diff --git a/luprex/core/Makefile b/luprex/core/Makefile
index ba3cc7db..035e3cd9 100644
--- a/luprex/core/Makefile
+++ b/luprex/core/Makefile
@@ -78,6 +78,7 @@ CORE_OBJ_FILES=\
 	obj/globaldb.o\
 	obj/sched.o\
 	obj/http.o\
+	obj/json.o\
 	obj/table.o\
 	obj/gui.o\
 	obj/luasnap.o\
diff --git a/luprex/core/cpp/idalloc.cpp b/luprex/core/cpp/idalloc.cpp
index c4a908d4..b77c7baa 100644
--- a/luprex/core/cpp/idalloc.cpp
+++ b/luprex/core/cpp/idalloc.cpp
@@ -87,12 +87,12 @@ void IdGlobalPool::deserialize(StreamBuffer *sb) {
 
 eng::string IdGlobalPool::debug_string() const {
     eng::ostringstream oss;
-    oss << "next_batch:" << util::hex64() << next_batch_ << " ";
-    oss << "next_id:" << util::hex64() << next_id_ << " ";
-    oss << "next_seqno: " << util::hex64() << next_seqno_ << " ";
+    oss << "next_batch:" << util::hex64.val(next_batch_) << " ";
+    oss << "next_id:" << util::hex64.val(next_id_) << " ";
+    oss << "next_seqno: " << util::hex64.val(next_seqno_) << " ";
     oss << "salvaged:";
     for (const int64_t val : salvaged_) {
-        oss << " " << util::hex64() << val;
+        oss << " " << util::hex64.val(val);
     }
     return oss.str();
 }
@@ -253,9 +253,9 @@ eng::string IdPlayerPool::debug_string() const {
     oss << "cap:" << fifo_capacity_ << " ids:";
     for (int i = 0; i < int(ranges_.size()); i++) {
         if (i > 0) oss << ",";
-        oss << util::hex64() << ranges_[i];
+        oss << util::hex64.val(ranges_[i]);
     }
-    oss << " seqno:" << util::hex64() << next_seqno_;
+    oss << " seqno:" << util::hex64.val(next_seqno_);
     return oss.str();
 }
 
