path: root/src/HtmlParser.c

#include "../include/HtmlParser.h"
#include <stdio.h>
#include <string.h>
#include <assert.h>

static HtmlStringView void_tags[] = {
    {"area", 4},
    {"base", 4},
    {"br", 2},
    {"col", 3},
    {"command", 7},
    {"embed", 5},
    {"hr", 2},
    {"img", 3},
    {"input", 5},
    {"keygen", 6},
    {"link", 4},
    {"meta", 4},
    {"param", 5},
    {"source", 6},
    {"track", 5},
    {"wbr", 3},
    {NULL, 0}
};

static HtmlStringView script_tag = {"script", 6};

static int string_view_equals(HtmlStringView *self, HtmlStringView *other) {
    return self->size == other->size && memcmp(self->data, other->data, self->size) == 0;
}

static int is_whitespace(int c) {
    switch(c) {
        case ' ':
        case '\n':
        case '\r':
        case '\t':
        case '\v':
            return 1;
        default:
            return 0;
    }
}

static int is_newline(int c) {
    return c == '\n' || c == '\r';
}

static void lstrip(const char *str, size_t size, const char **output_str, size_t *output_size, int(*strip_filter_func)(int)) {
    size_t i = 0;
    while(i < size && strip_filter_func(str[i])) {
        ++i;
    }
    *output_str = str + i;
    *output_size = size - i;
}

static void rstrip(const char *str, size_t size, size_t *output_size, int(*strip_filter_func)(int)) {
    ssize_t i = size - 1;
    while(i >= 0 && strip_filter_func(str[i])) {
        --i;
    }
    *output_size = i + 1;
}

static void strip(const char *str, size_t size, const char **output_str, size_t *output_size, int(*strip_filter_func)(int)) {
    lstrip(str, size, output_str, output_size, strip_filter_func);
    rstrip(*output_str, *output_size, output_size, strip_filter_func);
}

static int is_void_tag(HtmlStringView *tag_name) {
    HtmlStringView *tag_iter = &void_tags[0];
    /* !DOCTYPE, !--, etc.... */
    if(tag_name->size > 0 && tag_name->data[0] == '!')
        return 1;
    while(tag_iter->data) {
        if(string_view_equals(tag_name, tag_iter))
            return 1;
        ++tag_iter;
    }
    return 0;
}

static void html_parser_reset(HtmlParser *self) {
    self->offset = 0;
    self->tag_name.data = NULL;
    self->tag_name.size = 0;
    self->attribute_key.data = NULL;
    self->attribute_key.size = 0;
    self->attribute_value.data = NULL;
    self->attribute_value.size = 0;
    self->text.data = NULL;
    self->text.size = 0;
    self->text_stripped.data = NULL;
    self->text_stripped.size = 0;
    self->is_tag_void = 0;
    self->inside_script_tag = 0;
    self->unclosed_tags_offset = 0;
}

void html_parser_init(HtmlParser *self, const char *html_source, size_t len, HtmlParseCallback parse_callback, void *userdata) {
    self->source = html_source;
    self->source_len = len;
    self->parse_callback = parse_callback;
    self->callback_userdata = userdata;
}

void html_parser_deinit(HtmlParser *self) {
    (void)self;
}

static char html_parser_next_char(HtmlParser *self) {
    if(self->offset < self->source_len) {
        char c = self->source[self->offset];
        ++self->offset;
        return c;
    }
    return '\0';
}

static char html_parser_peek_char(HtmlParser *self) {
    if(self->offset < self->source_len) {
        char c = self->source[self->offset];
        return c;
    }
    return '\0';
}

static void html_parser_advance_char(HtmlParser *self) {
    if(self->offset < self->source_len)
        ++self->offset;
}

static int is_alpha(char c) {
    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}

static int is_digit(char c) {
    return c >= '0' && c <= '9';
}

static int is_identifier_char(char c) {
    return is_alpha(c) || is_digit(c) || c == '-' || c == '_' || c == '!';
}

static void html_parser_try_append_unclosed_tag(HtmlParser *self, const char *data, size_t size) {
    if(self->unclosed_tags_offset == UNCLOSED_TAGS_SIZE) {
        fprintf(stderr, "Reached the maximum number of unclosed tags! the html source is too broken\n");
        return;
    }
    self->unclosed_tags[self->unclosed_tags_offset].data = data;
    self->unclosed_tags[self->unclosed_tags_offset].size = size;
    ++self->unclosed_tags_offset;
}

static void html_parser_pop_unclosed_tag(HtmlParser *self) {
    assert(self->unclosed_tags_offset > 0);
    --self->unclosed_tags_offset;
}

static void html_parser_try_pop_unclosed_tag(HtmlParser *self) {
    if(self->unclosed_tags_offset > 0)
        --self->unclosed_tags_offset;
}

static int html_parser_try_get_top_unclosed_tag(HtmlParser *self, HtmlStringView *result) {
    if(self->unclosed_tags_offset > 0) {
        *result = self->unclosed_tags[self->unclosed_tags_offset - 1];
        return 1;
    }
    return 0;
}

static void html_parser_skip_whitespace(HtmlParser *self) {
    for(;;) {
        char c = html_parser_peek_char(self);
        if(is_whitespace(c)) {
            html_parser_advance_char(self);
        } else {
            break;
        }
    }
}

static int is_attribute_value_char(char c) {
    switch(c) {
        case '"':
        case '\'':
        case '`':
        case '<':
        case '>':
        case '&':
            return 0;
        default:
            return 1;
    }
}

