors="ignore")
-        else:
-            with open(filename, "r") as f:
-                while True:
-                    l = f.readline()
-                    if not l:
-                        break
-                    txt += l
+        txt = get_txt(filename, binary)
         sections = txt.split("\n")
         sections = [s for s in sections if s]
         callback(0.8, "Finish parsing.")