zeek/src/EventTrace.cc

// See the file "COPYING" in the main distribution directory for copyright.

#include "zeek/EventTrace.h"

#include <regex>

#include "zeek/Desc.h"
#include "zeek/EventHandler.h"
#include "zeek/Func.h"
#include "zeek/IPAddr.h"
#include "zeek/Reporter.h"
#include "zeek/ZeekString.h"

namespace zeek::detail {

std::unique_ptr<EventTraceMgr> event_trace_mgr;

// Helper function for generating a correct script-level representation
// of a string constant.
static std::string escape_string(const u_char* b, int len) {
    std::string res = "\"";

    for ( int i = 0; i < len; ++i ) {
        unsigned char c = b[i];

        switch ( c ) {
            case '\a': res += "\\a"; break;
            case '\b': res += "\\b"; break;
            case '\f': res += "\\f"; break;
            case '\n': res += "\\n"; break;
            case '\r': res += "\\r"; break;
            case '\t': res += "\\t"; break;
            case '\v': res += "\\v"; break;

            case '\\': res += "\\\\"; break;
            case '"': res += "\\\""; break;

            default:
                if ( isprint(c) )
                    res += c;
                else {
                    char buf[8192];
                    snprintf(buf, sizeof buf, "%03o", c);
                    res += "\\";
                    res += buf;
                }
                break;
        }
    }

    return res + "\"";
}

ValTrace::ValTrace(ValPtr _v) : v(std::move(_v)) {
    t = v->GetType();

    switch ( t->Tag() ) {
        case TYPE_LIST: TraceList(cast_intrusive<ListVal>(v)); break;

        case TYPE_RECORD: TraceRecord(cast_intrusive<RecordVal>(v)); break;

        case TYPE_TABLE: TraceTable(cast_intrusive<TableVal>(v)); break;

        case TYPE_VECTOR: TraceVector(cast_intrusive<VectorVal>(v)); break;

        default: break;
    }
}

bool ValTrace::operator==(const ValTrace& vt) const {
    auto& vt_v = vt.GetVal();
    if ( vt_v == v )
        return true;

    auto tag = t->Tag();

    if ( vt.GetType()->Tag() != tag )
        return false;

    switch ( tag ) {
        case TYPE_BOOL:
        case TYPE_INT:
        case TYPE_ENUM: return v->AsInt() == vt_v->AsInt();

        case TYPE_COUNT:
        case TYPE_PORT: return v->AsCount() == vt_v->AsCount();

        case TYPE_DOUBLE:
        case TYPE_INTERVAL:
        case TYPE_TIME: return v->AsDouble() == vt_v->AsDouble();

        case TYPE_STRING: return (*v->AsString()) == (*vt_v->AsString());

        case TYPE_ADDR: return v->AsAddr() == vt_v->AsAddr();

        case TYPE_SUBNET: return v->AsSubNet() == vt_v->AsSubNet();

        case TYPE_FUNC: return v->AsFunc() == vt_v->AsFunc();

        case TYPE_FILE: return v->AsFile() == vt_v->AsFile();

        case TYPE_PATTERN: return v->AsPattern() == vt_v->AsPattern();

        case TYPE_ANY: return v->AsSubNet() == vt_v->AsSubNet();

        case TYPE_TYPE: return v->AsType() == vt_v->AsType();

        case TYPE_OPAQUE: return false; // needs pointer equivalence

        case TYPE_LIST: return SameList(vt);

        case TYPE_RECORD: return SameRecord(vt);

        case TYPE_TABLE: return SameTable(vt);

        case TYPE_VECTOR: return SameVector(vt);

        default: reporter->InternalError("bad type in ValTrace::operator==");
    }
}

void ValTrace::ComputeDelta(const ValTrace* prev, DeltaVector& deltas) const {
    auto tag = t->Tag();

    if ( prev ) {
        ASSERT(prev->GetType()->Tag() == tag);

        auto& prev_v = prev->GetVal();

        if ( prev_v != v ) {
            if ( *this != *prev )
                deltas.emplace_back(std::make_unique<DeltaReplaceValue>(this, v));
            return;
        }
    }

