.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/channels/payment_channels/plot_01_spilman_channels.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_channels_payment_channels_plot_01_spilman_channels.py>`
        to download the full example code or to run this example in your browser via JupyterLite.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_channels_payment_channels_plot_01_spilman_channels.py:


Spilman and Hearn's one-way micropayment channels (2013)
========================================================

Paying for a stream by the second on chain costs a transaction, and a fee,
per payment. Jeremy Spilman's channel needs two. The payer locks the
channel's capacity in a 2-of-2 output, after the payee has signed a refund
that returns everything to the payer at a lock time. Each payment is a new
transaction from that output, paying the payee a little more; the payer
signs it and hands it over, and the payee countersigns and publishes only
the last one. Mike Hearn built the scheme into bitcoinj the same year.

For ``m`` payments the chain sees two transactions instead of ``m``:

.. math::

   \text{on-chain transactions} = 2 \quad\text{vs.}\quad m.

The payee must close before the refund's lock time, or the payer takes
everything back.

.. GENERATED FROM PYTHON SOURCE LINES 24-28

.. code-block:: Python

    import matplotlib.pyplot as plt

    import blockchainkit as bk








.. GENERATED FROM PYTHON SOURCE LINES 29-31

Streaming one coin a second for a minute
----------------------------------------

.. GENERATED FROM PYTHON SOURCE LINES 31-40

.. code-block:: Python


    channel = bk.channels.SpilmanChannel(
        "viewer", "streamer", payer_key=7, payee_key=5, capacity=100, expiry=144
    )
    paid = [channel.pay(1) for _ in range(60)]
    settlement = channel.close(height=30)
    print(dict(settlement.payouts))
    assert dict(settlement.payouts) == {"viewer": 40, "streamer": 60}





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    {'viewer': 40, 'streamer': 60}




.. GENERATED FROM PYTHON SOURCE LINES 41-45

A payee who waits too long
--------------------------
The refund becomes valid at height 144; the payer can then take back all
100 coins, although it signed payments worth 60.

.. GENERATED FROM PYTHON SOURCE LINES 45-74

.. code-block:: Python


    late = bk.channels.SpilmanChannel(
        "viewer", "streamer", payer_key=7, payee_key=5, capacity=100, expiry=144
    )
    for _ in range(60):
        late.pay(1)
    try:
        late.refund(height=143)
    except ValueError as error:
        print("at height 143:", error)
    refund = late.refund(height=144)
    assert refund.kind == "refund" and refund.payouts["streamer"] == 0

    fig, (left, right) = plt.subplots(1, 2, figsize=(11, 4))
    seconds = range(1, 61)
    left.step(seconds, paid, where="post", color="#2563eb", label="signed off chain")
    left.axhline(60, color="#16a34a", linestyle="--", label="settled on chain")
    left.set(xlabel="second", ylabel="coins paid to the streamer")
    left.set_title("Each payment is a signature, not a transaction")
    left.legend()
    right.plot(seconds, seconds, color="#dc2626", label="one transaction per payment")
    right.plot(seconds, [2] * 60, color="#16a34a", label="channel: fund and close")
    right.set(xlabel="payments", ylabel="transactions on chain")
    right.set_title("Two transactions for any number of payments")
    right.legend()
    fig.tight_layout()

    plt.show()




.. image-sg:: /api/gallery/channels/payment_channels/images/sphx_glr_plot_01_spilman_channels_001.png
   :alt: Each payment is a signature, not a transaction, Two transactions for any number of payments
   :srcset: /api/gallery/channels/payment_channels/images/sphx_glr_plot_01_spilman_channels_001.png
   :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    at height 143: the refund is locked until height 144




.. GENERATED FROM PYTHON SOURCE LINES 75-80

Exercise
--------
The payer can never take back what it has paid before the lock time,
because the payee holds a signed transaction for it. What stops the payee
from publishing an *earlier* payment, and why would it never want to?


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.671 seconds)


.. _sphx_glr_download_api_gallery_channels_payment_channels_plot_01_spilman_channels.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: lite-badge

      .. image:: images/jupyterlite_badge_logo.svg
        :target: ../../../../lite/lab/index.html?path=api/gallery/channels/payment_channels/plot_01_spilman_channels.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_01_spilman_channels.ipynb <plot_01_spilman_channels.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_01_spilman_channels.py <plot_01_spilman_channels.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_01_spilman_channels.zip <plot_01_spilman_channels.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_