initial commit

.github/FUNDING.yml

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+# These are supported funding model platforms
+
+github: taigrr # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]

LICENSE

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+Copyright (C) 2023 by Tai Groot <tai@taigrr.com>
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

README.md

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+# VidNumerator
+
+This is a tiny library that only exports one function: `EnumerateVideoDevices`.
+This function uses syscalls to efficiently determine which `/dev/videoN` devices
+are webcams and which are the additional metadata control handles.
+The list of strings returned are the full filepaths to valid devices.
+

go.mod

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+module github.com/taigrr/vidnumerator
+
+go 1.20
+
+require golang.org/x/sys v0.9.0

go.sum

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+golang.org/x/sys v0.9.0 h1:KS/R3tvhPqvJvwcKfnBHJwwthS11LRhmM5D59eEXa0s=
+golang.org/x/sys v0.9.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

vidnumerator.go

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+package vidnumerator
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	IOCNrBits   = 8
+	IOCTypeBits = 8
+	IOCSizeBits = 14
+	IOCDirBits  = 2
+	IOCNone     = 0
+	IOCWrite    = 1
+	IOCRead     = 2
+	IOCNrShift  = 0
+
+	IOCTypeShift = (IOCNrShift + IOCNrBits)
+	IOCSizeShift = (IOCTypeShift + IOCTypeBits)
+	IOCDirShift  = (IOCSizeShift + IOCSizeBits)
+
+	VidIOCQueryCap = (IOCRead << IOCDirShift) |
+		(uintptr('V') << IOCTypeShift) |
+		(0 << IOCNrShift) |
+		(unsafe.Sizeof(cap{}) << IOCSizeShift)
+)
+
+type cap struct {
+	driver       [16]uint8
+	card         [32]uint8
+	busInfo      [32]uint8
+	version      uint32
+	capabilities uint32
+	deviceCaps   uint32
+	reserved     [3]uint32
+}
+
+func (r *cap) QueryFd(fileDesciptor int) error {
+	if r == nil {
+		return fmt.Errorf("nil receiver")
+	}
+	_, _, errorNumber := unix.Syscall(
+		unix.SYS_IOCTL,
+		uintptr(fileDesciptor),
+		VidIOCQueryCap,
+		uintptr(unsafe.Pointer(r)),
+	)
+	if errorNumber != 0 {
+		return errorNumber
+	}
+	return nil
+}
+
+// this function checks the ioctl for VIDIOC_QUERYCAP to see if the device is a video capture device
+func EnumeratedVideoDevices() []string {
+	// list all files in the /dev directory
+	d, err := os.ReadDir("/dev")
+	if err != nil {
+		return []string{}
+	}
+	// iterate over the files in the directory
+	devNames := []string{}
+	for _, file := range d {
+		if file.IsDir() {
+			continue
+		}
+		fname := file.Name()
+		if !strings.HasPrefix(fname, "video") {
+			continue
+		}
+		fname = filepath.Join("/dev/", fname)
+		f, err := os.OpenFile(fname, os.O_RDONLY, 0o755)
+		if err != nil {
+			continue
+		}
+		fd := f.Fd()
+		ic := cap{}
+		err = ic.QueryFd(int(fd))
+		if err != nil {
+			continue
+		}
+		if ic.deviceCaps == 69206017 {
+			devNames = append(devNames, fname)
+		}
+	}
+	return devNames
+}