Default a scheme-less s3.* endpoint to TLS (closes #158)

With the s3.* config form and an endpoint written without a scheme,
use_ssl being omitted built an http:// endpoint, while config.example.yml
documented use_ssl as defaulting to true. Over plain HTTP a network
observer sees manifests, object names, sizes and the access key id, and
can alter responses.

use_ssl is now *bool: omitted (nil) means the default, TLS; only an
explicit use_ssl: false forces plain HTTP. This matches the s3:// URL
form, which already defaults to TLS. The config init template dropped its
misleading use_ssl line from the s3:// block (that key is never read for
URLs; ?ssl=false controls TLS there) and points at ?ssl=false instead.

Model: opus-4-8

internal/cli/config.go

@@ -192,8 +192,8 @@ storage_url: ""
 #   access_key_id: YOUR_ACCESS_KEY
 #   secret_access_key: YOUR_SECRET_KEY
 #   # region: us-east-1        # Default: us-east-1
-#   # use_ssl: true            # Default: true
 #   # part_size: 5MB           # Multipart upload part size. Default: 5MB
+#   # For the s3:// form, disable TLS with ?ssl=false in the URL, not use_ssl.
 
 # ─── OPTIONAL ────────────────────────────────────────────────────────────────
 

internal/config/config.go

@@ -162,8 +162,10 @@ type S3Config struct {
 	AccessKeyID     string `yaml:"access_key_id"`
 	SecretAccessKey string `yaml:"secret_access_key"`
 	Region          string `yaml:"region"`
-	UseSSL          bool   `yaml:"use_ssl"`
-	PartSize        Size   `yaml:"part_size"`
+	// UseSSL selects HTTPS for a scheme-less endpoint. Omitted (nil) means
+	// the default, TLS; set it to false only to force plain HTTP.
+	UseSSL   *bool `yaml:"use_ssl"`
+	PartSize Size  `yaml:"part_size"`
 }
 
 // Path wraps the config file path for fx dependency injection.

internal/storage/module.go

@@ -111,10 +111,11 @@ func storerFromParsedS3URL(parsed *URL, cfg *config.Config) (Storer, error) {
 func storerFromLegacyS3Config(cfg *config.Config) (Storer, error) {
 	endpoint := cfg.S3.Endpoint
 
-	// Ensure protocol is present
+	// Ensure protocol is present. Absent an explicit use_ssl, default to TLS;
+	// plain HTTP only when use_ssl is written as false.
 	if !strings.HasPrefix(endpoint, "http://") &&
 		!strings.HasPrefix(endpoint, "https://") {
-		if cfg.S3.UseSSL {
+		if cfg.S3.UseSSL == nil || *cfg.S3.UseSSL {
 			endpoint = "https://" + endpoint
 		} else {
 			endpoint = "http://" + endpoint

internal/storage/module_test.go

@@ -0,0 +1,61 @@
+package storage_test
+
+import (
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/vaultik/internal/config"
+	"sneak.berlin/go/vaultik/internal/storage"
+)
+
+// legacyS3Config returns a minimal s3.* (no storage_url) configuration with a
+// scheme-less endpoint. useSSL mirrors the config file: nil means the key is
+// omitted, a pointer means it was written explicitly.
+func legacyS3Config(useSSL *bool) *config.Config {
+	return &config.Config{
+		S3: config.S3Config{
+			Endpoint:        "s3.example.com",
+			Bucket:          "bucket",
+			AccessKeyID:     "key",
+			SecretAccessKey: "secret",
+			Region:          "us-east-1",
+			UseSSL:          useSSL,
+		},
+	}
+}
+
+// endpointScheme builds the storer from cfg and returns the scheme its
+// resolved endpoint carries (Info().Location is "endpoint/bucket").
+func endpointScheme(t *testing.T, cfg *config.Config) string {
+	t.Helper()
+
+	storer, err := storage.NewStorer(cfg)
+	if err != nil {
+		t.Fatalf("NewStorer: %v", err)
+	}
+
+	location := storer.Info().Location
+	switch {
+	case strings.HasPrefix(location, "https://"):
+		return "https"
+	case strings.HasPrefix(location, "http://"):
+		return "http"
+	default:
+		t.Fatalf("endpoint has no http(s) scheme: %q", location)
+
+		return ""
+	}
+}
+
+func TestLegacyS3SchemelessEndpointDefaultsToTLS(t *testing.T) {
+	t.Parallel()
+
+	if got := endpointScheme(t, legacyS3Config(nil)); got != "https" {
+		t.Errorf("use_ssl omitted: got %q scheme, want https", got)
+	}
+
+	no := false
+	if got := endpointScheme(t, legacyS3Config(&no)); got != "http" {
+		t.Errorf("use_ssl: false: got %q scheme, want http", got)
+	}
+}