    switch ( tag ) {
        case TYPE_BOOL:
        case TYPE_INT:
        case TYPE_ENUM:
        case TYPE_COUNT:
        case TYPE_PORT:
        case TYPE_DOUBLE:
        case TYPE_INTERVAL:
        case TYPE_TIME:
        case TYPE_STRING:
        case TYPE_ADDR:
        case TYPE_SUBNET:
        case TYPE_FUNC:
        case TYPE_PATTERN:
        case TYPE_TYPE:
            // These don't change in place.  No need to create
            // them as stand-alone variables, since we can just
            // use the constant representation instead.
            break;

        case TYPE_ANY:
        case TYPE_FILE:
        case TYPE_OPAQUE:
            // If we have a previous instance, we can ignore this
            // one, because we know it's equivalent (due to the
            // test at the beginning of this method), and it's
            // not meaningful to recurse inside it looking for
            // interior changes.
            if ( ! prev )
                deltas.emplace_back(std::make_unique<DeltaUnsupportedCreate>(this));
            break;

        case TYPE_LIST:
            // We shouldn't see these exposed directly, as they're
            // not manipulable at script-level.  An exception
            // might be for "any" types that are then decomposed
            // via compound assignment; for now, we don't support
            // those.
            reporter->InternalError("list type seen in ValTrace::ComputeDelta");
            break;

        case TYPE_RECORD:
            if ( prev )
                ComputeRecordDelta(prev, deltas);
            else
                deltas.emplace_back(std::make_unique<DeltaRecordCreate>(this));
            break;

        case TYPE_TABLE:
            if ( prev )
                ComputeTableDelta(prev, deltas);

            else if ( GetType()->AsTableType()->IsUnspecifiedTable() )
                // For unspecified values, we generate them
                // as empty constructors, because we don't
                // know their yield type and thus can't
                // create variables corresponding to them.
                break;

            else if ( t->Yield() )
                deltas.emplace_back(std::make_unique<DeltaTableCreate>(this));
            else
                deltas.emplace_back(std::make_unique<DeltaSetCreate>(this));
            break;

        case TYPE_VECTOR:
            if ( prev )
                ComputeVectorDelta(prev, deltas);

            else if ( GetType()->AsVectorType()->IsUnspecifiedVector() )
                // See above for empty tables/sets.
                break;

            else
                deltas.emplace_back(std::make_unique<DeltaVectorCreate>(this));
            break;

        default: reporter->InternalError("bad type in ValTrace::ComputeDelta");
    }
}

void ValTrace::TraceList(const ListValPtr& lv) {
    auto vals = lv->Vals();
    for ( auto& v : vals )
        elems.emplace_back(std::make_shared<ValTrace>(v));
}

void ValTrace::TraceRecord(const RecordValPtr& rv) {
    auto n = rv->NumFields();
    auto rt = rv->GetType<RecordType>();

    for ( auto i = 0U; i < n; ++i ) {
        auto f = rv->RawOptField(i);
        if ( f ) {
            auto val = f->ToVal(rt->GetFieldType(i));
            elems.emplace_back(std::make_shared<ValTrace>(val));
        }
        else
            elems.emplace_back(nullptr);
    }
}

void ValTrace::TraceTable(const TableValPtr& tv) {
    for ( auto& elem : tv->ToMap() ) {
        auto& key = elem.first;
        elems.emplace_back(std::make_shared<ValTrace>(key));

        auto& val = elem.second;
        if ( val )
            elems2.emplace_back(std::make_shared<ValTrace>(val));
    }
}

void ValTrace::TraceVector(const VectorValPtr& vv) {
    auto& vec = vv->RawVec();
    auto n = vec.size();
    auto& yt = vv->RawYieldType();
    auto& yts = vv->RawYieldTypes();

    for ( auto i = 0U; i < n; ++i ) {
        auto& elem = vec[i];
        if ( elem ) {
            auto& t = yts ? (*yts)[i] : yt;
            auto val = elem->ToVal(t);
            elems.emplace_back(std::make_shared<ValTrace>(val));
        }
        else
            elems.emplace_back(nullptr);
    }
}

bool ValTrace::SameList(const ValTrace& vt) const { return SameElems(vt); }

bool ValTrace::SameRecord(const ValTrace& vt) const { return SameElems(vt); }

bool ValTrace::SameTable(const ValTrace& vt) const {
    auto& vt_elems = vt.elems;
    auto n = elems.size();
    if ( n != vt_elems.size() )
        return false;

    auto& vt_elems2 = vt.elems2;
    auto n2 = elems2.size();
    if ( n2 != vt_elems2.size() )
        return false;

    ASSERT(n2 == 0 || n == n2);

    // We accommodate the possibility that keys are out-of-order
    // between the two sets of elements.

