engine: secretsCommand via HostExecutor (closes #23)

config/raw.go

@@ -47,6 +47,7 @@ type rawConfig struct {
 	OverrideFeatureInstallOrder []string                   `json:"overrideFeatureInstallOrder,omitempty"`
 
 	InitializeCommand    json.RawMessage `json:"initializeCommand,omitempty"`
+	SecretsCommand       json.RawMessage `json:"secretsCommand,omitempty"`
 	OnCreateCommand      json.RawMessage `json:"onCreateCommand,omitempty"`
 	UpdateContentCommand json.RawMessage `json:"updateContentCommand,omitempty"`
 	PostCreateCommand    json.RawMessage `json:"postCreateCommand,omitempty"`

config/resolve.go

@@ -130,6 +130,12 @@ func resolveFromRaw(raw *rawConfig, input ResolveInput) (*ResolvedConfig, error)
 	out.Lifecycle = lifecycle
 	out.Warnings = append(out.Warnings, addSource(lcWarns, input.ConfigPath)...)
 
+	secretsCmd, err := decodeLifecycleCommand(raw.SecretsCommand)
+	if err != nil {
+		return nil, &ConfigInvalidError{Path: input.ConfigPath, Message: fmt.Sprintf("/secretsCommand: %v", err)}
+	}
+	out.SecretsCommand = secretsCmd
+
 	// WaitFor passes through verbatim; the spec default (postCreate, or
 	// updateContent if any layer contributes one) is applied by Finalize
 	// after the metadata-merge pipeline.
@@ -490,6 +496,7 @@ func substituteAll(out *ResolvedConfig, ctx SubstitutionContext, source string)
 	}
 
 	substituteLifecycle(&out.Lifecycle, subStr)
+	substituteCommand(&out.SecretsCommand, "/secretsCommand", subStr)
 
 	switch s := out.Source.(type) {
 	case *ImageSource:

config/resolved.go

@@ -40,6 +40,15 @@ type ResolvedConfig struct {
 	Lifecycle LifecycleCommands
 	WaitFor   LifecyclePhase
 
+	// SecretsCommand is a host-side hook that runs before container start
+	// (analogous to initializeCommand) and whose stdout is parsed as
+	// key=value lines and merged into the container's environment. Unlike
+	// the lifecycle phases, it is not contributed by feature/base-image
+	// metadata layers — only the user's devcontainer.json sources it —
+	// so it is a single LifecycleCommand rather than a slice. Empty
+	// when devcontainer.json has no `secretsCommand`.
+	SecretsCommand LifecycleCommand
+
 	ForwardPorts         []PortSpec
 	PortsAttributes      map[string]PortAttributes
 	OtherPortsAttributes *PortAttributes

