libntech/libutils/mustache.c

/*
  Copyright 2021 Northern.tech AS

  This file is part of CFEngine 3 - written and maintained by Northern.tech AS.

  This program is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the
  Free Software Foundation; version 3.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

  To the extent this program is licensed as part of the Enterprise
  versions of CFEngine, the applicable Commercial Open Source License
  (COSL) may apply to this file if you as a licensee so wish it. See
  included file COSL.txt.
*/

#include <platform.h>
#include <mustache.h>

#include <string_lib.h>
#include <logging.h>
#include <alloc.h>
#include <sequence.h>

typedef enum
{
    TAG_TYPE_VAR,
    TAG_TYPE_VAR_UNESCAPED,
    TAG_TYPE_VAR_SERIALIZED,
    TAG_TYPE_VAR_SERIALIZED_COMPACT,
    TAG_TYPE_SECTION,
    TAG_TYPE_SECTION_END,
    TAG_TYPE_INVERTED,
    TAG_TYPE_COMMENT,
    TAG_TYPE_DELIM,
    TAG_TYPE_ERR,
    TAG_TYPE_NONE
} TagType;

typedef struct
{
    TagType type;
    const char *begin;
    const char *end;
    const char *content;
    size_t content_len;
} Mustache;

#define MUSTACHE_MAX_DELIM_SIZE 10

static bool IsSpace(char c)
{
    return c == '\t' || c == ' ';
}

static bool IsTagStandalone(const char *start, const char *tag_start, const char *tag_end, const char **line_begin, const char **line_end)
{
    assert(start != NULL);
    assert(tag_start != NULL);
    assert(tag_end != NULL);
    assert(line_begin != NULL);
    assert(line_end != NULL);

    assert(start <= tag_start);

    *line_begin = start;
    for (const char *cur = tag_start - 1; cur >= start; cur--)
    {
        if (IsSpace(*cur))
        {
            *line_begin = cur;
            if (cur == start)
            {
                break;
            }
            continue;
        }
        else if (*cur == '\n')
        {
            *line_begin = cur + 1;
            break;
        }
        else
        {
            return false;
        }
    }

    *line_end = NULL;
    for (const char *cur = tag_end; true; cur++)
    {
        if (IsSpace(*cur))
        {
            continue;
        }
        else if (*cur == '\n')
        {
            *line_end = cur + 1;
            break;
        }
        else if (*cur == '\r')
        {
            if (*(cur + 1) == '\n')
            {
                *line_end = cur + 2;
                break;
            }
            continue;
        }
        else if (*cur == '\0')
        {
            *line_end = cur;
            break;
        }
        else
        {
            return false;
        }
    }

    assert(*line_end);

    return true;
}

static bool IsTagTypeRenderable(TagType type)
{
    switch (type)
    {
    case TAG_TYPE_COMMENT:
    case TAG_TYPE_DELIM:
    case TAG_TYPE_ERR:
    case TAG_TYPE_INVERTED:
    case TAG_TYPE_SECTION:
    case TAG_TYPE_SECTION_END:
        return false;
    default:
        return true;
    }
}

static JsonElement *LookupVariable(Seq *hash_stack, const char *name, size_t name_len)
{
    assert(SeqLength(hash_stack) > 0);

    size_t num_comps = StringCountTokens(name, name_len, ".");

    JsonElement *base_var = NULL;
    {
        StringRef base_comp = StringGetToken(name, name_len, 0, ".");
        char *base_comp_str = xstrndup(base_comp.data, base_comp.len);

        if (strcmp("-top-", base_comp_str) == 0)
        {
            base_var = SeqAt(hash_stack, 0);
        }

        for (ssize_t i = SeqLength(hash_stack) - 1; i >= 0; i--)
        {
            JsonElement *hash = SeqAt(hash_stack, i);
            if (!hash)
            {
                continue;
            }

            if (JsonGetType(hash) == JSON_TYPE_OBJECT)
            {
                JsonElement *var = JsonObjectGet(hash, base_comp_str);
                if (var)
                {
                    base_var = var;
                    break;
                }
            }
        }
        free(base_comp_str);
    }

    if (!base_var)
    {
        return NULL;
    }

    for (size_t i = 1; i < num_comps; i++)
    {
        if (JsonGetType(base_var) != JSON_TYPE_OBJECT)
        {
            return NULL;
        }

