ucx/json.c

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2024 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "cx/json.h"
#include "cx/kv_list.h"

#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <inttypes.h>
#include <ctype.h>

/*
 * RFC 8259
 * https://tools.ietf.org/html/rfc8259
 */

static CxJsonValue cx_json_value_nothing = {.type = CX_JSON_NOTHING};

static void token_destroy(CxJsonToken *token) {
    if (token->allocated) {
        cx_strfree(&token->content);
        token->allocated = false;
    }
}

static int num_isexp(const char *content, size_t length, size_t pos) {
    if (pos >= length) {
        return 0;
    }

    int ok = 0;
    for (size_t i = pos; i < length; i++) {
        char c = content[i];
        if (isdigit((unsigned char)c)) {
            ok = 1;
        } else if (i == pos) {
            if (!(c == '+' || c == '-')) {
                return 0;
            }
        } else {
            return 0;
        }
    }

    return ok;
}

static CxJsonTokenType token_numbertype(const char *content, size_t length) {
    if (length == 0) return CX_JSON_TOKEN_ERROR;

    if (content[0] != '-' && !isdigit((unsigned char)content[0])) {
        return CX_JSON_TOKEN_ERROR;
    }

    CxJsonTokenType type = CX_JSON_TOKEN_INTEGER;
    for (size_t i = 1; i < length; i++) {
        if (content[i] == '.') {
            if (type == CX_JSON_TOKEN_NUMBER) {
                return CX_JSON_TOKEN_ERROR; // more than one decimal separator
            }
            type = CX_JSON_TOKEN_NUMBER;
        } else if (content[i] == 'e' || content[i] == 'E') {
            return num_isexp(content, length, i + 1) ? CX_JSON_TOKEN_NUMBER : CX_JSON_TOKEN_ERROR;
        } else if (!isdigit((unsigned char)content[i])) {
            return CX_JSON_TOKEN_ERROR; // char is not a digit, decimal separator or exponent sep
        }
    }

    return type;
}

static CxJsonToken token_create(CxJson *json, bool isstring, size_t start, size_t end) {
    cxmutstr str = cx_mutstrn(json->buffer.space + start, end - start);
    bool allocated = false;
    if (json->uncompleted.tokentype != CX_JSON_NO_TOKEN) {
        allocated = true;
        str = cx_strcat_m(json->uncompleted.content, 1, str);
        if (str.ptr == NULL) { // LCOV_EXCL_START
            return (CxJsonToken){CX_JSON_NO_TOKEN, false, {NULL, 0}};
        } // LCOV_EXCL_STOP
    }
    json->uncompleted = (CxJsonToken){0};
    CxJsonTokenType ttype;
    if (isstring) {
        ttype = CX_JSON_TOKEN_STRING;
    } else {
        cxstring s = cx_strcast(str);
        if (!cx_strcmp(s, "true") || !cx_strcmp(s, "false")
            || !cx_strcmp(s, "null")) {
            ttype = CX_JSON_TOKEN_LITERAL;
        } else {
            ttype = token_numbertype(str.ptr, str.length);
        }
    }
    if (ttype == CX_JSON_TOKEN_ERROR) {
        if (allocated) {
            cx_strfree(&str);
        }
        return (CxJsonToken){CX_JSON_TOKEN_ERROR, false, {NULL, 0}};
    }
    return (CxJsonToken){ttype, allocated, str};
}

static CxJsonTokenType char2ttype(char c) {
    switch (c) {
        case '[': {
            return CX_JSON_TOKEN_BEGIN_ARRAY;
        }
        case '{': {
            return CX_JSON_TOKEN_BEGIN_OBJECT;
        }
        case ']': {
            return CX_JSON_TOKEN_END_ARRAY;
        }
        case '}': {
            return CX_JSON_TOKEN_END_OBJECT;
        }
        case ':': {
            return CX_JSON_TOKEN_NAME_SEPARATOR;
        }
        case ',': {
            return CX_JSON_TOKEN_VALUE_SEPARATOR;
        }
        case '"': {
            return CX_JSON_TOKEN_STRING;
        }
        default: {
            if (isspace((unsigned char)c)) {
                return CX_JSON_TOKEN_SPACE;
            }
        }
    }
    return CX_JSON_NO_TOKEN;
}

static enum cx_json_status token_parse_next(CxJson *json, CxJsonToken *result) {
    // check if there is data in the buffer
    if (cxBufferEof(&json->buffer)) {
        return json->uncompleted.tokentype == CX_JSON_NO_TOKEN ?
            CX_JSON_NO_DATA : CX_JSON_INCOMPLETE_DATA;
    }

    // current token type and start index
    CxJsonTokenType ttype = json->uncompleted.tokentype;
    size_t token_part_start = json->buffer.pos;

    bool escape_end_of_string = ttype == CX_JSON_TOKEN_STRING
        && json->uncompleted.content.ptr[json->uncompleted.content.length-1] == '\\';

    for (size_t i = json->buffer.pos; i < json->buffer.size; i++) {
        char c = json->buffer.space[i];
        if (ttype != CX_JSON_TOKEN_STRING) {
            // currently non-string token
            CxJsonTokenType ctype = char2ttype(c); // start of new token?
            if (ttype == CX_JSON_NO_TOKEN) {
                if (ctype == CX_JSON_TOKEN_SPACE) {
                    json->buffer.pos++;
                    continue;
                } else if (ctype == CX_JSON_TOKEN_STRING) {
                    // begin string
                    ttype = CX_JSON_TOKEN_STRING;
                    token_part_start = i;
                } else if (ctype != CX_JSON_NO_TOKEN) {
                    // single-char token
                    json->buffer.pos = i + 1;
                    *result = (CxJsonToken){ctype, false, {NULL, 0}};
                    return CX_JSON_NO_ERROR;
                } else {
                    ttype = CX_JSON_TOKEN_LITERAL; // number or literal
                    token_part_start = i;
                }
            } else {
                // finish token
                if (ctype != CX_JSON_NO_TOKEN) {
                    *result = token_create(json, false, token_part_start, i);
                    if (result->tokentype == CX_JSON_NO_TOKEN) {
                        return CX_JSON_BUFFER_ALLOC_FAILED; // LCOV_EXCL_LINE
                    }
                    if (result->tokentype == CX_JSON_TOKEN_ERROR) {
                        return CX_JSON_FORMAT_ERROR_NUMBER;
                    }
                    json->buffer.pos = i;
                    return CX_JSON_NO_ERROR;
                }
            }
        } else {
            // currently inside a string
            if (escape_end_of_string) {
                escape_end_of_string = false;
            } else {
                if (c == '"') {
                    *result = token_create(json, true, token_part_start, i + 1);
                    if (result->tokentype == CX_JSON_NO_TOKEN) {
                        return CX_JSON_BUFFER_ALLOC_FAILED; // LCOV_EXCL_LINE
                    }
                    json->buffer.pos = i + 1;
                    return CX_JSON_NO_ERROR;
                } else if (c == '\\') {
                    escape_end_of_string = true;
                }
            }
        }
    }