secrets.go

@@ -0,0 +1,166 @@
+package devcontainer
+
+import (
+	"context"
+	"sort"
+	"strings"
+
+	"github.com/crunchloop/devcontainer/config"
+)
+
+// collectSecretsEnv merges UpOptions.ExtraContainerEnv with any
+// secretsCommand output and returns the result for use as
+// `extraEnv` in buildRunSpec / compose overrides. Caller-supplied
+// ExtraContainerEnv wins on key collision (explicit caller intent
+// trumps spec hooks). Returns nil when neither source contributes.
+//
+// Returns (nil, *LifecycleError) if RunSecretsCommand was requested
+// but the executor is missing or the host command failed.
+func (e *Engine) collectSecretsEnv(ctx context.Context, cfg *config.ResolvedConfig, opts UpOptions) (map[string]string, error) {
+	if !opts.RunSecretsCommand {
+		return opts.ExtraContainerEnv, nil
+	}
+	secrets, err := e.runSecretsCommand(ctx, cfg)
+	if err != nil {
+		return nil, err
+	}
+	if len(secrets) == 0 {
+		return opts.ExtraContainerEnv, nil
+	}
+	if len(opts.ExtraContainerEnv) == 0 {
+		return secrets, nil
+	}
+	out := make(map[string]string, len(secrets)+len(opts.ExtraContainerEnv))
+	for k, v := range secrets {
+		out[k] = v
+	}
+	for k, v := range opts.ExtraContainerEnv {
+		out[k] = v
+	}
+	return out, nil
+}
+
+// runSecretsCommand executes the host-side secretsCommand via the
+// engine's HostExecutor and returns its parsed key=value stdout as an
+// env map. Returns (nil, nil) when no secretsCommand is configured.
+//
+// secretsCommand is conceptually parallel to initializeCommand:
+// host-side, security-sensitive, opt-in. Where initializeCommand is
+// fire-and-forget (exit code only), secretsCommand exists specifically
+// to capture stdout and inject it into the container's environment
+// before container start.
+//
+// On non-zero host exit we return a *LifecycleError so callers can
+// surface stderr and the exit code via the same error shape used by
+// initializeCommand failures. The phase tag is "secretsCommand"
+// (synthetic — not a real LifecyclePhase, since it isn't an
+// in-container phase and has no marker).
+func (e *Engine) runSecretsCommand(ctx context.Context, cfg *config.ResolvedConfig) (map[string]string, error) {
+	if cfg.SecretsCommand.IsEmpty() {
+		return nil, nil
+	}
+	if e.opts.HostExecutor == nil {
+		return nil, &LifecycleError{
+			Phase: phaseSecretsCommand,
+			Cause: ErrHostExecutorNotConfigured,
+		}
+	}
+	if cfg.SecretsCommand.Single != nil {
+		return e.execSecretsHost(ctx, cfg, *cfg.SecretsCommand.Single)
+	}
+	// Parallel form: run each named command (sequentially, in name
+	// order) and merge results. Spec doesn't strictly bless parallel
+	// for secretsCommand, but the command shape is shared with
+	// initializeCommand so we accept it for symmetry. Duplicate keys
+	// are resolved last-write-wins by name order (lexicographic,
+	// matching execParallel's determinism).
+	names := make([]string, 0, len(cfg.SecretsCommand.Parallel))
+	for k := range cfg.SecretsCommand.Parallel {
+		names = append(names, k)
+	}
+	sort.Strings(names)
+	merged := map[string]string{}
+	for _, name := range names {
+		c := cfg.SecretsCommand.Parallel[name]
+		env, err := e.execSecretsHost(ctx, cfg, c)
+		if err != nil {
+			return nil, err
+		}
+		for k, v := range env {
+			merged[k] = v
+		}
+	}
+	if len(merged) == 0 {
+		return nil, nil
+	}
+	return merged, nil
+}
+
+func (e *Engine) execSecretsHost(ctx context.Context, cfg *config.ResolvedConfig, c config.Command) (map[string]string, error) {
+	res, err := e.opts.HostExecutor.ExecHost(ctx, HostCommand{
+		Shell:      c.Shell,
+		Exec:       c.Exec,
+		WorkingDir: cfg.LocalWorkspaceFolder,
+	})
+	if err != nil {
+		return nil, &LifecycleError{Phase: phaseSecretsCommand, Cause: err}
+	}
+	if res.ExitCode != 0 {
+		return nil, &LifecycleError{
+			Phase:    phaseSecretsCommand,
+			ExitCode: res.ExitCode,
+			Stdout:   res.Stdout,
+			Stderr:   res.Stderr,
+		}
+	}
+	return parseSecretsKV(res.Stdout), nil
+}
+
+// phaseSecretsCommand is the LifecycleError.Phase tag for
+// secretsCommand failures. Not a real lifecycle phase — used only so
+// callers can distinguish secretsCommand failures from
+// initializeCommand failures via errors.As + Phase.
+const phaseSecretsCommand config.LifecyclePhase = "secretsCommand"
+
+// parseSecretsKV parses a stdout stream of `KEY=VALUE` lines into a
+// map. Rules (intentionally narrow — secretsCommand stdout is
+// program-generated, not human-edited):
+//   - one entry per line
+//   - blank lines and lines starting with `#` (after leading
+//     whitespace) are ignored
+//   - leading/trailing whitespace around the key is trimmed; values
+//     are taken verbatim from after the first '=' (no quote
+//     stripping, no escape processing)
+//   - lines without `=`, or with an empty key after trimming, are
+//     skipped silently
+//
+// Deliberately no quote stripping or `\n` escape interpretation:
+// callers needing that should emit clean k=v from secretsCommand.
+// Doing magic here would silently mangle values that contain a
+// literal `"` or `\`.
+func parseSecretsKV(s string) map[string]string {
+	if s == "" {
+		return nil
+	}
+	out := map[string]string{}
+	for _, line := range strings.Split(s, "\n") {
+		line = strings.TrimSuffix(line, "\r")
+		trimmed := strings.TrimLeft(line, " \t")
+		if trimmed == "" || strings.HasPrefix(trimmed, "#") {
+			continue
+		}
+		i := strings.IndexByte(trimmed, '=')
+		if i <= 0 {
+			continue
+		}
+		key := strings.TrimRight(trimmed[:i], " \t")
+		if key == "" {
+			continue
+		}
+		out[key] = trimmed[i+1:]
+	}
+	if len(out) == 0 {
+		return nil
+	}
+	return out
+}