StrDiffSynch 2.2.6

This module calculates the difference from one string to another. If the origin string absorbs the difference, it becomes the other string. Thus, two endpoints could synchronize the strings by passing the difference.

StrDiffSynch

This module calculates the difference from one string to another. If the origin string absorbs the difference, it becomes the other string.

Thus, two endpoints could synchronize the strings by passing the difference.

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Install · Usage ·

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Install

StrDiffSynch in PyPI

pip install StrDiffSynch

Usage

StrDiff

One of two strings can change into the other when absorbing the difference from it to the other.

import json
from StrDiffSynch import StrDiff

data1 = json.dumps({"name": "davis", "other": {"age": 18}})
data2 = json.dumps({"name": "davis", "age": 18})
diff = StrDiff(data1, data2)
assert data1 + diff == data2
assert diff + data1 == data2

SynchBox

This class is used for synchronizing big string but not big enough to have to be stored in a database, among two endpoints. We will demonstrate with codes. You can type them in python console.

import asyncio

from StrDiffSynch import SynchBox

At endpoint A, set the SynchBox to contain the string.

synch_boxA = SynchBox('This is big data.')

Update the containing string.

synch_boxA.local_str = 'This is another big data.'

At endpoint B, set the SynchBox to contain a empty string.

synch_boxB = SynchBox('')

Get the string hash at endpoint B.

B_str_hash = synch_boxB.local_str_hash

Now endpoint A is commanded to synchronize endpoint B. Endpoint A needs to know the string hash at endpoint B, to calculate the difference data.

B_synch_data = synch_boxA.handle_remote_synch_command(B_str_hash)

Because no synchronization has happened, 'B_synch_data' would be the raw big string, 'This is another big data.' as demonstration.

Endpoint B gets 'B_synch_data' to synchronize itself.

synch_boxB.handle_local_synch_command(B_synch_data)
assert 'This is another big data.' == B_synch_data == synch_boxB.local_str

Now repeat to synchronize to see what will happen after the initial synchronization.

Well now that initial synchronization has happened, SynchBox will try to find the difference information between these two copy , which is usually much smaller than the raw string.

B_str_hash = synch_boxB.local_str_hash
B_synch_data = synch_boxA.handle_remote_synch_command(B_str_hash)
assert type(B_synch_data) != str and any(['h' == i[0] for i in B_synch_data])

At this step,there is nothing to change in fact.

old_B_local_str = synch_boxB.local_str
synch_boxB.handle_local_synch_command(B_synch_data)
assert synch_boxB.local_str == synch_boxA.local_str == old_B_local_str

Now repeat once more. Let's make some change at endpoint A.

synch_boxA.local_str += 'u28dy2'
B_str_hash = synch_boxB.local_str_hash
B_synch_data = synch_boxA.handle_remote_synch_command(B_str_hash)
assert type(B_synch_data) != str and any(['h' == i[0] for i in B_synch_data])
old_str = synch_boxB.local_str

Apply the change.

synch_boxB.handle_local_synch_command(B_synch_data)
assert synch_boxB.local_str == synch_boxA.local_str != old_str

Vice versa, endpoint B could synchronizes endpoint A. Let's make some change at endpoint B.

synch_boxB.local_str = synch_boxB.local_str[0:3] + synch_boxB.local_str[-3:]
str_hash = synch_boxA.local_str_hash
synch_data = synch_boxB.handle_remote_synch_command(str_hash)
assert type(synch_data) != str and any(['h' == i[0] for i in synch_data])
old_str = synch_boxA.local_str
synch_boxA.handle_local_synch_command(synch_data)
assert synch_boxB.local_str == synch_boxA.local_str != old_str

Well, everything is OK so far. However there is a possibility that the synchronization data can not be applied.

B_str_hash = synch_boxB.local_str_hash
B_synch_data = synch_boxA.handle_remote_synch_command(B_str_hash)
assert type(B_synch_data) != str and any(['h' == i[0] for i in B_synch_data])

Before the synchronization data comes, the string with the hash value B_str_hash changes for some reason.

synch_boxB.local_str = 'Hello world'

The coming data can't be handled.

try:
    synch_boxB.handle_local_synch_command(B_synch_data)
except AssertionError:
    print('Fail to handle_local_synch_command')

If you want to automatically handle this bad situation, you can pass the keyword parameter "strdiff_add_error_handler" to "handle_local_synch_command", to be called to fetch the raw string. For example,

def fetch_raw_string():
    return requests.get('http://www.baidu.com/raw-string')

We will demonstrate an easy example.

def fetch_raw_string():
    return synch_boxA.local_str


synch_boxB.handle_local_synch_command(B_synch_data, fetch_raw_string)
assert synch_boxB.local_str == synch_boxA.local_str

If you are using this module in a coroutine function, you can pass a coroutine function as the error handler to request. For example:

async def fetch_raw_string():
    async with aiohttp.ClientSession().get('http://www.baidu.com/raw-string') as r:
        return await r.text()

We will demonstrate an easy example:

async def fetch_raw_string():
    return synch_boxA.local_str


async def main():
    handle_local_synch_command_res = synch_boxB.handle_local_synch_command(B_synch_data, fetch_raw_string)
    # try to await the result only when necessary.
    if type(handle_local_synch_command_res) == asyncio.Task:
        await handle_local_synch_command_res
    assert synch_boxB.local_str == synch_boxA.local_str


asyncio.get_event_loop().run_until_complete(main())