        StringRef comp = StringGetToken(name, name_len, i, ".");
        char *comp_str = xstrndup(comp.data, comp.len);
        base_var = JsonObjectGet(base_var, comp_str);
        free(comp_str);

        if (!base_var)
        {
            return NULL;
        }
    }

    assert(base_var);
    return base_var;
}

static Mustache NextTag(const char *input,
                        const char *delim_start, size_t delim_start_len,
                        const char *delim_end, size_t delim_end_len)
{
    Mustache ret = {0};
    ret.type = TAG_TYPE_NONE;

    ret.begin = strstr(input, delim_start);
    if (!ret.begin)
    {
        return ret;
    }

    ret.content = ret.begin + delim_start_len;
    char *extra_end = NULL;

    switch (ret.content[0])
    {
    case '#':
        ret.type = TAG_TYPE_SECTION;
        ret.content++;
        break;
    case '^':
        ret.type = TAG_TYPE_INVERTED;
        ret.content++;
        break;
    case '/':
        ret.type = TAG_TYPE_SECTION_END;
        ret.content++;
        break;
    case '!':
        ret.type = TAG_TYPE_COMMENT;
        ret.content++;
        break;
    case '=':
        extra_end = "=";
        ret.type = TAG_TYPE_DELIM;
        ret.content++;
        break;
    case '{':
        extra_end = "}";
        // fall through
    case '&':
        ret.type = TAG_TYPE_VAR_UNESCAPED;
        ret.content++;
        break;
    case '%':
        ret.type = TAG_TYPE_VAR_SERIALIZED;
        ret.content++;
        break;
    case '$':
        ret.type = TAG_TYPE_VAR_SERIALIZED_COMPACT;
        ret.content++;
        break;
    default:
        ret.type = TAG_TYPE_VAR;
        break;
    }

    if (extra_end)
    {
        const char *escape_end = strstr(ret.content, extra_end);
        if (!escape_end || strncmp(escape_end + 1, delim_end, delim_end_len) != 0)
        {
            Log(LOG_LEVEL_ERR, "Broken mustache template, couldn't find end tag for quoted begin tag at '%20s'...", input);
            ret.type = TAG_TYPE_ERR;
            return ret;
        }

        ret.content_len = escape_end - ret.content;
        ret.end = escape_end + 1 + delim_end_len;
    }
    else
    {
        ret.end = strstr(ret.content, delim_end);
        if (!ret.end)
        {
            Log(LOG_LEVEL_ERR, "Broken Mustache template, could not find end delimiter after reading start delimiter at '%20s'...", input);
            ret.type = TAG_TYPE_ERR;
            return ret;
        }

        ret.content_len = ret.end - ret.content;
        ret.end += delim_end_len;
    }

    while (*ret.content == ' ' || *ret.content == '\t')
    {
        ret.content++;
        ret.content_len--;
    }

    while (ret.content_len > 0
           && (ret.content[ret.content_len - 1] == ' '
               || ret.content[ret.content_len - 1] == '\t'))
    {
        ret.content_len--;
    }

    return ret;
}

static void RenderHTMLContent(Buffer *out, const char *input, size_t len)
{
    for (size_t i = 0; i < len; i++)
    {
        switch (input[i])
        {
        case '&':
            BufferAppendString(out, "&amp;");
            break;

        case '"':
            BufferAppendString(out, "&quot;");
            break;

        case '<':
            BufferAppendString(out, "&lt;");
            break;

        case '>':
            BufferAppendString(out, "&gt;");
            break;

        default:
            BufferAppendChar(out, input[i]);
            break;
        }
    }
}

static void RenderContent(Buffer *out, const char *content, size_t len, bool html, bool skip_content)
{
    if (skip_content)
    {
        return;
    }

    if (html)
    {
        RenderHTMLContent(out, content, len);
    }
    else
    {
        BufferAppend(out, content, len);
    }
}

static bool RenderVariablePrimitive(Buffer *out, const JsonElement *primitive, const bool escaped, const char* json_key)
{
    if (json_key != NULL)
    {
        if (escaped)
        {
            RenderHTMLContent(out, json_key, strlen(json_key));
        }
        else
        {
            BufferAppendString(out, json_key);
        }
        return true;
    }