/* TODO: Unescape html characters in attribute value */
static void html_parser_parse_attribute_value_quoted(HtmlParser *self, char quote_symbol) {
    self->attribute_value.data = self->source + self->offset;
    for(;;) {
        char c = html_parser_peek_char(self);
        if(c == quote_symbol) {
            self->attribute_value.size = (self->source + self->offset) - self->attribute_value.data;
            html_parser_advance_char(self);
            break;
        } else if(c == '\0') {
            self->attribute_value.size = (self->source + self->offset) - self->attribute_value.data;
            break;
        } else {
            html_parser_advance_char(self);
        }
    }
    strip(self->attribute_value.data, self->attribute_value.size, &self->attribute_value.data, &self->attribute_value.size, is_newline);
}

static void html_parser_parse_attribute_value(HtmlParser *self) {
    self->attribute_value.data = self->source + self->offset;
    for(;;) {
        char c = html_parser_peek_char(self);
        if(!is_attribute_value_char(c) || c == '\0')
            break;
        else
            html_parser_advance_char(self);
    }
    self->attribute_value.size = (self->source + self->offset) - self->attribute_value.data;
}

static void html_parser_goto_end_of_js_string(HtmlParser *self, char quote_symbol) {
    int escape_quote = 0;
    for(;;) {
        char c = html_parser_next_char(self);
        if(!escape_quote && c == quote_symbol) {
            return;
        } else if(c == '\\') {
            escape_quote = !escape_quote;
        } else if(c == '\0') {
            return;
        } else {
            escape_quote = 0;
        }
    }
}

static void html_parser_goto_script_end_tag(HtmlParser *self) {
    self->text.data = self->source + self->offset;
    self->text.size = 0;
    for(;;) {
        char c = html_parser_peek_char(self);
        if(c == '"' || c == '\'') {
            html_parser_advance_char(self);
            html_parser_goto_end_of_js_string(self, c);
        } else if(c == '<' && self->offset + 7 < self->source_len && memcmp(self->source + self->offset + 1, "/script", 7) == 0) {
            self->text.size = (self->source + self->offset) - self->text.data;
            strip(self->text.data, self->text.size, &self->text.data, &self->text.size, is_whitespace);
            self->offset += 7;
            for(;;) {
                c = html_parser_peek_char(self);
                if(c == '>') {
                    html_parser_advance_char(self);
                    break;
                } else if(c == '\0') {
                    break;
                } else {
                    html_parser_advance_char(self);
                }
            }
            break;
        } else if(c == '\0') {
            self->text.size = (self->source + self->offset) - self->text.data;
            strip(self->text.data, self->text.size, &self->text.data, &self->text.size, is_whitespace);
            break;
        } else {
            html_parser_advance_char(self);
        }
    }
    self->parse_callback(self, HTML_PARSE_JAVASCRIPT_CODE, self->callback_userdata);
}

static void html_parser_goto_comment_end(HtmlParser *self) {
    for(;;) {
        if(self->source_len - self->offset >= 3 && memcmp(self->source + self->offset, "-->", 3) == 0) {
            self->offset += 3;
            break;
        }
        html_parser_advance_char(self);
    }
}

static void html_parser_parse_tag_start(HtmlParser *self) {
    int tag_name_found = 0;
    for(;;) {
        char c = html_parser_next_char(self);
        if(c == '>') {
            if(tag_name_found && self->is_tag_void)
                self->parse_callback(self, HTML_PARSE_TAG_END, self->callback_userdata);
            self->is_tag_void = 0;
            
            if(self->inside_script_tag) {
                self->inside_script_tag = 0;
                /* <script> tags require special handling since they can have </script> inside a javascript string */
                html_parser_goto_script_end_tag(self);
            }
            return;
        } else if(c == '/') {
            if(html_parser_peek_char(self) == '>') {
                html_parser_advance_char(self);
                if(tag_name_found) {
                    self->parse_callback(self, HTML_PARSE_TAG_END, self->callback_userdata);
                    if(!self->is_tag_void)
                        html_parser_try_pop_unclosed_tag(self);
                }
                self->is_tag_void = 0;
                self->inside_script_tag = 0;
                return;
            }
        } else if(is_identifier_char(c)) {
            HtmlStringView identifier;
            identifier.data = self->source + self->offset - 1;
            for(;;) {
                c = html_parser_peek_char(self);
                if(is_identifier_char(c)) {
                    html_parser_advance_char(self);
                } else {
                    break;
                }
            }
            identifier.size = (self->source + self->offset) - identifier.data;
            if(tag_name_found) {
                /* attribute name */
                self->attribute_key = identifier;
                self->attribute_value.data = NULL;
                self->attribute_value.size = 0;