    // The following is O(N^2), but presumably if tables are somehow
    // involved (in fact we can only get here if they're used as
    // indices into other tables), then they'll likely be small.
    for ( auto i = 0U; i < n; ++i ) {
        auto& elem_i = elems[i];

        // See if we can find a match for it.  If we do, we don't
        // have to worry that another entry matched it too, since
        // all table/set indices will be distinct.
        auto j = 0U;
        for ( ; j < n; ++j ) {
            auto& vt_elem_j = vt_elems[j];
            if ( *elem_i == *vt_elem_j )
                break;
        }

        if ( j == n )
            // No match for the index.
            return false;

        if ( n2 > 0 ) {
            // Need a match for the corresponding yield values.
            if ( *elems2[i] != *vt_elems2[j] )
                return false;
        }
    }

    return true;
}

bool ValTrace::SameVector(const ValTrace& vt) const { return SameElems(vt); }

bool ValTrace::SameElems(const ValTrace& vt) const {
    auto& vt_elems = vt.elems;
    auto n = elems.size();
    if ( n != vt_elems.size() )
        return false;

    for ( auto i = 0U; i < n; ++i ) {
        auto& trace_i = elems[i];
        auto& vt_trace_i = vt_elems[i];

        if ( trace_i && vt_trace_i ) {
            if ( *trace_i != *vt_trace_i )
                return false;
        }

        else if ( trace_i || vt_trace_i )
            return false;
    }

    return true;
}

bool ValTrace::SameSingleton(const ValTrace& vt) const { return ! IsAggr(t) && *this == vt; }

void ValTrace::ComputeRecordDelta(const ValTrace* prev, DeltaVector& deltas) const {
    auto& prev_elems = prev->elems;
    auto n = elems.size();
    if ( n != prev_elems.size() )
        reporter->InternalError("size inconsistency in ValTrace::ComputeRecordDelta");

    for ( auto i = 0U; i < n; ++i ) {
        const auto trace_i = elems[i].get();
        const auto prev_trace_i = prev_elems[i].get();

        if ( trace_i ) {
            if ( prev_trace_i ) {
                auto& v = trace_i->GetVal();
                auto& prev_v = prev_trace_i->GetVal();

                if ( v == prev_v ) {
                    trace_i->ComputeDelta(prev_trace_i, deltas);
                    continue;
                }

                if ( trace_i->SameSingleton(*prev_trace_i) )
                    // No further work needed.
                    continue;
            }

            deltas.emplace_back(std::make_unique<DeltaSetField>(this, i, trace_i->GetVal()));
        }

        else if ( prev_trace_i )
            deltas.emplace_back(std::make_unique<DeltaRemoveField>(this, i));
    }
}

void ValTrace::ComputeTableDelta(const ValTrace* prev, DeltaVector& deltas) const {
    auto& prev_elems = prev->elems;
    auto& prev_elems2 = prev->elems2;

    auto n = elems.size();
    auto is_set = elems2.size() == 0;
    auto prev_n = prev_elems.size();

    // We can't compare pointers for the indices because they're
    // new objects generated afresh by TableVal::ToMap.  So we do
    // explicit full comparisons for equality, distinguishing values
    // newly added, common to both, or (implicitly) removed.  We'll
    // then go through the common to check them further.
    //
    // Our approach is O(N^2), but presumably these tables aren't
    // large, and in any case generating event traces is not something
    // requiring high performance, so we opt for conceptual simplicity.

