Method getOCCValue

rest/doc_api.go:354–413

getOCCValue retrieves the optimistic concurrency control value for a document (Revision ID or CV) from several possible sources: - Query parameter "rev" - If-Match header - Body field "_rev" or "_cv" (if the body is provided in the request) It also validates that the provided OCC value exactly match

(optionalBody db.Body)

// - Body field "_rev" or "_cv" (if the body is provided in the request)
// It also validates that the provided OCC value exactly matches the corresponding body field if it exists in multiple places.
func (h *handler) getOCCValue(optionalBody db.Body) (occValue string, occValueType occVersionType, err error) {
	// skipBodyMatchValidation can skip the validation of the occValue inside the body, since in some cases we're pulling that value out of the body anyway.
	var skipBodyMatchValidation bool

	// occValue is the optimistic concurrency control value, which can be either the current rev ID or CV - used to prevent lost updates.
	// we grab occValue from either query param, Etag header, or request body (in that order)
	if revQuery := h.getQuery("rev"); revQuery != "" {
		occValue = revQuery
		// try to detect occ Values that are not URL Query escaped
		//   - `+` which can appear in base64 strings is converted to a space when not escaped properly
		// other characters are difficult to correctly detect, since the value is already unescaped
		if strings.ContainsAny(occValue, " ") {
			return "", 0, base.HTTPErrorf(http.StatusBadRequest, "Bad rev query parameter: %q - ensure this query parameter value is URL Encoded", occValue)
		}
		occValueType = guessOCCVersionTypeFromValue(occValue)
	} else if ifMatch, err := h.getEtag("If-Match"); err != nil {
		return "", 0, err
	} else if ifMatch != "" {
		occValue = ifMatch
		occValueType = guessOCCVersionTypeFromValue(occValue)
	} else if bodyCV, ok := optionalBody[db.BodyCV]; ok {
		if bodyCVStr, ok := bodyCV.(string); ok {
			occValue = bodyCVStr
			occValueType = VersionTypeCV
			skipBodyMatchValidation = true
		}
	} else if bodyRev, ok := optionalBody[db.BodyRev]; ok {
		if bodyRevStr, ok := bodyRev.(string); ok {
			occValue = bodyRevStr
			occValueType = VersionTypeRevTreeID
			skipBodyMatchValidation = true
		}
	} else {
		// empty occValue - treat as a create operation without any parent
		return "", VersionTypeRevTreeID, nil
	}

	// defensive measure against falling out of above without a type set
	if occValueType == VersionTypeUnknown {
		return "", 0, base.HTTPErrorf(http.StatusBadRequest, "Invalid version type for OCC value: %q", occValue)
	}

	// ensure the value provided matches exactly the one that may also be supplied in the body
	if !skipBodyMatchValidation {
		switch occValueType {
		case VersionTypeRevTreeID:
			if optionalBody[db.BodyRev] != nil && occValue != optionalBody[db.BodyRev] {
				return "", 0, base.HTTPErrorf(http.StatusBadRequest, "Revision IDs provided do not match")
			}
		case VersionTypeCV:
			if optionalBody[db.BodyCV] != nil && occValue != optionalBody[db.BodyCV] {
				return "", 0, base.HTTPErrorf(http.StatusBadRequest, "CVs provided do not match")
			}
		default:
			return "", 0, base.HTTPErrorf(http.StatusBadRequest, "Unknown version type provided: %q", occValue)
		}
	}