Consolidate the data directory mode into one owner (closes #288)

internal/datadir now owns the DATA_DIR mode as an exported constant,
DirPerm; internal/database consumes it in both places that create the
directory rather than keeping its own copy. datadir is the owner
because guarding and creating DATA_DIR is its whole purpose, and the
dependency runs the right way: datadir imports only the standard
library and the flock package, so database importing datadir adds no
cycle. A comment on DirPerm names it as the single source, chosen over
a source-scanning test because it survives refactoring and builds no
machinery that inspects the tree. The mode value is unchanged.

Model: opus-4-8

internal/database/database.go

@@ -17,12 +17,12 @@ import (
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/banner"
 	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/datadir"
 	"sneak.berlin/go/webhooker/internal/gormlog"
 	"sneak.berlin/go/webhooker/internal/logger"
 )
 
 const (
-	dataDirPerm       = 0750
 	randomPasswordLen = 16
 	sessionKeyLen     = 32
 )
@@ -185,7 +185,9 @@ func (d *Database) connect() error {
 // caller's decision.
 func (d *Database) connectTo(dataDir string) error {
 	// Ensure the data directory exists before opening the database.
-	err := os.MkdirAll(dataDir, dataDirPerm)
+	// datadir.DirPerm is the single source of the directory mode; this
+	// package creates the directory too, since either may run first.
+	err := os.MkdirAll(dataDir, datadir.DirPerm)
 	if err != nil {
 		return fmt.Errorf(
 			"creating data directory %s: %w",

internal/database/webhook_db_manager.go

@@ -13,6 +13,7 @@ import (
 	"gorm.io/driver/sqlite"
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/datadir"
 	"sneak.berlin/go/webhooker/internal/gormlog"
 	"sneak.berlin/go/webhooker/internal/logger"
 )
@@ -53,8 +54,9 @@ func NewWebhookDBManager(
 		log:     params.Logger.Get(),
 	}
 
-	// Create data directory if it doesn't exist
-	err := os.MkdirAll(m.dataDir, dataDirPerm)
+	// Create data directory if it doesn't exist. datadir.DirPerm is the
+	// single source of the directory mode; either package may run first.
+	err := os.MkdirAll(m.dataDir, datadir.DirPerm)
 	if err != nil {
 		return nil, fmt.Errorf(
 			"creating data directory %s: %w",

internal/datadir/lock.go

@@ -29,9 +29,11 @@ import (
 // process that was killed with SIGKILL blocks nothing.
 const LockFileName = "webhooker.lock"
 
-// dirPerm is the mode Acquire creates DATA_DIR with. It matches what
-// internal/database uses, since whichever runs first creates it.
-const dirPerm = 0o750
+// DirPerm is the mode DATA_DIR is created with. It is the single
+// source of that mode: internal/database consumes it rather than
+// keeping its own copy, so the two packages that both create the
+// directory cannot drift into disagreeing about its permissions.
+const DirPerm = 0o750
 
 // ErrLocked reports that another live process holds the data
 // directory. Callers that need to know whether a deployment is running
@@ -64,7 +66,7 @@ func Acquire(dir string) (*Lock, error) {
 		return nil, ErrNoDir
 	}
 
-	err := os.MkdirAll(dir, dirPerm)
+	err := os.MkdirAll(dir, DirPerm)
 	if err != nil {
 		return nil, fmt.Errorf(
 			"creating data directory %s: %w", dir, err,