    // Track which index values are newly added:
    std::set<const Val*> added_indices;

    // Track which entry traces are in common.  Indexed by previous
    // trace elem index, yielding current trace elem index.
    std::map<int, int> common_entries;

    for ( auto i = 0U; i < n; ++i ) {
        const auto trace_i = elems[i].get();

        bool common = false;

        for ( auto j = 0U; j < prev_n; ++j ) {
            const auto prev_trace_j = prev_elems[j].get();

            if ( *trace_i == *prev_trace_j ) {
                common_entries[j] = i;
                common = true;
                break;
            }
        }

        if ( ! common ) {
            auto v = trace_i->GetVal();

            if ( is_set )
                deltas.emplace_back(std::make_unique<DeltaSetSetEntry>(this, v));
            else {
                auto yield = elems2[i]->GetVal();
                deltas.emplace_back(std::make_unique<DeltaSetTableEntry>(this, v, yield));
            }

            added_indices.insert(v.get());
        }
    }

    for ( auto j = 0U; j < prev_n; ++j ) {
        auto common_pair = common_entries.find(j);
        if ( common_pair == common_entries.end() ) {
            auto& prev_trace = prev_elems[j];
            auto& v = prev_trace->GetVal();
            deltas.emplace_back(std::make_unique<DeltaRemoveTableEntry>(this, v));
            continue;
        }

        if ( is_set )
            continue;

        // If we get here, we're analyzing a table for which there's
        // a common index.  The remaining question is whether the
        // yield has changed.
        auto i = common_pair->second;
        auto& trace2 = elems2[i];
        const auto prev_trace2 = prev_elems2[j];

        auto& yield = trace2->GetVal();
        auto& prev_yield = prev_trace2->GetVal();

        if ( yield == prev_yield )
            // Same yield, look for differences in its sub-elements.
            trace2->ComputeDelta(prev_trace2.get(), deltas);

        else if ( ! trace2->SameSingleton(*prev_trace2) )
            deltas.emplace_back(std::make_unique<DeltaSetTableEntry>(this, elems[i]->GetVal(), yield));
    }
}

void ValTrace::ComputeVectorDelta(const ValTrace* prev, DeltaVector& deltas) const {
    auto& prev_elems = prev->elems;
    auto n = elems.size();
    auto prev_n = prev_elems.size();

    // TODO: The following hasn't been tested for robustness to vector holes.

    if ( n < prev_n ) {
        // The vector shrank in size.  Easiest to just build it
        // from scratch.
        deltas.emplace_back(std::make_unique<DeltaVectorCreate>(this));
        return;
    }

    // Look for existing entries that need reassignment.
    auto i = 0U;
    for ( ; i < prev_n; ++i ) {
        const auto trace_i = elems[i].get();
        const auto prev_trace_i = prev_elems[i].get();

        auto& elem_i = trace_i->GetVal();
        auto& prev_elem_i = prev_trace_i->GetVal();

        if ( elem_i == prev_elem_i )
            trace_i->ComputeDelta(prev_trace_i, deltas);
        else if ( ! trace_i->SameSingleton(*prev_trace_i) )
            deltas.emplace_back(std::make_unique<DeltaVectorSet>(this, i, elem_i));
    }

    // Now append any new entries.
    for ( ; i < n; ++i ) {
        auto& trace_i = elems[i];
        auto& elem_i = trace_i->GetVal();
        deltas.emplace_back(std::make_unique<DeltaVectorAppend>(this, i, elem_i));
    }
}

std::string ValDelta::Generate(ValTraceMgr* vtm) const { return "<bad ValDelta>"; }

std::string DeltaReplaceValue::Generate(ValTraceMgr* vtm) const { return std::string(" = ") + vtm->ValName(new_val); }

std::string DeltaSetField::Generate(ValTraceMgr* vtm) const {
    auto rt = vt->GetType()->AsRecordType();
    auto f = rt->FieldName(field);
    return std::string("$") + f + " = " + vtm->ValName(new_val);
}

std::string DeltaRemoveField::Generate(ValTraceMgr* vtm) const {
    auto rt = vt->GetType()->AsRecordType();
    auto f = rt->FieldName(field);
    return std::string("delete ") + vtm->ValName(vt) + "$" + f;
}

std::string DeltaRecordCreate::Generate(ValTraceMgr* vtm) const {
    auto rv = cast_intrusive<RecordVal>(vt->GetVal());
    auto rt = rv->GetType<RecordType>();
    auto n = rt->NumFields();