    if (ttype == CX_JSON_NO_TOKEN) {
        return CX_JSON_NO_DATA;
    } else {
        // uncompleted token
        size_t uncompleted_len = json->buffer.size - token_part_start;
        if (json->uncompleted.tokentype == CX_JSON_NO_TOKEN) {
            // current token is uncompleted
            // save current token content
            CxJsonToken uncompleted = {
                ttype, true,
                cx_strdup(cx_strn(json->buffer.space + token_part_start, uncompleted_len))
            };
            if (uncompleted.content.ptr == NULL) {
                return CX_JSON_BUFFER_ALLOC_FAILED; // LCOV_EXCL_LINE
            }
            json->uncompleted = uncompleted;
        } else {
            // previously we also had an uncompleted token
            // combine the uncompleted token with the current token
            assert(json->uncompleted.allocated);
            cxmutstr str = cx_strcat_m(json->uncompleted.content, 1,
                cx_strn(json->buffer.space + token_part_start, uncompleted_len));
            if (str.ptr == NULL) {
                return CX_JSON_BUFFER_ALLOC_FAILED; // LCOV_EXCL_LINE
            }
            json->uncompleted.content = str;
        }
        // advance the buffer position - we saved the stuff in the uncompleted token
        json->buffer.pos += uncompleted_len;
        return CX_JSON_INCOMPLETE_DATA;
    }
}

// converts a Unicode codepoint to utf8
static unsigned codepoint_to_utf8(uint32_t codepoint, char *output_buf) {
    if (codepoint <= 0x7F) {
        *output_buf = (char)codepoint;
        return 1;
    } else if (codepoint <= 0x7FF) {
        output_buf[0] = (char)(0xC0 | ((codepoint >> 6) & 0x1F));
        output_buf[1] = (char)(0x80 | (codepoint & 0x3F));
        return 2;
    } else if (codepoint <= 0xFFFF) {
        output_buf[0] = (char)(0xE0 | ((codepoint >> 12) & 0x0F));
        output_buf[1] = (char)(0x80 | ((codepoint >> 6) & 0x3F));
        output_buf[2] = (char)(0x80 | (codepoint & 0x3F));
        return 3;
    } else if (codepoint <= 0x10FFFF) {
        output_buf[0] = (char)(0xF0 | ((codepoint >> 18) & 0x07));
        output_buf[1] = (char)(0x80 | ((codepoint >> 12) & 0x3F));
        output_buf[2] = (char)(0x80 | ((codepoint >> 6) & 0x3F));
        output_buf[3] = (char)(0x80 | (codepoint & 0x3F));
        return 4;
    }
    
    return 0; // LCOV_EXCL_LINE
}

// converts a utf16 surrogate pair to utf8
static inline uint32_t utf16pair_to_codepoint(uint16_t c0, uint16_t c1) {
    return ((c0 - 0xD800) << 10) + (c1 - 0xDC00) + 0x10000;
}

static unsigned unescape_unicode_string(cxstring str, char *utf8buf) {
    // str is supposed to start with "\uXXXX" or "\uXXXX\uXXXX"
    // remaining bytes in the string are ignored (str may be larger!)

    if (str.length < 6 || str.ptr[0] != '\\' || str.ptr[1] != 'u') {
        return 0;
    }

    unsigned utf8len = 0;
    cxstring ustr1 = { str.ptr + 2, 4};
    uint16_t utf16a, utf16b;
    if (!cx_strtou16_lc(ustr1, &utf16a, 16, "")) {
        uint32_t codepoint;
        if (utf16a < 0xD800 || utf16a > 0xE000) {
            // character is in the Basic Multilingual Plane
            // and encoded as a single utf16 char
            codepoint = utf16a;
            utf8len = codepoint_to_utf8(codepoint, utf8buf);
        } else if (utf16a >= 0xD800 && utf16a <= 0xDBFF) {
            // character is encoded as a surrogate pair
            // get next 6 bytes
            if (str.length >= 12) {
                if (str.ptr[6] == '\\' && str.ptr[7] == 'u') {
                    cxstring ustr2 = { str.ptr+8, 4 };
                    if (!cx_strtou16_lc(ustr2, &utf16b, 16, "")
                            && utf16b >= 0xDC00 && utf16b <= 0xDFFF) {
                        codepoint = utf16pair_to_codepoint(utf16a, utf16b);
                        utf8len = codepoint_to_utf8(codepoint, utf8buf);
                    }
                }
            }
        }
    }
    return utf8len;
}

static cxmutstr unescape_string(const CxAllocator *a, cxmutstr str) {
    // note: this function expects that str contains the enclosing quotes!

    cxmutstr result;
    result.length = 0;
    result.ptr = cxMalloc(a, str.length - 1);
    if (result.ptr == NULL) return result; // LCOV_EXCL_LINE

    bool u = false;
    for (size_t i = 1; i < str.length - 1; i++) {
        char c = str.ptr[i];
        if (u) {
            u = false;
            if (c == 'n') {
                c = '\n';
            } else if (c == '"') {
                c = '"';
            } else if (c == 't') {
                c = '\t';
            } else if (c == 'r') {
                c = '\r';
            } else if (c == '\\') {
                c = '\\';
            } else if (c == '/') {
                c = '/'; // always unescape, we don't need settings here
            } else if (c == 'f') {
                c = '\f';
            } else if (c == 'b') {
                c = '\b';
            } else if (c == 'u') {
                char utf8buf[4];
                unsigned utf8len = unescape_unicode_string(
                    cx_strn(str.ptr + i - 1, str.length - i),
                    utf8buf
                );
                if(utf8len > 0) {
                    i += utf8len < 4 ? 4 : 10;
                    // add all bytes from utf8buf except the last char
                    // to the result (last char will be added below)
                    utf8len--;
                    c = utf8buf[utf8len];
                    for (unsigned x = 0; x < utf8len; x++) {
                        result.ptr[result.length++] = utf8buf[x];
                    }
                } else {
                    // decoding failed, ignore the entire sequence
                    result.ptr[result.length++] = '\\';
                }
            } else {
                // TODO: discuss the behavior for unrecognized escape sequences
                //       most parsers throw an error here - we just ignore it
                result.ptr[result.length++] = '\\'; // LCOV_EXCL_LINE
            }

            result.ptr[result.length++] = c;
        } else {
            if (c == '\\') {
                u = true;
            } else {
                result.ptr[result.length++] = c;
            }
        }
    }
    result.ptr[result.length] = 0;

    return result;
}

static cxmutstr escape_string(cxstring str, bool escape_slash) {
    // note: this function produces the string without enclosing quotes
    // the reason is that we don't want to allocate memory just for that
    CxBuffer buf = {0};

    bool all_printable = true;
    for (size_t i = 0; i < str.length; i++) {
        unsigned char c = str.ptr[i];
        bool escape = c < 0x20 || c == '\\' || c == '"'
            || (escape_slash && c == '/');

