QR Code scanner

[luke-jr]

Core is currently missing any way to scan QR Codes. We should add this.

[TheBlueMatt]

Do other desktop wallets have that? How many people really want to scan a QR code on their desktop?

On 03/04/17 01:57, Luke Dashjr wrote:

Core is currently missing any way to scan QR Codes. We should add this.

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[luke-jr]

FWIW, I started (and I think did most of the hard parts?) this in my qrcode branch, but I don't intend to finish it now since I don't really have a way to test it... so if someone else wants to complete it, feel free (but mention here so we don't duplicate work)

Do other desktop wallets have that?

At least Electrum does.

How many people really want to scan a QR code on their desktop?

There's also no reason to assume Core is running only on a desktop...

[jonasschnelli]

The Digital Bitbox Desktop App (based on this project, same build system, QT/C++11) has a QRCode scanner in case someone wants to extend this: https://github.com/digitalbitbox/dbb-app/blob/e7ce27112a4d44ba0b821e84f1178f6590caa6ec/src/qt/qrcodescanner.cpp

From what I can tell is that to get the dependencies right (deterministic gitian builds!) this can be very hard.

Maybe it's simpler to have a third party scanning app that execute a bitcoin: link (which then opens in Bitcoin-Qt).

[laanwj]

Qt has built-in support for cameras now? I was about to go on a rant that this would involve a lot of platform specific code, but wow, that kind of changes everything.

[jonasschnelli]

QtMultimedia has built in camera support. The complicated part is to get the all-static deterministic binary on linux. And why not provide a third party application that is not part of the "important" binary? It could scan and pass it over the bitcoin: URL scheme into Bitcoin-Qt.

[laanwj]

The complicated part is to get the all-static deterministic binary on linux.

Ouch, indeed. Would need at least dynamic loading of the underlying C libraries used for accessing the cameras, so that there is only an optional dependency.

And why not provide a third party application that is not part of the "important" binary? It could scan and pass it over the bitcoin: URL scheme into Bitcoin-Qt.

I tend to agree that this use case is 100% implementable with an external utility, without any modifications to our current code. This is what bitcoin: URL support was designed for. I guess the only thing missing from a user point of view is a way to launch the utility from Bitcoin Core's GUI.

[luke-jr]

Qt does indeed have camera support, but I was using ZBar, which does both the camera and QR Code stuff.

Deterministic binary can be "no QR scanning supported" for the initial implementation if that's difficult for some reason. AFAIK cameras just use a normal file descriptor, so I don't see why it'd be a huge problem...

A third-party application won't integrate nicely... users want a QR Scan button on the Send tab :)

[SoraKohaku]

nice for next development i hope :)

as i see phone only can do that. not for desktop. but if it's added will be nice when shopping online. If that great put all shop online with QR :)

[luke-jr]

Hm, QR scan the display? Not what I had in mind, but interesting idea nonetheless...

[SoraKohaku]

i still learn for vc programming but i know vb.net. if possible. i wanna make Bitcoin Core great(used vc of course). my idea can converted here?~permission needed

[luke-jr]

@FndNur1Labs Bitcoin Core is C++, not Visual . While we don't care what IDE you use, you'll have a much easier time with something GCC/LLVM-based and/or on Linux. But this is off-topic here, so if you have further questions/comments along those lines, please bring it up in the #bitcoin-core-dev IRC channel instead.

[laanwj]

A third-party application won't integrate nicely... users want a QR Scan button on the Send tab :)

There's no reason why a QR scan button in the send tab couldn't invoke an external utility. This is what many of the phone apps do too. They just launch whatever QR scanner the user has installed.

[SoraKohaku]

@luke-jr ok sir and @laanwj so no support for desktop. thank you for information

[benma]

@TheBlueMatt

Do other desktop wallets have that? How many people really want to scan a QR code on their desktop?

It is handy when you want to send some funds to your mobile wallet. I use the atrocious qtqr tool to scan the mobile wallet's QR code.

[laanwj]

I use the atrocious qtqr tool to scan the mobile wallet's QR code.

What is so atrocious about it?