    std::string args;

    for ( auto i = 0; i < n; ++i ) {
        auto v_i = rv->GetField(i);
        if ( v_i ) {
            if ( ! args.empty() )
                args += ", ";

            args += std::string("$") + rt->FieldName(i) + "=" + vtm->ValName(v_i);
        }
    }

    auto name = rt->GetName();
    if ( name.empty() )
        name = "record";

    return std::string(" = ") + name + "(" + args + ")";
}

std::string DeltaSetSetEntry::Generate(ValTraceMgr* vtm) const {
    return std::string("add ") + vtm->ValName(vt) + "[" + vtm->ValName(index) + "]";
}

std::string DeltaSetTableEntry::Generate(ValTraceMgr* vtm) const {
    return std::string("[") + vtm->ValName(index) + "] = " + vtm->ValName(new_val);
}

std::string DeltaRemoveTableEntry::Generate(ValTraceMgr* vtm) const {
    return std::string("delete ") + vtm->ValName(vt) + "[" + vtm->ValName(index) + "]";
}

std::string DeltaSetCreate::Generate(ValTraceMgr* vtm) const {
    auto sv = cast_intrusive<TableVal>(vt->GetVal());
    auto members = sv->ToMap();

    std::string args;

    for ( auto& m : members ) {
        if ( ! args.empty() )
            args += ", ";

        args += vtm->ValName(m.first);
    }

    auto name = sv->GetType()->GetName();
    if ( name.empty() )
        name = "set";

    return std::string(" = ") + name + "(" + args + ")";
}

std::string DeltaTableCreate::Generate(ValTraceMgr* vtm) const {
    auto tv = cast_intrusive<TableVal>(vt->GetVal());
    auto members = tv->ToMap();

    std::string args;

    for ( auto& m : members ) {
        if ( ! args.empty() )
            args += ", ";

        args += std::string("[") + vtm->ValName(m.first) + "] = " + vtm->ValName(m.second);
    }

    auto name = tv->GetType()->GetName();
    if ( name.empty() )
        name = "table";

    return std::string(" = ") + name + "(" + args + ")";
}

std::string DeltaVectorSet::Generate(ValTraceMgr* vtm) const {
    return std::string("[") + std::to_string(index) + "] = " + vtm->ValName(elem);
}

std::string DeltaVectorAppend::Generate(ValTraceMgr* vtm) const {
    return std::string("[") + std::to_string(index) + "] = " + vtm->ValName(elem);
}

std::string DeltaVectorCreate::Generate(ValTraceMgr* vtm) const {
    auto& elems = vt->GetElems();
    std::string vec;

    for ( auto& e : elems ) {
        if ( vec.size() > 0 )
            vec += ", ";

        vec += vtm->ValName(e->GetVal());
    }

    return std::string(" = vector(") + vec + ")";
}

std::string DeltaUnsupportedCreate::Generate(ValTraceMgr* vtm) const {
    return " = UNSUPPORTED " + obj_desc_short(vt->GetVal()->GetType().get());
}

EventTrace::EventTrace(const ScriptFunc* _ev, double _nt, size_t event_num) : ev(_ev), nt(_nt) {
    auto ev_name = std::regex_replace(ev->GetName(), std::regex(":"), "_");

    name = ev_name + "_" + std::to_string(event_num) + "__et";
}

void EventTrace::Generate(FILE* f, ValTraceMgr& vtm, const DeltaGenVec& dvec, std::string successor,
                          int num_pre) const {
    int offset = 0;
    for ( auto& d : dvec ) {
        auto& val = d.GetVal();

        if ( d.IsFirstDef() && vtm.IsGlobal(val) ) {
            auto& val_name = vtm.ValName(val);

            std::string type_name;
            auto& t = val->GetType();
            auto& tn = t->GetName();
            if ( tn.empty() ) {
                ODesc d;
                t->Describe(&d);
                type_name = d.Description();
            }
            else
                type_name = tn;

            auto anno = offset < num_pre ? " # from script" : "";

            fprintf(f, "global %s: %s;%s\n", val_name.c_str(), type_name.c_str(), anno);
        }