        if (all_printable && escape) {
            size_t capa = str.length + 32;
            char *space = cxMallocDefault(capa);
            if (space == NULL) return cx_mutstrn(NULL, 0);
            cxBufferInit(&buf, NULL, space, capa, CX_BUFFER_AUTO_EXTEND);
            cxBufferWrite(str.ptr, 1, i, &buf);
            all_printable = false;
        }
        if (escape) {
            cxBufferPut(&buf, '\\');
            if (c == '\"') {
                cxBufferPut(&buf, '\"');
            } else if (c == '\n') {
                cxBufferPut(&buf, 'n');
            } else if (c == '\t') {
                cxBufferPut(&buf, 't');
            } else if (c == '\r') {
                cxBufferPut(&buf, 'r');
            } else if (c == '\\') {
                cxBufferPut(&buf, '\\');
            } else if (c == '/') {
                cxBufferPut(&buf, '/');
            } else if (c == '\f') {
                cxBufferPut(&buf, 'f');
            } else if (c == '\b') {
                cxBufferPut(&buf, 'b');
            } else {
                char code[6];
                snprintf(code, sizeof(code), "u%04x", (unsigned int) c);
                cxBufferPutString(&buf, code);
            }
        } else if (!all_printable) {
            cxBufferPut(&buf, c);
        }
    }
    cxmutstr ret;
    if (all_printable) {
        // don't copy the string when we don't need to escape anything
        ret = cx_mutstrn((char*)str.ptr, str.length);
    } else {
        ret = cx_mutstrn(buf.space, buf.size);
    }
    cxBufferDestroy(&buf);
    return ret;
}

static CxJsonObject json_create_object_map(const CxAllocator *allocator) {
    CxMap *map = cxKvListCreateAsMap(allocator, CX_STORE_POINTERS);
    if (map == NULL) return NULL; // LCOV_EXCL_LINE
    cxSetCompareFunc(map, cxJsonCompare);
    cxSetDestructor(map, cxJsonValueFree);
    return map;
}

static void json_free_object_map(CxJsonObject obj) {
    cxMapFree(obj);
}

static CxJsonValue* json_create_value(CxJson *json, CxJsonValueType type) {
    CxJsonValue *v = cxCalloc(json->allocator, 1, sizeof(CxJsonValue));
    if (v == NULL) return NULL; // LCOV_EXCL_LINE

    // initialize the value
    v->type = type;
    v->allocator = json->allocator;
    if (type == CX_JSON_ARRAY) {
        if (cx_array_init_a(json->allocator, v->array, 16)) {
            goto create_json_value_exit_error; // LCOV_EXCL_LINE
        }
    } else if (type == CX_JSON_OBJECT) {
        v->object = json_create_object_map(json->allocator);
        if (v->object == NULL) goto create_json_value_exit_error; // LCOV_EXCL_LINE
    }

    // add the new value to a possible parent
    if (json->vbuf.size > 0) {
        CxJsonValue *parent = json->vbuf.data[json->vbuf.size - 1];
        assert(parent != NULL);
        if (parent->type == CX_JSON_ARRAY) {
            if (cx_array_add_a(json->allocator, parent->array, &v)) {
                goto create_json_value_exit_error; // LCOV_EXCL_LINE
            }
        } else if (parent->type == CX_JSON_OBJECT) {
            // the member was already created after parsing the name
            // store the pointer of the uncompleted value in the map
            assert(json->uncompleted_member_name.ptr != NULL);
            if (cxMapPut(parent->object, json->uncompleted_member_name, v)) {
                goto create_json_value_exit_error; // LCOV_EXCL_LINE
            }
            cx_strfree_a(json->allocator, &json->uncompleted_member_name);
        } else {
            assert(false); // LCOV_EXCL_LINE
        }
    }

    // add the new value to the stack, if it is an array or object
    if (type == CX_JSON_ARRAY || type == CX_JSON_OBJECT) {
        if (json->vbuf.size >= json->vbuf.capacity) {
            int alloc_error;
            if (json->vbuf.data == json->vbuf_internal) {
                alloc_error = cx_array_copy_to_new(json->vbuf, json->vbuf.size+1);
            } else {
                alloc_error = cx_array_reserve(json->vbuf, json->vbuf.size+1);
            }
            if (alloc_error) {
                goto create_json_value_exit_error; // LCOV_EXCL_LINE
            }
        }
        json->vbuf.data[json->vbuf.size] = v;
        json->vbuf.size++;
    }

    // if currently no value is parsed, this is now the value of interest
    if (json->parsed == NULL) {
        json->parsed = v;
    }

    return v;
    // LCOV_EXCL_START
create_json_value_exit_error:
    cxJsonValueFree(v);
    return NULL;
    // LCOV_EXCL_STOP
}

#define JP_STATE_VALUE_BEGIN         0
#define JP_STATE_VALUE_END          10
#define JP_STATE_VALUE_BEGIN_OBJ     1
#define JP_STATE_OBJ_SEP_OR_CLOSE   11
#define JP_STATE_VALUE_BEGIN_AR      2
#define JP_STATE_ARRAY_SEP_OR_CLOSE 12
#define JP_STATE_OBJ_NAME_OR_CLOSE   5
#define JP_STATE_OBJ_NAME            6
#define JP_STATE_OBJ_COLON           7

void cxJsonInit(CxJson *json, const CxAllocator *allocator) {
    if (allocator == NULL) {
        allocator = cxDefaultAllocator;
    }
    
    memset(json, 0, sizeof(CxJson));
    json->allocator = allocator;

    cx_array_init_fixed(json->states, json->states_internal, 1);
    json->states.data[0] = JP_STATE_VALUE_BEGIN;
    cx_array_init_fixed(json->vbuf, json->vbuf_internal, 0);
}

void cxJsonDestroy(CxJson *json) {
    cxBufferDestroy(&json->buffer);
    if (json->states.data != json->states_internal) {
        cx_array_free(json->states);
    }
    if (json->vbuf.data != json->vbuf_internal) {
        cx_array_free(json->vbuf);
    }
    cxJsonValueFree(json->parsed);
    json->parsed = NULL;
    token_destroy(&json->uncompleted);
    cx_strfree_a(json->allocator, &json->uncompleted_member_name);
}

void cxJsonReset(CxJson *json) {
    const CxAllocator *allocator = json->allocator;
    cxJsonDestroy(json);
    cxJsonInit(json, allocator);
}

int cxJsonFilln(CxJson *json, const char *buf, size_t size) {
    if (cxBufferEof(&json->buffer)) {
        // reinitialize the buffer
        cxBufferDestroy(&json->buffer);
        if (buf == NULL) buf = ""; // buffer must not be initialized with NULL
        cxBufferInit(&json->buffer, NULL, (char*) buf,
                     size, CX_BUFFER_AUTO_EXTEND | CX_BUFFER_COPY_ON_WRITE);
        json->buffer.size = size;
        return 0;
    } else {
        return size != cxBufferAppend(buf, 1, size, &json->buffer);
    }
}

static void json_add_state(CxJson *json, int state) {
    // we have guaranteed the necessary space
    // therefore, we can safely add the state in the simplest way possible
    json->states.data[json->states.size++] = state;
}

