Depthai USB Support

[TheMutta]

Purpose

This branch adds the ability to Depthai to communicate with Gate via USB through XLink

Specification

All the API calls in the DepthaiGate class use USB communication if TCP/IP is not available
None / not applicable

Dependencies & Potential Impact

All the dependencies are already integrated in XLink

Deployment Plan

The changes don't affect the normal functioning via TCP/IP and don't break existing features, they can be rolled out easily.

Testing & Validation

The branch was tested by using all the API calls, which all completed successfully.

[TheMutta]

bugbot run

[cursor]

Bug: USB Fallback Missing Error Handling

The createSession() USB fallback implementation in DeviceGate.cpp is missing an error check after reading the USB response header. Unlike other USB methods in the file, it does not verify request.RequestNum == RESPONSE_ERROR. This allows the code to proceed with memory allocation and JSON parsing using potentially invalid request.RequestSize or error data, which can lead to memory corruption, crashes, or incorrect behavior.

src/device/DeviceGate.cpp#L237-L244

depthai-core/src/device/DeviceGate.cpp

Lines 237 to 244 in fa9efd6

	XLinkPlatformGateRead(&request, sizeof(request));
	char *respBuffer = new char[request.RequestSize + 1];
	XLinkPlatformGateRead(respBuffer, request.RequestSize);
	respBuffer[request.RequestSize]= '\0';
	auto resp = nlohmann::json::parse(respBuffer);
	delete[] respBuffer;
	spdlog::debug("DeviceGate createSession response: {}", resp.dump());

Fix in Cursor • Fix in Web

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Bug: USB Firmware Upload Fails JSON Binary Handling

The USB communication path incorrectly embeds the firmware package (a std::vector<uint8_t>) directly into a JSON object. Unlike the HTTP path which uses multipart form data for binary uploads, JSON does not natively support raw binary data. This format mismatch will prevent the server from correctly processing the firmware package.

src/device/DeviceGate.cpp#L260-L266

depthai-core/src/device/DeviceGate.cpp

Lines 260 to 266 in fa9efd6

	nlohmann::json uploadFwpBody = {{"sessionId", sessionId},
	{"file", package}};
	request.RequestNum = UPLOAD_FWP;
	request.RequestSize = uploadFwpBody.dump().size();
	XLinkPlatformGateWrite(&request, sizeof(USBRequest_t));
	XLinkPlatformGateWrite((void*)uploadFwpBody.dump().c_str(), uploadFwpBody.dump().size());

Fix in Cursor • Fix in Web

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[themarpe]

Lets use C++ here - eg a vector /w reserve or resize and pass its "data()" to XLink to not have to manually new & delete

[moratom]

Thanks @TheMutta!

I'm thinking if I'd be safer here to define an interface (pure virtual class) and then do two implementations, so we have compile-time safety to a degree that we implemented all current (and potential future) calls to gate.
What do you think?

[moratom]

Can we cross link the XLink PR in this PRs description? Thanks!

[moratom]

whitespace change

[moratom]

is this cross platform?

[themarpe]

My 2c, can just skip packed by making both uint32_t or swapping them around

[TheMutta]

It's definitely cross platform

[moratom]

Needs to be removed

[themarpe]

Issue with Gate being in an "wrong state / timeout"
Pass a timeout explicitly here, instead of using a default.
Align the timeout, with Gate impl.

[themarpe]

Pin down "who" retries in this case when Gate isn't yet available