Creating a custom ODBC driver

Another option: Instead of creating a ODBC driver, implement a back end that talks the wire protocol that another database (Postgresql or MySQL for instance) uses.

Your users can then download and use for instance the Postgresql ODBC driver.

Exactly what back-end database you choose to emulate should probably depend the most on how well the wire protocol format is documented.

Both Postgres and MySQL has decent documentation for their client-server protocols.

A simple Python 2.7 example of a server backend that understands parts of the Postgresql wire protocol is below. The example script creates a server that listens to port 9876. I can use the command psql -h localhost -p 9876 to connect to the server. Any query executed will return a result set with columns abc and def and two rows, all values NULL.

Reading the Postgresql docs and using something like wireshark to inspect real protocol traffic would make it pretty simple to implement a Postgresql-compatible back end.

import SocketServer
import struct

def char_to_hex(char):
    retval = hex(ord(char))
    if len(retval) == 4:
        return retval[-2:]
        assert len(retval) == 3
        return "0" + retval[-1]

def str_to_hex(inputstr):
    return " ".join(char_to_hex(char) for char in inputstr)

class Handler(SocketServer.BaseRequestHandler):
    def handle(self):
        print "handle()"


    def send_queryresult(self):
        fieldnames = ['abc', 'def']
        HEADERFORMAT = "!cih"
        fields="".join(self.fieldname_msg(name) for name in fieldnames)
        rdheader = struct.pack(HEADERFORMAT, 'T', struct.calcsize(HEADERFORMAT) - 1 + len(fields), len(fieldnames))
        self.send_to_socket(rdheader + fields)

        rows = [[1, 2], [3, 4]]
        DRHEADER = "!cih"
        for row in rows:
            dr_data = struct.pack("!ii", -1, -1)
            dr_header = struct.pack(DRHEADER, 'D', struct.calcsize(DRHEADER) - 1 + len(dr_data), 2)
            self.send_to_socket(dr_header + dr_data)


    def send_CommandComplete(self):
        HFMT = "!ci"
        msg = "SELECT 2\x00"
        self.send_to_socket(struct.pack(HFMT, "C", struct.calcsize(HFMT) - 1 + len(msg)) + msg)

    def fieldname_msg(self, name):
        tableid = 0
        columnid = 0
        datatypeid = 23
        datatypesize = 4
        typemodifier = -1
        format_code = 0 # 0=text 1=binary
        return name + "\x00" + struct.pack("!ihihih", tableid, columnid, datatypeid, datatypesize, typemodifier, format_code)

    def read_socket(self):
        print "Trying recv..."
        data = self.request.recv(1024)
        print "Received {} bytes: {}".format(len(data), repr(data))
        print "Hex: {}".format(str_to_hex(data))
        return data

    def send_to_socket(self, data):
        print "Sending {} bytes: {}".format(len(data), repr(data))
        print "Hex: {}".format(str_to_hex(data))
        return self.request.sendall(data)

    def read_Query(self):
        data = self.read_socket()
        msgident, msglen = struct.unpack("!ci", data[0:5])
        assert msgident == "Q"
        print data[5:]

    def send_ReadyForQuery(self):
        self.send_to_socket(struct.pack("!cic", 'Z', 5, 'I'))

    def read_PasswordMessage(self):
        data = self.read_socket()
        b, msglen = struct.unpack("!ci", data[0:5])
        assert b == "p"
        print "Password: {}".format(data[5:])

    def read_SSLRequest(self):
        data = self.read_socket()
        msglen, sslcode = struct.unpack("!ii", data)
        assert msglen == 8
        assert sslcode == 80877103

    def read_StartupMessage(self):
        data = self.read_socket()
        msglen, protoversion = struct.unpack("!ii", data[0:8])
        print "msglen: {}, protoversion: {}".format(msglen, protoversion)
        assert msglen == len(data)
        parameters_string = data[8:]
        print parameters_string.split('\x00')

    def send_AuthenticationOK(self):
        self.send_to_socket(struct.pack("!cii", 'R', 8, 0))

    def send_AuthenticationClearText(self):
        self.send_to_socket(struct.pack("!cii", 'R', 8, 3))

if __name__ == "__main__":
    server = SocketServer.TCPServer(("localhost", 9876), Handler)

Example command line psql session:

$ psql -h localhost -p 9876
psql (9.1.6, server 0.0.0)
WARNING: psql version 9.1, server version 0.0.
         Some psql features might not work.
Type "help" for help.

codeape=> Select;
 abc | def
(2 rows)


An ODBC driver that speaks the Postgresql protocol should work as well (but I have not tried it yet).

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