diff --git a/luprex/core/cpp/json.cpp b/luprex/core/cpp/json.cpp
new file mode 100644
index 00000000..b3c85037
--- /dev/null
+++ b/luprex/core/cpp/json.cpp
@@ -0,0 +1,724 @@
+#include "json.hpp"
+#include "luastack.hpp"
+#include "util.hpp"
+#include <string_view>
+#include <ostream>
+#include <cmath>
+#include <iomanip>
+#include <cstdio>
+#include <cstdlib>
+
+
+#define NOINDENT_LEVEL 1000
+
+LuaTokenConstant(json_null, "null", "");
+LuaTokenConstant(json_object, "object", "");
+
+static void indent(eng::ostringstream &oss, int level) {
+    if (level < NOINDENT_LEVEL) {
+        oss << std::endl;
+        for (int i = 0; i < level; i++) {
+            oss << "  ";
+        }
+    }
+}
+
+static bool length_exceeded(eng::ostringstream &oss, int maxlen) {
+    return oss.tellp() > maxlen;
+}
+
+template <class... ARGS>
+inline void store_error(eng::ostringstream &oss, const ARGS & ... args) {
+    oss.str("");
+    util::send_to_stream(oss, args...);
+}
+
+static void store_length_error(eng::ostringstream &oss, int maxlen) {
+    store_error(oss, "maximum json length exceeded: ", maxlen);
+}
+
+static bool use_array_representation(lua_State *L) {
+    int top = lua_gettop(L);
+    int nfound = 0;
+    while (true) {
+        lua_rawgeti(L, top, nfound + 1);
+        bool null = lua_isnil(L, -1);
+        lua_settop(L, top);
+        if (null) break;
+        nfound += 1;
+    }
+    return (nfound == lua_nkeys(L, top));
+}
+
+static bool encode_key(lua_State *L, eng::ostringstream &oss);
+static bool encode_value(lua_State *L, eng::ostringstream &oss, int level, int maxlen);
+
+
+// The goal here is to emit a double in such a way that
+// when we read it back in, we get the *exact* same number.
+//
+// In the worst case, you can accomplish this by using 17
+// digits of precision - that's enough to uniquely identify
+// all double values (see the following URL).  However, 17
+// digits tends to produce unnecessary repeating decimals.
+// So we try 16 digits first, which tends to remove those
+// repeating decimals, but sometimes produces losses.
+// If that doesn't work, we fall back to 17 digits.
+//
+// https://randomascii.wordpress.com/2012/03/08/float-precisionfrom-zero-to-100-digits-2/
+//
+static void encode_double_lossless(double value, eng::ostringstream &oss) {
+    char buffer[80];
+    sprintf(buffer, "%.16g", value);
+    if (strtod(buffer, nullptr) != value) {
+        sprintf(buffer, "%.17g", value);
+        assert(strtod(buffer, nullptr) == value);
+    }
+    oss << buffer;
+}
+
+static bool encode_nil(lua_State *L, eng::ostringstream &oss) {
+    oss << "null";
+    return true;
+}
+
+static bool encode_token(lua_State *L, eng::ostringstream &oss) {
+    LuaToken token(lua_touserdata(L, -1));
+    if (token == LuaToken("jsonnull")) {
+        oss << "null";
+        return true;
+    } else {
+        store_error(oss, "cannot encode token: [", token.str(), "]");
+        return false;
+    }
+}
+
+static bool encode_number(lua_State *L, eng::ostringstream &oss) {
+    lua_Number value = lua_tonumber(L, -1);
+    if (std::isnan(value) || std::isinf(value)) {
+        store_error(oss, "cannot encode infinity or NAN");
+        return false;
+    }
+    int64_t ivalue = int64_t(value);
+    if (double(ivalue) == value) {
+        oss << ivalue;
+    } else {
+        encode_double_lossless(value, oss);
+    }
+    return true;
+}
+
+static bool encode_number_key(lua_State *L, eng::ostringstream &oss) {
+    lua_Number value = lua_tonumber(L, -1);
+    int64_t ivalue = int64_t(value);
+    if (double(ivalue) != value) {
+        store_error(oss, "cannot encode floating point numbers in table keys");
+        return false;
+    }
+    if (ivalue >= 0) {
+        oss << "\"\\uE000+" << ivalue << '"';
+    } else {
+        oss << "\"\\uE000-" << -ivalue << '"';
+    }
+    return true;
+}
+
+static bool encode_boolean(lua_State *L, eng::ostringstream &oss) {
+    int flag = lua_toboolean(L, -1);
+    oss << (flag ? "true" : "false");
+    return true;
+}
+
+static bool encode_string(lua_State *L, eng::ostringstream &oss) {
+    size_t len;
+    const char *s = lua_tolstring(L, -1, &len);
+    std::string_view str(s, len);
+    oss << '"';
+    if (sv::valid_utf8(str) && !sv::has_prefix(str, "")) {
+        // Output the string in the straightforward way,
+        // using traditional json escaping.
+        for (char c : str) {
+            switch (c) {
+                case '\\': oss << "\\\\"; break;
+                case '"' : oss << "\\\""; break;
+                case '\b': oss << "\\b"; break;
+                case '\f': oss << "\\f"; break;
+                case '\r': oss << "\\r"; break;
+                case '\n': oss << "\\n"; break;
+                case '\t': oss << "\\t"; break;
+                default: {
+                    if (c < 32) {
+                        oss << "\\u" << util::hex16.val(c);
+                    } else {
+                        oss << c;
+                    }
+                }
+            }
+        }
+    } else {
+        // Output as a base64-encoded string.
+        oss << "\\uE000=";
+        util::base64_encode(str, &oss);
+    }
+    oss << '"';
+    return true;
+}
+
+static bool encode_array(lua_State *L, eng::ostringstream &oss, int level, int maxlen) {
+    lua_checkstack(L, 20);
+    int top = lua_gettop(L);
+    oss << "[";
+    level ++;
+    int i = 1;
+    while (true) {
+        lua_rawgeti(L, top, i);
+        if (lua_isnil(L, -1)) break;
+        if (i > 1) oss << ",";
+        indent(oss, level);
+        bool ok = encode_value(L, oss, level, maxlen);
+        lua_settop(L, top);
+        if (!ok) return false;
+        if (length_exceeded(oss, maxlen)) {
+            store_length_error(oss, maxlen);
+            return false;
+        }
+        i += 1;
+    }
+    lua_settop(L, top);
+    level --;
+    indent(oss, level);
+    oss << "]";
+    return true;
+}
+
+static bool encode_object(lua_State *L, eng::ostringstream &oss, int level, int maxlen) {
+    lua_checkstack(L, 20);
+    int top = lua_gettop(L);
+    oss << "{";
+    level ++;
+    lua_pushnil(L);
+    int i = 1;
+    while (lua_next(L, top) != 0) {
+        // Check for [json.object]=true, if so skip.
+        if (lua_islightuserdata(L, -2) &&
+            lua_isboolean(L, -1) &&
+            (LuaToken(lua_touserdata(L, -2)) == LuaToken("object")) &&
+            (lua_toboolean(L, -1) == 1)) {
+            lua_pop(L, 1);
+            continue;
+        }
+
+        lua_pushvalue(L, -2);
+        // Stack now has key, value, key
+        assert(lua_gettop(L) == top + 3);
+        if (i > 1) oss << ",";
+        indent(oss, level);
+        bool ok = encode_key(L, oss);
+        if (!ok) {
+            lua_settop(L, top);
+            return false;
+        }
+        if (length_exceeded(oss, maxlen)) {
+            store_length_error(oss, maxlen);
+            lua_settop(L, top);
+            return false;
+        }
+        lua_pop(L, 1);
+        // Stack now has key, value
+        assert(lua_gettop(L) == top + 2);
+        oss << ((level < NOINDENT_LEVEL) ? " : " : ":");
+        ok = encode_value(L, oss, level, maxlen);
+        assert(lua_gettop(L) == top + 2);
+        if (!ok) {
+            lua_settop(L, top);
+            return false;
+        }
+        if (length_exceeded(oss, maxlen)) {
+            store_length_error(oss, maxlen);
+            lua_settop(L, top);
+            return false;
+        }
+        lua_pop(L, 1);
+        // Stack now just has key.
+        assert(lua_gettop(L) == top + 1);
+        i += 1;
+    }
+    // Stack should be back to where we started.
+    assert(lua_gettop(L) == top);
+    level --;
+    indent(oss, level);
+    oss << "}";
+    return true;
+}
+
+static bool encode_key(lua_State *L, eng::ostringstream &oss) {
+    int type = lua_type(L, -1);
+    switch (type) {
+        case LUA_TSTRING: return encode_string(L, oss);
+        case LUA_TNUMBER: return encode_number_key(L, oss);
+        case LUA_TBOOLEAN:
+        case LUA_TTABLE: {
+            store_error(oss, "cannot encode '", lua_typename(L, type), "' in table keys");
+            return false;
+        }
+        default: {
+            store_error(oss, "cannot encode '", lua_typename(L, type), "'");
+            return false;
+        }
+    }
+}
+
+static bool encode_value(lua_State *L, eng::ostringstream &oss, int level, int maxlen) {
+    int type = lua_type(L, -1);
+    switch (type) {
+        case LUA_TNIL: return encode_nil(L, oss);
+        case LUA_TNUMBER: return encode_number(L, oss);
+        case LUA_TBOOLEAN: return encode_boolean(L, oss);
+        case LUA_TSTRING: return encode_string(L, oss);
+        case LUA_TLIGHTUSERDATA: return encode_token(L, oss);
+        case LUA_TTABLE: {
+            if (use_array_representation(L)) {
+                return encode_array(L, oss, level, maxlen);
+            } else {
+                return encode_object(L, oss, level, maxlen);
+            }
+        }
+        default: {
+            store_error(oss, "cannot encode '", lua_typename(L, type), "'");
+            return false;
+        }
+    }
+}
+
+static bool decode_value(lua_State *L, std::string_view &v);
+
+static bool decode_id(lua_State *L, std::string_view &v) {
+    std::string_view id = sv::read_ascii_identifier(v);
+    if (id == "null") lua_pushlightuserdata(L, LuaToken("null").voidvalue());
+    else if (id == "true") lua_pushboolean(L, 1);
+    else if (id == "false") lua_pushboolean(L, 0);
+    else return false;
+    return true;
+}
+
+static bool decode_number(lua_State *L, std::string_view &v) {
+    std::string_view n = sv::read_number(v, true, true, true, true);
+    if (n.empty()) return false;
+
+    // If it's an integer, make sure it fits in a lua double
+    // losslessly.  If it's a double, some loss in precision
+    // is OK.
+    if (sv::valid_number(n, true, true, false, false)) {
+        int64_t i = sv::to_int64(n);
+        if (!LuaStack::int64_storable(i)) return false;
+        lua_pushnumber(L, double(i));
+        return true;
+    } else {
+        double d = sv::to_double(n);
+        if (std::isnan(d) || std::isinf(d)) return false;
+        lua_pushnumber(L, d);
+        return true;
+    }
+}
+
+static bool decode_base64_string(lua_State *L, std::string_view &v) {
+    // We've already read the starting quote and the E000
+    // escape sequence at this point.
+
+    // Skip the equal sign.
+    if (!sv::read_prefix(v, "=")) return false;
+    
+    // Find the end of the quoted string.
+    const char *p = v.data();
+    const char *l = p + v.size();
+    while (true) {
+        if (p == l) return false;
+        if (*p < 32) return false;
+        if (*p == '"') break;
+        p++;
+    }
+    std::string_view b64 = v.substr(0, p - v.data());
+    v.remove_prefix(b64.size() + 1);
+    eng::ostringstream oss;
+    if (!util::base64_decode(b64, &oss)) return false;
+    eng::string str = oss.str();
+    lua_pushlstring(L, str.c_str(), str.size());
+    return true;
+}
+
+static bool decode_int_string(lua_State *L, std::string_view &v) {
+    // We've already read the starting quote and the E000
+    // escape sequence at this point.
+
+    // Parse the number and the closing quote.
+    std::string_view n = sv::read_number(v, true, true, false, false);
+    if (n.empty()) return false;
+    if (!sv::read_prefix(v, "\"")) {
+        return false;
+    }
+
+    // Make sure the number fits in a lua double,
+    // and push it on the stack.
+    int64_t i = sv::to_int64(n);
+    if (!LuaStack::int64_storable(i)) {
+        return false;
+    }
+    lua_pushnumber(L, double(i));
+    return true;
+}
+
+static bool decode_standard_string(lua_State *L, std::string_view &v) {
+    // We've already read the starting quote at this point.
+    eng::ostringstream oss;
+    while (true) {
+        // Get the next codepoint.
+        int32_t c = sv::read_codepoint_utf8(v);
+
+        // If it's a control character or invalid codepoint, reject.
+        if (c < 32) return false;
+
+        // If it is an unescaped quote, that's end of string.
+        if (c == '"') break;
+
+        // If it's a backslash, then deal with the escape sequence.
+        if (c == '\\') {
+            char next = sv::read_ascii_char(v);
+            switch (next) {
+                case '"': oss << '"'; break;
+                case '\\': oss << '\\'; break;
+                case '/': oss << '/'; break;
+                case 'r': oss << '\r'; break;
+                case 'n': oss <<'\n'; break;
+                case 'b': oss << '\b'; break;