    switch (JsonGetPrimitiveType(primitive))
    {
    case JSON_PRIMITIVE_TYPE_STRING:
        if (escaped)
        {
            RenderHTMLContent(out, JsonPrimitiveGetAsString(primitive), strlen(JsonPrimitiveGetAsString(primitive)));
        }
        else
        {
            BufferAppendString(out, JsonPrimitiveGetAsString(primitive));
        }
        return true;

    case JSON_PRIMITIVE_TYPE_INTEGER:
        {
            char *str = StringFromLong(JsonPrimitiveGetAsInteger(primitive));
            BufferAppendString(out, str);
            free(str);
        }
        return true;

    case JSON_PRIMITIVE_TYPE_REAL:
        {
            char *str = StringFromDouble(JsonPrimitiveGetAsReal(primitive));
            BufferAppendString(out, str);
            free(str);
        }
        return true;

    case JSON_PRIMITIVE_TYPE_BOOL:
        BufferAppendString(out, JsonPrimitiveGetAsBool(primitive) ? "true" : "false");
        return true;

    case JSON_PRIMITIVE_TYPE_NULL:
        return true;

    default:
        assert(!"Unrecognised JSON primitive type");
    }
    return false;
}

static bool RenderVariableContainer(Buffer *out, const JsonElement *container, bool compact)
{
    Writer *w = StringWriter();
    if (compact)
    {
        JsonWriteCompact(w, container);
    }
    else
    {
        JsonWrite(w, container, 0);
    }

    BufferAppendString(out, StringWriterData(w));
    WriterClose(w);
    return true;
}

static bool RenderVariable(Buffer *out,
                           const char *content, size_t content_len,
                           TagType conversion,
                           Seq *hash_stack,
                           const char *json_key)
{
    JsonElement *var = NULL;
    bool escape = conversion == TAG_TYPE_VAR;
    bool serialize = conversion == TAG_TYPE_VAR_SERIALIZED;
    bool serialize_compact = conversion == TAG_TYPE_VAR_SERIALIZED_COMPACT;

    const bool item_mode = strncmp(content, ".", content_len) == 0;
    const bool key_mode = strncmp(content, "@", content_len) == 0;

    if (item_mode || key_mode)
    {
        var = SeqAt(hash_stack, SeqLength(hash_stack) - 1);

        // Leave this in, it's really useful when debugging here but useless otherwise
        // for (int i=1; i < SeqLength(hash_stack); i++)
        // {
        //     JsonElement *dump = SeqAt(hash_stack, i);
        //     Writer *w = StringWriter();
        //     JsonWrite(w, dump, 0);
        //     Log(LOG_LEVEL_ERR, "RenderVariable: at hash_stack position %d, we found var '%s'", i, StringWriterClose(w));
        // }
    }
    else
    {
        var = LookupVariable(hash_stack, content, content_len);
    }

    if (key_mode && json_key == NULL)
    {
        Log(LOG_LEVEL_WARNING, "RenderVariable: {{@}} Mustache tag must be used in a context where there's a valid key or iteration position");
        return false;
    }

    if (!var)
    {
        return true;
    }

    switch (JsonGetElementType(var))
    {
    case JSON_ELEMENT_TYPE_PRIMITIVE:
        // note that this also covers 'serialize' on primitives
        return RenderVariablePrimitive(out, var, escape, key_mode ? json_key : NULL);

    case JSON_ELEMENT_TYPE_CONTAINER:
        if (serialize || serialize_compact)
        {
            return RenderVariableContainer(out, var, serialize_compact);
        }
        else if (key_mode)
        {
            // this will only use the JSON key property, which we know is good
            // because we return false earlier otherwise
            return RenderVariablePrimitive(out, var, escape, json_key);
        }
        else if (item_mode)
        {
            // This can happen in 2 cases:
            // if you try to use {{.}} on the top element (without iterating)
            // if you try to use {{.}} while iterating and the current element is a container
            // In both cases we want to give an error(warning) since this is not clear in the
            // mustache spec
            Log(LOG_LEVEL_WARNING,
                "{{.}} mustache tag cannot expand a container without specifying conversion"
                " - consider {{$.}} or {{%%.}}");
            return false;
        }
    }

    assert(false);
    return false;
}

static bool SetDelimiters(const char *content, size_t content_len,
                          char *delim_start, size_t *delim_start_len,
                          char *delim_end, size_t *delim_end_len)
{
    size_t num_tokens = StringCountTokens(content, content_len, " \t");
    if (num_tokens != 2)
    {
        Log(LOG_LEVEL_WARNING, "Could not parse delimiter mustache, number of tokens is %zu, expected 2 in '%s'",
            num_tokens, content);
        return false;
    }

