MXS-2310: Add offline schema generation script

The script generates the required .avsc files without requiring a direct
connection to the database. This makes it easier to generate schemas in
more secure installations where direct access and installing dependencies
might not be easy.

server/modules/protocol/examples/cdc_one_schema.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2016 MariaDB Corporation Ab
+#
+# Use of this software is governed by the Business Source License included
+# in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+#
+# Change Date: 2022-01-01
+#
+# On the date above, in accordance with the Business Source License, use
+# of this software will be governed by version 2 or later of the General
+# Public License.
+
+import json
+import sys
+import argparse
+
+parser = argparse.ArgumentParser(description = """
+
+This program generates a schema file for a single table by reading a tab
+separated list of field and type names from the standard input.
+
+To use this script, pipe the output of the `mysql` command line into the
+`cdc_one_schema.py` script:
+
+  mysql -ss -u <user> -p -h <host> -P <port> -e 'DESCRIBE `<database>`.`<table>`'|./cdc_one_schema.py <database> <table>
+
+Replace the <user>, <host>, <port>, <database> and <table> with appropriate
+values and run the command. Note that the `-ss` parameter is mandatory as that
+will generate the tab separated output instead of the default pretty-printed
+output.
+
+An .avsc file named after the database and table name will be generated in the
+current working directory. Copy this file to the location pointed by the
+`avrodir` parameter of the avrorouter.
+
+Alternatively, you can also copy the output of the `mysql` command to a file and
+feed it into the script if you cannot execute the SQL command directly:
+
+  # On the database server
+  mysql -ss -u <user> -p -h <host> -P <port> -e 'DESCRIBE `<database>`.`<table>`' > schema.tsv
+  # On the MaxScale server
+  ./cdc_one_schema.py <database> <table> < schema.tsv
+
+""", formatter_class=argparse.RawDescriptionHelpFormatter)
+parser.add_argument("DATABASE", help="The database name where the table is located")
+parser.add_argument("TABLE", help="The name of the table")
+
+opts = parser.parse_args(sys.argv[1:])
+
+def parse_field(row):
+    res = dict()
+    parts = row[1].lower().split('(')
+    name = parts[0]
+
+    res["real_type"] = name
+
+    if len(parts) > 1 and name not in ["enum", "set", "decimal"]:
+        res["length"] = int(parts[1].split(')')[0])
+    else:
+        res["length"] = -1
+
+    type = "string"
+
+    if name in ("date", "datetime", "time", "timestamp", "year", "tinytext", "text",
+	        "mediumtext", "longtext", "char", "varchar", "enum", "set"):
+        type = "string"
+    elif name in ("tinyblob", "blob", "mediumblob", "longblob", "binary", "varbinary"):
+        type = "bytes"
+    elif name in ("int", "smallint", "mediumint", "integer", "tinyint", "short", "bit"):
+        type = "int"
+    elif name in ("float"):
+        type = "float"
+    elif name in ("double", "decimal"):
+        type = "double"
+    elif name in ("long", "bigint"):
+        type = "long"
+
+    res["type"] = ["null", type]
+
+    res["name"] = row[0].lower()
+
+    return res
+
+try:
+    schema = dict(namespace="MaxScaleChangeDataSchema.avro", type="record", name="ChangeRecord", fields=[])
+    for line in sys.stdin:
+        schema["fields"].append(parse_field(line.split('\t')))
+
+    print("Creating: {}.{}.000001.avsc".format(opts.DATABASE, opts.TABLE))
+    dest = open("{}.{}.000001.avsc".format(opts.DATABASE, opts.TABLE), 'w')
+    dest.write(json.dumps(schema))
+    dest.close()
+
+except Exception as e:
+    print(e)
+    exit(1)
+