Fix #43: Support COPY FROM LOCAL (#386)

Author: sitingren

README.md

@@ -437,6 +437,9 @@ connection.commit()
 
 **Copy** :
 
+There are 2 methods to do copy:
+
+Method 1: "COPY FROM STDIN" sql with Cursor.copy()
 ```python
 cur = connection.cursor()
 cur.copy("COPY test_copy (id, name) from stdin DELIMITER ',' ",  csv)
@@ -450,6 +453,52 @@ with open("/tmp/binary_file.csv", "rb") as fs:
                 fs, buffer_size=65536)
 ```
 
+Method 2: "COPY FROM LOCAL" sql with Cursor.execute() 
+
+```python
+import sys
+import vertica_python
+
+conn_info = {'host': '127.0.0.1',
+             'user': 'some_user',
+             'password': 'some_password',
+             'database': 'a_database',
+             # False by default
+             #'disable_copy_local': True,
+             # Don't support executing COPY LOCAL operations with prepared statements
+             'use_prepared_statements': False
+             }
+
+with vertica_python.connect(**conn_info) as connection:
+    cur = connection.cursor()
+    
+    # Copy from local file
+    cur.execute("COPY table(field1, field2) FROM LOCAL"
+                " 'data_Jan_*.csv','data_Feb_01.csv' DELIMITER ','"
+                " REJECTED DATA 'path/to/write/rejects.txt'"
+                " EXCEPTIONS 'path/to/write/exceptions.txt'",
+                buffer_size=65536
+    )
+    print("Rows loaded:", cur.fetchall())
+    
+    # Copy from local stdin
+    cur.execute("COPY table(field1, field2) FROM LOCAL STDIN DELIMITER ','", copy_stdin=sys.stdin)
+    print("Rows loaded:", cur.fetchall())
+
+    # Copy from local stdin (compound statements)
+    with open('f1.csv', 'r') as fs1, open('f2.csv', 'r') as fs2:
+        cur.execute("COPY tlb1(field1, field2) FROM LOCAL STDIN DELIMITER ',';"
+                    "COPY tlb2(field1, field2) FROM LOCAL STDIN DELIMITER ',';",
+                    copy_stdin=[fs1, fs2], buffer_size=65536)
+    print("Rows loaded 1:", cur.fetchall())
+    cur.nextset()
+    print("Rows loaded 2:", cur.fetchall())
+```
+When connection option `disable_copy_local` set to True, disables COPY LOCAL operations, including copying data from local files/stdin and using local files to store data and exceptions. You can use this property to prevent users from writing to and copying from files on a Vertica host, including an MC host. Note that this property doesn't apply to `Cursor.copy()`.
+
+The data for copying from/writing to local files is streamed in chunks of `buffer_size` bytes, which defaults to 128 * 2 ** 10.
+
+When executing "COPY FROM LOCAL STDIN", `copy_stdin` should be a file-like object or a list of file-like objects (specifically, any object with a `read()` method).
 
 **Cancel the current database operation** :
 

vertica_python/os_utils.py

@@ -0,0 +1,63 @@
+# Copyright (c) 2020 Micro Focus or one of its affiliates.
+#
+# 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 __future__ import print_function, division, absolute_import
+
+import errno
+import os
+
+
+def ensure_dir_exists(filepath):
+    """Ensure that a directory exists
+
+    If it doesn't exist, try to create it and protect against a race condition
+    if another process is doing the same.
+    """
+    directory = os.path.dirname(filepath)
+    if directory != '' and not os.path.exists(directory):
+        try:
+            os.makedirs(directory)
+        except OSError as e:
+            if e.errno != errno.EEXIST:
+                raise
+
+def check_file_readable(filename):
+    """Ensure this is a readable file"""
+    if not os.path.exists(filename):
+        raise OSError('{} does not exist'.format(filename))
+    elif not os.path.isfile(filename):
+        raise OSError('{} is not a file'.format(filename))
+    elif not os.access(filename, os.R_OK):
+        raise OSError('{} is not readable'.format(filename))
+
+def check_file_writable(filename):
+    """Ensure this is a writable file. If the file doesn't exist,
+       ensure its directory is writable.
+    """
+    if os.path.exists(filename):
+        if not os.path.isfile(filename):
+            raise OSError('{} is not a file'.format(filename))
+        if not os.access(filename, os.W_OK):
+            raise OSError('{} is not writable'.format(filename))
+    # If target does not exist, check permission on parent dir
+    ensure_dir_exists(filename)
+    pdir = os.path.dirname(filename)
+    if not pdir:
+        pdir = '.'
+    if not os.path.isdir(pdir):
+        raise OSError('{} is not a directory'.format(pdir))
+    if not os.access(pdir, os.W_OK):
+        raise OSError('Directory {} is not writable'.format(pdir))
+