Add safe artifact previews

coordinator/internal/usecase/preview.go

@@ -0,0 +1,146 @@
+package usecase
+
+import (
+	"context"
+	"encoding/csv"
+	"errors"
+	"io"
+	"mime"
+	"strings"
+
+	"github.com/google/uuid"
+
+	"github.com/emil28092005/SciMesh/coordinator/internal/domain"
+)
+
+// The preview is deliberately a diagnostic aid, never a full artifact
+// viewer. These limits bound both memory use and storage reads.
+const (
+	previewMaxRows  = 30
+	previewMaxBytes = 64 * 1024
+)
+
+// ArtifactPreviewView is the safe, bounded data rendered by the operator UI.
+// It deliberately contains neither storage keys nor worker-local details.
+type ArtifactPreviewView struct {
+	JobID       string
+	ArtifactID  string
+	Filename    string
+	Diagnostic  bool
+	Previewable bool
+	Reason      string
+	Headers     []string
+	Rows        [][]string
+	Truncated   bool
+	RowLimit    int
+	ByteLimit   int64
+}
+
+// PreviewArtifact reads the beginning of a job-scoped CSV result. Partial
+// results are diagnostic; a final result is available only after the reducer
+// has persisted it as this job's completed result.
+type PreviewArtifact struct {
+	read  UIReadRepository
+	blobs BlobStore
+}
+
+func NewPreviewArtifact(read UIReadRepository, blobs BlobStore) *PreviewArtifact {
+	return &PreviewArtifact{read: read, blobs: blobs}
+}
+
+func (p *PreviewArtifact) Execute(ctx context.Context, jobID, artifactID uuid.UUID) (ArtifactPreviewView, error) {
+	job, err := p.read.GetJob(ctx, jobID)
+	if err != nil {
+		return ArtifactPreviewView{}, err
+	}
+	artifacts, err := p.read.ListArtifactsByJob(ctx, jobID)
+	if err != nil {
+		return ArtifactPreviewView{}, err
+	}
+
+	var artifact *domain.Artifact
+	for i := range artifacts {
+		if artifacts[i].ID == artifactID {
+			artifact = &artifacts[i]
+			break
+		}
+	}
+	if artifact == nil || !previewableArtifact(*job, *artifact) {
+		// Use one response for an unknown artifact, another job's artifact, and
+		// an artifact that is not yet public. This avoids leaking its state.
+		return ArtifactPreviewView{}, domain.ErrArtifactNotFound
+	}
+
+	view := ArtifactPreviewView{
+		JobID:      jobID.String(),
+		ArtifactID: artifact.ID.String(),
+		Filename:   artifact.Filename,
+		Diagnostic: artifact.Kind == domain.ArtifactPartialResult,
+		RowLimit:   previewMaxRows,
+		ByteLimit:  previewMaxBytes,
+	}
+	if !isCSVArtifact(artifact) {
+		view.Reason = "This artifact is not a CSV file, so it cannot be shown as text here. Download it instead."
+		return view, nil
+	}
+	if artifact.SizeBytes == 0 {
+		view.Reason = "This artifact is empty."
+		return view, nil
+	}
+
+	body, err := p.blobs.Open(ctx, artifact.StorageKey)
+	if err != nil {
+		return ArtifactPreviewView{}, err
+	}
+	defer func() { _ = body.Close() }()
+
+	limited := &io.LimitedReader{R: body, N: previewMaxBytes}
+	reader := csv.NewReader(limited)
+	reader.FieldsPerRecord = -1 // a byte limit may end inside a record
+
+	headers, err := reader.Read()
+	if err != nil {
+		view.Reason = "This artifact could not be read as CSV."
+		return view, nil
+	}
+	view.Headers = append([]string(nil), headers...)
+	view.Rows = make([][]string, 0, previewMaxRows)
+	for len(view.Rows) < previewMaxRows {
+		record, readErr := reader.Read()
+		if readErr != nil {
+			if !errors.Is(readErr, io.EOF) {
+				view.Truncated = true
+			}
+			break
+		}
+		view.Rows = append(view.Rows, append([]string(nil), record...))
+	}
+
+	if artifact.SizeBytes > previewMaxBytes {
+		view.Truncated = true
+	} else if len(view.Rows) == previewMaxRows {
+		if _, readErr := reader.Read(); readErr == nil {
+			view.Truncated = true
+		}
+	}
+	view.Previewable = true
+	return view, nil
+}
+
+func previewableArtifact(job domain.Job, artifact domain.Artifact) bool {
+	if artifact.Kind == domain.ArtifactPartialResult {
+		return true
+	}
+	return artifact.Kind == domain.ArtifactFinalResult &&
+		job.Status == domain.JobCompleted &&
+		job.ResultArtifactID != nil &&
+		*job.ResultArtifactID == artifact.ID
+}
+
+func isCSVArtifact(artifact *domain.Artifact) bool {
+	mediaType, _, err := mime.ParseMediaType(artifact.ContentType)
+	if err == nil && strings.EqualFold(mediaType, "text/csv") {
+		return true
+	}
+	return strings.HasSuffix(strings.ToLower(artifact.Filename), ".csv")
+}