+                case 'f': oss << '\f'; break;
+                case 't': oss << '\t'; break;
+                case 'u': {
+                    std::string_view hexdigits = sv::read_nbytes(v, 4);
+                    if (hexdigits.size() != 4) return false;
+                    uint64_t codepoint = sv::to_hex64(hexdigits, 0x10000);
+                    if (codepoint >= 0x10000) return false;
+                    if (!util::write_codepoint_utf8(codepoint, &oss)) return false;
+                    break;
+                }
+                default: return false;
+            }
+            continue;
+        }
+
+        // Any other codepoint should be echoed into stream.
+        util::write_codepoint_utf8(c, &oss);
+    }
+    eng::string result = oss.str();
+    lua_pushlstring(L, result.c_str(), result.size());
+    return true;
+}
+
+static bool decode_string(lua_State *L, std::string_view &v) {
+    if (!sv::read_prefix(v, "\"")) return false;
+
+    // Check for codepoint E000, the escape sequence.
+    if (sv::read_prefix(v, "") ||
+        sv::read_prefix(v, "\\uE000") ||
+        sv::read_prefix(v, "\\ue000")) {
+        char c = sv::zfront(v);
+        if (c == '=') return decode_base64_string(L, v);
+        else if ((c=='-') || (c=='+')) return decode_int_string(L, v);
+        else return false;
+    } else {
+        return decode_standard_string(L, v);
+    }
+}
+
+static bool decode_array(lua_State *L, std::string_view &v) {
+    if (!sv::read_prefix(v, "[")) return false;
+    lua_newtable(L);
+    int tabpos = lua_gettop(L);
+    int next = 1;
+    while (true) {
+        v = sv::ltrim(v);
+        if (sv::zfront(v) == ']') {
+            v.remove_prefix(1);
+            return true;
+        }
+        if (!decode_value(L, v)) {
+            return false;
+        }
+        v = sv::ltrim(v);
+        if (sv::zfront(v) == ',') {
+            v.remove_prefix(1);
+        }
+        lua_rawseti(L, tabpos, next++);
+    }
+}
+
+static bool decode_object(lua_State *L, std::string_view &v) {
+    if (!sv::read_prefix(v, "{")) return false;
+    lua_newtable(L);
+    int tabpos = lua_gettop(L);
+    while (true) {
+        v = sv::ltrim(v);
+        if (sv::zfront(v) == '}') {
+            v.remove_prefix(1);
+            return true;
+        }
+        if (!decode_string(L, v)) {
+            return false;
+        }
+        v = sv::ltrim(v);
+        if (!sv::read_prefix(v, ":")) {
+            return false;
+        }
+        if (!decode_value(L, v)) {
+            return false;
+        }
+        v = sv::ltrim(v);
+        if (sv::zfront(v) == ',') {
+            v.remove_prefix(1);
+        }
+        lua_rawset(L, tabpos);
+    }
+}
+
+// Decode a single value.
+//
+// On success, pushes the value on the stack and returns true.
+// On failure, pushes NIL on the stack and returns false.
+//
+static bool decode_value(lua_State *L, std::string_view &v) {
+    lua_checkstack(L, 20);
+    int top = lua_gettop(L);
+
+    // Skip blanks.
+    v = sv::ltrim(v);
+
+    // Try to read something.
+    char c = sv::zfront(v);
+    bool result;
+    if (c == '"') result = decode_string(L, v);
+    else if (c == '[') result = decode_array(L, v);
+    else if (c == '{') result = decode_object(L, v);
+    else if (sv::ascii_isalpha(c)) result = decode_id(L, v);
+    else result = decode_number(L, v);
+    
+    // On failure, the decode routines may leave junk
+    // on the stack, in which case it's our job to clean up.
+    if (result == false) {
+        lua_settop(L, top);
+        lua_pushnil(L);
+    }
+
+    // Now there should be exactly one new value on the stack.
+    assert(lua_gettop(L) == top + 1);
+    return result;
+}
+
+namespace json {
+
+eng::string encode(LuaStack &LS, LuaSlot in, eng::string &out, bool indent, int maxlen) {
+    eng::ostringstream oss;
+
+    // Call the recursive encoder.  Clean up any crap on the lua stack afterward.
+    int top = lua_gettop(LS.state());
+    lua_pushvalue(LS.state(), in.index());
+    bool ok = encode_value(LS.state(), oss, indent ? 0 : NOINDENT_LEVEL, maxlen);
+    lua_settop(LS.state(), top);
+
+    // One last check for overruns.
+    if (ok && length_exceeded(oss, maxlen)) {
+        store_length_error(oss, maxlen);
+        ok = false;
+    }
+
+    // Produce the return value.
+    if (ok) {
+        out = oss.str();
+        return "";
+    } else {
+        out = "";
+        return oss.str();
+    }
+}
+
+bool decode(LuaStack &LS, LuaSlot out, std::string_view v) {
+    lua_State *L = LS.state();
+
+    // Try to read a single value from the view.
+    bool ok = decode_value(L, v);
+    lua_replace(L, out.index());
+    if (!ok) return false;
+
+    // There should be nothing left of the input text.
+    if (v.size() > 0) {
+        lua_pushnil(L);
+        lua_replace(L, out.index());
+        return false;
+    }
+
+    // Special case: if the top-level result is jsonnull,
+    // then change it to nil.
+    if (LS.istoken(out)) {
+        LS.set(out, LuaNil);
+    }
+
+    return true;
+}
+
+} // namespace util
+
+
+LuaDefine(json_encode, "data, indent, maxlen",
+    "|Encode a lua data structure returning a json string."
+    "|"
+    "|Data is the value being encoded.  Indent is a flag,"
+    "|if it's true, then the json is indented nicely,"
+    "|otherwise, it is packed tightly.  Maxlen is the maximum"
+    "|length in bytes of the encoded json string."
+    "|"
+    "|Usually, Lua data translates straightforwardly to json."
+    "|However, there are a number of special cases to be"
+    "|aware of:"
+    "|"
+    "|- Closures and threads cannot be encoded.  These will"
+    "|  cause the encoder to abort."
+    "|"
+    "|- The numbers infinity and NAN cannot be encoded."
+    "|  Both of these will cause the encoder to abort."
+    "|"
+    "|- You must specify a size-limit to the encoded"
+    "|  string.  Exceeding the size limit causes the"
+    "|  encoder to abort."
+    "|"
+    "|- Recursive data structures will cause the encoder to"
+    "|  loop infinitely until the size-limit is exceeded,"
+    "|  causing the encoder to abort."
+    "|"
+    "|- There is no way to represent math.huge or math.nan in"
+    "|  json.  Encoding math.nan will cause the encoder to abort,"
+    "|  as expected.  However, encoding math.huge will emit null,"
+    "|  which is probably not what you would expect."
+    "|"
+    "|- Lua tables cannot contain 'nil', but json objects and"
+    "|  arrays can contain null.  If you want the encoder to"
+    "|  emit a json object or array containing null, you must"
+    "|  use token json.null to represent null."
+    "|"
+    "|- Json objects, like lua tables, are key-value stores."
+    "|  However, json objects can only have string keys.  Our"
+    "|  encoder uses a workaround to transparently"
+    "|  allow mixing string and integer keys in json tables."
+    "|  See 'encoding  difficult data' below."
+    "|"
+    "|- Json strings are required to be valid utf-8.  Our encoder"
+    "|  uses a workaround to transparently allow the use of"
+    "|  arbitrary 8-bit-clean strings.  See 'encoding difficult"
+    "|  data' below."
+    "|"
+    "|- Lua tables containing contiguous integer keys from 1-n are"
+    "|  autodetected to be json arrays.  Empty tables are also"
+    "|  emitted as json arrays.  All other tables are emitted"
+    "|  as json objects."
+    "|"
+    "|- You can force a table to be emitted as a json object"
+    "|  by putting the key-value pair table[json.object]=true"
+    "|  into the table.  This special key is not emitted, but"
+    "|  it triggers json object mode.  This is the only way"
+    "|  to emit an empty json object (a truly empty table is"
+    "|  emitted as a json array.)"
+    "|"
+    "|Encoding Difficult Data:"
+    "|"
+    "|Normally, json doesn't allow integer table keys, and it"
+    "|doesn't allow strings that aren't valid utf-8.  Our"
+    "|json encoder and decoder, on the other hand, can"
+    "|encode and decode integer table keys and 8-bit-clean"
+    "|strings transparently.  This is accomplished without"
+    "|violating the json specification, by encoding such"
+    "|values as utf-8 strings:"
+    "|"
+    "|    '123'       (encoded integer 123)"
+    "|    '=aGVsbG8=' (binary string encoded as base64)"
+    "|"
+    "|Those encodings start with utf-8 codepoint E000."
+    "|This codepoint probably shows up in your text editor"
+    "|as a little rectangle.  When the decoder sees codepoint"
+    "|E000 at the beginning of a string, it automatically"
+    "|decodes the string back into its original form."
+    "|"
+    "|The one price for this behavior is that the encoder"
+    "|cannot literally emit strings that start"
+    "|with codepoint E000.  If the encoder detects such a"
+    "|string, it will emit it as a base64-encoded string."
+    "|This should be uncommon, since codepoint E000 is"
+    "|reserved."
+    "|"
+    "|Note that integers are only encoded when they are"
+    "|used as table keys.  Otherwise, numbers are emitted"
+    "|straightforwardly."
+    "|") {
+    LuaArg data, indent, maxlen;
+    LuaRet encoded;
+    LuaStack LS(L, data, indent, maxlen, encoded);
+    eng::string out;
+    eng::string error = json::encode(LS, data, out, LS.ckboolean(indent), LS.ckint(maxlen));
+    if (!error.empty()) {
+        luaL_error(L, "%s", error.c_str());
+        LS.set(encoded, LuaNil);
+        return LS.result();
+    } else {
+        LS.set(encoded, out);
+        return LS.result();
+    }
+}
+
+LuaDefine(json_decode, "data",
+    "|Decode a json expression into a lua data structure."
+    "|"
+    "|Data that was generated by our own encoder is almost"
+    "|8-bit clean.  That includes difficult cases, like"
+    "|binary strings, floating point numbers, and tables"
+    "|with mixed string and integer keys.  The exception"
+    "|are the kinds of data that can't be encoded at all:"
+    "|See doc(json.encode) for details about what"
+    "|can and cannot be encoded."
+    "|"
+    "|Some json may contain 'null' inside objects and"
+    "|arrays.  Lua tables can't store nil, so instead, we"
+    "|store the token json.null.  If that's not what you"
+    "|want, you can use json.stripnulls to strip out"
+    "|the json.null values from a data structure and"
+    "|replace them with nil."
+    "|"
+    "|") {
+    LuaArg encoded;
+    LuaRet data;
+    LuaStack LS(L, encoded, data);
+    std::string_view v = LS.ckstringview(encoded);
+    bool ok = json::decode(LS, data, v);
+    if (!ok) {
+        luaL_error(L, "invalid json string.");
+    }
+    return LS.result();
+}
+
+// LuaDefine(base64_encode, "data", "") {
+//     LuaArg str;
+//     LuaRet ret;
+//     LuaStack LS(L, str, ret);
+//     eng::string cstr = LS.ckstring(str);
+//     eng::ostringstream oss;
+//     util::base64_encode(cstr, &oss);
+//     LS.set(ret, oss.str());
+//     return LS.result();
+// }
+
+// LuaDefine(base64_decode, "data", "") {
+//     LuaArg str;
+//     LuaRet ret;
+//     LuaStack LS(L, str, ret);
+//     eng::string cstr = LS.ckstring(str);
+//     eng::ostringstream oss;
+//     util::base64_decode(cstr, &oss);
+//     LS.set(ret, oss.str());
+//     return LS.result();
+// }
+
diff --git a/luprex/core/cpp/json.hpp b/luprex/core/cpp/json.hpp
new file mode 100644
index 00000000..a1dcd018
--- /dev/null
+++ b/luprex/core/cpp/json.hpp
@@ -0,0 +1,33 @@
+// Encode lua data structure into json, and decode them again.
+//
+// See the doc(http.jsonencode) to read about limitations of the encoder.
+//
+#ifndef JSON_HPP
+#define JSON_HPP
+
+#include "luastack.hpp"
+#include "wrap-string.hpp"
+#include <string_view>
+
+namespace json {
+    // Encode json.
+    //
+    // See doc(http.jsonencode) for a lot more information.
+    //
+    // Returns an error message.  If the error message is an
+    // empty string, then the encoding was successful.
+    //
+    eng::string encode(LuaStack &LS, LuaSlot in, eng::string &out, bool indent, int maxlen);
+
+    // Decode json.
+    //
+    // See doc(http.jsondecode) for a lot more information.
+    //
+    // The only error condition is syntactically invalid json.
+    // In that case, we return false.
+    //
+    bool decode(LuaStack &LS, LuaSlot out, std::string_view in);
+}
+    
+#endif // JSON_HPP
+
diff --git a/luprex/core/cpp/luastack.cpp b/luprex/core/cpp/luastack.cpp
index 75904bbb..c938fa4b 100644
--- a/luprex/core/cpp/luastack.cpp
+++ b/luprex/core/cpp/luastack.cpp
@@ -2,6 +2,7 @@
 #include <iostream>
 #include <cassert>
 #include <cstdio>
+#include <climits>
 
