Two sparse fixes from Yuxuan Shui.

[rsync.git] / compat.c

/*
 * Compatibility routines for older rsync protocol versions.
 *
 * Copyright (C) Andrew Tridgell 1996
 * Copyright (C) Paul Mackerras 1996
 * Copyright (C) 2004-2020 Wayne Davison
 *
 * 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; either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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, visit the http://fsf.org website.
 */

#include "rsync.h"

extern int am_server;
extern int am_sender;
extern int local_server;
extern int inplace;
extern int recurse;
extern int use_qsort;
extern int allow_inc_recurse;
extern int preallocate_files;
extern int append_mode;
extern int fuzzy_basis;
extern int read_batch;
extern int write_batch;
extern int delay_updates;
extern int checksum_seed;
extern int basis_dir_cnt;
extern int prune_empty_dirs;
extern int protocol_version;
extern int protect_args;
extern int preserve_uid;
extern int preserve_gid;
extern int preserve_atimes;
extern int preserve_acls;
extern int preserve_xattrs;
extern int xfer_flags_as_varint;
extern int need_messages_from_generator;
extern int delete_mode, delete_before, delete_during, delete_after;
extern int do_compression;
extern int do_compression_level;
extern char *shell_cmd;
extern char *partial_dir;
extern char *dest_option;
extern char *files_from;
extern char *filesfrom_host;
extern char *checksum_choice;
extern char *compress_choice;
extern filter_rule_list filter_list;
extern int need_unsorted_flist;
#ifdef ICONV_OPTION
extern iconv_t ic_send, ic_recv;
extern char *iconv_opt;
#endif
extern struct name_num_obj valid_checksums;

int remote_protocol = 0;
int file_extra_cnt = 0; /* count of file-list extras that everyone gets */
int inc_recurse = 0;
int compat_flags = 0;
int use_safe_inc_flist = 0;
int want_xattr_optim = 0;
int proper_seed_order = 0;
int inplace_partial = 0;
int do_negotiated_strings = 0;

/* These index values are for the file-list's extra-attribute array. */
int pathname_ndx, depth_ndx, atimes_ndx, uid_ndx, gid_ndx, acls_ndx, xattrs_ndx, unsort_ndx;

int receiver_symlink_times = 0; /* receiver can set the time on a symlink */
int sender_symlink_iconv = 0;   /* sender should convert symlink content */

#ifdef ICONV_OPTION
int filesfrom_convert = 0;
#endif

#define MAX_NSTR_STRLEN 256

struct name_num_obj valid_compressions = {
        "compress", NULL, NULL, 0, 0, {
                { CPRES_ZLIBX, "zlibx", NULL },
                { CPRES_ZLIB, "zlib", NULL },
#ifdef SUPPORT_ZSTD
                /* TODO decide where in the default preference order this should go. */
                { CPRES_ZSTD, "zstd", NULL },
#endif
#ifdef SUPPORT_LZ4
                /* TODO decide where in the default preference order this should go. */
                { CPRES_LZ4, "lz4", NULL },
#endif
                { CPRES_NONE, "none", NULL },
                { 0, NULL, NULL }
        }
};

#define CF_INC_RECURSE   (1<<0)
#define CF_SYMLINK_TIMES (1<<1)
#define CF_SYMLINK_ICONV (1<<2)
#define CF_SAFE_FLIST    (1<<3)
#define CF_AVOID_XATTR_OPTIM (1<<4)
#define CF_CHKSUM_SEED_FIX (1<<5)
#define CF_INPLACE_PARTIAL_DIR (1<<6)
#define CF_VARINT_FLIST_FLAGS (1<<7)

static const char *client_info;

/* The server makes sure that if either side only supports a pre-release
 * version of a protocol, that both sides must speak a compatible version
 * of that protocol for it to be advertised as available. */
static void check_sub_protocol(void)
{
        char *dot;
        int their_protocol, their_sub;
#if SUBPROTOCOL_VERSION != 0
        int our_sub = protocol_version < PROTOCOL_VERSION ? 0 : SUBPROTOCOL_VERSION;
#else
        int our_sub = 0;
#endif

        /* client_info starts with VER.SUB string if client is a pre-release. */
        if (!(their_protocol = atoi(client_info))
         || !(dot = strchr(client_info, '.'))
         || !(their_sub = atoi(dot+1))) {
#if SUBPROTOCOL_VERSION != 0
                if (our_sub)
                        protocol_version--;
#endif
                return;
        }

        if (their_protocol < protocol_version) {
                if (their_sub)
                        protocol_version = their_protocol - 1;
                return;
        }

        if (their_protocol > protocol_version)
                their_sub = 0; /* 0 == final version of older protocol */
        if (their_sub != our_sub)
                protocol_version--;
}

void set_allow_inc_recurse(void)
{
        client_info = shell_cmd ? shell_cmd : "";

        if (!recurse || use_qsort)
                allow_inc_recurse = 0;
        else if (!am_sender
         && (delete_before || delete_after
          || delay_updates || prune_empty_dirs))
                allow_inc_recurse = 0;
        else if (am_server && !local_server
         && (strchr(client_info, 'i') == NULL))
                allow_inc_recurse = 0;
}

void parse_compress_choice(int final_call)
{
        if (valid_compressions.negotiated_name)
                do_compression = valid_compressions.negotiated_num;
        else if (compress_choice) {
                struct name_num_item *nni = get_nni_by_name(&valid_compressions, compress_choice, -1);
                if (!nni) {
                        rprintf(FERROR, "unknown compress name: %s\n", compress_choice);
                        exit_cleanup(RERR_UNSUPPORTED);
                }
                do_compression = nni->num;
        } else if (do_compression)
                do_compression = CPRES_ZLIB;
        else
                do_compression = CPRES_NONE;