#define return_rec(code) \
    token_destroy(&token); \
    return code

static enum cx_json_status json_parse(CxJson *json) {
    // Reserve a pointer for a possibly read value
    CxJsonValue *vbuf = NULL;

    // grab the next token
    CxJsonToken token;
    {
        enum cx_json_status ret = token_parse_next(json, &token);
        if (ret != CX_JSON_NO_ERROR) {
            return ret;
        }
    }

    // pop the current state
    assert(json->states.size > 0);
    int state = json->states.data[--json->states.size];

    // guarantee that at least two more states fit into the array
    const size_t required_states_depth = json->states.size + 2;
    if (required_states_depth >= json->states.capacity) {
        int alloc_error;
        if (json->states.data == json->states_internal) {
            alloc_error = cx_array_copy_to_new(json->states, required_states_depth);
        } else {
            alloc_error = cx_array_reserve(json->states, required_states_depth);
        }
        if (alloc_error) {
            return CX_JSON_BUFFER_ALLOC_FAILED; // LCOV_EXCL_LINE
        }
    }


    //  0 JP_STATE_VALUE_BEGIN          value begin
    // 10 JP_STATE_VALUE_END            expect value end
    //  1 JP_STATE_VALUE_BEGIN_OBJ      value begin (inside object)
    // 11 JP_STATE_OBJ_SEP_OR_CLOSE     object, expect separator, objclose
    //  2 JP_STATE_VALUE_BEGIN_AR       value begin (inside array)
    // 12 JP_STATE_ARRAY_SEP_OR_CLOSE   array, expect separator or arrayclose
    //  5 JP_STATE_OBJ_NAME_OR_CLOSE    object, expect name or objclose
    //  6 JP_STATE_OBJ_NAME             object, expect name
    //  7 JP_STATE_OBJ_COLON            object, expect ':'

    if (state < 3) {
        // push expected end state to the stack
        json_add_state(json, 10 + state);
        switch (token.tokentype) {
            case CX_JSON_TOKEN_BEGIN_ARRAY: {
                if (json_create_value(json, CX_JSON_ARRAY) == NULL) {
                    return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
                }
                json_add_state(json, JP_STATE_VALUE_BEGIN_AR);
                return_rec(CX_JSON_NO_ERROR);
            }
            case CX_JSON_TOKEN_BEGIN_OBJECT: {
                if (json_create_value(json, CX_JSON_OBJECT) == NULL) {
                    return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
                }
                json_add_state(json, JP_STATE_OBJ_NAME_OR_CLOSE);
                return_rec(CX_JSON_NO_ERROR);
            }
            case CX_JSON_TOKEN_END_ARRAY: {
                if (state == JP_STATE_VALUE_BEGIN_AR) {
                    // discard the array from the value buffer
                    json->vbuf.size--;
                    json->states.size--;
                    return_rec(CX_JSON_NO_ERROR);
                } else {
                    return_rec(CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN);
                }
            }
            case CX_JSON_TOKEN_STRING: {
                if ((vbuf = json_create_value(json, CX_JSON_STRING)) == NULL) {
                    return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
                }
                cxmutstr str = unescape_string(json->allocator, token.content);
                if (str.ptr == NULL) {
                    return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
                }
                vbuf->string = str;
                return_rec(CX_JSON_NO_ERROR);
            }
            case CX_JSON_TOKEN_INTEGER:
            case CX_JSON_TOKEN_NUMBER: {
                int type = token.tokentype == CX_JSON_TOKEN_INTEGER ? CX_JSON_INTEGER : CX_JSON_NUMBER;
                if (NULL == (vbuf = json_create_value(json, type))) {
                    return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
                }
                if (type == CX_JSON_INTEGER) {
                    if (cx_strtoi64(token.content, &vbuf->integer, 10)) {
                        return_rec(CX_JSON_FORMAT_ERROR_NUMBER);
                    }
                } else {
                    if (cx_strtod(token.content, &vbuf->number)) {
                        // TODO: at the moment this is unreachable, because the tokenizer is already stricter than cx_strtod()
                        return_rec(CX_JSON_FORMAT_ERROR_NUMBER);  // LCOV_EXCL_LINE
                    }
                }
                return_rec(CX_JSON_NO_ERROR);
            }
            case CX_JSON_TOKEN_LITERAL: {
                if ((vbuf = json_create_value(json, CX_JSON_LITERAL)) == NULL) {
                    return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
                }
                if (0 == cx_strcmp(token.content, "true")) {
                    vbuf->literal = CX_JSON_TRUE;
                } else if (0 == cx_strcmp(token.content, "false")) {
                    vbuf->literal = CX_JSON_FALSE;
                } else {
                    vbuf->literal = CX_JSON_NULL;
                }
                return_rec(CX_JSON_NO_ERROR);
            }
            default: {
                return_rec(CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN);
            }
        }
    } else if (state == JP_STATE_ARRAY_SEP_OR_CLOSE) {
        // expect ',' or ']'
        if (token.tokentype == CX_JSON_TOKEN_VALUE_SEPARATOR) {
            json_add_state(json, JP_STATE_VALUE_BEGIN_AR);
            return_rec(CX_JSON_NO_ERROR);
        } else if (token.tokentype == CX_JSON_TOKEN_END_ARRAY) {
            // discard the array from the value buffer
            json->vbuf.size--;
            return_rec(CX_JSON_NO_ERROR);
        } else {
            return_rec(CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN);
        }
    } else if (state == JP_STATE_OBJ_NAME_OR_CLOSE || state == JP_STATE_OBJ_NAME) {
        if (state == JP_STATE_OBJ_NAME_OR_CLOSE && token.tokentype == CX_JSON_TOKEN_END_OBJECT) {
            // discard the obj from the value buffer
            json->vbuf.size--;
            return_rec(CX_JSON_NO_ERROR);
        } else {
            // expect string
            if (token.tokentype != CX_JSON_TOKEN_STRING) {
                return_rec(CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN);
            }

            // add new entry
            cxmutstr name = unescape_string(json->allocator, token.content);
            if (name.ptr == NULL) {
                return_rec(CX_JSON_VALUE_ALLOC_FAILED); // LCOV_EXCL_LINE
            }
            assert(json->uncompleted_member_name.ptr == NULL);
            json->uncompleted_member_name = name;
            assert(json->vbuf.size > 0);

