contextmanager.go

package netdicom

import (
	"fmt"

	"github.com/msz-kp/go-dicom"
	"github.com/msz-kp/go-dicom/dicomlog"
	"github.com/msz-kp/go-dicom/dicomuid"
	"github.com/msz-kp/go-netdicom/pdu"
)

type contextManagerEntry struct {
	contextID         byte
	abstractSyntaxUID string
	transferSyntaxUID string
	result            pdu.PresentationContextResult // was this mapping accepted by the server?
}

// contextManager manages mappings between a contextID and the corresponding
// abstract-syntax UID (aka SOP).  UID is of form "1.2.840.10008.5.1.4.1.1.1.2".
// UIDs are static and global. They are defined in
// https://www.dicomlibrary.com/dicom/sop/.
//
// On the other hand, contextID is allocated anew during each association
// handshake.  ContextID values are 1, 3, 5, etc.  One contextManager is created
// per association.
type contextManager struct {
	label string // for diagnostics only.

	// The two maps are inverses of each other.
	contextIDToAbstractSyntaxNameMap map[byte]*contextManagerEntry
	abstractSyntaxNameToContextIDMap map[string]*contextManagerEntry

	// Info about the the other side of the communication, gleaned from
	// A-ASSOCIATE-* pdu.
	peerMaxPDUSize int
	// UID that identifies the peer type. It's supposed to be globally unique.
	peerImplementationClassUID string
	// Implementation version, virtually meaningless since its format isn't standardiszed.
	peerImplementationVersionName string

	// tmpRequests used only on the client (requestor) side. It holds the
	// contextid->presentationcontext mapping generated from the
	// A_ASSOCIATE_RQ PDU. Once an A_ASSOCIATE_AC PDU arrives, tmpRequests
	// is matched against the response PDU and
	// contextid->{abstractsyntax,transfersyntax} mappings are filled.
	tmpRequests map[byte]*pdu.PresentationContextItem
}

// Create an empty contextManager
func newContextManager(label string) *contextManager {
	c := &contextManager{
		label:                            label,
		contextIDToAbstractSyntaxNameMap: make(map[byte]*contextManagerEntry),
		abstractSyntaxNameToContextIDMap: make(map[string]*contextManagerEntry),
		peerMaxPDUSize:                   16384, // The default value used by Osirix & pynetdicom.
		tmpRequests:                      make(map[byte]*pdu.PresentationContextItem),
	}
	return c
}

// Pick the first matching transfer syntax UID appeares in allTransferSyntaxes
// - If one of the client proposed transfer syntaxes matches the server's preferred transfer syntax, then that transfer syntax is accepted.
// - If the client does not propose a transfer syntax that matches the server's preferred transfer syntax, the first transfer syntax in the client's list of proposed syntaxes is accepted.
// - If none of the proposed transfer syntaxes are supported, just pick the first preferred transfer syntax:
//   Implicit VR Little Endian Transfer Syntax (UID = "1.2.840.10008.1.2 "),
//   which shall be supported by every conformant DICOM Implementation.
func pickFirstPreferedTransferSyntax(proposedTransferSyntaxUIDs []string) string {
	for _, syntaxUID := range allTransferSyntaxes {
		for _, proposed := range proposedTransferSyntaxUIDs {
			if syntaxUID == proposed {
				return syntaxUID
			}
		}
	}
	return allTransferSyntaxes[0]
}

