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>

deepdoc/parser/utils.py

@@ -0,0 +1,29 @@
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+from rag.nlp import find_codec
+
+
+def get_txt(fnm: str, binary=None) -> str:
+    txt = ""
+    if binary:
+        encoding = find_codec(binary)
+        txt = binary.decode(encoding, errors="ignore")
+    else:
+        with open(fnm, "r") as f:
+            while True:
+                line = f.readline()
+                if not line:
+                    break
+                txt += line
+    return txt