internal/app/state/data: check full entry behaviour

This eventually gets relocated to internal/app.

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

1 files changed, 43 insertions, 0 deletions

diff --git a/internal/app/state/data.go b/internal/app/state/data.go
new file mode 100644
index 00000000..3c289f94
--- /dev/null
+++ b/internal/app/state/data.go
@@ -0,0 +1,43 @@
+package state
+
+import (
+	"encoding/gob"
+	"fmt"
+	"io"
+	"os"
+
+	"hakurei.app/hst"
+)
+
+// entryEncode encodes [hst.State] into [io.Writer] with the state entry header.
+// entryEncode does not validate the embedded [hst.Config] value.
+//
+// A non-nil error returned by entryEncode is of type [hst.AppError].
+func entryEncode(w io.Writer, s *hst.State) error {
+	if err := entryWriteHeader(w, s.Enablements.Unwrap()); err != nil {
+		return &hst.AppError{Step: "encode state header", Err: err}
+	} else if err = gob.NewEncoder(w).Encode(s); err != nil {
+		return &hst.AppError{Step: "encode state body", Err: err}
+	} else {
+		return nil
+	}
+}
+
+// entryDecode decodes [hst.State] from [io.Reader] and stores the result in the value pointed to by p.
+// entryDecode validates the embedded [hst.Config] value.
+//
+// A non-nil error returned by entryDecode is of type [hst.AppError].
+func entryDecode(r io.Reader, p *hst.State) error {
+	if et, err := entryReadHeader(r); err != nil {
+		return &hst.AppError{Step: "decode state header", Err: err}
+	} else if err = gob.NewDecoder(r).Decode(&p); err != nil {
+		return &hst.AppError{Step: "decode state body", Err: err}
+	} else if err = p.Config.Validate(); err != nil {
+		return err
+	} else if p.Enablements.Unwrap() != et {
+		return &hst.AppError{Step: "validate state enablement", Err: os.ErrInvalid,
+			Msg: fmt.Sprintf("state entry %s has unexpected enablement byte %#x, %#x", p.ID.String(), byte(p.Enablements.Unwrap()), byte(et))}
+	} else {
+		return nil
+	}
+}