        ++offset;
    }

    fprintf(f, "event %s()\n", name.c_str());
    fprintf(f, "\t{\n");

    offset = 0;
    for ( auto& d : dvec ) {
        fprintf(f, "\t");

        auto& val = d.GetVal();
        bool define_local = d.IsFirstDef() && ! vtm.IsGlobal(val);

        if ( define_local )
            fprintf(f, "local ");

        if ( d.NeedsLHS() ) {
            fprintf(f, "%s", vtm.ValName(val).c_str());

            if ( define_local )
                fprintf(f, ": %s", obj_desc_short(val->GetType().get()).c_str());
        }

        auto anno = offset < num_pre ? " # from script" : "";

        fprintf(f, "%s;%s\n", d.RHS().c_str(), anno);

        ++offset;
    }

    if ( ! dvec.empty() )
        fprintf(f, "\n");

    fprintf(f, "\tevent %s(%s);\n\n", ev->GetName().c_str(), args.c_str());

    if ( successor.empty() ) {
        // The following isn't necessary with our current approach
        // to managing chains of events, which avoids having to set
        // exit_only_after_terminate=T.
        // fprintf(f, "\tterminate();\n");
    }
    else {
        auto tm = vtm.TimeConstant(nt);
        fprintf(f, "\tset_network_time(%s);\n", tm.c_str());
        fprintf(f, "\tevent __EventTrace::%s();\n", successor.c_str());
    }

    fprintf(f, "\t}\n");
}

void EventTrace::Generate(FILE* f, ValTraceMgr& vtm, const EventTrace* predecessor, std::string successor) const {
    if ( predecessor ) {
        auto& pre_deltas = predecessor->post_deltas;
        int num_pre = pre_deltas.size();

        if ( num_pre > 0 ) {
            auto total_deltas = pre_deltas;
            total_deltas.insert(total_deltas.end(), deltas.begin(), deltas.end());
            Generate(f, vtm, total_deltas, successor, num_pre);
            return;
        }
    }

    Generate(f, vtm, deltas, std::move(successor));
}

void ValTraceMgr::TraceEventValues(std::shared_ptr<EventTrace> et, const zeek::Args* args) {
    curr_ev = std::move(et);

    auto num_vals = vals.size();

    std::string ev_args;
    for ( auto& a : *args ) {
        AddVal(a);

        if ( ! ev_args.empty() )
            ev_args += ", ";

        ev_args += ValName(a);
    }

    curr_ev->SetArgs(std::move(ev_args));

    // Now look for any values newly-processed with this event and
    // remember them so we can catch uses of them in future events.
    for ( auto i = num_vals; i < vals.size(); ++i ) {
        processed_vals.insert(vals[i].get());
        ASSERT(val_names.count(vals[i].get()) > 0);
    }
}

void ValTraceMgr::FinishCurrentEvent(const zeek::Args* args) {
    auto num_vals = vals.size();

    curr_ev->SetDoingPost();

    for ( auto& a : *args )
        AddVal(a);

    for ( auto i = num_vals; i < vals.size(); ++i )
        processed_vals.insert(vals[i].get());
}

const std::string& ValTraceMgr::ValName(const ValPtr& v) {
    auto find = val_names.find(v.get());
    if ( find == val_names.end() )
        find = val_names.insert({v.get(), GenValName(v)}).first;

    ValUsed(v);

    return find->second;
}

std::string ValTraceMgr::TimeConstant(double t) {
    if ( t < std::max(base_time, 1e6) )
        return "double_to_time(" + std::to_string(t) + ")";

    if ( ! base_time )
        base_time = t;

    if ( t == base_time )
        return "double_to_time(__base_time)";

    t -= base_time;
    return "double_to_time(__base_time + " + std::to_string(t) + ")";
}

void ValTraceMgr::AddVal(ValPtr v) {
    auto mapping = val_map.find(v.get());

    if ( mapping == val_map.end() )
        NewVal(v);
    else {
        auto vt = std::make_shared<ValTrace>(v);
        AssessChange(vt.get(), mapping->second.get());
        val_map[v.get()] = std::move(vt);
    }
}

void ValTraceMgr::NewVal(ValPtr v) {
    // Make sure the Val sticks around into the future.
    vals.push_back(v);

