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
 )
@@ -70,6 +76,80 @@ type common struct {
 	// Address of underlying [Cache], should be zeroed or made unusable after
 	// Cure returns and must not be exposed directly.
 	cache *Cache
+
+	// 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
+}
+
+// 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 (c *common) prepareStatus() error {
+	if c.statusPath != nil || c.status != nil {
+		return c.statusErr
+	}
+
+	c.statusPath = c.cache.base.Append(
+		dirStatus,
+		c.ids,
+	)
+	if c.status, c.statusErr = os.OpenFile(
+		c.statusPath.String(),
+		syscall.O_CREAT|syscall.O_EXCL|syscall.O_WRONLY,
+		0400,
+	); c.statusErr != nil {
+		return c.statusErr
+	}
+
+	if _, c.statusErr = c.status.WriteString(statusHeader); c.statusErr != nil {
+		c.close(&c.statusErr)
+	}
+	return c.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 (c *common) GetStatusWriter() (io.Writer, error) {
+	err := c.prepareStatus()
+	return c.status, err
+}
+
+// close closes status and joins its errors 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.
+//
+// close must be deferred by [Cache.Cure] if common is passed to any Cure
+// implementation.
+func (c *common) close(errP *error) {
+	if c.status == nil {
+		return
+	}
+
+	if err := c.status.Close(); err != nil {
+		*errP = errors.Join(*errP, err)
+	}
+	if *errP != nil {
+		*errP = errors.Join(*errP, os.Remove(c.statusPath.String()))
+	}
+	c.status = nil
 }
 
 // TContext is passed to [TrivialArtifact.Cure] and provides information and
@@ -169,7 +249,7 @@ 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 +455,9 @@ 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 +1026,9 @@ 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 {
@@ -952,7 +1036,7 @@ func (c *Cache) openFile(f FileArtifact) (r io.ReadCloser, err error) {
 				}
 			}()
 		}
-		return f.Cure(&RContext{common{c}})
+		return f.Cure(&RContext{common{cache: c, ids: Encode(id.Value())}})
 	}
 	return
 }
@@ -1448,7 +1532,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 		if err = c.enterCure(a, curesExempt); err != nil {
 			return
 		}
-		r, err = f.Cure(&RContext{common{c}})
+		r, err = f.Cure(&RContext{common{cache: c, ids: ids}})
 		if err == nil {
 			if checksumPathname == nil || c.IsStrict() {
 				h := sha512.New384()
@@ -1527,7 +1611,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 	t := TContext{
 		c.base.Append(dirWork, ids),
 		c.base.Append(dirTemp, ids),
-		common{c},
+		common{cache: c, ids: ids},
 	}
 	switch ca := a.(type) {
 	case TrivialArtifact:
@@ -1714,6 +1798,7 @@ func open(
 	for _, name := range []string{
 		dirIdentifier,
 		dirChecksum,
+		dirStatus,
 		dirWork,
 	} {
 		if err := os.MkdirAll(base.Append(name).String(), 0700); err != nil &&