Previously if an import of a dependent module (usb1, hid) failed, import
of the whole transport module would fail. This was resolved by catching
ImportErrors in the all_transports method.
This had two drawbacks:
- if something other than ImportError happened - e.g., libusb would
raise OSError if it couldn't find libusb.so - all_transports would crash
anyway
- at the same time, if a legitimately needed dependency
(typing_extensions) was missing, this would be masked by the ImportError
handling.
Instead, we unconditionally import the modules, and inside each one,
wrap dependencies in a try-except.
As an added benefit, it is now possible to disable a transport just by
setting SomeTransport.ENABLED = False
This commit breaks session handling (which matters with Bridge) and
regresses Bridge to an older code state. Both of these issues will be
rectified in subsequent commits.
Explanation of this big API reshuffle follows:
* protocols are moved to trezorlib.transport, and to a single common file.
* there is a cleaner definition of Transport and Protocol API (see below)
* fully valid mypy type hinting
* session handle counters and open handle counters mostly went away. Transports
and Protocols are meant to be "raw" APIs; TrezorClient will implement
context-handler-based sessions, session tracking, etc.
I'm calling this a "reshuffle" because it involved very small number of
code changes. Most of it is moving things around where they sit better.
The API changes are as follows.
Transport is now a thing that can:
* open and close sessions
* read and write protobuf messages
* enumerate and find devices
Some transports (all except bridge) are technically bytes-based and need
a separate protocol implementation (because we have two existing protocols,
although only the first one is actually used). Hence a protocol superclass.
Protocol is a thing that *also* can:
* open and close sessions
* read and write protobuf messages
For that, it requires a `handle`.
Handle is a physical layer for a protocol. It can:
* open and close some sort of device connection
(this is distinct from session! Connection is a channel over which you can
send data. Session is a logical arrangement on top of that; you can have
multiple sessions on a single connection.)
* read and write 64-byte chunks of data
With that, we introduce ProtocolBasedTransport, which simply delegates
the appropriate Transport functionality to respective Protocol methods.
hid and webusb transports are ProtocolBasedTransport-s that provide separate
device handles. HidHandle and WebUsbHandle existed before, but the distinction
of functionality between a Transport and its Handle was unclear. Some methods
were moved and now the handles implement the Handle API, while the transports
provide the enumeration parts of the Transport API, as well as glue between
the respective Protocols and Handles.
udp transport is also a ProtocolBasedTransport, but it acts as its own handle.
(That might be changed. For now, I went with the pre-existing structure.)
In addition, session_begin/end is renamed to begin/end_session to keep
consistent verb_noun naming.
This allows us to return early from a `write`, which we need in cases
where we want to perform an operation inbetween `read` and `write` -
namely, callback for ButtonRequest should technically be invoked after
returning ButtonAck but before waiting for device's response.
Of course that doesn't really work. The callback will actually be
invoked _before_ ButtonAck, so there's still the condition that it must
return immediately or the device gets stuck with a black screen.
But doing this allows us to write code *as if* it worked, which lets the
other transports run free and wild, by which I mean, do the Right Thing
This clarifies the intent: the project is licenced under terms
of LGPL version 3 only, but the standard headers cover only "3 or later",
so we had to rewrite them.
In the same step, we removed author information from individual files
in favor of "SatoshiLabs and contributors", and include an AUTHORS
file that lists the contributors.
Apologies to those whose names are missing; please contact us if you wish
to add your info to the AUTHORS file.