 LuaSpecial LuaRegistry(LUA_REGISTRYINDEX);
 LuaNilMarker LuaNil;
@@ -17,6 +18,15 @@ LuaFunctionReg::LuaFunctionReg(const char *n, const char *a, const char *d, bool
     All = this;
 }
 
+LuaConstantReg::LuaConstantReg(const char *n, const char *d, LuaToken tokenvalue, lua_Number numbervalue) {
+    name_ = n;
+    docs_ = d;
+    tokenvalue_ = tokenvalue;
+    numbervalue_ = numbervalue;
+    next_ = All;
+    All = this;
+}
+
 const LuaFunctionReg *LuaFunctionReg::lookup(lua_CFunction fn) {
     for (const LuaFunctionReg *r = All; r != 0; r = r->next_) {
         if (r->func_ == fn) {
@@ -27,6 +37,20 @@ const LuaFunctionReg *LuaFunctionReg::lookup(lua_CFunction fn) {
 }
 
 LuaFunctionReg *LuaFunctionReg::All;
+LuaConstantReg *LuaConstantReg::All;
+
+
+eng::string LuaToken::str() const {
+    uint64_t token = (uint64_t)value;
+    char buffer[9];
+    for (int i = 0; i < 8; i++) {
+        unsigned char c = token;
+        buffer[7-i] = c;
+        token >>= 8;
+    }
+    buffer[8] = 0;
+    return eng::string(buffer);
+}
 
 static int panicf(lua_State *L) {
     const char *p = lua_tostring(L, -1);
@@ -107,11 +131,23 @@ eng::string LuaStack::ckstring(LuaSlot s) const {
     return eng::string(str, len);
 }
 
+std::string_view LuaStack::ckstringview(LuaSlot s) const {
+    luaL_checktype(L_, s, LUA_TSTRING);
+    size_t len;
+    const char *str = lua_tolstring(L_, s, &len);
+    return std::string_view(str, len);
+}
+
 lua_State *LuaStack::ckthread(LuaSlot s) const {
     luaL_checktype(L_, s, LUA_TTHREAD);
     return lua_tothread(L_, s);
 }
 
+LuaToken LuaStack::cktoken(LuaSlot s) const {
+    luaL_checktype(L_, s, LUA_TLIGHTUSERDATA);
+    return LuaToken(lua_touserdata(L_, s));
+}
+
 void LuaStack::count_slots_finalize(int narg, int nvar, int nret) {
     narg_ = narg;
     nret_ = nret;
diff --git a/luprex/core/cpp/luastack.hpp b/luprex/core/cpp/luastack.hpp
index 2d427984..4c5d852c 100644
--- a/luprex/core/cpp/luastack.hpp
+++ b/luprex/core/cpp/luastack.hpp
@@ -226,6 +226,40 @@ int LuaTypeTagValue(lua_State *L) { return 0; }
 #define LUA_TT_GLOBALDB      22
 #define LUA_TT_CLASS         23
 
+// We use lightuserdata to store 'tokens': short
+// strings of 8 characters or less.  These tokens
+// are useful as unique markers.  The 8 characters
+// are packed into a uint64.
+
+struct LuaToken {
+private:
+    static constexpr uint64_t literal_to_token(const char *str) {
+        uint64_t result = 0;
+        for (int i = 0; i < 8; i++) {
+            unsigned char c = *str;
+            result = (result << 8) + c;
+            if (*str) str++;
+        }
+        return result;
+    }
+public:
+    uint64_t value;
+
+    template<class T>
+    LuaToken(T arg) = delete;
+
+    constexpr LuaToken(const char *str) : value(literal_to_token(str)) {}
+    LuaToken(uint64_t v) : value(v) {}
+    LuaToken(void *v) : value((uint64_t)v) {}
+    LuaToken() : value(0) {}
+
+    bool empty() const { return value == 0; }
+    bool operator ==(const LuaToken &other) const { return value == other.value; }
+    void *voidvalue() const { return (void*)value; }
+
+    eng::string str() const;
+};
+
 class LuaStack : public eng::nevernew {
 private:
     int narg_;
@@ -302,6 +336,7 @@ private:
     void push_any_value(lua_Integer s) const { lua_pushinteger(L_, s); }
     void push_any_value(lua_CFunction s) const { lua_pushcfunction(L_, s); }
     void push_any_value(bool b) const { lua_pushboolean(L_, b ? 1:0); }
+    void push_any_value(LuaToken token) const { lua_pushlightuserdata(L_, (void*)(token.value)); }
 
     // Push multiple values on the stack, in order, by type.
     template<typename T0, typename... T>
@@ -354,6 +389,7 @@ public:
     bool isboolean(LuaSlot s) const { return lua_type(L_, s) == LUA_TBOOLEAN; }
     bool isnil(LuaSlot s) const { return lua_type(L_, s) == LUA_TNIL; }
     bool iscfunction(LuaSlot s) const { return lua_iscfunction(L_, s) != 0; }
+    bool istoken(LuaSlot s) const { return lua_islightuserdata(L_, s) != 0; }
 
     void checktable(LuaSlot index) const { checktype(index, LUA_TTABLE); }
     void checkstring(LuaSlot index) const { checktype(index, LUA_TSTRING); }
@@ -362,13 +398,16 @@ public:
     void checkfunction(LuaSlot index) const { checktype(index, LUA_TFUNCTION); }
     void checkboolean(LuaSlot index) const { checktype(index, LUA_TBOOLEAN); }
     void checknil(LuaSlot index) const { checktype(index, LUA_TNIL); }
+    void checktoken(LuaSlot index) const { checktype(index, LUA_TLIGHTUSERDATA); }
 
     bool ckboolean(LuaSlot s) const;
     lua_Integer ckinteger(LuaSlot s) const;
     int ckint(LuaSlot s) const;
     lua_Number cknumber(LuaSlot s) const;
     eng::string ckstring(LuaSlot s) const;
+    std::string_view ckstringview(LuaSlot s) const;
     lua_State *ckthread(LuaSlot s) const;
+    LuaToken cktoken(LuaSlot s) const;
     
     void clearmetatable(LuaSlot tab) const;
     void setmetatable(LuaSlot tab, LuaSlot mt) const;
@@ -472,8 +511,29 @@ public:
     // Lua flagbits manipulation: visited bit.
     bool getvisited(LuaSlot tab) const;
     void setvisited(LuaSlot tab, bool visited) const;
+
+    // Return true if the int64 value can be stored as a lua number.
+    static bool int64_storable(int64_t v) { return (v <= MAXINT) && (v >= -MAXINT); }
 };
 
