int redisvFormatCommand(char **target, const char *format, va_list ap) {
    const char *c = format;
    char *cmd = NULL; /* final command */
    int pos; /* position in final command */
    hisds curarg, newarg; /* current argument */
    int touched = 0; /* was the current argument touched? */
    char **curargv = NULL, **newargv = NULL;
    int argc = 0;
    int totlen = 0;
    int error_type = 0; /* 0 = no error; -1 = memory error; -2 = format error */
    int j;

    /* Abort if there is not target to set */
    if (target == NULL)
        return -1;

    /* Build the command string accordingly to protocol */
    curarg = hi_sdsempty();
    if (curarg == NULL)
        return -1;

    while(*c != '\0') {
        if (*c != '%' || c[1] == '\0') {
            if (*c == ' ') {
                if (touched) {
                    newargv = hi_realloc(curargv,sizeof(char*)*(argc+1));
                    if (newargv == NULL) goto memory_err;
                    curargv = newargv;
                    curargv[argc++] = curarg;
                    totlen += bulklen(hi_sdslen(curarg));

                    /* curarg is put in argv so it can be overwritten. */
                    curarg = hi_sdsempty();
                    if (curarg == NULL) goto memory_err;
                    touched = 0;
                }
            } else {
                newarg = hi_sdscatlen(curarg,c,1);
                if (newarg == NULL) goto memory_err;
                curarg = newarg;
                touched = 1;
            }
        } else {
            char *arg;
            size_t size;

            /* Set newarg so it can be checked even if it is not touched. */
            newarg = curarg;

            switch(c[1]) {
            case 's':
                arg = va_arg(ap,char*);
                size = strlen(arg);
                if (size > 0)
                    newarg = hi_sdscatlen(curarg,arg,size);
                break;
            case 'b':
                arg = va_arg(ap,char*);
                size = va_arg(ap,size_t);
                if (size > 0)
                    newarg = hi_sdscatlen(curarg,arg,size);
                break;
            case '%':
                newarg = hi_sdscat(curarg,"%");
                break;
            default:
                /* Try to detect printf format */
                {
                    static const char intfmts[] = "diouxX";
                    static const char flags[] = "#0-+ ";
                    char _format[16];
                    const char *_p = c+1;
                    size_t _l = 0;
                    va_list _cpy;

                    /* Flags */
                    while (*_p != '\0' && strchr(flags,*_p) != NULL) _p++;

                    /* Field width */
                    while (*_p != '\0' && isdigit(*_p)) _p++;

                    /* Precision */
                    if (*_p == '.') {
                        _p++;
                        while (*_p != '\0' && isdigit(*_p)) _p++;
                    }

                    /* Copy va_list before consuming with va_arg */
                    va_copy(_cpy,ap);

                    /* Integer conversion (without modifiers) */
                    if (strchr(intfmts,*_p) != NULL) {
                        va_arg(ap,int);
                        goto fmt_valid;
                    }

                    /* Double conversion (without modifiers) */
                    if (strchr("eEfFgGaA",*_p) != NULL) {
                        va_arg(ap,double);
                        goto fmt_valid;
                    }

                    /* Size: char */
                    if (_p[0] == 'h' && _p[1] == 'h') {
                        _p += 2;
                        if (*_p != '\0' && strchr(intfmts,*_p) != NULL) {
                            va_arg(ap,int); /* char gets promoted to int */
                            goto fmt_valid;
                        }
                        goto fmt_invalid;
                    }

                    /* Size: short */
                    if (_p[0] == 'h') {
                        _p += 1;
                        if (*_p != '\0' && strchr(intfmts,*_p) != NULL) {
                            va_arg(ap,int); /* short gets promoted to int */
                            goto fmt_valid;
                        }
                        goto fmt_invalid;
                    }

                    /* Size: long long */
                    if (_p[0] == 'l' && _p[1] == 'l') {
                        _p += 2;
                        if (*_p != '\0' && strchr(intfmts,*_p) != NULL) {
                            va_arg(ap,long long);
                            goto fmt_valid;
                        }
                        goto fmt_invalid;
                    }

                    /* Size: long */
                    if (_p[0] == 'l') {
                        _p += 1;
                        if (*_p != '\0' && strchr(intfmts,*_p) != NULL) {
                            va_arg(ap,long);
                            goto fmt_valid;
                        }
                        goto fmt_invalid;
                    }

                fmt_invalid:
                    va_end(_cpy);
                    goto format_err;

                fmt_valid:
                    _l = (_p+1)-c;
                    if (_l < sizeof(_format)-2) {
                        memcpy(_format,c,_l);
                        _format[_l] = '\0';
                        newarg = hi_sdscatvprintf(curarg,_format,_cpy);

                        /* Update current position (note: outer blocks
                         * increment c twice so compensate here) */
                        c = _p-1;
                    }

                    va_end(_cpy);
                    break;
                }
            }

            if (newarg == NULL) goto memory_err;
            curarg = newarg;

            touched = 1;
            c++;
        }
        c++;
    }

    /* Add the last argument if needed */
    if (touched) {
        newargv = hi_realloc(curargv,sizeof(char*)*(argc+1));
        if (newargv == NULL) goto memory_err;
        curargv = newargv;
        curargv[argc++] = curarg;
        totlen += bulklen(hi_sdslen(curarg));
    } else {
        hi_sdsfree(curarg);
    }

    /* Clear curarg because it was put in curargv or was free'd. */
    curarg = NULL;

    /* Add bytes needed to hold multi bulk count */
    totlen += 1+countDigits(argc)+2;

    /* Build the command at protocol level */
    cmd = hi_malloc(totlen+1);
    if (cmd == NULL) goto memory_err;

    pos = sprintf(cmd,"*%d\r\n",argc);
    for (j = 0; j < argc; j++) {
        pos += sprintf(cmd+pos,"$%zu\r\n",hi_sdslen(curargv[j]));
        memcpy(cmd+pos,curargv[j],hi_sdslen(curargv[j]));
        pos += hi_sdslen(curargv[j]);
        hi_sdsfree(curargv[j]);
        cmd[pos++] = '\r';
        cmd[pos++] = '\n';
    }
    assert(pos == totlen);
    cmd[pos] = '\0';

    hi_free(curargv);
    *target = cmd;
    return totlen;

format_err:
    error_type = -2;
    goto cleanup;

memory_err:
    error_type = -1;
    goto cleanup;

cleanup:
    if (curargv) {
        while(argc--)
            hi_sdsfree(curargv[argc]);
        hi_free(curargv);
    }

    hi_sdsfree(curarg);
    hi_free(cmd);

    return error_type;
}