    auto vt = std::make_shared<ValTrace>(v);
    AssessChange(vt.get(), nullptr);
    val_map[v.get()] = std::move(vt);
}

void ValTraceMgr::ValUsed(const ValPtr& v) {
    ASSERT(val_names.count(v.get()) > 0);
    if ( processed_vals.count(v.get()) > 0 )
        // We saw this value when processing a previous event.
        globals.insert(v.get());
}

void ValTraceMgr::AssessChange(const ValTrace* vt, const ValTrace* prev_vt) {
    DeltaVector deltas;

    vt->ComputeDelta(prev_vt, deltas);

    // Used to track deltas across the batch, to suppress redundant ones
    // (which can arise due to two aggregates both including the same
    // sub-element).
    std::unordered_set<std::string> previous_deltas;

    for ( auto& d : deltas ) {
        auto vp = d->GetValTrace()->GetVal();
        auto v = vp.get();
        auto rhs = d->Generate(this);

        bool needs_lhs = d->NeedsLHS();
        bool is_first_def = false;

        if ( needs_lhs && val_names.count(v) == 0 ) {
            TrackVar(v);
            is_first_def = true;
        }

        ASSERT(val_names.count(v) > 0);

        // The "/" in the following is just to have a delimiter
        // to make sure the string is unambiguous.
        auto full_delta = val_names[v] + "/" + rhs;
        if ( previous_deltas.count(full_delta) > 0 )
            continue;

        previous_deltas.insert(std::move(full_delta));

        ValUsed(vp);
        curr_ev->AddDelta(vp, std::move(rhs), needs_lhs, is_first_def);
    }

    auto& v = vt->GetVal();
    if ( IsAggr(v->GetType()) && (prev_vt || ! IsUnspecifiedAggregate(v)) )
        ValUsed(vt->GetVal());
}

void ValTraceMgr::TrackVar(const Val* v) {
    std::string base_name = IsUnsupported(v) ? "UNSUPPORTED" : "val";
    val_names[v] = "__" + base_name + std::to_string(num_vars++);
}

std::string ValTraceMgr::GenValName(const ValPtr& v) {
    if ( IsAggr(v->GetType()) && ! IsUnspecifiedAggregate(v) ) { // Aggregate shouldn't exist; create it
        ASSERT(val_map.count(v.get()) == 0);
        NewVal(v);
        return val_names[v.get()];
    }

    // Non-aggregate (or unspecified aggregate) can be expressed using
    // a constant.
    auto t = v->GetType();
    auto tag = t->Tag();
    std::string rep;
    bool track_constant = false;

    switch ( tag ) {
        case TYPE_STRING: {
            auto s = v->AsStringVal();
            rep = escape_string(s->Bytes(), s->Len());
            track_constant = s->Len() > 0;
            break;
        }

        case TYPE_LIST: {
            auto lv = cast_intrusive<ListVal>(v);
            for ( auto& v_i : lv->Vals() ) {
                if ( ! rep.empty() )
                    rep += ", ";

                rep += ValName(v_i);
            }
            break;
        }

        case TYPE_FUNC: rep = v->AsFunc()->GetName(); break;

        case TYPE_TIME: {
            auto tm = v->AsDouble();
            rep = TimeConstant(tm);

            if ( tm > 0.0 && rep.find("__base_time") == std::string::npos )
                // We're not representing it using base_time.
                track_constant = true;

            break;
        }

        case TYPE_INTERVAL: rep = "double_to_interval(" + std::to_string(v->AsDouble()) + ")"; break;

        case TYPE_TABLE: rep = t->Yield() ? "table()" : "set()"; break;

        case TYPE_VECTOR: rep = "vector()"; break;

        case TYPE_PATTERN:
        case TYPE_PORT:
        case TYPE_ADDR:
        case TYPE_SUBNET: {
            ODesc d;
            v->Describe(&d);
            rep = d.Description();
            track_constant = true;

            if ( tag == TYPE_ADDR || tag == TYPE_SUBNET ) {
                // Fix up deficiency that IPv6 addresses are
                // described without surrounding []'s.
                const auto& addr = tag == TYPE_ADDR ? v->AsAddr() : v->AsSubNet().Prefix();
                if ( addr.GetFamily() == IPv6 )
                    rep = "[" + rep + "]";
            }
        } break;