+class LuaConstantReg : public eng::nevernew {
+private:
+    const char *name_;
+    const char *docs_;
+    LuaToken tokenvalue_;
+    lua_Number numbervalue_;
+    LuaConstantReg *next_;
+
+public:
+    static LuaConstantReg *All;
+    LuaConstantReg(const char *name, const char *docs, LuaToken tokenvalue, lua_Number numbervalue);
+
+    const char *get_name() const { return name_; }
+    const char *get_docs() const { return docs_; }
+    LuaToken get_tokenvalue() const { return tokenvalue_; }
+    lua_Number get_numbervalue() const { return numbervalue_; }
+    LuaConstantReg *next() const { return next_; }
+};
 
 class LuaFunctionReg : public eng::nevernew {
 private:
@@ -498,6 +558,11 @@ public:
     void set_func(lua_CFunction fn) { func_ = fn; }
 };
 
+#define LuaTokenConstant(name, tvalue, docs) \
+    LuaConstantReg reg_##name(#name, docs, LuaToken(tvalue), 0);
+
+#define LuaNumberConstant(name, nvalue, docs) \
+    LuaConstantReg reg_##name(#name, docs, LuaToken(), nvalue);
 
 #define LuaDefine(name, args, docs) \
     int lfn_##name(lua_State *L); \
@@ -518,4 +583,5 @@ public:
 #define LuaStringify(x) #x
 #define LuaAssert(L, x) if (!(x)) { luaL_error((L), "Assert failed: %s (file %s line %d)", LuaStringify(x), __FILE__, __LINE__); }
 #define LuaAssertStrEq(L, x, y) { eng::string _s1_(x); eng::string _s2_(y); if (_s1_ != _s2_) luaL_error((L), "Assert failed: value=%s (file %s line %d)", _s1_.c_str(), __FILE__, __LINE__); }
+
 #endif // LUASTACK_HPP
diff --git a/luprex/core/cpp/pprint.cpp b/luprex/core/cpp/pprint.cpp
index eada8c22..61a2c918 100644
--- a/luprex/core/cpp/pprint.cpp
+++ b/luprex/core/cpp/pprint.cpp
@@ -5,6 +5,7 @@
 #include "table.hpp"
 
 #include <iostream>
+#include <cmath>
 
 
 void atomic_print(LuaStack &LS, LuaSlot val, bool quote, std::ostream *os) {
@@ -23,11 +24,15 @@ void atomic_print(LuaStack &LS, LuaSlot val, bool quote, std::ostream *os) {
         return;
     case LUA_TNUMBER: {
         double value = LS.cknumber(val);
-        int64_t ivalue = int64_t(value);
-        if (double(ivalue) == value) {
-            (*os) << ivalue;
+        if (std::isnan(value)) {
+            (*os) << "nan";
         } else {
-            (*os) << value;
+            int64_t ivalue = int64_t(value);
+            if (double(ivalue) == value) {
+                (*os) << ivalue;
+            } else {
+                (*os) << value;
+            }
         }
         return;
     }
@@ -38,6 +43,11 @@ void atomic_print(LuaStack &LS, LuaSlot val, bool quote, std::ostream *os) {
         (*os) << "<function>";
         return;
     }
+    case LUA_TLIGHTUSERDATA: {
+        LuaToken token = LS.cktoken(val);
+        (*os) << "[" << token.str() << "]";
+        return;
+    }
     default:
         (*os) << "<" << lua_typename(LS.state(), tt) << ">";
         return;
diff --git a/luprex/core/cpp/source.cpp b/luprex/core/cpp/source.cpp
index 9ef21c4a..ccb9142e 100644
--- a/luprex/core/cpp/source.cpp
+++ b/luprex/core/cpp/source.cpp
@@ -56,8 +56,7 @@ LuaDefine(classname, "classtable", "get the class name from a class table") {
     return LS.result();
 }
 
-static void get_reg_name(const LuaFunctionReg *reg, std::string_view &classname, std::string_view &funcname) {
-    std::string_view name(reg->get_name());
+static void get_reg_name(std::string_view name, std::string_view &classname, std::string_view &funcname) {
     size_t upos = name.find('_');
     if (upos == std::string_view::npos) {
         funcname = name;
@@ -280,7 +279,7 @@ static void source_load_cfunctions(lua_State *L) {
         if ((func != nullptr) && (!r->get_sandbox())) {
             std::string_view classname;
             std::string_view funcname;
-            get_reg_name(r, classname, funcname);
+            get_reg_name(r->get_name(), classname, funcname);
             if (classname.empty()) {
                 LS.getglobaltable(classobj);
                 LS.rawset(classobj, funcname, func);
@@ -293,6 +292,31 @@ static void source_load_cfunctions(lua_State *L) {
     LS.result();
 }
 
+// Load all the 'LuaConstant' constants into the lua state.
+//
+static void source_load_cconstants(lua_State *L) {
+    LuaVar classobj, value;
+    LuaStack LS(L, classobj, value);
+    for (auto r = LuaConstantReg::All; r != nullptr; r=r->next()) {
+        if (r->get_tokenvalue().empty()) {
+            LS.set(value, r->get_numbervalue());
+        } else {
+            LS.set(value, r->get_tokenvalue());
+        }
+        std::string_view classname;
+        std::string_view funcname;
+        get_reg_name(r->get_name(), classname, funcname);
+        if (classname.empty()) {
+            LS.getglobaltable(classobj);
+            LS.rawset(classobj, funcname, value);
+        } else {
+            LS.makeclass(classobj, classname);
+            LS.rawset(classobj, funcname, value);
+        }
+    }
+    LS.result();
+}
+
 // Run all the closures from the source database.
 //
 static eng::string source_load_lfunctions(lua_State *L) {
@@ -341,18 +365,12 @@ static eng::string source_load_lfunctions(lua_State *L) {
 
 eng::string SourceDB::rebuild() {
     lua_State *L = lua_state_;
-    LuaVar mathclass;
-    LuaStack LS(L, mathclass);
+    LuaVar mathclass, httpclass, jsonnull;
+    LuaStack LS(L, mathclass, httpclass, jsonnull);
     source_clear_globals(L);
     source_load_cfunctions(L);
+    source_load_cconstants(L);    
     eng::string errs = source_load_lfunctions(L);
-
-    // A few builtin constants.  These are hardwired.
-    LS.makeclass(mathclass, "math");
-    LS.rawset(mathclass, "pi", M_PI);
-    LS.rawset(mathclass, "huge", HUGE_VAL);
-    LS.rawset(mathclass, "maxint", LuaStack::MAXINT);
-
     LS.result();
     return errs;
 }
@@ -466,7 +484,7 @@ void SourceDB::register_lua_builtins() {
     for (auto reg = LuaFunctionReg::All; reg != nullptr; reg=reg->next()) {
         std::string_view funcname;
         std::string_view classname;
-        get_reg_name(reg, classname, funcname);
+        get_reg_name(reg->get_name(), classname, funcname);
         if (classname.empty()) {
             LS.getglobaltable(classtab);
         } else {
@@ -524,7 +542,7 @@ eng::string SourceDB::function_docs(const LuaStack &LS0, LuaSlot fn) {
         }
         std::string_view classname;
         std::string_view funcname;
-        get_reg_name(reg, classname, funcname);
+        get_reg_name(reg->get_name(), classname, funcname);
         eng::ostringstream oss;
         util::StringVec docs = util::split_docstring(reg->get_docs());
         oss << "function ";
@@ -747,6 +765,11 @@ LuaDefineBuiltin(math_sqrt, "x", "return the square root of x");
 LuaDefineBuiltin(math_tan, "x", "return the tangent of x in radians");
 LuaDefineBuiltin(math_tanh, "x", "return the hyperbolic tangent of x in radians");
 LuaSandboxBuiltin(math_log10, "", "");
+LuaNumberConstant(math_pi, M_PI, "");
+LuaNumberConstant(math_huge, HUGE_VAL, "");
+LuaNumberConstant(math_nan, NAN, "");
+LuaNumberConstant(math_maxint, LuaStack::MAXINT, "");
+
 // math.random and math.randomseed are in world-accessor.cpp, because
 // generating random numbers must manipulate global state which is
 // stored in the world model.
diff --git a/luprex/core/cpp/util.cpp b/luprex/core/cpp/util.cpp
index dd3c2ecd..0f22c9cc 100644
--- a/luprex/core/cpp/util.cpp
+++ b/luprex/core/cpp/util.cpp
@@ -65,8 +65,10 @@ bool valid_double(string_view value) {
 
 int64_t to_int64(string_view value, int64_t errval) {
     int64_t result;
-    const char *last = value.data() + value.size();
-    auto r = std::from_chars(value.data(), last, result, 10);
+    const char *p = value.data();
+    const char *last = p + value.size();
+    if ((p < last) && (*p == '+')) p++;
+    auto r = std::from_chars(p, last, result, 10);
     if (r.ec != std::errc()) return errval;
     if (r.ptr != last) return errval;
     return result;
@@ -74,6 +76,7 @@ int64_t to_int64(string_view value, int64_t errval) {
 
 uint64_t to_hex64(string_view value, uint64_t errval) {
     uint64_t result;
+    if (sv::zfront(value) == '-') return errval;
     const char *last = value.data() + value.size();
     auto r = std::from_chars(value.data(), last, result, 16);
     if (r.ec != std::errc()) return errval;
@@ -204,6 +207,15 @@ string_view read_to_line(string_view &source) {
     return result;
 }
 