[benma]

The UI is surprisingly bad. For example, when the scanner recognizes the QR code, the video stream keeps going with the QR code marked with a green rectangle. To see its contents / perform an action, you have to click it. It is irritating doing that and holding the phone steady at the same time.

A sane QR code reader (bascially any other I have seen) automatically continues when it recognizes the code, which is the only thing a user reasonably wants.

Once it is decoded, it is shown in a dialog with two buttons: Edit/OK. A first time user clicks 'OK', expecting something to happen, but the dialog disappears and nothing happens. Repeat the clumsy scanning. You are supposed to copy/paste the contents from the dialog box (or hit edit and get it from the textarea used to encode QR codes).

Usual features as opening an encoded url or performing registered actions don't exist (edit: it might exist, but it is not easy to discover how it works). Copying is the only thing you can do. That isn't so bad, but then it should simply do that or give you a button to do it instead of manually selecting and copying it.

[laanwj]

You could try contributing to the project to increase its usefulness. At least reporting these issues. Just like Bitcoin Core it's open source.

If the go-to QR scanner for Ubuntu is "atrocious", I'd say much is to be gained by improving that, also for non-bitcoin users.

[benma]

I have considered that but haven't gotten around it it (also put off by LaunchPad, to be honest). Now that I typed it, I'll see what I can do.

Edit: https://bugs.launchpad.net/qr-tools/+bug/1671481 https://bugs.launchpad.net/qr-tools/+bug/1671482 https://bugs.launchpad.net/qr-tools/+bug/1671484

[laanwj]

Thanks!

[SoraKohaku]

@laanwj that only ubuntu. is can do by Debian OS?Or just ubuntu....

[mariodian]

Isn't it the common practice to put a sticker over laptop's camera for privacy reasons? If that's the case (and empirically it is) then this feature wouldn't make much sense.

However, scanning the display for a QR code is an interesting idea. I even remember needing this feature once and spent around half an hour looking for an app which can do that.

[laanwj]

Isn't it the common practice to put a sticker over laptop's camera for privacy reasons?

Yep.

However, scanning the display for a QR code is an interesting idea.

That's indeed a quite interesting idea. Would be easily possible on many OSes at the moment. Though on the long run it might be complicated by the ongoing initiative to sandbox applications so that they can't 'spy' on others.

[jonasschnelli]

However, scanning the display for a QR code is an interesting idea.

Well,... if you have a QRCode scanner installed, all you need is to uncover your laptops camera and use something that reflects well (mirroring cellphone back). If it's a bitcoin URI, it will launch/trigger Bitcoin-Qt.

[laanwj]

something that reflects well (mirroring cellphone back).

I didn't know - QR codes are mirror-invariant?

[mariodian]

I didn't know - QR codes are mirror-invariant?

Some apps can handle it. I tested it on iOS with CrazyScan and Copay and it works. Other app (Scan - QR Code and Barcode Reader) couldn't read it.

[Sjors]

Concept ACK. There are situations where I don't want to use a mobile mobile wallet for payments in meat-space. I've had to use clumsy workarounds several times now to get a Bitcoin address of off someone sitting right next to me.

To add to the list of "desktop" wallets that support scanning QR code: blockchain.info web wallet

If deterministic builds are an issue, I would prefer dropping Linux support (or using a differently library) for that feature over making an external utility. Ideally though I'd like to have my cake and eat it too :-)

[Sjors]

This may also be relevant for:

• mobile QT support: #16883 (QML based mobile GUI)
• scan PSBT signed by a hardware wallet (e.g. https://github.com/cryptoadvance/specter-diy)

[icota]

I have used qzxing for scanning QR and it integrates very nicely with Qt (both C++ and QML). It's a lighter dependency as well because it only does image processing on top of QtMultimedia which, in turn, handles the camera(s) in a platform-independent fashion (tested this on Linux, macOS, Android). Like others have commented the real problem is introducing a new dependency in an orderly fashion and getting a deterministic binary built.

I think launching an external app to scan the QR is an attack vector. It is safer and better UX to have this integrated.

[promag]

I think qzxing build system isn't very mature right? It doesn't even allow to only build qrcode support?

[icota]

Yes, I'm afraid so.

[promag]

@icota right, but that's not a problem, let's improve it, I think @ftylitak doesn't mind.

