The sample contract serves as a demonstration of general QVM logic.
It is capable of:
registering users into the database
storing the last registered user's name in the database
echoing the previous user's name to STDOUT
incrementing the total registered user count
storing above counter in the database
Sample smart contract code
import os
import sys
def getenv(key, deft):
return os.getenv(key) or deft
def get_int_env(key, deft):
try:
return int(getenv(key, ""))
except Exception:
return deft
def stdout_writeln(s):
sys.stdout.write(s + "\n")
def stderr_writeln(s):
sys.stderr.write(s + "\n")
def contract(argv):
# THIS SAMPLE ONLY SUPPORTS THE "register" FUNCTION
if len(argv) == 3 and argv[1] == "register":
# GET THE CURRENT USER'S NAME OR DEFAULT TO "unknown" IF THIS IS THE FIRST CALL
previous_name = getenv("DB_USER_CURRENT", "unknown")
# GET THE TOTAL USER COUNT
total_user_count = get_int_env("DB_TOTALUSERS", 0)
# WRITE PREVIOUS USER NAME TO STDOUT
stdout_writeln("OUT=prevname: " + previous_name)
# UPDATE CURRENT USER NAME BY WRITING IT TO DB
stdout_writeln("DBW=USER_CURRENT=" + argv[2])
# STORE USER NAME UNDER A STORAGE SLOT FOR PERSISTENCE (CURRENT GETS OVERWRITTEN ON EACH CALL)
stdout_writeln("DBW=USER_%d=%s" % (total_user_count, argv[2]))
# INCREMENT THE TOTAL USER COUNT
stdout_writeln("DBW=TOTALUSERS=%d" % (total_user_count+1))
# CONTRACT RAN SUCCESSFULLY, EXIT WITH ZERO CODE
sys.exit(0)
# WRONG INVOCATION
if len(argv) >= 2:
stderr_writeln("Wrong CMD: %s" % argv[1])
sys.exit(1)
stderr_writeln("Wrong argv!")
sys.exit(1)
if __name__ == '__main__':
contract(sys.argv)
Save the smart contract
Open a text editor and save above sample contract as main.py file.