    StringRef first = StringGetToken(content, content_len, 0, " \t");
    if (first.len > MUSTACHE_MAX_DELIM_SIZE)
    {
        Log(LOG_LEVEL_WARNING, "New mustache start delimiter exceeds the allowed size of %d in '%s'",
            MUSTACHE_MAX_DELIM_SIZE, content);
        return false;
    }
    strncpy(delim_start, first.data, first.len);
    delim_start[first.len] = '\0';
    *delim_start_len = first.len;

    StringRef second = StringGetToken(content, content_len, 1, " \t");
    if (second.len > MUSTACHE_MAX_DELIM_SIZE)
    {
        Log(LOG_LEVEL_WARNING, "New mustache start delimiter exceeds the allowed size of %d in '%s'",
            MUSTACHE_MAX_DELIM_SIZE, content);
        return false;
    }
    strncpy(delim_end, second.data, second.len);
    delim_end[second.len] = '\0';
    *delim_end_len = second.len;

    return true;
}

static bool IsKeyExtensionVar(TagType tag_type, const char *tag_start,
                              char *delim_start, size_t delim_start_len,
                              char *delim_end, size_t delim_end_len)
{
    /* This whole function is ugly, but tries to avoid memory allocation and copying. */

    /* the easiest case first: {{@}} */
    if (tag_type == TAG_TYPE_VAR)
    {
        if (StringStartsWith(tag_start, delim_start) &&
            *(tag_start + delim_start_len) == '@' &&
            StringStartsWith(tag_start + delim_start_len + 1, delim_end))
        {
            return true;
        }
        else
        {
            /* no other way a VAR could be {{@}} */
            return false;
        }
    }

    if (tag_type == TAG_TYPE_VAR_UNESCAPED)
    {
        /* the case with unescaped form using &: {{&@}} */
        if  (StringStartsWith(tag_start, delim_start) &&
             StringStartsWith(tag_start + delim_start_len, "&@") &&
             StringStartsWith(tag_start + delim_start_len + 2, delim_end))
        {
            return true;
        }

        /* the special case of unescaped form using {{{@}}} iff "{{" and "}}" are
         * used as delimiters */
        if ((delim_start_len == 2) && (delim_end_len == 2) &&
            StringEqual(delim_start, "{{") &&
            StringEqual(delim_end, "}}") &&
            StringStartsWith(tag_start, "{{{@}}}"))
        {
            return true;
        }
    }

    /* nothing else is our special '@' variable inside delimiters */
    return false;
}

/**
 * Checks if a Json object in the current context (specified by #input) should
 * be iterated over or not.
 *
 * We need to iterate over a Json object if the current section directly
 * contains (not in a subsection) our {{@}} mustache extension.
 */
static bool ShouldIterateObject(const char *input,
                                char *delim_start, size_t delim_start_len,
                                char *delim_end, size_t delim_end_len)
{
    assert (input != NULL);

    size_t loc_delim_start_len = delim_start_len;
    char loc_delim_start[MUSTACHE_MAX_DELIM_SIZE] = {0};
    strncpy(loc_delim_start, delim_start, delim_start_len);

    size_t loc_delim_end_len = delim_end_len;
    char loc_delim_end[MUSTACHE_MAX_DELIM_SIZE] = {0};
    strncpy(loc_delim_end, delim_end, delim_end_len);