            // next state
            json_add_state(json, JP_STATE_OBJ_COLON);
            return_rec(CX_JSON_NO_ERROR);
        }
    } else if (state == JP_STATE_OBJ_COLON) {
        // expect ':'
        if (token.tokentype != CX_JSON_TOKEN_NAME_SEPARATOR) {
            return_rec(CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN);
        }
        // next state
        json_add_state(json, JP_STATE_VALUE_BEGIN_OBJ);
        return_rec(CX_JSON_NO_ERROR);
    } else if (state == JP_STATE_OBJ_SEP_OR_CLOSE) {
        // expect ',' or '}'
        if (token.tokentype == CX_JSON_TOKEN_VALUE_SEPARATOR) {
            json_add_state(json, JP_STATE_OBJ_NAME);
            return_rec(CX_JSON_NO_ERROR);
        } else if (token.tokentype == CX_JSON_TOKEN_END_OBJECT) {
            // discard the obj from the value buffer
            json->vbuf.size--;
            return_rec(CX_JSON_NO_ERROR);
        } else {
            return_rec(CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN);
        }
    } else {
        // should be unreachable
        assert(false);
        return_rec(-1); // LCOV_EXCL_LINE
    }
}

CxJsonStatus cxJsonNext(CxJson *json, CxJsonValue **value) {
    // initialize output value
    *value = &cx_json_value_nothing;

    // check if the buffer has been filled
    if (json->buffer.space == NULL) {
        return CX_JSON_NULL_DATA;
    }

    // parse data
    CxJsonStatus result;
    do {
        result = json_parse(json);
        if (result == CX_JSON_NO_ERROR && json->states.size == 1) {
            // final state reached
            assert(json->states.data[0] == JP_STATE_VALUE_END);
            assert(json->vbuf.size == 0);

            // write output value
            *value = json->parsed;
            json->parsed = NULL;

            // re-initialize state machine
            json->states.data[0] = JP_STATE_VALUE_BEGIN;

            return CX_JSON_NO_ERROR;
        }
    } while (result == CX_JSON_NO_ERROR);

    // the parser might think there is no data
    // but when we did not reach the final state,
    // we know that there must be more to come
    if (result == CX_JSON_NO_DATA && json->states.size > 1) {
        return CX_JSON_INCOMPLETE_DATA;
    }

    return result;
}

CxJsonStatus cx_json_from_string(const CxAllocator *allocator,
            cxstring str, CxJsonValue **value) {
    *value = &cx_json_value_nothing;
    CxJson parser;
    cxJsonInit(&parser, allocator);
    if (cxJsonFill(&parser, str)) {
        // LCOV_EXCL_START
        cxJsonDestroy(&parser);
        return CX_JSON_BUFFER_ALLOC_FAILED;
        // LCOV_EXCL_STOP
    }
    CxJsonStatus status = cxJsonNext(&parser, value);
    // check if we consume the total string
    CxJsonValue *chk_value = NULL;
    CxJsonStatus chk_status = CX_JSON_NO_DATA;
    if (status == CX_JSON_NO_ERROR) {
        chk_status = cxJsonNext(&parser, &chk_value);
    }
    cxJsonDestroy(&parser);
    if (chk_status == CX_JSON_NO_DATA) {
        return status;
    } else {
        cxJsonValueFree(*value);
        // if chk_value is nothing, the free is harmless
        cxJsonValueFree(chk_value);
        *value = &cx_json_value_nothing;
        return CX_JSON_FORMAT_ERROR_UNEXPECTED_TOKEN;
    }

}

void cxJsonValueFree(CxJsonValue *value) {
    if (value == NULL || value->type == CX_JSON_NOTHING) return;
    switch (value->type) {
        case CX_JSON_OBJECT: {
            json_free_object_map(value->object);
            break;
        }
        case CX_JSON_ARRAY: {
            for (size_t i = 0; i < value->array.size; i++) {
                cxJsonValueFree(value->array.data[i]);
            }
            cx_array_free_a(value->allocator, value->array);
            break;
        }
        case CX_JSON_STRING: {
            cxFree(value->allocator, value->string.ptr);
            break;
        }
        default: {
            break;
        }
    }
    cxFree(value->allocator, value);
}

CxJsonValue* cxJsonCreateObj(const CxAllocator* allocator) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxJsonValue* v = cxMalloc(allocator, sizeof(CxJsonValue));
    if (v == NULL) return NULL;
    v->allocator = allocator;
    v->type = CX_JSON_OBJECT;
    v->object = json_create_object_map(allocator);
    if (v->object == NULL) { // LCOV_EXCL_START
        cxFree(allocator, v);
        return NULL;
        // LCOV_EXCL_STOP
    }
    return v;
}

CxJsonValue* cxJsonCreateArr(const CxAllocator* allocator, size_t capacity) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxJsonValue* v = cxMalloc(allocator, sizeof(CxJsonValue));
    if (v == NULL) return NULL;
    v->allocator = allocator;
    v->type = CX_JSON_ARRAY;
    if (capacity > 0) {
        if (cx_array_init_a(allocator, v->array, capacity)) {
            // LCOV_EXCL_START
            cxFree(allocator, v);
            return NULL;
            // LCOV_EXCL_STOP
        }
    } else {
        v->array.data = NULL;
        v->array.size = v->array.capacity = 0;
    }
    return v;
}

CxJsonValue* cxJsonCreateNumber(const CxAllocator* allocator, double num) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxJsonValue* v = cxMalloc(allocator, sizeof(CxJsonValue));
    if (v == NULL) return NULL;
    v->allocator = allocator;
    v->type = CX_JSON_NUMBER;
    v->number = num;
    return v;
}

CxJsonValue* cxJsonCreateInteger(const CxAllocator* allocator, int64_t num) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxJsonValue* v = cxMalloc(allocator, sizeof(CxJsonValue));
    if (v == NULL) return NULL;
    v->allocator = allocator;
    v->type = CX_JSON_INTEGER;
    v->integer = num;
    return v;
}

CxJsonValue* cx_json_create_string(const CxAllocator* allocator, cxstring str) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxJsonValue* v = cxMalloc(allocator, sizeof(CxJsonValue));
    if (v == NULL) return NULL;
    v->allocator = allocator;
    v->type = CX_JSON_STRING;
    cxmutstr s = cx_strdup_a(allocator, str);
    if (s.ptr == NULL) { cxFree(allocator, v); return NULL; }
    v->string = s;
    return v;
}

CxJsonValue* cxJsonCreateLiteral(const CxAllocator* allocator, CxJsonLiteral lit) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxJsonValue* v = cxMalloc(allocator, sizeof(CxJsonValue));
    if (v == NULL) return NULL;
    v->allocator = allocator;
    v->type = CX_JSON_LITERAL;
    v->literal = lit;
    return v;
}

