internal/pkg: write per-artifact logs

This is currently only used by execArtifact. A later patch will add additional logging facilities.

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

internal/pkg/pkg.go

@@ -28,15 +28,21 @@ import (
 	"unsafe"
 
 	"hakurei.app/container/check"
+	"hakurei.app/internal/info"
 	"hakurei.app/internal/lockedfile"
 	"hakurei.app/message"
 )
 
+const (
+	// programName is the string identifying this build system.
+	programName = "internal/pkg"
+)
+
 type (
 	// A Checksum is a SHA-384 checksum computed for a cured [Artifact].
 	Checksum = [sha512.Size384]byte
 
-	// An ID is a unique identifier returned by [Artifact.ID]. This value must
+	// An ID is a unique identifier returned by [KnownIdent.ID]. This value must
 	// be deterministically determined ahead of time.
 	ID Checksum
 )
@@ -81,20 +87,75 @@ type TContext struct {
 	// Populated during [Cache.Cure].
 	work, temp *check.Absolute
 
+	// Target [Artifact] encoded identifier.
+	ids string
+	// Pathname status was created at.
+	statusPath *check.Absolute
+	// File statusHeader and logs are written to.
+	status *os.File
+	// Error value during prepareStatus.
+	statusErr error
+
 	common
 }
 
+// statusHeader is the header written to all status files in dirStatus.
+var statusHeader = func() string {
+	s := programName
+	if v := info.Version(); v != info.FallbackVersion {
+		s += " " + v
+	}
+	s += " (" + runtime.GOARCH + ")"
+	if name, err := os.Hostname(); err == nil {
+		s += " on " + name
+	}
+	s += "\n\n"
+	return s
+}()
+
+// prepareStatus initialises the status file once.
+func (t *TContext) prepareStatus() error {
+	if t.statusPath != nil || t.status != nil {
+		return t.statusErr
+	}
+
+	t.statusPath = t.cache.base.Append(
+		dirStatus,
+		t.ids,
+	)
+	if t.status, t.statusErr = os.OpenFile(
+		t.statusPath.String(),
+		syscall.O_CREAT|syscall.O_EXCL|syscall.O_WRONLY,
+		0400,
+	); t.statusErr != nil {
+		return t.statusErr
+	}
+
+	_, t.statusErr = t.status.WriteString(statusHeader)
+	return t.statusErr
+}
+
+// GetStatusWriter returns a [io.Writer] for build logs. The caller must not
+// seek this writer before the position it was first returned in.
+func (t *TContext) GetStatusWriter() (io.Writer, error) {
+	err := t.prepareStatus()
+	return t.status, err
+}
+
 // destroy destroys the temporary directory and joins its errors with the error
 // referred to by errP. If the error referred to by errP is non-nil, the work
 // directory is removed similarly. [Cache] is responsible for making sure work
 // is never left behind for a successful [Cache.Cure].
 //
+// If implementation had requested status, it is closed with error joined with
+// the error referred to by errP. If the error referred to by errP is non-nil,
+// the status file is removed from the filesystem.
+//
 // destroy must be deferred by [Cache.Cure] if [TContext] is passed to any Cure
 // implementation. It should not be called prior to that point.
 func (t *TContext) destroy(errP *error) {
 	if chmodErr, removeErr := removeAll(t.temp); chmodErr != nil || removeErr != nil {
 		*errP = errors.Join(*errP, chmodErr, removeErr)
-		return
 	}
 
 	if *errP != nil {
@@ -106,6 +167,16 @@ func (t *TContext) destroy(errP *error) {
 			*errP = nil
 		}
 	}
+
+	if t.status != nil {
+		if err := t.status.Close(); err != nil {
+			*errP = errors.Join(*errP, err)
+		}
+		if *errP != nil {
+			*errP = errors.Join(*errP, os.Remove(t.statusPath.String()))
+		}
+		t.status = nil
+	}
 }
 
 // Unwrap returns the underlying [context.Context].
@@ -169,7 +240,7 @@ type FContext struct {
 }
 
 // InvalidLookupError is the identifier of non-dependency [Artifact] looked up
-// via [FContext.Pathname] by a misbehaving [Artifact] implementation.
+// via [FContext.GetArtifact] by a misbehaving [Artifact] implementation.
 type InvalidLookupError ID
 
 func (e InvalidLookupError) Error() string {
@@ -375,6 +446,9 @@ const (
 	// dirChecksum is the directory name appended to Cache.base for storing
 	// artifacts named after their [Checksum].
 	dirChecksum = "checksum"
+	// dirStatus is the directory name appended to Cache.base for storing
+	// artifact metadata and logs named after their [ID].
+	dirStatus = "status"
 
 	// dirWork is the directory name appended to Cache.base for working
 	// pathnames set up during [Cache.Cure].
@@ -943,8 +1017,9 @@ func (c *Cache) openFile(f FileArtifact) (r io.ReadCloser, err error) {
 		if !errors.Is(err, os.ErrNotExist) {
 			return
 		}
+		id := c.Ident(f)
 		if c.msg.IsVerbose() {
-			rn := reportName(f, c.Ident(f))
+			rn := reportName(f, id)
 			c.msg.Verbosef("curing %s in memory...", rn)
 			defer func() {
 				if err == nil {
@@ -1527,6 +1602,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 	t := TContext{
 		c.base.Append(dirWork, ids),
 		c.base.Append(dirTemp, ids),
+		ids, nil, nil, nil,
 		common{c},
 	}
 	switch ca := a.(type) {
@@ -1714,6 +1790,7 @@ func open(
 	for _, name := range []string{
 		dirIdentifier,
 		dirChecksum,
+		dirStatus,
 		dirWork,
 	} {
 		if err := os.MkdirAll(base.Append(name).String(), 0700); err != nil &&