AergoLite﹢Python

Here are the instructions for using AergoLite on Python.

First you need to install AergoLite on your computer.

Then follow the instructions for your platform:

Linux

There are mainly 2 options to make Python use the modified SQLite library containing AergoLite:

A. Use the LD_LIBRARY_PATH when running your application

LD_LIBRARY_PATH=/usr/local/lib/aergolite python app.py

B. Make the wrapper library use AergoLite by default

For this we need patchelf:

git clone https://github.com/NixOS/patchelf
cd patchelf
./bootstrap.sh
./configure
make
sudo make install

Then execute this command:

sudo patchelf --replace-needed libsqlite3.so.0 libaergolite.so /usr/lib/python2.7/lib-dynload/_sqlite3.so

Note: The _sqlite3.so name will be slightly different depending on your platform.

To check if it was successful:

objdump -p /usr/lib/python2.7/lib-dynload/_sqlite3.so | grep NEEDED

Mac

The OSX does not allow to modify the pre-installed Python libraries so we need to install another copy of sqlite3 module from here

After installing it, change the SQLite library path in the wrapper:

sudo install_name_tool -change /usr/lib/libsqlite3.dylib /usr/local/lib/libaergolite.dylib /Library/Python/2.7/site-packages/pysqlite2/_sqlite3.so

Or:

sudo install_name_tool -change /usr/lib/libsqlite3.dylib /usr/local/lib/aergolite/libsqlite3.dylib /Library/Python/2.7/site-packages/pysqlite2/_sqlite3.so

To check if it worked:

otool -L /Library/Python/2.7/site-packages/pysqlite2/_sqlite3.so

Windows

Replace the sqlite3.dll file in the folder \Python\DLLs with the one containing AergoLite.

Usage

Then we can use the sqlite3 module normally, passing a URI in the place of the filename.

Example code:

import platform
import time
if platform.system() == "Darwin":
  import pysqlite2.dbapi2 as sqlite3
else:
  import sqlite3

sqlite_version = "3.27.2"
if sqlite3.sqlite_version != sqlite_version:
  print("wrong SQLite version. expected: " + sqlite_version + " found: " + sqlite3.sqlite_version)
  import sys
  sys.exit(1)

admin_pubkey = 'Am...'
conn = sqlite3.connect('file:data.db?blockchain=on&discovery=local:4329&password=test&admin=' + admin_pubkey)

cur = conn.cursor()

cur.execute("pragma blockchain_status")
print(cur.fetchone()[0])

print("waiting approval...")
while True:
  cur.execute("pragma db_is_ready")
  if cur.fetchone()[0] == 1: break
  time.sleep(60)
print("OK. this node is part of the blockchain network")

cur.execute("select * from sqlite_master where type='table'")
print(cur.fetchall())

conn.close()

Signing a transaction from the blockchain admin:

def on_sign_transaction(data):
  print "txn to be signed: " + data
  signature = sign(data, privkey)
  return hex(pubkey) + ":" + hex(signature)

conn.create_function("sign_transaction", 1, on_sign_transaction)

Receiving a notification of a processed transaction:

def on_processed_transaction(nonce, status):
  print "transaction " + str(nonce) + ": " + status
  return None

conn.create_function("transaction_notification", 2, on_processed_transaction)

Receiving notification of local db update:

def on_db_update(arg):
  print "update received"
  return None

conn.create_function("update_notification", 1, on_db_update)