// LCOV_EXCL_START
// never called as long as malloc() does not return NULL
static void json_arr_free_temp(CxJsonValue** values, size_t count) {
    for (size_t i = 0; i < count; i++) {
        if (values[i] == NULL) break;
        cxJsonValueFree(values[i]);
    }
    cxFreeDefault(values);
}
// LCOV_EXCL_STOP

int cxJsonArrAddNumbers(CxJsonValue* arr, const double* num, size_t count) {
    CxJsonValue** values = cxCallocDefault(count, sizeof(CxJsonValue*));
    if (values == NULL) return -1;
    for (size_t i = 0; i < count; i++) {
        values[i] = cxJsonCreateNumber(arr->allocator, num[i]);
        if (values[i] == NULL) { json_arr_free_temp(values, count); return -1; }
    }
    int ret = cxJsonArrAddValues(arr, values, count);
    cxFreeDefault(values);
    return ret;
}

int cxJsonArrAddIntegers(CxJsonValue* arr, const int64_t* num, size_t count) {
    CxJsonValue** values = cxCallocDefault(count, sizeof(CxJsonValue*));
    if (values == NULL) return -1;
    for (size_t i = 0; i < count; i++) {
        values[i] = cxJsonCreateInteger(arr->allocator, num[i]);
        if (values[i] == NULL) { json_arr_free_temp(values, count); return -1; }
    }
    int ret = cxJsonArrAddValues(arr, values, count);
    cxFreeDefault(values);
    return ret;
}

int cxJsonArrAddStrings(CxJsonValue* arr, const char* const* str, size_t count) {
    CxJsonValue** values = cxCallocDefault(count, sizeof(CxJsonValue*));
    if (values == NULL) return -1;
    for (size_t i = 0; i < count; i++) {
        values[i] = cxJsonCreateString(arr->allocator, str[i]);
        if (values[i] == NULL) { json_arr_free_temp(values, count); return -1; }
    }
    int ret = cxJsonArrAddValues(arr, values, count);
    cxFreeDefault(values);
    return ret;
}

int cxJsonArrAddCxStrings(CxJsonValue* arr, const cxstring* str, size_t count) {
    CxJsonValue** values = cxCallocDefault(count, sizeof(CxJsonValue*));
    if (values == NULL) return -1;
    for (size_t i = 0; i < count; i++) {
        values[i] = cxJsonCreateString(arr->allocator, str[i]);
        if (values[i] == NULL) { json_arr_free_temp(values, count); return -1; }
    }
    int ret = cxJsonArrAddValues(arr, values, count);
    cxFreeDefault(values);
    return ret;
}

int cxJsonArrAddLiterals(CxJsonValue* arr, const CxJsonLiteral* lit, size_t count) {
    CxJsonValue** values = cxCallocDefault(count, sizeof(CxJsonValue*));
    if (values == NULL) return -1;
    for (size_t i = 0; i < count; i++) {
        values[i] = cxJsonCreateLiteral(arr->allocator, lit[i]);
        if (values[i] == NULL) { json_arr_free_temp(values, count); return -1; }
    }
    int ret = cxJsonArrAddValues(arr, values, count);
    cxFreeDefault(values);
    return ret;
}

int cxJsonArrAddValues(CxJsonValue* arr, CxJsonValue* const* val, size_t count) {
    assert(arr->type == CX_JSON_ARRAY);
    return cx_array_add_array_a(arr->allocator, arr->array, val, count);
}

int cx_json_obj_put(CxJsonValue* obj, cxstring name, CxJsonValue* child) {
    return cxMapPut(obj->object, name, child);
}

CxJsonValue* cx_json_obj_put_obj(CxJsonValue* obj, cxstring name) {
    CxJsonValue* v = cxJsonCreateObj(obj->allocator);
    if (v == NULL) return NULL;
    if (cxJsonObjPut(obj, name, v)) { cxJsonValueFree(v); return NULL; }
    return v;
}

CxJsonValue* cx_json_obj_put_arr(CxJsonValue* obj, cxstring name, size_t capacity) {
    CxJsonValue* v = cxJsonCreateArr(obj->allocator, capacity);
    if (v == NULL) return NULL;
    if (cxJsonObjPut(obj, name, v)) { cxJsonValueFree(v); return NULL; }
    return v;
}

CxJsonValue* cx_json_obj_put_number(CxJsonValue* obj, cxstring name, double num) {
    CxJsonValue* v = cxJsonCreateNumber(obj->allocator, num);
    if (v == NULL) return NULL;
    if (cxJsonObjPut(obj, name, v)) { cxJsonValueFree(v); return NULL; }
    return v;
}

CxJsonValue* cx_json_obj_put_integer(CxJsonValue* obj, cxstring name, int64_t num) {
    CxJsonValue* v = cxJsonCreateInteger(obj->allocator, num);
    if (v == NULL) return NULL;
    if (cxJsonObjPut(obj, name, v)) { cxJsonValueFree(v); return NULL; }
    return v;
}

CxJsonValue* cx_json_obj_put_string(CxJsonValue* obj, cxstring name, cxstring str) {
    CxJsonValue* v = cxJsonCreateString(obj->allocator, str);
    if (v == NULL) return NULL;
    if (cxJsonObjPut(obj, name, v)) { cxJsonValueFree(v); return NULL; }
    return v;
}

CxJsonValue* cx_json_obj_put_literal(CxJsonValue* obj, cxstring name, CxJsonLiteral lit) {
    CxJsonValue* v = cxJsonCreateLiteral(obj->allocator, lit);
    if (v == NULL) return NULL;
    if (cxJsonObjPut(obj, name, v)) { cxJsonValueFree(v); return NULL;}
    return v;
}

CxJsonValue *cxJsonArrGet(const CxJsonValue *value, size_t index) {
    if (index >= value->array.size) {
        return &cx_json_value_nothing;
    }
    return value->array.data[index];
}

CxJsonValue *cxJsonArrRemove(CxJsonValue *value, size_t index) {
    if (index >= value->array.size) {
        return NULL;
    }
    CxJsonValue *ret = value->array.data[index];
    // TODO: replace with a low level cx_array_remove()
    size_t count = value->array.size - index - 1;
    if (count > 0) {
        memmove(value->array.data + index, value->array.data + index + 1, count * sizeof(CxJsonValue*));
    }
    value->array.size--;
    return ret;
}

char *cxJsonAsString(const CxJsonValue *value) {
    return value->string.ptr;
}

cxstring cxJsonAsCxString(const CxJsonValue *value) {
    return cx_strcast(value->string);
}

cxmutstr cxJsonAsCxMutStr(const CxJsonValue *value) {
    return value->string;
}

double cxJsonAsDouble(const CxJsonValue *value) {
    if (value->type == CX_JSON_INTEGER) {
        return (double) value->integer;
    } else {
        return value->number;
    }
}

int64_t cxJsonAsInteger(const CxJsonValue *value) {
    if (value->type == CX_JSON_INTEGER) {
        return value->integer;
    } else {
        return (int64_t) value->number;
    }
}

CxIterator cxJsonArrIter(const CxJsonValue *value) {
    return cx_array_iterator_ptr(value->array);
}

CxMapIterator cxJsonObjIter(const CxJsonValue *value) {
    return cxMapIterator(value->object);
}

CxJsonValue *cx_json_obj_get(const CxJsonValue *value, cxstring name) {
    CxJsonValue *v = cxMapGet(value->object, name);
    if (v == NULL) {
        return &cx_json_value_nothing;
    } else {
        return v;
    }
}