+bool read_prefix(string_view &source, string_view prefix) {
+    if (0 == source.compare(0, prefix.size(), prefix)) {
+        source.remove_prefix(prefix.size());
+        return true;
+    } else {
+        return false;
+    }
+}
+
 string_view read_to_space(string_view &source) {
     size_t pos1 = 0;
     while ((pos1 < source.size()) && (!ascii_isspace(source[pos1]))) {
@@ -243,57 +255,119 @@ string_view read_ascii_identifier(string_view &source) {
     return result;
 }
 
+std::string_view read_number(string_view &source, bool plus, bool minus, bool dec, bool exp) {
+    const char *p = source.data();
+    const char *l = p + source.size();
+    if (p == l) return source.substr(0, 0);
+    char sign = *p;
+    if (sign == '+') {
+        if (!plus) return source.substr(0, 0);
+        p++;
+    }
+    if (sign == '-') {
+        if (!minus) return source.substr(0, 0);
+        p++;
+    }
+    if (p == l) return source.substr(0, 0);
+    bool have_digits = false;
+    while ((p < l) && (ascii_isdigit(*p))) {
+        have_digits = true;
+        p++;
+    }
+    if ((p < l) && dec && (*p == '.')) {
+        p++;
+        while ((p < l) && (ascii_isdigit(*p))) {
+            have_digits = true;
+            p++;
+        }
+    }
+    if (!have_digits) return source.substr(0, 0);
+    if ((p < l) && exp && ((*p == 'e')||(*p == 'E'))) {
+        p++;
+        if ((p < l) && ((*p == '+') || (*p == '-'))) {
+            p++;
+        }
+        bool have_exp = false;
+        while ((p < l) && (ascii_isdigit(*p))) {
+            have_exp = true;
+            p++;
+        }
+        if (!have_exp) return source.substr(0, 0);
+    }
+    string_view result = source.substr(0, p - source.data());
+    source.remove_prefix(result.size());
+    return result;
+}
+
+int32_t read_ascii_char(string_view &source) {
+    if (source.empty()) return -1;
+    int32_t result = source.front();
+    source.remove_prefix(1);
+    return result;
+}
+
+int32_t read_codepoint_utf8(string_view &source) {
+    size_t size = source.size();
+    if (size == 0) return -1;
+    const unsigned char *bytes = (const unsigned char *)source.data();
+    int codepoint;
+    size_t seqlen;
+    if ((bytes[0] & 0x80) == 0x00) {
+        // U+0000 to U+007F
+        codepoint = (bytes[0] & 0x7F);
+        seqlen = 1;
+    } else if ((bytes[0] & 0xE0) == 0xC0) {
+        // U+0080 to U+07FF
+        codepoint = (bytes[0] & 0x1F);
+        seqlen = 2;
+    } else if ((bytes[0] & 0xF0) == 0xE0) {
+        // U+0800 to U+FFFF
+        codepoint = (bytes[0] & 0x0F);
+        seqlen = 3;
+    } else if ((bytes[0] & 0xF8) == 0xF0) {
+        // U+10000 to U+10FFFF
+        codepoint = (bytes[0] & 0x07);
+        seqlen = 4;
+    } else {
+        return -1;
+    }
+
+    if (seqlen > size) {
+        return -1;
+    }
+
+    for (size_t i = 1; i < seqlen; ++i) {
+        if ((bytes[i] & 0xC0) != 0x80) return -1;
+        codepoint = (codepoint << 6) | (bytes[i] & 0x3F);
+    }
+
+    if ((codepoint > 0x10FFFF) ||
+        ((codepoint >= 0xD800) && (codepoint <= 0xDFFF)) ||
+        ((codepoint <= 0x007F) && (seqlen != 1)) ||
+        ((codepoint >= 0x0080) && (codepoint <= 0x07FF) && (seqlen != 2)) ||
+        ((codepoint >= 0x0800) && (codepoint <= 0xFFFF) && (seqlen != 3)) ||
+        ((codepoint >= 0x10000) && (codepoint <= 0x1FFFFF) && (seqlen != 4))) {
+        return -1;
+    }
+
+    source.remove_prefix(seqlen);
+    return codepoint;
+}
+
 bool valid_utf8(string_view s)
 {
-    const unsigned char *bytes = (const unsigned char *)s.data();
-    const unsigned char *tail = bytes + s.size();
-    unsigned int codepoint;
-    int seqlen;
-
-    while (bytes < tail) {
-        if ((bytes[0] & 0x80) == 0x00) {
-            // U+0000 to U+007F
-            codepoint = (bytes[0] & 0x7F);
-            seqlen = 1;
-        } else if ((bytes[0] & 0xE0) == 0xC0) {
-            // U+0080 to U+07FF
-            codepoint = (bytes[0] & 0x1F);
-            seqlen = 2;
-        } else if ((bytes[0] & 0xF0) == 0xE0) {
-            // U+0800 to U+FFFF
-            codepoint = (bytes[0] & 0x0F);
-            seqlen = 3;
-        } else if ((bytes[0] & 0xF8) == 0xF0) {
-            // U+10000 to U+10FFFF
-            codepoint = (bytes[0] & 0x07);
-            seqlen = 4;
-        } else {
-            return false;
-        }
-
-        if (bytes + seqlen > tail) {
-            return false;
-        }
-
-        for (int i = 1; i < seqlen; ++i) {
-            if ((bytes[i] & 0xC0) != 0x80) return false;
-            codepoint = (codepoint << 6) | (bytes[i] & 0x3F);
-        }
-
-        if ((codepoint > 0x10FFFF) ||
-            ((codepoint >= 0xD800) && (codepoint <= 0xDFFF)) ||
-            ((codepoint <= 0x007F) && (seqlen != 1)) ||
-            ((codepoint >= 0x0080) && (codepoint <= 0x07FF) && (seqlen != 2)) ||
-            ((codepoint >= 0x0800) && (codepoint <= 0xFFFF) && (seqlen != 3)) ||
-            ((codepoint >= 0x10000) && (codepoint <= 0x1FFFFF) && (seqlen != 4))) {
-            return false;
-        }
-
-        bytes += seqlen;
+    while (!s.empty()) {
+        int32_t codepoint = read_codepoint_utf8(s);
+        if (codepoint < 0) return false;
     }
     return true;
 }
 
+bool valid_number(string_view s, bool plus, bool minus, bool dec, bool exp) {
+    read_number(s, plus, minus, dec, exp);
+    return s.empty();
+}
+
 } // namespace sv
 
 
@@ -334,6 +408,8 @@ void quote_string(const eng::string &s, std::ostream *os) {
                 (*os) << (usesinglequote ? "\"" : "\\\"");
             } else if (c == '\'') {
                 (*os) << (usesinglequote ? "\\'" : "'");
+            } else if (c == '\\') {
+                (*os) << "\\\\"; 
             } else {
                 (*os) << c;
             }
@@ -344,7 +420,7 @@ void quote_string(const eng::string &s, std::ostream *os) {
             case '\t': (*os) << "\\t"; break;
             case '\r': (*os) << "\\r"; break;
             default:
-                (*os) << "\\" << std::setfill('0') << std::setw(3) << value;
+                (*os) << "\\" << dec.width(3).fill('0').val(value);
                 break;
             }
         }
@@ -352,6 +428,52 @@ void quote_string(const eng::string &s, std::ostream *os) {
     (*os) << (usesinglequote ? '\'' : '"');
 }
 
