Complete artifact binary transfer streaming

platform/service/artifact_download.go

@@ -3,6 +3,7 @@ package service
 import (
 	"errors"
 	"fmt"
+	"io"
 	"net/url"
 	"sort"
 	"strings"
@@ -16,6 +17,11 @@ import (
 const artifactDownloadStorageBehavior = "platform-durable-artifact-store"
 const artifactPayloadCacheLimit = 4 * 1024 * 1024
 
+type ArtifactContentStream struct {
+	Content domain.ArtifactContent
+	Body    io.ReadCloser
+}
+
 func (svc *CoreService) GetArtifactForSession(sessionID string, artifactID string) (domain.Artifact, error) {
 	artifact, err := svc.store.Artifacts().Get(strings.TrimSpace(artifactID))
 	if err != nil {
@@ -74,22 +80,11 @@ func (svc *CoreService) ReadArtifactContentForSession(sessionID string, request
 	if artifact.State != domain.ArtifactStateAvailable {
 		return domain.ArtifactContent{}, validationError("artifact must be available before download")
 	}
-	limit := request.Limit
-	if limit == 0 {
-		if request.Offset == 0 {
-			limit = int(artifact.SizeBytes)
-		} else {
-			limit = validator.MaxArtifactDownloadBytes
-		}
+	offset, length, partial, err := artifactContentBounds(artifact, request)
+	if err != nil {
+		return domain.ArtifactContent{}, err
 	}
-	if request.Offset > artifact.SizeBytes {
-		return domain.ArtifactContent{}, validationError("artifact range exceeds metadata")
-	}
-	remaining := artifact.SizeBytes - request.Offset
-	if int64(limit) > remaining {
-		limit = int(remaining)
-	}
-	payload, err := svc.artifactStore.ReadPayloadRange(artifact.ID, request.Offset, limit)
+	payload, err := svc.artifactStore.ReadPayloadRange(artifact.ID, offset, int(length))
 	if err != nil {
 		return domain.ArtifactContent{}, err
 	}
@@ -99,12 +94,12 @@ func (svc *CoreService) ReadArtifactContentForSession(sessionID string, request
 		ArtifactID:      artifact.ID,
 		Filename:        filename,
 		ContentType:     contentType,
-		Offset:          request.Offset,
+		Offset:          offset,
 		SizeBytes:       int64(len(part)),
 		TotalSizeBytes:  artifact.SizeBytes,
 		Checksum:        artifact.Checksum,
 		ContentChecksum: validator.BytesChecksum(part),
-		Partial:         request.Offset != 0 || int64(len(part)) != artifact.SizeBytes,
+		Partial:         partial,
 		RangeSupported:  true,
 		Payload:         part,
 		StorageBehavior: artifactDownloadStorageBehavior,
@@ -116,6 +111,66 @@ func (svc *CoreService) ReadArtifactContentForSession(sessionID string, request
 	return domain.CopyArtifactContent(content), nil
 }
 
+func (svc *CoreService) OpenArtifactContentStreamForSession(sessionID string, request domain.ArtifactContentRequest) (ArtifactContentStream, error) {
+	request = domain.CopyArtifactContentRequest(request)
+	if err := validator.ValidateArtifactContentRequest(request); err != nil {
+		return ArtifactContentStream{}, err
+	}
+	artifact, err := svc.GetArtifactForSession(sessionID, request.ArtifactID)
+	if err != nil {
+		return ArtifactContentStream{}, err
+	}
+	if artifact.State != domain.ArtifactStateAvailable {
+		return ArtifactContentStream{}, validationError("artifact must be available before download")
+	}
+	offset, length, partial, err := artifactContentBounds(artifact, request)
+	if err != nil {
+		return ArtifactContentStream{}, err
+	}
+	contentChecksum := artifact.Checksum
+	if partial {
+		payload, err := svc.artifactStore.ReadPayloadRange(artifact.ID, offset, int(length))
+		if err != nil {
+			return ArtifactContentStream{}, err
+		}
+		contentChecksum = validator.BytesChecksum(payload)
+	}
+	reader, err := svc.artifactStore.OpenPayloadRange(artifact.ID, offset, length)
+	if err != nil {
+		return ArtifactContentStream{}, err
+	}
+	filename, contentType := svc.artifactDownloadPresentation(artifact)
+	content := domain.ArtifactContent{ArtifactID: artifact.ID, Filename: filename, ContentType: contentType, Offset: offset, SizeBytes: length, TotalSizeBytes: artifact.SizeBytes, Checksum: artifact.Checksum, ContentChecksum: contentChecksum, Partial: partial, RangeSupported: true, StorageBehavior: artifactDownloadStorageBehavior, ServedAt: svc.now()}
+	if err := validator.ValidateArtifactContent(content); err != nil {
+		_ = reader.Close()
+		return ArtifactContentStream{}, err
+	}
+	return ArtifactContentStream{Content: domain.CopyArtifactContent(content), Body: reader}, nil
+}
+
+func artifactContentBounds(artifact domain.Artifact, request domain.ArtifactContentRequest) (int64, int64, bool, error) {
+	if request.Offset > artifact.SizeBytes {
+		return 0, 0, false, validationError("artifact range exceeds metadata")
+	}
+	length := int64(request.Limit)
+	if request.Limit == 0 {
+		if request.Offset == 0 {
+			length = artifact.SizeBytes
+		} else {
+			length = int64(validator.MaxArtifactDownloadBytes)
+		}
+	}
+	remaining := artifact.SizeBytes - request.Offset
+	if length > remaining {
+		length = remaining
+	}
+	if length <= 0 {
+		return 0, 0, false, validationError("artifact range is empty")
+	}
+	partial := request.Offset != 0 || length != artifact.SizeBytes
+	return request.Offset, length, partial, nil
+}
+
 func (svc *CoreService) authorizeArtifactAccess(sessionID string, artifact domain.Artifact) error {
 	user, err := svc.GetCurrentUser(sessionID)
 	if err != nil {