    /* This loop should only terminate when the answer is clear and thus the
     * whole function returns. It's iterating over the template which has to end
     * somewhere (if it's not NUL-terminated, we have a much bigger issue than
     * this loop). */
    while (true)
    {
        Mustache tag = NextTag(input,
                               loc_delim_start, loc_delim_start_len,
                               loc_delim_end, loc_delim_end_len);
        switch (tag.type)
        {
        case TAG_TYPE_ERR:
        case TAG_TYPE_NONE:
        case TAG_TYPE_SECTION:
        case TAG_TYPE_SECTION_END:
            /* these clearly mean there cannot be {{@}} directly in the current section */
            return false;
        case TAG_TYPE_VAR:
        case TAG_TYPE_VAR_UNESCAPED:
            /* check if the variable is {{@}} respecting possibly changed delimiters */
            if (IsKeyExtensionVar(tag.type, tag.begin,
                                  loc_delim_start, loc_delim_start_len,
                                  loc_delim_end, loc_delim_end_len))
            {
                return true;
            }
            else
            {
                /* just continue to the next tag */
                break;
            }
        case TAG_TYPE_DELIM:
            if (!SetDelimiters(tag.content, tag.content_len,
                               loc_delim_start, &loc_delim_start_len,
                               loc_delim_end, &loc_delim_end_len))
            {
                return false;
            }
            break;

        default:
            /* just continue to the next tag */
            break;
        }
        /* move on in the template */
        input = tag.end;
    }
    return false;
}

static bool Render(Buffer *out, const char *start, const char *input, Seq *hash_stack,
                   const char *json_key,
                   char *delim_start, size_t *delim_start_len,
                   char *delim_end, size_t *delim_end_len,
                   bool skip_content,
                   const char *section,
                   const char **section_end)
{
    while (true)
    {
        if (!input)
        {
            Log(LOG_LEVEL_ERR, "Unexpected end to Mustache template");
            return false;
        }

        Mustache tag = NextTag(input, delim_start, *delim_start_len, delim_end, *delim_end_len);

        {
            const char *line_begin = NULL;
            const char *line_end = NULL;
            if (!IsTagTypeRenderable(tag.type)
                && tag.end != NULL
                && IsTagStandalone(start, tag.begin, tag.end, &line_begin, &line_end))
            {
                RenderContent(out, input, line_begin - input, false, skip_content);
                input = line_end;
            }
            else
            {
                RenderContent(out, input, tag.begin - input, false, skip_content);
                input = tag.end;
            }
        }

        switch (tag.type)
        {
        case TAG_TYPE_ERR:
            return false;

        case TAG_TYPE_DELIM:
            if (!SetDelimiters(tag.content, tag.content_len,
                               delim_start, delim_start_len,
                               delim_end, delim_end_len))
            {
                return false;
            }
            continue;

        case TAG_TYPE_COMMENT:
            continue;

        case TAG_TYPE_NONE:
            return true;

        case TAG_TYPE_VAR_SERIALIZED:
        case TAG_TYPE_VAR_SERIALIZED_COMPACT:
        case TAG_TYPE_VAR_UNESCAPED:
        case TAG_TYPE_VAR:
            if (!skip_content)
            {
                if (tag.content_len > 0)
                {
                    if (!RenderVariable(out, tag.content, tag.content_len, tag.type, hash_stack, json_key))
                    {
                        return false;
                    }
                }
                else
                {
                    RenderContent(out, delim_start, *delim_start_len, false, false);
                    RenderContent(out, delim_end, *delim_end_len, false, false);
                }
            }
            continue;

        case TAG_TYPE_INVERTED:
        case TAG_TYPE_SECTION:
            {
                char *cur_section = xstrndup(tag.content, tag.content_len);
                JsonElement *var = LookupVariable(hash_stack, tag.content, tag.content_len);
                SeqAppend(hash_stack, var);

                if (!var)
                {
                    /* XXX: no variable with the name of the section, why are we renderning anything? */
                    const char *cur_section_end = NULL;
                    if (!Render(out, start, input, hash_stack, NULL, delim_start, delim_start_len, delim_end, delim_end_len,
                                skip_content || tag.type != TAG_TYPE_INVERTED, cur_section, &cur_section_end))
                    {
                        free(cur_section);
                        return false;
                    }
                    free(cur_section);
                    input = cur_section_end;
                    continue;
                }

                switch (JsonGetElementType(var))
                {
                case JSON_ELEMENT_TYPE_PRIMITIVE:
                    if (JsonGetPrimitiveType(var) == JSON_PRIMITIVE_TYPE_BOOL)
                    {
                        bool skip = skip_content || (!JsonPrimitiveGetAsBool(var) ^ (tag.type == TAG_TYPE_INVERTED));