// Called by the user (client) to produce a list to be embedded in an
// A_REQUEST_RQ.Items. The PDU is sent when running as a service user (client).
// maxPDUSize is the maximum PDU size, in bytes, that the clients is willing to
// receive. maxPDUSize is encoded in one of the items.
func (m *contextManager) generateAssociateRequest(
	sopClassUIDs []string, transferSyntaxUIDs []string, maxPDUSize uint32) []pdu.SubItem {
	items := []pdu.SubItem{
		&pdu.ApplicationContextItem{
			Name: pdu.DICOMApplicationContextItemName,
		}}
	var contextID byte = 1
	for _, sop := range sopClassUIDs {
		syntaxItems := []pdu.SubItem{
			&pdu.AbstractSyntaxSubItem{Name: sop},
		}
		for _, syntaxUID := range transferSyntaxUIDs {
			syntaxItems = append(syntaxItems, &pdu.TransferSyntaxSubItem{Name: syntaxUID})
		}
		item := &pdu.PresentationContextItem{
			Type:      pdu.ItemTypePresentationContextRequest,
			ContextID: contextID,
			Result:    0, // must be zero for request
			Items:     syntaxItems,
		}
		items = append(items, item)
		m.tmpRequests[contextID] = item
		contextID += 2 // must be odd.
	}
	items = append(items,
		&pdu.UserInformationItem{
			Items: []pdu.SubItem{
				&pdu.UserInformationMaximumLengthItem{maxPDUSize},
				&pdu.ImplementationClassUIDSubItem{dicom.GoDICOMImplementationClassUID},
				&pdu.ImplementationVersionNameSubItem{dicom.GoDICOMImplementationVersionName}}})

	return items
}

// Called when A_ASSOCIATE_RQ pdu arrives, on the provider side. Returns a list of items to be sent in
// the A_ASSOCIATE_AC pdu.
func (m *contextManager) onAssociateRequest(requestItems []pdu.SubItem) ([]pdu.SubItem, error) {
	responses := []pdu.SubItem{
		&pdu.ApplicationContextItem{
			Name: pdu.DICOMApplicationContextItemName,
		},
	}
	for _, requestItem := range requestItems {
		switch ri := requestItem.(type) {
		case *pdu.ApplicationContextItem:
			if ri.Name != pdu.DICOMApplicationContextItemName {
				dicomlog.Vprintf(0, "dicom.onAssociateRequest(%s): Found illegal applicationcontextname. Expect %v, found %v",
					m.label, ri.Name, pdu.DICOMApplicationContextItemName)
			}
		case *pdu.PresentationContextItem:
			var sopUID string
			var proposedTransferSyntaxUIDs []string
			for _, subItem := range ri.Items {
				switch c := subItem.(type) {
				case *pdu.AbstractSyntaxSubItem:
					if sopUID != "" {
						return nil, fmt.Errorf("dicom.onAssociateRequest: Multiple AbstractSyntaxSubItem found in %v",
							ri.String())
					}
					sopUID = c.Name
				case *pdu.TransferSyntaxSubItem:
					proposedTransferSyntaxUIDs = append(proposedTransferSyntaxUIDs, c.Name)
				default:
					return nil, fmt.Errorf("dicom.onAssociateRequest: Unknown subitem in PresentationContext: %s",
						subItem.String())
				}
			}
			var pickedTransferSyntaxUID = pickFirstPreferedTransferSyntax(proposedTransferSyntaxUIDs)
			if sopUID == "" || pickedTransferSyntaxUID == "" {
				return nil, fmt.Errorf("dicom.onAssociateRequest: SOP or transfersyntax not found in PresentationContext: %v",
					ri.String())
			}
			responses = append(responses, &pdu.PresentationContextItem{
				Type:      pdu.ItemTypePresentationContextResponse,
				ContextID: ri.ContextID,
				Result:    0, // accepted
				Items:     []pdu.SubItem{&pdu.TransferSyntaxSubItem{Name: pickedTransferSyntaxUID}}})
			dicomlog.Vprintf(2, "dicom.onAssociateRequest(%s): Provider(%p): addmapping %v %v %v",
				m.label, m, sopUID, pickedTransferSyntaxUID, ri.ContextID)
			// TODO(saito) Callback the service provider instead of accepting the sopclass blindly.
			addContextMapping(m, sopUID, pickedTransferSyntaxUID, ri.ContextID, pdu.PresentationContextAccepted)
		case *pdu.UserInformationItem:
			for _, subItem := range ri.Items {
				switch c := subItem.(type) {
				case *pdu.UserInformationMaximumLengthItem:
					if int(c.MaximumLengthReceived) > 0 {
						m.peerMaxPDUSize = int(c.MaximumLengthReceived)
					}
				case *pdu.ImplementationClassUIDSubItem:
					m.peerImplementationClassUID = c.Name
				case *pdu.ImplementationVersionNameSubItem:
					m.peerImplementationVersionName = c.Name