[ftylitak]

Hello all, I am the maintainer of QZXing and I am open to any change as long as it is useful.

If you like to describe the change needed, I would gladly get involved with it.

[icota]

Hi @ftylitak, I guess the first question is how hard would it be to make it possible to configure QZXing to build a static library with QR decode support only? Thanks for helping.

[ftylitak]

Hello @icota,

the answer is that it is quite easy to do such a modification so I will make first sample and get back to you withinn the comming days (if not today).

[laanwj]

If deterministic builds are an issue, I would prefer dropping Linux support (or using a differently library) for that feature over making an external utility. Ideally though I'd like to have my cake and eat it too :-)

Yes, I think it's fine to have it disabled in the release builds for Linux.

It's impossible to do this on Linux with the current way we package executables there for widest distribution support. E.g. when statically linking Qt. The tree of dependencies requires for webcam input on Linux is huge, there's no way we can (nor want to) statically link Linux' whole multimedia system.

In principle, using Flatpak as a distribution medium could solve this as it allows dynamically linking against the system Qt, which can be assumed to have the multimedia library. Also, distro-built Bitcoin packages, as well as manually built ones, won't suffer from this problem.

In any case, just targeting MacOSX and Windows binaries for this is fine in the initial release, no need to increase the scope to Linux cross-distro compatibility nightmares.

[promag]

If we add qzxing then we can drop qrencode.

[ftylitak]

An update from QZXing side.

I have created a (Work-In-Progress) pull request in QZXing that when completed, will provide more freedom to select the library parts needed to be built. https://github.com/ftylitak/qzxing/pull/141

@promag (or any other), would you like to take a look at the approach? Any input is welcomed.

[icota]

Thanks for the conditional build @ftylitak. If the project is otherwise stable could you do an official release? This would be a starting point to adding it as an optional Bitcoin Core dependency and potentially getting rid of qrencode.

[ftylitak]

@icota indeed I long wanted to make an official release. There is a specific bug which holds me back that might be affecting you as well.

Since you mentioned the qrencode library I understand that you are interested in the Qr encoding part as well, correct? Currently in QZXing when encoding QR codes, the output image is correct for input strings that do not exceed the 106 characters with Low error correction mode.

Is this bug a blocking point for you?

This input will be useful for me to make proper prioritization.

[promag]

@ftylitak is the fix hard (is there an issue)? If not I think we can wait.

[Sjors]

We use [BIP21]() URIs to communicate an address + amount + arbitrary label. The UI enforces a limit of 255 characters (MAX_URI_LENGTH). The BIP does not impose a maximum, but it refers to RFC3986 which recommends 255 (although it's not clear if that recommendation includes parameters).

Here's a maximum lenght example on macOS (testnet):

[ftylitak]

Ok, it is confirmed that if the example of @Sjors is decoded and re-encoded, the encoded image is wrong.

So, I will put an effort to fix the issue in the coming days and get back to you.

[Sjors]

Thanks. In the future we might want to use QR code to transfer partially signed transactions (PSBT) to hardware wallets with a camera. Those might be even bigger, though we can worry about that later.

[andronoob]

@Sjors

In the future we might want to use QR code to transfer partially signed transactions (PSBT) to hardware wallets with a camera.

Data capacity of one single QR code is too small (3KB). To avoid hitting such limit, Electrum has already done something that made me feel uncomfortable.

[andronoob]

To be frank, I think PSBT lacks something like chunked encoding/sequence number/checksum/fountain code.

[ftylitak]

Greetings,

the Qr code encoding in QZXing is now fixed. You can freely give it a try and see if it works for you case.

In the coming days I will do the official release though the code is already available on the master branch.

[Rspigler]

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I am setting a bounty for this issue (QR code scanner) for $300 to be paid in Bitcoin.

The bounty will be split between devs (author and substantial reviews) as I see most fair.

Thank you!

Robert Spigler

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[Bosch-0]

I am setting a bounty for this issue (QR code scanner) for $300 to be paid in Bitcoin.

@Rspigler https://bitcoinbounties.org/

[fanquake]

Moved too https://github.com/bitcoin-core/gui/issues/670.