                        const char *cur_section_end = NULL;
                        if (!Render(out, start, input, hash_stack, NULL, delim_start, delim_start_len, delim_end, delim_end_len,
                                    skip, cur_section, &cur_section_end))
                        {
                            free(cur_section);
                            return false;
                        }
                        free(cur_section);
                        input = cur_section_end;
                        continue;
                    }
                    else
                    {
                        Log(LOG_LEVEL_WARNING, "Mustache sections can only take a boolean or a container (array or map) value, but section '%s' isn't getting one of those.",
                            cur_section);
                        free(cur_section);
                        return false;
                    }
                    break;

                case JSON_ELEMENT_TYPE_CONTAINER:
                    switch (JsonGetContainerType(var))
                    {
                    case JSON_CONTAINER_TYPE_OBJECT:
                        {
                            if (!ShouldIterateObject(input, delim_start, *delim_start_len, delim_end, *delim_end_len))
                            {
                                const char *cur_section_end = NULL;

                                if (!Render(out, start, input,
                                            hash_stack,
                                            NULL,
                                            delim_start, delim_start_len, delim_end, delim_end_len,
                                            skip_content || tag.type == TAG_TYPE_INVERTED, cur_section, &cur_section_end))
                                {
                                    free(cur_section);
                                    return false;
                                }
                                input = cur_section_end;
                                free(cur_section);
                                break;
                            }
                        }
                        /* fall through */
                        /* Because iterated objects and arrays are processed in the
                         * same way */
                    case JSON_CONTAINER_TYPE_ARRAY:
                        if (JsonLength(var) > 0)
                        {
                            const char *cur_section_end = NULL;
                            for (size_t i = 0; i < JsonLength(var); i++)
                            {
                                JsonElement *child_hash = JsonAt(var, i);
                                SeqAppend(hash_stack, child_hash);

                                Buffer *kstring = BufferNew();
                                if (JSON_CONTAINER_TYPE_OBJECT == JsonGetContainerType(var))
                                {
                                    BufferAppendString(kstring, JsonElementGetPropertyName(child_hash));
                                }
                                else
                                {
                                    BufferAppendF(kstring, "%zu", i);
                                }

                                if (!Render(out, start, input,
                                            hash_stack,
                                            BufferData(kstring),
                                            delim_start, delim_start_len, delim_end, delim_end_len,
                                            skip_content || tag.type == TAG_TYPE_INVERTED, cur_section, &cur_section_end))
                                {
                                    free(cur_section);
                                    BufferDestroy(kstring);
                                    return false;
                                }

                                BufferDestroy(kstring);
                            }
                            input = cur_section_end;
                            free(cur_section);
                        }
                        else
                        {
                            /* XXX: empty array -- why are we rendering anything? */
                            const char *cur_section_end = NULL;
                            if (!Render(out, start, input, hash_stack, NULL, delim_start, delim_start_len, delim_end, delim_end_len,
                                        tag.type != TAG_TYPE_INVERTED, cur_section, &cur_section_end))
                            {
                                free(cur_section);
                                return false;
                            }
                            free(cur_section);
                            input = cur_section_end;
                        }
                        break;
                    }
                    break;
                }
            }
            continue;
        case TAG_TYPE_SECTION_END:
            if (!section)
            {
                char *varname = xstrndup(tag.content, tag.content_len);
                Log(LOG_LEVEL_WARNING, "Unknown section close in mustache template '%s'", varname);
                free(varname);
                return false;
            }
            else
            {
                SeqRemove(hash_stack, SeqLength(hash_stack) - 1);
                *section_end = input;
                return true;
            }
            break;

        default:
            assert(false);
            return false;
        }
    }

    assert(false);
}

bool MustacheRender(Buffer *out, const char *input, const JsonElement *hash)
{
    char delim_start[MUSTACHE_MAX_DELIM_SIZE] = "{{";
    size_t delim_start_len = strlen(delim_start);

    char delim_end[MUSTACHE_MAX_DELIM_SIZE] = "}}";
    size_t delim_end_len = strlen(delim_end);

    Seq *hash_stack = SeqNew(10, NULL);
    SeqAppend(hash_stack, (JsonElement*)hash);

    bool success = Render(out, input, input,
                          hash_stack,
                          NULL,
                          delim_start, &delim_start_len,
                          delim_end, &delim_end_len,
                          false, NULL, NULL);

    SeqDestroy(hash_stack);

    return success;
}