uri_idea.c

// This is pseudocode / example to explain what kind of implementation I mean.
// I have not checked it for off-by-one errors, 100% accurate C compliance, etc.
// It's just to show what I mean, implementation wise.

#define SOME_DEFAULT_SIZE 20

char *vlc_uri_compose(const vlc_url_t *uri)
{
    char *buf, *enc;
    size_t len = SOME_DEFAULT_SIZE;
    size_t pos = 0;

    buf = calloc(len, 1);

    if (buf == NULL)
        return NULL;

    if (uri->psz_protocol != NULL) {
        // The following should be made into a function that uses va_list. or a macro.
        int n = snprintf(buf, "%s:", uri->psz_protocol);
        if (n + 1 >= len + pos) {
            char *tmp = realloc(buf, n * 2); //arbitrary, could easily be n + 3, etc.
            if (tmp != NULL) {
                buf = tmp;
                pos = n;
                len = pos + 
            } else {
                goto error;
            }
        }
    }

    if (uri->psz_host != NULL)
    {
        if (pos + 2 + 1 < len) {
            buf[pos++] = '/';
            buf[pos++] = '/';
        } else {
            //realloc stuff or error or whatever
        }

        if (uri->psz_username != NULL)
        {
            enc = vlc_uri_encode(uri->psz_username);
            if (enc == NULL)
                goto error;

            if (pos + strlen(enc) + 1 > len) {
                //realloc here
            }

            buf[pos++] = '\0';
            strcat(&buf[pos], enc); // Guaranteed to be big enough. Would be better off using memcpy or strncpy or strncat. Just used here for example psuedocode.
            pos += strlen(enc);
            free(enc);

            if (uri->psz_password != NULL)
            {
                enc = vlc_uri_encode(uri->psz_password);
                if (unlikely(enc == NULL))
                    goto error;

                int writ = vlc_snprintf_realloc_thing(&buf, len, pos, ":%s", enc); // Pretend this is the macro/func I alluded to above. Could also be done using normal copies and '=' operators, since it's just %s and one character.
                if (writ <= 0) {
                    //rrror stuff
                }
                pos += writ;
                free(enc);
            }
            if (pos + 1 + 1 < len) {
                buf[pos++] = '@'
            } else {
                //realloc or err stuff
            }
        }

        const char *fmt;

        if (strchr(uri->psz_host, ':') != NULL)
            fmt = (uri->i_port != 0) ? "[%s]:%d" : "[%s]";
        else
            fmt = (uri->i_port != 0) ? "%s:%d" : "%s";
        /* No IDNA decoding here. Seems unnecessary, dangerous even. */
        int writ = vlc_snprintf_realloc_thing(&buf, len, pos, fmt, uri->psz_host, uri->i_port);
        if (write <= 0) {
            //error
        }
    }

    if (uri->psz_path != NULL) {
        if (pos + strlen(uri->psz_path) + 1 < len) {
            //realloc stuff
        }
        strcat(&buf[pos], uri->psz_path); // same comment as last usage
        pos += strlen(uri->psz_path);
    }
    if (uri->psz_option != NULL) {
        int writ = vlc_snprintf_realloc_thing(&buf, len, pos, "?%s", uri->psz_option); //same comment as the last few
        if (writ <= 0) {
            //error
        }
    }

    if (pos + 1 < len) {
        //realloc
    }
    buf[pos] = '\0';

    return buf;

error:
    free(buf);
    return NULL;
}