                html_parser_skip_whitespace(self);
                c = html_parser_peek_char(self);
                if(c == '=') {
                    html_parser_advance_char(self);
                    html_parser_skip_whitespace(self);
                    c = html_parser_peek_char(self);
                    if(c == '"' || c == '\'' || c == '`') {
                        html_parser_advance_char(self);
                        html_parser_parse_attribute_value_quoted(self, c);
                    } else if(is_attribute_value_char(c)) {
                        html_parser_advance_char(self);
                        html_parser_parse_attribute_value(self);
                    }
                }
                self->parse_callback(self, HTML_PARSE_ATTRIBUTE, self->callback_userdata);
            } else {
                /* tag name */
                self->tag_name = identifier;
                tag_name_found = 1;
                if(self->tag_name.size == 3 && memcmp(self->tag_name.data, "!--", 3) == 0) {
                    html_parser_goto_comment_end(self);
                    return;
                }
                self->is_tag_void = is_void_tag(&self->tag_name);
                if(!self->is_tag_void) {
                    html_parser_try_append_unclosed_tag(self, self->tag_name.data, self->tag_name.size);
                    self->inside_script_tag = string_view_equals(&self->tag_name, &script_tag);
                }
                self->parse_callback(self, HTML_PARSE_TAG_START, self->callback_userdata);
            }
        } else if(c == '\0') {
            return;
        }
    }
}

static void html_parser_parse_tag_end(HtmlParser *self) {
    int tag_name_found = 0;
    for(;;) {
        char c = html_parser_peek_char(self);
        if(c == '>') {
            html_parser_advance_char(self);
            return;
        } else if(!tag_name_found && is_identifier_char(c)) {
            HtmlStringView tag_end_name;
            tag_end_name.data = self->source + self->offset;
            html_parser_advance_char(self);
            for(;;) {
                c = html_parser_peek_char(self);
                if(is_identifier_char(c)) {
                    html_parser_advance_char(self);
                } else {
                    break;
                }
            }
            tag_end_name.size = (self->source + self->offset) - tag_end_name.data;
            tag_name_found = 1;

            /* void tags close themselves, this is probably invalid html but we choose to ignore it silently */
            if(is_void_tag(&tag_end_name)) {
                fprintf(stderr, "Warning: got end tag for void tag '%.*s'\n", (int)tag_end_name.size, tag_end_name.data);
                continue;
            }

            ssize_t found_start_tag_index = -1;
            for(ssize_t i = self->unclosed_tags_offset - 1; i >= 0; --i) {
                if(string_view_equals(&self->unclosed_tags[i], &tag_end_name)) {
                    found_start_tag_index = i;
                    break;
                }
            }

            if(found_start_tag_index != -1) {
                for(; self->unclosed_tags_offset > (size_t)found_start_tag_index; --self->unclosed_tags_offset) {
                    self->tag_name = self->unclosed_tags[self->unclosed_tags_offset - 1];
                    self->parse_callback(self, HTML_PARSE_TAG_END, self->callback_userdata);
                }
            } else {
                fprintf(stderr, "Warning: start tag not found for end tag '%.*s'\n", (int)tag_end_name.size, tag_end_name.data);
            }
        } else if(c == '\0') {
            return;
        } else {
            html_parser_advance_char(self);
        }
    }
}

void html_parser_parse(HtmlParser *self) {
    html_parser_reset(self);
    for(;;) {
        char c = html_parser_next_char(self);
        if(c == '<') {
            if(html_parser_peek_char(self) == '/') {
                html_parser_advance_char(self);
                html_parser_parse_tag_end(self);
            } else {
                html_parser_parse_tag_start(self);
            }
        } else if(c == '\0') {
            break;
        } else {
            self->text.data = (self->source + self->offset) - 1;
            for(;;) {
                c = html_parser_peek_char(self);
                if(c == '<' || c == '\0')
                    break;
                else
                    html_parser_advance_char(self);
            }
            self->text.size = (self->source + self->offset) - self->text.data;
            strip(self->text.data, self->text.size, &self->text_stripped.data, &self->text_stripped.size, is_whitespace);
            self->parse_callback(self, HTML_PARSE_TEXT, self->callback_userdata);
        }
    }

    HtmlStringView top_unclosed_tag;
    while(html_parser_try_get_top_unclosed_tag(self, &top_unclosed_tag)) {
        self->tag_name = top_unclosed_tag;
        self->parse_callback(self, HTML_PARSE_TAG_END, self->callback_userdata);
        html_parser_pop_unclosed_tag(self);
    }
}