ext: isolate from container/std

These are too general to belong in the container package. This targets the v0.4 release to reduce the wrapper maintenance burden.

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

ext/ext.go

@@ -0,0 +1,78 @@
+// Package ext provides wrappers around nonportable system interfaces.
+package ext
+
+import (
+	"encoding/json"
+	"iter"
+	"strconv"
+)
+
+// checked in container/seccomp
+type (
+	// Uint is equivalent to C.uint.
+	Uint = uint32
+	// Int is equivalent to C.int.
+	Int = int32
+)
+
+// SyscallNum represents an architecture-specific, Linux syscall number.
+type SyscallNum Int
+
+// Syscalls returns an iterator over all wired syscalls.
+func Syscalls() iter.Seq2[string, SyscallNum] {
+	return func(yield func(string, SyscallNum) bool) {
+		for name, num := range syscallNum {
+			if !yield(name, num) {
+				return
+			}
+		}
+		for name, num := range syscallNumExtra {
+			if !yield(name, num) {
+				return
+			}
+		}
+	}
+}
+
+// SyscallResolveName resolves a syscall number from its string representation.
+func SyscallResolveName(name string) (num SyscallNum, ok bool) {
+	if num, ok = syscallNum[name]; ok {
+		return
+	}
+	num, ok = syscallNumExtra[name]
+	return
+}
+
+// MarshalJSON resolves the name of [Syscall] and encodes it as a [json] string.
+// If such a name does not exist, the syscall number is encoded instead.
+func (num *SyscallNum) MarshalJSON() ([]byte, error) {
+	n := *num
+	for name, cur := range Syscalls() {
+		if cur == n {
+			return json.Marshal(name)
+		}
+	}
+	return json.Marshal(n)
+}
+
+// SyscallNameError is returned when trying to unmarshal an invalid syscall name into [ScmpSyscall].
+type SyscallNameError string
+
+func (e SyscallNameError) Error() string {
+	return "invalid syscall name " + strconv.Quote(string(e))
+}
+
+// UnmarshalJSON looks up the syscall number corresponding to name encoded in data
+// by calling [SyscallResolveName].
+func (num *SyscallNum) UnmarshalJSON(data []byte) error {
+	var name string
+	if err := json.Unmarshal(data, &name); err != nil {
+		return err
+	}
+	if n, ok := SyscallResolveName(name); !ok {
+		return SyscallNameError(name)
+	} else {
+		*num = n
+		return nil
+	}
+}