feat(admin): add routed task evidence details

admin/internal/server/evidence.go

@@ -0,0 +1,193 @@
+package server
+
+import (
+	"errors"
+	"io"
+	"mime"
+	"mime/multipart"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+	"unicode/utf8"
+
+	"cmbuyer/admin/internal/evidence"
+
+	"github.com/gin-gonic/gin"
+)
+
+const (
+	maxEvidenceRequestBytes = evidence.MaxFileBytes + 64<<10
+	maxEvidenceFieldBytes   = 4 << 10
+)
+
+var evidenceFieldNames = map[string]struct{}{
+	"upload_key": {}, "attempt_id": {}, "kind": {}, "privacy_tier": {}, "sha256": {}, "captured_at": {},
+}
+
+func uploadEvidence(options Options) gin.HandlerFunc {
+	return func(context *gin.Context) {
+		// Authentication deliberately precedes content-type parsing and every body read. A rejected
+		// device must not make the service spool or inspect a potentially sensitive upload.
+		principal, authenticated := options.DeviceAuthenticator.Authenticate(context.Request)
+		if !authenticated {
+			context.Status(http.StatusUnauthorized)
+			return
+		}
+
+		boundary, ok := multipartBoundary(context.GetHeader("Content-Type"))
+		if !ok {
+			context.Status(http.StatusUnsupportedMediaType)
+			return
+		}
+		context.Request.Body = http.MaxBytesReader(context.Writer, context.Request.Body, maxEvidenceRequestBytes)
+		reader := multipart.NewReader(context.Request.Body, boundary)
+		fields := make(map[string]string, len(evidenceFieldNames))
+		var staged evidence.StagedFile
+		hasFile := false
+		discard := func() {
+			if hasFile {
+				options.Evidence.Discard(staged)
+			}
+		}
+
+		for {
+			part, err := reader.NextPart()
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			if err != nil {
+				discard()
+				writeMultipartError(context, err)
+				return
+			}
+			name := part.FormName()
+			if name == "file" {
+				if hasFile || part.FileName() == "" || !exactPNGContentType(part.Header.Get("Content-Type")) {
+					_ = part.Close()
+					discard()
+					context.Status(http.StatusUnsupportedMediaType)
+					return
+				}
+				staged, err = options.Evidence.Stage(part, evidence.PNGContentType)
+				_ = part.Close()
+				if err != nil {
+					writeEvidenceStoreError(context, err)
+					return
+				}
+				hasFile = true
+				continue
+			}
+			if _, allowed := evidenceFieldNames[name]; !allowed || part.FileName() != "" {
+				_ = part.Close()
+				discard()
+				context.Status(http.StatusBadRequest)
+				return
+			}
+			if _, duplicate := fields[name]; duplicate {
+				_ = part.Close()
+				discard()
+				context.Status(http.StatusBadRequest)
+				return
+			}
+			value, err := io.ReadAll(io.LimitReader(part, maxEvidenceFieldBytes+1))
+			_ = part.Close()
+			if err != nil || len(value) == 0 || len(value) > maxEvidenceFieldBytes || !utf8.Valid(value) {
+				discard()
+				context.Status(http.StatusBadRequest)
+				return
+			}
+			fields[name] = string(value)
+		}
+		if !hasFile || len(fields) != len(evidenceFieldNames) {
+			discard()
+			context.Status(http.StatusBadRequest)
+			return
+		}
+		captured, err := time.Parse(time.RFC3339Nano, fields["captured_at"])
+		if err != nil || !strings.HasSuffix(fields["captured_at"], "Z") {
+			discard()
+			context.Status(http.StatusBadRequest)
+			return
+		}
+		asset, replayed, err := options.Evidence.Commit(context.Request.Context(), principal, evidence.UploadMetadata{
+			UploadKey: fields["upload_key"], TaskID: context.Param("id"), AttemptID: fields["attempt_id"],
+			Kind: fields["kind"], PrivacyTier: fields["privacy_tier"], SHA256: fields["sha256"], CapturedAt: captured.UTC(),
+		}, staged)
+		if err != nil {
+			writeEvidenceStoreError(context, err)
+			return
+		}
+		status := http.StatusCreated
+		if replayed {
+			status = http.StatusOK
+		}
+		context.JSON(status, asset)
+	}
+}
+
+func readEvidence(options Options) gin.HandlerFunc {
+	return func(context *gin.Context) {
+		if !options.Sessions.IsAuthenticated(context.Request) {
+			context.Status(http.StatusUnauthorized)
+			return
+		}
+		asset, file, err := options.Evidence.Open(context.Request.Context(), context.Param("asset_id"))
+		if errors.Is(err, evidence.ErrNotFound) {
+			context.Status(http.StatusNotFound)
+			return
+		}
+		if err != nil {
+			context.Status(http.StatusInternalServerError)
+			return
+		}
+		defer file.Close()
+		context.Header("Content-Type", evidence.PNGContentType)
+		context.Header("Content-Length", strconv.FormatInt(asset.ByteSize, 10))
+		context.Header("Content-Disposition", `inline; filename="evidence.png"`)
+		context.Header("Cache-Control", "no-store")
+		context.Header("X-Content-Type-Options", "nosniff")
+		context.Status(http.StatusOK)
+		if _, err := io.Copy(context.Writer, file); err != nil {
+			_ = context.Error(err)
+		}
+	}
+}
+
+func multipartBoundary(value string) (string, bool) {
+	mediaType, parameters, err := mime.ParseMediaType(value)
+	if err != nil || mediaType != "multipart/form-data" || len(parameters) != 1 || parameters["boundary"] == "" {
+		return "", false
+	}
+	return parameters["boundary"], true
+}
+
+func exactPNGContentType(value string) bool {
+	mediaType, parameters, err := mime.ParseMediaType(value)
+	return err == nil && mediaType == evidence.PNGContentType && len(parameters) == 0
+}
+
+func writeMultipartError(context *gin.Context, err error) {
+	var tooLarge *http.MaxBytesError
+	if errors.As(err, &tooLarge) {
+		context.Status(http.StatusRequestEntityTooLarge)
+		return
+	}
+	context.Status(http.StatusBadRequest)
+}
+
+func writeEvidenceStoreError(context *gin.Context, err error) {
+	var tooLarge *http.MaxBytesError
+	switch {
+	case errors.As(err, &tooLarge):
+		context.Status(http.StatusRequestEntityTooLarge)
+	case errors.Is(err, evidence.ErrTooLarge):
+		context.Status(http.StatusRequestEntityTooLarge)
+	case errors.Is(err, evidence.ErrInvalid):
+		context.Status(http.StatusBadRequest)
+	case errors.Is(err, evidence.ErrConflict):
+		context.Status(http.StatusConflict)
+	default:
+		context.Status(http.StatusInternalServerError)
+	}
+}