				}
			}
		}
	}
	responses = append(responses,
		&pdu.UserInformationItem{
			Items: []pdu.SubItem{
				&pdu.UserInformationMaximumLengthItem{MaximumLengthReceived: uint32(DefaultMaxPDUSize)},
				&pdu.ImplementationClassUIDSubItem{dicom.GoDICOMImplementationClassUID},
				&pdu.ImplementationVersionNameSubItem{dicom.GoDICOMImplementationVersionName},
			}})
	dicomlog.Vprintf(1, "dicom.onAssociateRequest(%s): Received associate request, #contexts:%v, maxPDU:%v, implclass:%v, version:%v",
		m.label, len(m.contextIDToAbstractSyntaxNameMap),
		m.peerMaxPDUSize, m.peerImplementationClassUID, m.peerImplementationVersionName)
	return responses, nil
}

// Called by the user (client) to when A_ASSOCIATE_AC PDU arrives from the provider.
func (m *contextManager) onAssociateResponse(responses []pdu.SubItem) error {
	for _, responseItem := range responses {
		switch ri := responseItem.(type) {
		case *pdu.PresentationContextItem:
			var pickedTransferSyntaxUID string
			for _, subItem := range ri.Items {
				switch c := subItem.(type) {
				case *pdu.TransferSyntaxSubItem:
					// Just pick the first syntax UID proposed by the client.
					if pickedTransferSyntaxUID == "" {
						pickedTransferSyntaxUID = c.Name
					} else {
						return fmt.Errorf("Multiple syntax UIDs returned in A_ASSOCIATE_AC: %v", ri.String())
					}
				default:
					return fmt.Errorf("Unknown subitem %s in PresentationContext: %s", subItem.String(), ri.String())
				}
			}
			request, ok := m.tmpRequests[ri.ContextID]
			if !ok {
				return fmt.Errorf("Unknown context ID %d for A_ASSOCIATE_AC: %v",
					ri.ContextID,
					ri.String())
			}
			found := false
			var sopUID string
			for _, subItem := range request.Items {
				switch c := subItem.(type) {
				case *pdu.AbstractSyntaxSubItem:
					sopUID = c.Name
				case *pdu.TransferSyntaxSubItem:
					if c.Name == pickedTransferSyntaxUID {
						found = true
						break
					}
				}
			}
			if sopUID == "" {
				return fmt.Errorf("dicom.onAssociateResponse(%s): The A-ASSOCIATE request lacks the abstract syntax item for tag %v (this shouldn't happen)", m.label, ri.ContextID)
			}
			if ri.Result != pdu.PresentationContextAccepted {
				dicomlog.Vprintf(0, "dicom.onAssociateResponse(%s): Abstract syntax %v, transfer syntax %v was rejected by the server: %s", m.label, dicomuid.UIDString(sopUID), dicomuid.UIDString(pickedTransferSyntaxUID), ri.Result.String())
			}
			if !found {
				// Generally, we expect the server to pick a
				// transfer syntax that's in the A-ASSOCIATE-RQ
				// list, but it's not required to do so - e.g.,
				// Osirix SCP. That being the case, I'm not sure
				// the point of reporting the list in
				// A-ASSOCIATE-RQ, but that's only one of
				// DICOM's pointless complexities.
				dicomlog.Vprintf(0, "dicom.onAssociateResponse(%s): The server picked TransferSyntaxUID '%s' for %s, which is not in the list proposed, %v",
					m.label,
					dicomuid.UIDString(pickedTransferSyntaxUID),
					dicomuid.UIDString(sopUID),
					request.Items)
			}
			addContextMapping(m, sopUID, pickedTransferSyntaxUID, ri.ContextID, ri.Result)
		case *pdu.UserInformationItem:
			for _, subItem := range ri.Items {
				switch c := subItem.(type) {
				case *pdu.UserInformationMaximumLengthItem:
					if int(c.MaximumLengthReceived) > 0 {
						m.peerMaxPDUSize = int(c.MaximumLengthReceived)
					}
				case *pdu.ImplementationClassUIDSubItem:
					m.peerImplementationClassUID = c.Name
				case *pdu.ImplementationVersionNameSubItem:
					m.peerImplementationVersionName = c.Name