+void base64_encode(std::string_view str, std::ostream *oss) {
+    const char *encode_tab = 
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+    const char *s = str.data();
+    size_t size = str.size();
+    for (size_t i = 0; i < size; i += 3) {
+        uint32_t block = ((unsigned char)(s[i])) << 16;
+        if (i + 1 < size) block |= ((unsigned char)(s[i + 1])) << 8;
+        if (i + 2 < size) block |= ((unsigned char)(s[i + 2]));
+        (*oss) << encode_tab[(block>>18)&0x3F];
+        (*oss) << encode_tab[(block>>12)&0x3F];
+        (*oss) << ((i + 1 < size) ? encode_tab[(block>>6)&0x3F] : '=');
+        (*oss) << ((i + 2 < size) ? encode_tab[(block>>0)&0x3F] : '=');
+    }
+}
+
+bool base64_decode(std::string_view str, std::ostream *oss) {
+    uint32_t chunk = 0;
+    int fill = 0;
+    int skip = 0;
+    bool clean = true;
+    for (int i = 0; i < int(str.size()); i++) {
+        char c = str[i];
+        uint32_t value;
+
+        if      ((c >= 'A') && (c <= 'Z')) value = c - 'A';
+        else if ((c >= 'a') && (c <= 'z')) value = c - 'a' + 26;
+        else if ((c >= '0') && (c <= '9')) value = c - '0' + 52;
+        else if (c == '+') value = 62;
+        else if (c == '/') value = 63;
+        else if (c == '=') { value = 0; skip ++; }
+        else { clean=false; continue; }
+
+        chunk = (chunk << 6) | value;
+        fill ++;
+        if (fill == 4) {
+            oss->put((chunk>>16) & 0xFF);
+            if (skip < 2) oss->put((chunk>>8) & 0xFF);
+            if (skip < 1) oss->put(chunk & 0xFF);
+            chunk = 0; fill = 0; skip = 0;
+        }
+    }
+    if (fill != 0) clean = false;
+    return clean;
+}
+
 IdVector id_vector_create(int64_t id1, int64_t id2, int64_t id3, int64_t id4) {
     IdVector result;
     if (id1 >= 0) result.push_back(id1);
@@ -406,8 +528,7 @@ HashValue hash_id_vector(const IdVector &idv) {
 
 eng::string hash_to_hex(const HashValue &hv) {
     eng::ostringstream oss;
-    oss << std::hex << std::setw(16) << std::setfill('0') << hv.first;
-    oss << std::hex << std::setw(16) << std::setfill('0') << hv.second;
+    oss << hex64.val(hv.first) << hex64.val(hv.second);
     return oss.str();    
 }
 static inline uint64_t Rot64(uint64_t x, int k)
@@ -530,6 +651,52 @@ eng::string toupper(eng::string input) {
     return input;
 }
 
+static void buffer_codepoint_utf8(int32_t scp, char *buffer) {
+    uint32_t cp = (uint32_t)scp;
+    unsigned char *c = (unsigned char *)buffer;
+    if (cp <= 0x7F) {
+        c[0] = cp;
+        c[1] = 0;
+    }
+    else if (cp <= 0x7FF) {
+        c[0] = (cp>>6)+192;
+        c[1] = (cp&63)+128;
+        c[2] = 0;
+    }
+    else if (cp <= 0xFFFF) {
+        if (0xd800 <= cp && cp <= 0xdfff) {
+            c[0] = 0;
+        } else {
+            c[0] = (cp>>12)+224;
+            c[1] = ((cp>>6)&63)+128;
+            c[2] = (cp&63)+128;
+            c[3] = 0;
+        }
+    }
+    else if (cp <= 0x10FFFF) {
+        c[0] = (cp>>18)+240;
+        c[1] = ((cp>>12)&63)+128;
+        c[2] = ((cp>>6)&63)+128;
+        c[3] = (cp&63)+128;
+        c[4] = 0;
+    } else {
+        c[0] = 0;
+    }
+}
+
+eng::string get_codepoint_utf8(uint32_t cp) {
+    char buffer[5];
+    buffer_codepoint_utf8(cp, buffer);
+    return eng::string(buffer);
+}
+
+bool write_codepoint_utf8(int32_t cp, std::ostream *s) {
+    char buffer[5];
+    buffer_codepoint_utf8(cp, buffer);
+    (*s) << buffer;
+    return buffer[0] != 0;
+}
+
 double distance_squared(double x1, double y1, double x2, double y2) {
     double dx = x1 - x2;
     double dy = y1 - y2;
@@ -549,35 +716,20 @@ eng::string XYZ::debug_string() const {
     return oss.str();
 }
 
-
 } // namespace util
 
-std::ostream &operator<<(std::ostream &oss, const util::hex64 &v) {
-    oss << "0x" << std::setw(16) << std::setfill('0') << std::hex;
-    return oss;
-}
 
-std::ostream &operator<<(std::ostream &oss, const util::hex32 &v) {
-    oss << "0x" << std::setw(8) << std::setfill('0') << std::hex;
-    return oss;
-}
-
-std::ostream &operator<<(std::ostream &oss, const util::hex16 &v) {
-    oss << "0x" << std::setw(4) << std::setfill('0') << std::hex;
-    return oss;
-}
-
-std::ostream &operator<<(std::ostream &oss, const util::hex8 &v) {
-    oss << "0x" << std::setw(2) << std::setfill('0') << std::hex;
-    return oss;
+static std::string_view read_number_x(const char *p, bool plus, bool minus, bool dec, bool exp) {
+    std::string_view source = p;
+    return sv::read_number(source, plus, minus, dec, exp);
 }
 
 LuaDefine(unittests_util, "", "some unit tests") {
         // test str_to_int64, str_to_double
     LuaAssert(L, sv::to_int64("123") == 123);
-    LuaAssert(L, sv::to_int64("123.4") == INT64_MIN);
-    LuaAssert(L, sv::to_int64("12ab") == INT64_MIN);
-    LuaAssert(L, sv::to_int64("") == INT64_MIN);
+    LuaAssert(L, sv::to_int64("123.4") == INT64_MAX);
+    LuaAssert(L, sv::to_int64("12ab") == INT64_MAX);
+    LuaAssert(L, sv::to_int64("") == INT64_MAX);
     LuaAssert(L, sv::to_double("123.5") == 123.5);
     LuaAssert(L, std::isnan(sv::to_double("12ab")));
     LuaAssert(L, std::isnan(sv::to_double("")));
@@ -689,6 +841,20 @@ LuaDefine(unittests_util, "", "some unit tests") {
     LuaAssert(L, util::hash_to_double(0x1000000000000000) == 1.0/16.0);
     LuaAssert(L, util::hash_to_double(0x7000000000000000) == 7.0/16.0);
     LuaAssert(L, util::hash_to_double(0xF000000000000000) == 15.0/16.0);
+
+    // Test read_number allowing everything.
+    LuaAssert(L, read_number_x("123x", true, true, true, true) == "123");
+    LuaAssert(L, read_number_x("123.3x", true, true, true, true) == "123.3");
+    LuaAssert(L, read_number_x("123.x", true, true, true, true) == "123.");
+    LuaAssert(L, read_number_x("123..x", true, true, true, true) == "123.");
+    LuaAssert(L, read_number_x("-123x", true, true, true, true) == "-123");
+    LuaAssert(L, read_number_x("+123x", true, true, true, true) == "+123");
+    LuaAssert(L, read_number_x("+-123x", true, true, true, true) == "");
+    LuaAssert(L, read_number_x("-123.02e05x", true, true, true, true) == "-123.02e05");
+    LuaAssert(L, read_number_x("-123e-5x", true, true, true, true) == "-123e-5");
+    LuaAssert(L, read_number_x("-123e+5x", true, true, true, true) == "-123e+5");
+    LuaAssert(L, read_number_x("-123e+x", true, true, true, true) == "");
+    
     return 0;
 }
 
diff --git a/luprex/core/cpp/util.hpp b/luprex/core/cpp/util.hpp
index 45bbcf17..43ec4ada 100644
--- a/luprex/core/cpp/util.hpp
+++ b/luprex/core/cpp/util.hpp
@@ -26,6 +26,9 @@
 #include <utility>
 #include <algorithm>
 #include <string_view>
+#include <cstdint>
+#include <limits>
+#include <iomanip>
 
 #include "luastack.hpp"
 #include "spookyv2.hpp"
@@ -59,9 +62,17 @@ bool valid_double(string_view v);
 bool valid_int64(string_view v);
 bool valid_hex64(string_view v);
 
-// Parse numbers as int32, int64, or double.  Returns errval on failure.
+// Convert strings to numbers.  Returns errval on failure.
+//
+// The integer parser accepts a sequence of digits,
+// with or without a + or - sign.   The hex parser
+// does not allow a + or - sign.  For both the int64
+// and hex64 parser, it is a failure if the number
+// does not fit in 64 bits.  The double parser does
+// not accept the strings 'nan' or 'inf'.
+//
 double to_double(string_view v, double errval = std::numeric_limits<double>::quiet_NaN());
-int64_t to_int64(string_view v, int64_t errval = std::numeric_limits<int64_t>::min());
+int64_t to_int64(string_view v, int64_t errval = std::numeric_limits<int64_t>::max());
 uint64_t to_hex64(string_view v, uint64_t errval = std::numeric_limits<uint64_t>::max());
 
 // Trim whitspace from a string_view.
@@ -115,6 +126,13 @@ string_view read_to_sep(string_view &source, char sep);
 //
 string_view read_to_line(string_view &source);
 
