OsOperations::read_binary(self, filename, start_pos) is added

It is a specialized function to read binary data from files.

Author: dmitry-lipetsk

testgres/operations/local_ops.py

@@ -308,6 +308,17 @@ def readlines(self, filename, num_lines=0, binary=False, encoding=None):
                         buffers * max(2, int(num_lines / max(cur_lines, 1)))
                     )  # Adjust buffer size
 
+    def read_binary(self, filename, start_pos):
+        assert type(filename) == str  # noqa: E721
+        assert type(start_pos) == int  # noqa: E721
+        assert start_pos >= 0
+
+        with open(filename, 'rb') as file:  # open in a binary mode
+            file.seek(start_pos, os.SEEK_SET)
+            r = file.read()
+            assert type(r) == bytes  # noqa: E721
+            return r
+
     def isfile(self, remote_file):
         return os.path.isfile(remote_file)
 

testgres/operations/os_ops.py

@@ -98,6 +98,12 @@ def read(self, filename, encoding, binary):
     def readlines(self, filename):
         raise NotImplementedError()
 
+    def read_binary(self, filename, start_pos):
+        assert type(filename) == str  # noqa: E721
+        assert type(start_pos) == int  # noqa: E721
+        assert start_pos >= 0
+        raise NotImplementedError()
+
     def isfile(self, remote_file):
         raise NotImplementedError()
 

testgres/operations/remote_ops.py

@@ -340,6 +340,16 @@ def readlines(self, filename, num_lines=0, binary=False, encoding=None):
 
         return lines
 
+    def read_binary(self, filename, start_pos):
+        assert type(filename) == str  # noqa: E721
+        assert type(start_pos) == int  # noqa: E721
+        assert start_pos >= 0
+
+        cmd = "tail -c +{} {}".format(start_pos + 1, __class__._escape_path(filename))
+        r = self.exec_command(cmd)
+        assert type(r) == bytes  # noqa: E721
+        return r
+
     def isfile(self, remote_file):
         stdout = self.exec_command("test -f {}; echo $?".format(remote_file))
         result = int(stdout.strip())
@@ -386,6 +396,15 @@ def db_connect(self, dbname, user, password=None, host="localhost", port=5432):
         )
         return conn
 
+    def _escape_path(path):
+        assert type(path) == str  # noqa: E721
+        assert path != ""  # Ok?
+
+        r = "'"
+        r += path
+        r += "'"
+        return r
+
 
 def normalize_error(error):
     if isinstance(error, bytes):

tests/test_local.py

@@ -1,4 +1,7 @@
+import os
+
 import pytest
+import re
 
 from testgres import ExecUtilException
 from testgres import LocalOperations
@@ -52,3 +55,45 @@ def test_exec_command_failure__expect_error(self):
         assert error == b'/bin/sh: 1: nonexistent_command: not found\n'
         assert exit_status == 127
         assert result == b''
+
+    def test_read_binary__spec(self):
+        """
+        Test LocalOperations::read_binary.
+        """
+        filename = __file__  # current file
+
+        with open(filename, 'rb') as file:  # open in a binary mode
+            response0 = file.read()
+
+        assert type(response0) == bytes  # noqa: E721
+
+        response1 = self.operations.read_binary(filename, 0)
+        assert type(response1) == bytes  # noqa: E721
+        assert response1 == response0
+
+        response2 = self.operations.read_binary(filename, 1)
+        assert type(response2) == bytes  # noqa: E721
+        assert len(response2) < len(response1)
+        assert len(response2) + 1 == len(response1)
+        assert response2 == response1[1:]
+
+        response3 = self.operations.read_binary(filename, len(response1))
+        assert type(response3) == bytes  # noqa: E721
+        assert len(response3) == 0
+
+        response4 = self.operations.read_binary(filename, len(response2))
+        assert type(response4) == bytes  # noqa: E721
+        assert len(response4) == 1
+        assert response4[0] == response1[len(response1) - 1]
+
+        response5 = self.operations.read_binary(filename, len(response1) + 1)
+        assert type(response5) == bytes  # noqa: E721
+        assert len(response5) == 0
+
+    def test_read_binary__spec__unk_file(self):
+        """
+        Test LocalOperations::read_binary with unknown file.
+        """
+
+        with pytest.raises(FileNotFoundError, match=re.escape("[Errno 2] No such file or directory: '/dummy'")):
+            self.operations.read_binary("/dummy", 0)

tests/test_remote.py

@@ -1,6 +1,7 @@
 import os
 
 import pytest
+import re
 
 from testgres import ExecUtilException
 from testgres import RemoteOperations
@@ -181,6 +182,48 @@ def test_read_binary_file(self):
 
         assert isinstance(response, bytes)
 
+    def test_read_binary__spec(self):
+        """
+        Test RemoteOperations::read_binary.
+        """
+        filename = __file__  # currnt file
+
+        with open(filename, 'rb') as file:  # open in a binary mode
+            response0 = file.read()
+
+        assert type(response0) == bytes  # noqa: E721
+
+        response1 = self.operations.read_binary(filename, 0)
+        assert type(response1) == bytes  # noqa: E721
+        assert response1 == response0
+
+        response2 = self.operations.read_binary(filename, 1)
+        assert type(response2) == bytes  # noqa: E721
+        assert len(response2) < len(response1)
+        assert len(response2) + 1 == len(response1)
+        assert response2 == response1[1:]
+
+        response3 = self.operations.read_binary(filename, len(response1))
+        assert type(response3) == bytes  # noqa: E721
+        assert len(response3) == 0
+
+        response4 = self.operations.read_binary(filename, len(response2))
+        assert type(response4) == bytes  # noqa: E721
+        assert len(response4) == 1
+        assert response4[0] == response1[len(response1) - 1]
+
+        response5 = self.operations.read_binary(filename, len(response1) + 1)
+        assert type(response5) == bytes  # noqa: E721
+        assert len(response5) == 0
+
+    def test_read_binary__spec__unk_file(self):
+        """
+        Test RemoteOperations::read_binary with unknown file.
+        """
+
+        with pytest.raises(ExecUtilException, match=re.escape("tail: cannot open '/dummy' for reading: No such file or directory")):
+            self.operations.read_binary("/dummy", 0)
+
     def test_touch(self):
         """
         Test touch for creating a new file or updating access and modification times of an existing file.