CxJsonValue *cx_json_obj_remove(CxJsonValue *value, cxstring name) {
    CxJsonValue *v = NULL;
    cxMapRemoveAndGet(value->object, name, &v);
    return v;
}

CxJsonWriter cxJsonWriterCompact(void) {
    return (CxJsonWriter) {
        false,
        6,
        false,
        4,
        false
    };
}

CxJsonWriter cxJsonWriterPretty(bool use_spaces) {
    return (CxJsonWriter) {
        true,
        6,
        use_spaces,
        4,
        false
    };
}

static int cx_json_writer_indent(
    void *target,
    cx_write_func wfunc,
    const CxJsonWriter *settings,
    unsigned int depth
) {
    if (depth == 0) return 0;

    // determine the width and characters to use
    const char* indent; // for 32 prepared chars
    size_t width = depth;
    if (settings->indent_space) {
        if (settings->indent == 0) return 0;
        width *= settings->indent;
        indent = "                                ";
    } else {
        indent = "\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t";
    }

    // calculate the number of write calls and write
    size_t full = width / 32;
    size_t remaining = width % 32;
    for (size_t i = 0; i < full; i++) {
        if (32 != wfunc(indent, 1, 32, target)) return 1;
    }
    if (remaining != wfunc(indent, 1, remaining, target)) return 1;

    return 0;
}


int cx_json_write_rec(
    void *target,
    const CxJsonValue *value,
    cx_write_func wfunc,
    const CxJsonWriter *settings,
    unsigned int depth
) {
    // keep track of written items
    // the idea is to reduce the number of jumps for error checking
    size_t actual = 0, expected = 0;

    // small buffer for number to string conversions
    char numbuf[40];

    // recursively write the values
    switch (value->type) {
        case CX_JSON_OBJECT: {
            const char *begin_obj = "{\n";
            if (settings->pretty) {
                actual += wfunc(begin_obj, 1, 2, target);
                expected += 2;
            } else {
                actual += wfunc(begin_obj, 1, 1, target);
                expected++;
            }
            depth++;
            CxMapIterator member_iter = cxJsonObjIter(value);
            cx_foreach(const CxMapEntry *, member, member_iter) {
                // possible indentation
                if (settings->pretty) {
                    if (cx_json_writer_indent(target, wfunc, settings, depth)) {
                        return 1; // LCOV_EXCL_LINE
                    }
                }

                // the name
                actual += wfunc("\"", 1, 1, target);
                cxstring key = cx_strn(member->key->data, member->key->len);
                cxmutstr name = escape_string(key, settings->escape_slash);
                actual += wfunc(name.ptr, 1, name.length, target);
                actual += wfunc("\"", 1, 1, target);
                const char *obj_name_sep = ": ";
                if (settings->pretty) {
                    actual += wfunc(obj_name_sep, 1, 2, target);
                    expected += 4 + name.length;
                } else {
                    actual += wfunc(obj_name_sep, 1, 1, target);
                    expected += 3 + name.length;
                }
                if (name.ptr != key.ptr) {
                    cx_strfree(&name);
                }

                // the value
                if (cx_json_write_rec(target, member->value, wfunc, settings, depth)) return 1;

                // end of object-value
                if (member_iter.index < member_iter.elem_count - 1) {
                    const char *obj_value_sep = ",\n";
                    if (settings->pretty) {
                        actual += wfunc(obj_value_sep, 1, 2, target);
                        expected += 2;
                    } else {
                        actual += wfunc(obj_value_sep, 1, 1, target);
                        expected++;
                    }
                } else {
                    if (settings->pretty) {
                        actual += wfunc("\n", 1, 1, target);
                        expected ++;
                    }
                }
            }
            depth--;
            if (settings->pretty) {
                if (cx_json_writer_indent(target, wfunc, settings, depth)) return 1;
            }
            actual += wfunc("}", 1, 1, target);
            expected++;
            break;
        }
        case CX_JSON_ARRAY: {
            actual += wfunc("[", 1, 1, target);
            expected++;
            CxIterator iter = cxJsonArrIter(value);
            cx_foreach(CxJsonValue*, element, iter) {
                if (cx_json_write_rec(
                        target, element,
                        wfunc, settings, depth)
                ) {
                    return 1; // LCOV_EXCL_LINE
                }

                if (iter.index < iter.elem_count - 1) {
                    const char *arr_value_sep = ", ";
                    if (settings->pretty) {
                        actual += wfunc(arr_value_sep, 1, 2, target);
                        expected += 2;
                    } else {
                        actual += wfunc(arr_value_sep, 1, 1, target);
                        expected++;
                    }
                }
            }
            actual += wfunc("]", 1, 1, target);
            expected++;
            break;
        }
        case CX_JSON_STRING: {
            actual += wfunc("\"", 1, 1, target);
            cxmutstr str = escape_string(cx_strcast(value->string),
                settings->escape_slash);
            actual += wfunc(str.ptr, 1, str.length, target);
            actual += wfunc("\"", 1, 1, target);
            expected += 2 + str.length;
            if (str.ptr != value->string.ptr) {
                cx_strfree(&str);
            }
            break;
        }
        case CX_JSON_NUMBER: {
            int precision = settings->frac_max_digits;
            // because of the way how %g is defined, we need to
            // double the precision and truncate ourselves
            precision = 1 + (precision > 15 ? 30 : 2 * precision);
            snprintf(numbuf, 40, "%.*g", precision, value->number);
            char *dot, *exp;
            unsigned char max_digits;
            // find the decimal separator and hope that it's one of . or ,
            dot = strchr(numbuf, '.');
            if (dot == NULL) {
                dot = strchr(numbuf, ',');
            }
            if (dot == NULL) {
                // no decimal separator found
                // output everything until a possible exponent
                max_digits = 30;
                dot = numbuf;
            } else {
                // found a decimal separator
                // output everything until the separator
                // and set max digits to what the settings say
                size_t len = dot - numbuf;
                actual += wfunc(numbuf, 1, len, target);
                expected += len;
                max_digits = settings->frac_max_digits;
                if (max_digits > 15) {
                    max_digits = 15;
                }
                // locale independent separator
                if (max_digits > 0) {
                    actual += wfunc(".", 1, 1, target);
                    expected++;
                }
                dot++;
            }
            // find the exponent
            exp = strchr(dot, 'e');
            if (exp == NULL) {
                // no exponent - output the rest
                if (max_digits > 0) {
                    size_t len = strlen(dot);
                    if (len > max_digits) {
                        len = max_digits;
                    }
                    actual += wfunc(dot, 1, len, target);
                    expected += len;
                }
            } else {
                // exponent found - truncate the frac digits
                // and then output the rest
                if (max_digits > 0) {
                    size_t len = exp - dot - 1;
                    if (len > max_digits) {
                        len = max_digits;
                    }
                    actual += wfunc(dot, 1, len, target);
                    expected += len;
                }
                actual += wfunc("e", 1, 1, target);
                expected++;
                exp++;
                size_t len = strlen(exp);
                actual += wfunc(exp, 1, len, target);
                expected += len;
            }
            break;
        }
        case CX_JSON_INTEGER: {
            snprintf(numbuf, 32, "%" PRIi64, value->integer);
            size_t len = strlen(numbuf);
            actual += wfunc(numbuf, 1, len, target);
            expected += len;
            break;
        }
        case CX_JSON_LITERAL: {
            if (value->literal == CX_JSON_TRUE) {
                actual += wfunc("true", 1, 4, target);
                expected += 4;
            } else if (value->literal == CX_JSON_FALSE) {
                actual += wfunc("false", 1, 5, target);
                expected += 5;
            } else {
                actual += wfunc("null", 1, 4, target);
                expected += 4;
            }
            break;
        }
        case CX_JSON_NOTHING: {
            // deliberately supported as an empty string!
            // users might want to just write the result
            // of a get operation without testing the value
            // and therefore this should not blow up
            break;
        }
        default: assert(false); // LCOV_EXCL_LINE
    }

