lsup_rdf/src/codec_ttl.c

#include "codec_ttl.h"
#include "parser_ttl.h"

/** @brief List of characters to be escaped in serialized literals.
 *
 * @sa https://www.w3.org/TR/n-triples/#grammar-production-ECHAR
 */
#define LIT_ECHAR "\t\b\n\r\f\"\'\\"

/** @brief Regex of characters to be escaped in serialized IRIs.
 *
 * @sa https://www.w3.org/TR/n-triples/#grammar-production-IRIREF
 */
#define IRI_ECHAR_PTN "[\x00-\x20<>\"\\{\\}\\|\\^`\\\\]"


/* * * Static prototypes. * * */

static LSUP_rc escape_lit (const char *in, char **out_p);


/* * * Codec functions. * * */

static LSUP_rc
term_to_ttl (const LSUP_Term *term, const LSUP_NSMap *nsm, char **out_p)
{
    LSUP_rc rc;
    char *out = NULL, *tmp, *escaped;
    const char *metadata = NULL;
    size_t buf_len;

    // Free previous content if not NULL.
    if (*out_p != NULL) out = realloc (*out_p, 0);

    switch (term->type) {
        case LSUP_TERM_IRIREF:
            tmp = realloc (out, strlen (term->data) + 3);
            if (UNLIKELY (!tmp)) return LSUP_MEM_ERR;
            out = tmp;

            sprintf (out, "<%s>", term->data);
            rc = LSUP_OK;
            break;

        case LSUP_TERM_LITERAL:
            // Calculate string length.
            if (escape_lit (term->data, &escaped) != LSUP_OK)
                return LSUP_ERROR;
            buf_len = strlen (escaped) + 3; // Room for "" and terminator

            if (
                term->datatype != 0
                && term->datatype != LSUP_default_datatype
            ) {
                metadata = term->datatype->data;
                buf_len += strlen (metadata) + 4; // Room for ^^<>
            }

            tmp = realloc (out, buf_len);
            if (UNLIKELY (!tmp)) return LSUP_MEM_ERR;
            out = tmp;

            sprintf (out, "\"%s\"", escaped);
            free (escaped);

            // Add datatype.
            if (metadata)
                out = strcat (strcat (strcat (out, "^^<"), metadata), ">");

            rc = LSUP_OK;

            break;

        case LSUP_TERM_LT_LITERAL:
            // Calculate string length.
            if (escape_lit (term->data, &escaped) != LSUP_OK)
                return LSUP_ERROR;
            buf_len = strlen (escaped) + 3; // Room for "" and terminator

            if (term->lang != 0) {
                metadata = term->lang;
                buf_len += strlen (metadata) + 1; // Room for @
            }

            tmp = realloc (out, buf_len);
            if (UNLIKELY (!tmp)) return LSUP_MEM_ERR;
            out = tmp;

            sprintf (out, "\"%s\"", escaped);
            free (escaped);

            // Add lang.
            if (metadata) out = strcat (strcat (out, "@"), metadata);

            rc = LSUP_OK;

            break;

        case LSUP_TERM_BNODE:
            tmp = realloc (out, strlen (term->data) + 3);
            if (UNLIKELY (!tmp)) return LSUP_MEM_ERR;
            out = tmp;

            sprintf (out, "_:%s", term->data);
            rc = LSUP_OK;

            break;

        default:
            out = NULL;
            rc = LSUP_VALUE_ERR;
    }

    *out_p = out;
    return rc;
}


static LSUP_CodecIterator *
gr_to_ttl_init (const LSUP_Graph *gr);


static LSUP_rc
gr_to_ttl_iter (LSUP_CodecIterator *it, unsigned char **res) {
    LSUP_rc rc = LSUP_graph_iter_next (it->gr_it, it->trp);
    if (rc != LSUP_OK) goto finally;

    term_to_ttl (it->trp->s, it->nsm, &it->str_s);
    term_to_ttl (it->trp->p, it->nsm, &it->str_p);
    term_to_ttl (it->trp->o, it->nsm, &it->str_o);

    // 3 term separators + dot + newline + terminal = 6
    unsigned char *tmp = realloc (
            *res, strlen (it->str_s) + strlen (it->str_p)
            + strlen (it->str_o) + 6);
    if (UNLIKELY (!tmp)) {
        *res = NULL;
        rc = LSUP_MEM_ERR;
        goto finally;
    }

    sprintf ((char*)tmp, "%s %s %s .\n", it->str_s, it->str_p, it->str_o);
    *res = tmp;

    it->cur++;

finally:
    LSUP_term_free (it->trp->s); it->trp->s = NULL;
    LSUP_term_free (it->trp->p); it->trp->p = NULL;
    LSUP_term_free (it->trp->o); it->trp->o = NULL;

    return rc;
}


static void
gr_to_ttl_done (LSUP_CodecIterator *it)
{
    LSUP_graph_iter_free (it->gr_it);
    LSUP_triple_free (it->trp);
    free (it->rep);
    free (it->str_s);
    free (it->str_p);
    free (it->str_o);
    free (it);
}


const LSUP_Codec ttl_codec = {
    .name               = "Turtle",
    .mimetype           = "text/turtle",
    .extension          = "ttl",

    .encode_term        = term_to_ttl,

    .encode_graph_init  = gr_to_ttl_init,
    .encode_graph_iter  = gr_to_ttl_iter,
    .encode_graph_done  = gr_to_ttl_done,

    .decode_term        = LSUP_ttl_parse_term,
    .decode_graph       = LSUP_ttl_parse_doc,
};


/* * * Other internal functions. * * */

/** Replace non-printable characters with their literal byte.
 *
 *  Escape backslash is to be added separately.
 */
static inline char replace_char(const char c) {
    switch (c) {
        case '\t': return 't';
        case '\b': return 'b';
        case '\n': return 'n';
        case '\r': return 'r';
        case '\f': return 'f';
        default: return c;
    }
}


static LSUP_CodecIterator *
gr_to_ttl_init (const LSUP_Graph *gr)
{
    LSUP_CodecIterator *it;
    MALLOC_GUARD (it, NULL);

    it->codec = &ttl_codec;
    it->gr_it = LSUP_graph_lookup(gr, NULL, NULL, NULL, &it->cur);
    it->nsm = LSUP_graph_namespace (gr);
    it->cur = 0;
    it->trp = TRP_DUMMY;
    it->rep = NULL;
    it->str_s = NULL;
    it->str_p = NULL;
    it->str_o = NULL;

    return it;
}


/** @brief Add escape character (backslash) to illegal literal characters.
 */
static LSUP_rc
escape_lit (const char *in, char **out_p)
{
    size_t out_size = strlen (in) + 1;

    // Expand output string size to accommodate escape characters.
    for (
            size_t i = strcspn (in, LIT_ECHAR);
            i < strlen (in);
            i += strcspn (in + i + 1, LIT_ECHAR) + 1) {
        out_size ++;
    }

    char *out = calloc (1, out_size);
    if (UNLIKELY (!out)) return LSUP_MEM_ERR;

    size_t boundary;
    boundary = strcspn (in, LIT_ECHAR);
    for (size_t i = 0, j = 0;;) {
        out = strncat (out, in + i, boundary);

        i += boundary;
        j += boundary;
        if (i >= strlen (in)) break;

        out[j++] = '\\';
        out[j++] = replace_char (in[i++]);
        boundary = strcspn (in + i, LIT_ECHAR);
    }

    *out_p = out;
    return 0;
}