container: move out of toplevel

This allows slightly easier use of the vanity url. This also provides some disambiguation between low level containers and hakurei app containers.

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

container/params.go

@@ -0,0 +1,47 @@
+package container
+
+import (
+	"encoding/gob"
+	"errors"
+	"os"
+	"strconv"
+)
+
+var (
+	ErrNotSet  = errors.New("environment variable not set")
+	ErrInvalid = errors.New("bad file descriptor")
+)
+
+// Setup appends the read end of a pipe for setup params transmission and returns its fd.
+func Setup(extraFiles *[]*os.File) (int, *gob.Encoder, error) {
+	if r, w, err := os.Pipe(); err != nil {
+		return -1, nil, err
+	} else {
+		fd := 3 + len(*extraFiles)
+		*extraFiles = append(*extraFiles, r)
+		return fd, gob.NewEncoder(w), nil
+	}
+}
+
+// Receive retrieves setup fd from the environment and receives params.
+func Receive(key string, e any, v **os.File) (func() error, error) {
+	var setup *os.File
+
+	if s, ok := os.LookupEnv(key); !ok {
+		return nil, ErrNotSet
+	} else {
+		if fd, err := strconv.Atoi(s); err != nil {
+			return nil, err
+		} else {
+			setup = os.NewFile(uintptr(fd), "setup")
+			if setup == nil {
+				return nil, ErrInvalid
+			}
+			if v != nil {
+				*v = setup
+			}
+		}
+	}
+
+	return setup.Close, gob.NewDecoder(setup).Decode(e)
+}