				}
			}
		}
	}
	dicomlog.Vprintf(1, "dicom.onAssociateResponse(%s): Received associate response, #contexts:%v, maxPDU:%v, implclass:%v, version:%v",
		m.label,
		len(m.contextIDToAbstractSyntaxNameMap),
		m.peerMaxPDUSize, m.peerImplementationClassUID, m.peerImplementationVersionName)
	return nil
}

// Add a mapping between a (global) UID and a (per-session) context ID.
func addContextMapping(
	m *contextManager,
	abstractSyntaxUID string,
	transferSyntaxUID string,
	contextID byte,
	result pdu.PresentationContextResult) {
	dicomlog.Vprintf(2, "dicom.addContextMapping(%v): Map context %d -> %s, %s",
		m.label, contextID, dicomuid.UIDString(abstractSyntaxUID),
		dicomuid.UIDString(transferSyntaxUID))
	doassert(result >= 0 && result <= 4, result)
	doassert(contextID%2 == 1, contextID)
	if result == 0 {
		doassert(abstractSyntaxUID != "", abstractSyntaxUID)
		doassert(transferSyntaxUID != "", transferSyntaxUID)
	}
	e := &contextManagerEntry{
		abstractSyntaxUID: abstractSyntaxUID,
		transferSyntaxUID: transferSyntaxUID,
		contextID:         contextID,
		result:            result,
	}
	m.contextIDToAbstractSyntaxNameMap[contextID] = e
	m.abstractSyntaxNameToContextIDMap[abstractSyntaxUID] = e
}

func (m *contextManager) checkContextRejection(e *contextManagerEntry) error {
	if e.result != pdu.PresentationContextAccepted {
		return fmt.Errorf("dicom.checkContextRejection %v: Trying to use rejected context <%v, %v>: %s",
			m.label,
			dicomuid.UIDString(e.abstractSyntaxUID),
			dicomuid.UIDString(e.transferSyntaxUID),
			e.result.String())
	}
	return nil
}

// Convert an UID to a context ID.
func (m *contextManager) lookupByAbstractSyntaxUID(name string) (contextManagerEntry, error) {
	e, ok := m.abstractSyntaxNameToContextIDMap[name]
	if !ok {
		return contextManagerEntry{}, fmt.Errorf("dicom.checkContextRejection %v: Unknown syntax %s", m.label, dicomuid.UIDString(name))
	}
	err := m.checkContextRejection(e)
	if err != nil {
		return contextManagerEntry{}, err
	}
	return *e, nil
}

// Convert a contextID to a UID.
func (m *contextManager) lookupByContextID(contextID byte) (contextManagerEntry, error) {
	e, ok := m.contextIDToAbstractSyntaxNameMap[contextID]
	if !ok {
		return contextManagerEntry{}, fmt.Errorf("dicom.lookupByContextID %v: Unknown context ID %d", m.label, contextID)
	}
	err := m.checkContextRejection(e)
	if err != nil {
		return contextManagerEntry{}, err
	}
	return *e, nil
}