internal/kobject: process uevent message

This deals with environment variables generally present in every message.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/kobject/event.go

@@ -0,0 +1,90 @@
+package kobject
+
+import (
+	"errors"
+	"strconv"
+	"strings"
+	"unsafe"
+
+	"hakurei.app/internal/uevent"
+)
+
+// Event is a [uevent.Message] with known environment variables processed.
+type Event struct {
+	// alloc_uevent_skb: action_string
+	Action uevent.KobjectAction `json:"action"`
+	// alloc_uevent_skb: devpath
+	DevPath string `json:"devpath"`
+
+	// Uninterpreted environment variable pairs. An entry missing a separator
+	// gains the value "\x00".
+	Env map[string]string `json:"env"`
+
+	// SEQNUM value set by the kernel.
+	Sequence uint64 `json:"seqnum"`
+	// SYNTH_UUID value set on trigger, nil denotes a non-synthetic event.
+	Synth *uevent.UUID `json:"synth_uuid,omitempty"`
+	// SUBSYSTEM value set by the kernel.
+	Subsystem string `json:"subsystem"`
+}
+
+// Populate populates e with the contents of a [uevent.Message].
+//
+// The ACTION and DEVPATH environment variables are ignored and assumed to be
+// consistent with the header.
+func (e *Event) Populate(reportErr func(error), m *uevent.Message) {
+	if reportErr == nil {
+		reportErr = func(error) {}
+	}
+
+	*e = Event{
+		Action:  m.Action,
+		DevPath: m.DevPath,
+		Env:     make(map[string]string),
+	}
+
+	for _, s := range m.Env {
+		k, v, ok := strings.Cut(s, "=")
+		if !ok {
+			if _, ok = e.Env[s]; !ok {
+				e.Env[s] = "\x00"
+			}
+			continue
+		}
+
+		switch k {
+		case "ACTION", "DEVPATH":
+			continue
+
+		case "SEQNUM":
+			seq, err := strconv.ParseUint(v, 10, 64)
+			if err != nil {
+				if _e := errors.Unwrap(err); _e != nil {
+					err = _e
+				}
+				reportErr(err)
+
+				e.Env[k] = v
+				continue
+			}
+			e.Sequence = seq
+
+		case "SYNTH_UUID":
+			var uuid uevent.UUID
+			err := uuid.UnmarshalText(unsafe.Slice(unsafe.StringData(v), len(v)))
+			if err != nil {
+				reportErr(err)
+
+				e.Env[k] = v
+				continue
+			}
+			e.Synth = &uuid
+
+		case "SUBSYSTEM":
+			e.Subsystem = v
+
+		default:
+			e.Env[k] = v
+		}
+	}
+}