    return expected != actual;
}

int cxJsonWrite(
    void *target,
    const CxJsonValue *value,
    cx_write_func wfunc,
    const CxJsonWriter *settings
) {
    assert(target != NULL);
    assert(value != NULL);
    assert(wfunc != NULL);

    CxJsonWriter writer_default = cxJsonWriterCompact();
    if (settings == NULL) {
        settings = &writer_default;
    }
    return cx_json_write_rec(target, value, wfunc, settings, 0);
}

static cxmutstr cx_json_to_string(CxJsonValue *value, const CxAllocator *allocator, CxJsonWriter *writer) {
    if (allocator == NULL) allocator = cxDefaultAllocator;
    CxBuffer buffer;
    if (cxBufferInit(&buffer, allocator, NULL, 128,
                     CX_BUFFER_AUTO_EXTEND | CX_BUFFER_DO_NOT_FREE)) {
        return (cxmutstr){NULL, 0};
    }
    if (cx_json_write_rec(&buffer, value, cxBufferWriteFunc, writer, 0)
            || cxBufferTerminate(&buffer)) {
        // LCOV_EXCL_START
        buffer.flags &= ~CX_BUFFER_DO_NOT_FREE;
        cxBufferDestroy(&buffer);
        return (cxmutstr){NULL, 0};
        // LCOV_EXCL_STOP
    } else {
        cxmutstr str = cx_mutstrn(buffer.space, buffer.size);
        cxBufferDestroy(&buffer);
        return str;
    }

}

cxmutstr cxJsonToString(const CxAllocator *allocator, CxJsonValue *value) {
    CxJsonWriter writer = cxJsonWriterCompact();
    return cx_json_to_string(value, allocator, &writer);
}

cxmutstr cxJsonToPrettyString(const CxAllocator *allocator, CxJsonValue *value) {
    CxJsonWriter writer = cxJsonWriterPretty(true);
    return cx_json_to_string(value, allocator, &writer);
}

int cxJsonCompare(const CxJsonValue *json, const CxJsonValue *other) {
    if (json == other) return 0;
    if (json == NULL || other == NULL) return -1;
    if (json->type != other->type) {
        if (!cxJsonIsNumber(json)) return -1;
        if (!cxJsonIsNumber(other)) return -1;
    }
    switch (json->type) {
        case CX_JSON_NOTHING:
            return 0;
        case CX_JSON_OBJECT:
            return cxMapCompare(json->object, other->object);
        case CX_JSON_ARRAY:
            if (json->array.size != other->array.size) return -1;
            for (size_t i = 0; i < json->array.size; i++) {
                const int d = cxJsonCompare(json->array.data[i], other->array.data[i]);
                if (d != 0) return d;
            }
            return 0;
        case CX_JSON_STRING:
            return cx_strcmp(json->string, other->string);
        case CX_JSON_INTEGER:
            if (other->type == CX_JSON_INTEGER) {
                return cx_vcmp_int64(json->integer, other->integer);
            } else {
                return cx_vcmp_double(cxJsonAsDouble(json), other->number);
            }
        case CX_JSON_NUMBER:
            return cx_vcmp_double(json->number, cxJsonAsDouble(other));
        case CX_JSON_LITERAL:
            return json->literal == other->literal ? 0 : -1;
        default:
            // LCOV_EXCL_START
            // unreachable
            assert(false);
            return -1;
            // LCOV_EXCL_STOP
    }
}

CxJsonValue* cxJsonClone(const CxJsonValue* value, const CxAllocator* allocator) {
    return cx_json_clone_func(NULL, value, allocator, NULL);
}

CxJsonValue* cx_json_clone_func(CxJsonValue* target, const CxJsonValue* source,
        const CxAllocator* allocator, cx_attr_unused void *data) {
    if (source == NULL || source->type == CX_JSON_NOTHING) {
        return &cx_json_value_nothing;
    }
    if (allocator == NULL) allocator = cxDefaultAllocator;

#define return_value(v) { \
        CxJsonValue *ret = v; \
        if (target == NULL) { \
            return ret; \
        } else { \
            *target = *ret; \
            cxFree(allocator, ret); \
            return target; \
        } \
    }

    switch (source->type) {
        case CX_JSON_OBJECT: {
            CxJsonValue *obj = cxJsonCreateObj(allocator);
            if (obj == NULL) return NULL; // LCOV_EXCL_LINE
            if (cxMapClone(obj->object, source->object, cxJsonCloneFunc, allocator, NULL)) {
                // LCOV_EXCL_START
                cxJsonValueFree(obj);
                return NULL;
                // LCOV_EXCL_STOP
            }
            return_value(obj);
        }
        case CX_JSON_ARRAY: {
            const size_t elem_count = source->array.size;
            CxJsonValue *arr = cxJsonCreateArr(allocator, elem_count);
            if (arr == NULL) return NULL; // LCOV_EXCL_LINE
            arr->array.size = elem_count;
            for (size_t i = 0 ; i < elem_count ; i++) {
                CxJsonValue *e = cx_json_clone_func(NULL, source->array.data[i], allocator, NULL);
                if (e == NULL) {
                    // LCOV_EXCL_START
                    cxJsonValueFree(arr);
                    return NULL;
                    // LCOV_EXCL_STOP
                }
                arr->array.data[i] = e;
            }
            return_value(arr);
        }
        case CX_JSON_STRING:
            return_value(cxJsonCreateString(allocator, source->string));
        case CX_JSON_INTEGER:
            return_value(cxJsonCreateInteger(allocator, source->integer));
        case CX_JSON_NUMBER:
            return_value(cxJsonCreateNumber(allocator, source->number));
        case CX_JSON_LITERAL:
            return_value(cxJsonCreateLiteral(allocator, source->literal));
        default:
            // LCOV_EXCL_START
            // unreachable
            assert(false);
            return NULL;
            // LCOV_EXCL_STOP
    }
#undef return_value
}