        default: {
            ODesc d;
            v->Describe(&d);
            rep = d.Description();
        }
    }

    val_names[v.get()] = rep;
    vals.push_back(v);

    if ( track_constant )
        constants[tag].insert(rep);

    std::array<std::string, NUM_TYPES> constants;

    return rep;
}

bool ValTraceMgr::IsUnspecifiedAggregate(const ValPtr& v) const {
    auto t = v->GetType()->Tag();

    if ( t == TYPE_TABLE && v->GetType<TableType>()->IsUnspecifiedTable() )
        return true;

    if ( t == TYPE_VECTOR && v->GetType<VectorType>()->IsUnspecifiedVector() )
        return true;

    return false;
}

bool ValTraceMgr::IsUnsupported(const Val* v) const {
    auto t = v->GetType()->Tag();
    return t == TYPE_ANY || t == TYPE_FILE || t == TYPE_OPAQUE;
}

EventTraceMgr::EventTraceMgr(const std::string& trace_file) {
    f = fopen(trace_file.c_str(), "w");
    if ( ! f )
        reporter->FatalError("can't open event trace file %s: %s", trace_file.c_str(), strerror(errno));
}

EventTraceMgr::~EventTraceMgr() {
    if ( f ) {
        if ( fclose(f) )
            // Not fatal, won't do anything with it anymore anyhow.
            reporter->Error("failed to close event trace file: %s", strerror(errno));

        f = nullptr;
    }
}

void EventTraceMgr::Generate() {
    if ( events.empty() )
        return;

    fprintf(f, "module __EventTrace;\n\n");

    auto bt = vtm.GetBaseTime();

    if ( bt )
        fprintf(f, "global __base_time = %.06f;\n\n", bt);

    for ( auto& e : events )
        fprintf(f, "global %s: event();\n", e->GetName());

    fprintf(f, "\nevent zeek_init() &priority=-999999\n");
    fprintf(f, "\t{\n");
    fprintf(f, "\tevent __EventTrace::%s();\n", events.front()->GetName());
    fprintf(f, "\t}\n");

    for ( auto i = 0U; i < events.size(); ++i ) {
        fprintf(f, "\n");

        auto predecessor = i > 0 ? events[i - 1] : nullptr;
        auto successor = i + 1 < events.size() ? events[i + 1]->GetName() : "";
        events[i]->Generate(f, vtm, predecessor.get(), successor);
    }

    const auto& constants = vtm.GetConstants();

    for ( auto tag = 0; tag < NUM_TYPES; ++tag ) {
        auto& c_t = constants[tag];
        if ( c_t.empty() && (tag != TYPE_TIME || ! bt) )
            continue;

        fprintf(f, "\n# constants of type %s:\n", type_name(TypeTag(tag)));
        if ( tag == TYPE_TIME && bt )
            fprintf(f, "#\t__base_time = %.06f\n", bt);

        for ( auto& c : c_t )
            fprintf(f, "#\t%s\n", c.c_str());
    }
}

void EventTraceMgr::StartEvent(const ScriptFunc* ev, const zeek::Args* args) {
    if ( script_events.count(ev->GetName()) > 0 )
        return;

    auto nt = run_state::network_time;
    if ( nt == 0.0 || ev->GetName() == "zeek_init" )
        return;

    if ( ! vtm.GetBaseTime() )
        vtm.SetBaseTime(nt);

    auto et = std::make_shared<EventTrace>(ev, nt, events.size());
    events.emplace_back(et);

    vtm.TraceEventValues(std::move(et), args);
}

void EventTraceMgr::EndEvent(const ScriptFunc* ev, const zeek::Args* args) {
    if ( script_events.count(ev->GetName()) > 0 )
        return;

    if ( run_state::network_time > 0.0 && ev->GetName() != "zeek_init" )
        vtm.FinishCurrentEvent(args);
}

void EventTraceMgr::ScriptEventQueued(const EventHandlerPtr& h) { script_events.insert(h->Name()); }

} // namespace zeek::detail