internal/params: relocate from package container

This does not make sense as part of the public API, so make it internal.

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

2 files changed, 173 insertions, 0 deletions

diff --git a/internal/params/params.go b/internal/params/params.go
new file mode 100644
index 00000000..6f1962af
--- /dev/null
+++ b/internal/params/params.go
@@ -0,0 +1,42 @@
+// Package params provides helpers for receiving setup payload from parent.
+package params
+
+import (
+	"encoding/gob"
+	"errors"
+	"os"
+	"strconv"
+	"syscall"
+)
+
+// ErrReceiveEnv is returned by [Receive] if setup fd is not present in environment.
+var ErrReceiveEnv = errors.New("environment variable not set")
+
+// Receive retrieves setup fd from the environment and receives params.
+//
+// The file descriptor written to the value pointed to by fdp must not be passed
+// to any system calls. It is made available for ordering file descriptor only.
+func Receive(key string, v any, fdp *int) (func() error, error) {
+	var setup *os.File
+
+	if s, ok := os.LookupEnv(key); !ok {
+		return nil, ErrReceiveEnv
+	} else {
+		if fd, err := strconv.Atoi(s); err != nil {
+			if _err := errors.Unwrap(err); _err != nil {
+				err = _err
+			}
+			return nil, err
+		} else {
+			setup = os.NewFile(uintptr(fd), "setup")
+			if setup == nil {
+				return nil, syscall.EDOM
+			}
+			if fdp != nil {
+				*fdp = fd
+			}
+		}
+	}
+
+	return setup.Close, gob.NewDecoder(setup).Decode(v)
+}
diff --git a/internal/params/params_test.go b/internal/params/params_test.go
new file mode 100644
index 00000000..86c165b8
--- /dev/null
+++ b/internal/params/params_test.go
@@ -0,0 +1,131 @@
+package params_test
+
+import (
+	"encoding/gob"
+	"errors"
+	"os"
+	"slices"
+	"strconv"
+	"syscall"
+	"testing"
+
+	"hakurei.app/internal/params"
+)
+
+func TestSetupReceive(t *testing.T) {
+	t.Run("not set", func(t *testing.T) {
+		const key = "TEST_ENV_NOT_SET"
+		{
+			v, ok := os.LookupEnv(key)
+			t.Cleanup(func() {
+				if ok {
+					if err := os.Setenv(key, v); err != nil {
+						t.Fatalf("Setenv: error = %v", err)
+					}
+				} else {
+					if err := os.Unsetenv(key); err != nil {
+						t.Fatalf("Unsetenv: error = %v", err)
+					}
+				}
+			})
+		}
+
+		if _, err := params.Receive(key, nil, nil); !errors.Is(err, params.ErrReceiveEnv) {
+			t.Errorf("Receive: error = %v, want %v", err, params.ErrReceiveEnv)
+		}
+	})
+
+	t.Run("format", func(t *testing.T) {
+		const key = "TEST_ENV_FORMAT"
+		t.Setenv(key, "")
+
+		if _, err := params.Receive(key, nil, nil); !errors.Is(err, strconv.ErrSyntax) {
+			t.Errorf("Receive: error = %v, want %v", err, strconv.ErrSyntax)
+		}
+	})
+
+	t.Run("range", func(t *testing.T) {
+		const key = "TEST_ENV_RANGE"
+		t.Setenv(key, "-1")
+
+		if _, err := params.Receive(key, nil, nil); !errors.Is(err, syscall.EDOM) {
+			t.Errorf("Receive: error = %v, want %v", err, syscall.EDOM)
+		}
+	})
+
+	t.Run("setup receive", func(t *testing.T) {
+		check := func(t *testing.T, useNilFdp bool) {
+			const key = "TEST_SETUP_RECEIVE"
+			payload := []uint64{syscall.MS_MGC_VAL, syscall.MS_MGC_MSK, syscall.MS_ASYNC, syscall.MS_ACTIVE}
+
+			encoderDone := make(chan error, 1)
+			extraFiles := make([]*os.File, 0, 1)
+			if r, w, err := os.Pipe(); err != nil {
+				t.Fatalf("Setup: error = %v", err)
+			} else {
+				t.Cleanup(func() {
+					if err = errors.Join(r.Close(), w.Close()); err != nil {
+						t.Fatal(err)
+					}
+				})
+
+				extraFiles = append(extraFiles, r)
+				if deadline, ok := t.Deadline(); ok {
+					if err = w.SetDeadline(deadline); err != nil {
+						t.Fatal(err)
+					}
+				}
+				go func() { encoderDone <- gob.NewEncoder(w).Encode(payload) }()
+			}
+
+			if len(extraFiles) != 1 {
+				t.Fatalf("extraFiles: len = %v, want 1", len(extraFiles))
+			}
+
+			var dupFd int
+			if fd, err := syscall.Dup(int(extraFiles[0].Fd())); err != nil {
+				t.Fatalf("Dup: error = %v", err)
+			} else {
+				syscall.CloseOnExec(fd)
+				dupFd = fd
+				t.Setenv(key, strconv.Itoa(fd))
+			}
+
+			var (
+				gotPayload []uint64
+				fdp        *int
+			)
+			if !useNilFdp {
+				fdp = new(int)
+			}
+			var closeFile func() error
+			if f, err := params.Receive(key, &gotPayload, fdp); err != nil {
+				t.Fatalf("Receive: error = %v", err)
+			} else {
+				closeFile = f
+
+				if !slices.Equal(payload, gotPayload) {
+					t.Errorf("Receive: %#v, want %#v", gotPayload, payload)
+				}
+			}
+			if !useNilFdp {
+				if *fdp != dupFd {
+					t.Errorf("Fd: %d, want %d", *fdp, dupFd)
+				}
+			}
+
+			if err := <-encoderDone; err != nil {
+				t.Errorf("Encode: error = %v", err)
+			}
+
+			if closeFile != nil {
+				if err := closeFile(); err != nil {
+					t.Errorf("Close: error = %v", err)
+				}
+			}
+		}
+
+		t.Run("fp", func(t *testing.T) { check(t, false) })
+		t.Run("nil", func(t *testing.T) { check(t, true) })
+	})
+}