+// Read a prefix string from a string_view.
+//
+// Returns false if the string view doesn't start with
+// the specified prefix.
+//
+bool read_prefix(string_view &source, string_view prefix); 
+
 // Read from a string_view until whitespace is reached.
 //
 // If there's any whitespace in the source, returns the text
@@ -136,9 +154,46 @@ string_view read_nbytes(string_view &source, int nbytes);
 //
 string_view read_ascii_identifier(string_view &source);
 
+// Read a number from a string view
+//
+// This is basically a regex pattern matching routine
+// hardwired with the regex for numbers.  You must
+// specify which of the following parts of the regex
+// are allowed or not:
+//
+//  * plus sign
+//  * minus sign
+//  * decimal point
+//  * scientific notation exponents
+//
+// Returns the number as a string_view.  There is
+// no guarantee that the number is small enough to
+// fit into any particular number of bits.  This
+// always uses base 10.
+//
+std::string_view read_number(string_view &source, bool plus, bool minus, bool dec, bool exp);
+
+// Read an ascii character from a string.
+//
+// Returns -1 if the string is empty.
+//
+int32_t read_ascii_char(string_view &source);
+
+// Read a UTF8 codepoint from a string_view.
+//
+// If the next thing in the string_view isn't a valid
+// codepoint, returns -1 and doesn't update the view.
+//
+int32_t read_codepoint_utf8(string_view &source);
+
 // Return true if the string is valid utf-8.
 bool valid_utf8(string_view s);
 
+// Return true if the number conforms to the spec.
+// See read_number for more information.
+//
+bool valid_number(string_view v, bool plus, bool minus, bool dec, bool exp);
+
 } // namespace sv
 
 namespace util {
@@ -175,6 +230,16 @@ double profiling_clock();
 // Output a string to a stream using Lua string escaping and quoting.
 void quote_string(const eng::string &str, std::ostream *os);
 
+// base64 encode.
+void base64_encode(std::string_view v, std::ostream *oss);
+
+// base64 decode.
+//
+// Returns true if the base64 was 'clean' base64, as
+// opposed to base64 with extraneous characters.
+//
+bool base64_decode(std::string_view v, std::ostream *oss);
+
 // ID vector quick create.
 IdVector id_vector_create(int64_t id1=-1, int64_t id2=-1, int64_t id3=-1, int64_t id4=-1);
 
@@ -219,6 +284,14 @@ eng::string repeat_string(const eng::string &a, int n);
 eng::string tolower(eng::string input);
 eng::string toupper(eng::string input);
 
+// Convert a codepoint number into a utf8 string.
+// If the codepoint is invalid, returns empty string.
+eng::string get_codepoint_utf8(int32_t cp);
+
+// Write a codepoint in utf8 to a stream.
+// If the codepoint is invalid, writes nothing and returns false.
+bool write_codepoint_utf8(int32_t cp, std::ostream *out);
+
 // Calculate distance between two points
 double distance_squared(double x1, double y1, double x2, double y2);
 
@@ -249,12 +322,6 @@ struct XYZ {
     eng::string debug_string() const;
 };
 
-// These are formatting directives that can be sent to a std::ostream.
-class hex64 {};
-class hex32 {};
-class hex16 {};
-class hex8 {};
-
 class NullStreamBuffer : public std::streambuf
 {
 public:
@@ -264,24 +331,62 @@ public:
 // send_to_stream: send all arguments to the specified stream.
 inline void send_to_stream(std::ostream &os) {}
 template <class ARG, class... REST>
-inline void send_to_stream(std::ostream &os, ARG arg, REST & ... rest) {
+inline void send_to_stream(std::ostream &os, const ARG &arg, const REST & ... rest) {
     os << arg;
     send_to_stream(os, rest...);
 }
 
 // ss: convert all arguments to a string by sending them to a stringstream.
 template <class... ARGS>
-inline eng::string ss(ARGS & ... args) {
+inline eng::string ss(const ARGS & ... args) {
     eng::ostringstream oss;
     send_to_stream(oss, args...);
     return oss.str();
 }
 
+// This is a better way to do std::setfill, std::hex, std::setprecision
+//
+// Usage examples:
+//   std::cout << util::hex.width(5).fill('0').val(123)
+//   std::cout << util::dec.fill('$').precision(val(123)
+//
+template <class VALUE>
+class FormattedNumber {
+public:
+    VALUE value_;
+    bool hex_;
+    int width_;
+    char fill_;
+    int precision_;
+
+    constexpr FormattedNumber(VALUE v, bool h, int w, char f, int p)
+        : value_(v), hex_(h), width_(w), fill_(f), precision_(p) {}
+
+    constexpr FormattedNumber width(int w) const { return FormattedNumber(value_, hex_, w, fill_, precision_); }
+    constexpr FormattedNumber fill(char f) const { return FormattedNumber(value_, hex_, width_, f, precision_); }
+    constexpr FormattedNumber precision(int p) const { return FormattedNumber(value_, hex_, width_, fill_, p); }
+
+    template <class NVALUE>
+    constexpr FormattedNumber val(NVALUE v) const { return FormattedNumber(v, hex_, width_, fill_, precision_); }
+};
+
+constexpr auto hex = FormattedNumber<int>(0, true, 0, '0', 6);
+constexpr auto hex8 = FormattedNumber<int>(0, true, 2, '0', 6);
+constexpr auto hex16 = FormattedNumber<int>(0, true, 4, '0', 6);
+constexpr auto hex32 = FormattedNumber<int>(0, true, 8, '0', 6);
+constexpr auto hex64 = FormattedNumber<int>(0, true, 16, '0', 6);
+constexpr auto dec = FormattedNumber<int>(0, false, 0, ' ', 6);
+
 } // namespace util
 
-std::ostream &operator<<(std::ostream &oss, const util::hex64 &v);
-std::ostream &operator<<(std::ostream &oss, const util::hex32 &v);
-std::ostream &operator<<(std::ostream &oss, const util::hex16 &v);
-std::ostream &operator<<(std::ostream &oss, const util::hex8 &v);
+template<class VALUE>
+inline std::ostream &operator<<(std::ostream &oss, util::FormattedNumber<VALUE> n) {
+    if (n.hex_) oss << std::hex;
+    else oss << std::dec;
+    oss << std::setprecision(n.precision_) << std::setfill(n.fill_) << std::setw(n.width_) << n.value_;
+    oss << std::dec << std::setfill(' ') << std::setprecision(6);
+    return oss;
+}
+
 
 #endif // UTIL_HPP
diff --git a/luprex/core/cpp/world-difftab.cpp b/luprex/core/cpp/world-difftab.cpp
index 1dad1037..59f0c10f 100644
--- a/luprex/core/cpp/world-difftab.cpp
+++ b/luprex/core/cpp/world-difftab.cpp
@@ -56,6 +56,10 @@ static bool equivalent_values(LuaStack &MLS, LuaSlot mval, LuaSlot mtnmap,
         if (SLS.type(sval) != LUA_TSTRING) return false;
         return MLS.ckstring(mval) == SLS.ckstring(sval);
     }
+    case LUA_TLIGHTUSERDATA: {
+        if (SLS.type(sval) != LUA_TLIGHTUSERDATA) return false;
+        return MLS.cktoken(mval) == SLS.cktoken(sval);
+    }
     case LUA_TFUNCTION: {
         // Cannot really compare.  Just return true if the types match.
         return SLS.type(sval) == MLS.type(mval);
@@ -105,6 +109,11 @@ static void transmit_value(LuaStack &MLS, LuaSlot mval, LuaSlot mtnmap, StreamBu
         sb->write_string(MLS.ckstring(mval));
         return;
     }
+    case LUA_TLIGHTUSERDATA: {
+        sb->write_uint8(LUA_TLIGHTUSERDATA);
+        sb->write_uint64(MLS.cktoken(mval).value);
+        return;
+    }
     case LUA_TT_GENERAL: {
         int midx = get_table_number(MLS, mval, mtnmap);
         if (midx == 0) {
@@ -151,6 +160,10 @@ static void transmit_value_debug_string(StreamBuffer *sb, eng::ostringstream &os
         oss << sb->read_string();
         return;
     }
+    case LUA_TLIGHTUSERDATA: {
+        LuaToken token(sb->read_uint64());
+        oss << "[" << token.str() << "]";
+    }
     case LUA_TT_GENERAL: {
         oss << "table " << sb->read_int32();
         return;
@@ -270,6 +283,12 @@ static void set_transmitted_value(LuaStack &LS, LuaSlot tangibles, LuaSlot ntmap
         LS.set(target, value);
         return;
     }
+    case LUA_TLIGHTUSERDATA: {
+        LuaToken value(sb->read_uint64());
+        DebugLine(dbc) << dbinfo << "[" << value.str() << "]";
+        LS.set(target, value);
+        return;
+    }
     case LUA_TT_GENERAL: {
         int index = sb->read_int32();
         DebugLine(dbc) << dbinfo << "table " << index;