        if (do_compression != CPRES_NONE && final_call)
                init_compression_level(); /* There's a chance this might turn compression off! */

        if (do_compression == CPRES_NONE)
                compress_choice = NULL;

        if (final_call && DEBUG_GTE(NSTR, am_server ? 3 : 1)
         && (do_compression != CPRES_NONE || do_compression_level != CLVL_NOT_SPECIFIED)) {
                const char *c_s = am_server ? "Server" : "Client";
                if (do_compression != CPRES_NONE && valid_compressions.negotiated_name) {
                        rprintf(FINFO, "%s negotiated compress: %s (level %d)\n",
                                c_s, valid_compressions.negotiated_name, do_compression_level);
                } else {
                        struct name_num_item *nni = get_nni_by_num(&valid_compressions, do_compression);
                        rprintf(FINFO, "%s compress: %s (level %d)\n",
                                c_s, nni ? nni->name : "UNKNOWN", do_compression_level);
                }
        }
}

struct name_num_item *get_nni_by_name(struct name_num_obj *nno, const char *name, int len)
{
        struct name_num_item *nni;

        if (len < 0)
                len = strlen(name);

        for (nni = nno->list; nni->name; nni++) {
                if (strncasecmp(name, nni->name, len) == 0 && nni->name[len] == '\0')
                        return nni;
        }

        return NULL;
}

struct name_num_item *get_nni_by_num(struct name_num_obj *nno, int num)
{
        struct name_num_item *nni;

        for (nni = nno->list; nni->name; nni++) {
                if (num == nni->num)
                        return nni;
        }

        return NULL;
}

static void init_nno_saw(struct name_num_obj *nno, int val)
{
        struct name_num_item *nni;
        int cnt;

        if (!nno->saw_len) {
                for (nni = nno->list; nni->name; nni++) {
                        if (nni->num >= nno->saw_len)
                                nno->saw_len = nni->num + 1;
                }
        }

        if (!nno->saw) {
                if (!(nno->saw = new_array0(uchar, nno->saw_len)))
                        out_of_memory("init_nno_saw");

                /* We'll take this opportunity to make sure that the main_name values are set right. */
                for (cnt = 1, nni = nno->list; nni->name; nni++, cnt++) {
                        if (nno->saw[nni->num])
                                nni->main_name = nno->list[nno->saw[nni->num]-1].name;
                        else
                                nno->saw[nni->num] = cnt;
                }
        }

        memset(nno->saw, val, nno->saw_len);
}

/* Simplify the user-provided string so that it contains valid names without any duplicates.
 * It also sets the "saw" flags to a 1-relative count of which name was seen first. */
static int parse_nni_str(struct name_num_obj *nno, const char *from, char *tobuf, int tobuf_len)
{
        char *to = tobuf, *tok = NULL;
        int cnt = 0;

        while (1) {
                if (*from == ' ' || !*from) {
                        if (tok) {
                                struct name_num_item *nni = get_nni_by_name(nno, tok, to - tok);
                                if (nni && !nno->saw[nni->num]) {
                                        nno->saw[nni->num] = ++cnt;
                                        if (nni->main_name) {
                                                to = tok + strlcpy(tok, nni->main_name, tobuf_len - (tok - tobuf));
                                                if (to - tobuf >= tobuf_len) {
                                                        to = tok - 1;
                                                        break;
                                                }
                                        }
                                } else
                                        to = tok - (tok != tobuf);
                                tok = NULL;
                        }
                        if (!*from++)
                                break;
                        continue;
                }
                if (!tok) {
                        if (to != tobuf)
                                *to++ = ' ';
                        tok = to;
                }
                if (to - tobuf >= tobuf_len - 1) {
                        to = tok - (tok != tobuf);
                        break;
                }
                *to++ = *from++;
        }
        *to = '\0';

        return to - tobuf;
}

static void recv_negotiate_str(int f_in, struct name_num_obj *nno, char *tmpbuf, int len)
{
        struct name_num_item *ret = NULL;

        if (len < 0)
                len = read_vstring(f_in, tmpbuf, MAX_NSTR_STRLEN);

        if (DEBUG_GTE(NSTR, am_server ? 3 : 2)) {
                if (am_server)
                        rprintf(FINFO, "Client %s list (on server): %s\n", nno->type, tmpbuf);
                else
                        rprintf(FINFO, "Server %s list (on client): %s\n", nno->type, tmpbuf);
        }

        if (len > 0) {
                int best = nno->saw_len; /* We want best == 1 from the client list, so start with a big number. */
                char *tok;
                if (am_server)
                        init_nno_saw(nno, 1); /* Since we're parsing client names, anything we parse first is #1. */
                for (tok = strtok(tmpbuf, " \t"); tok; tok = strtok(NULL, " \t")) {
                        struct name_num_item *nni = get_nni_by_name(nno, tok, -1);
                        if (!nni || !nno->saw[nni->num] || best <= nno->saw[nni->num])
                                continue;
                        ret = nni;
                        best = nno->saw[nni->num];
                        if (best == 1)
                                break;
                }
                if (ret) {
                        free(nno->saw);
                        nno->saw = NULL;
                        nno->negotiated_name = ret->main_name ? ret->main_name : ret->name;
                        nno->negotiated_num = ret->num;
                        return;
                }
        }

        if (!am_server)
                rprintf(FERROR, "Failed to negotiate a common %s\n", nno->type);
        exit_cleanup(RERR_UNSUPPORTED);
}

/* The saw buffer is initialized and used to store ordinal values from 1 to N
 * for the order of the args in the array.  If dup_markup == '\0', duplicates
 * are removed otherwise the char is prefixed to the duplicate term and, if it
 * is an opening paren/bracket/brace, the matching closing char is suffixed. */
int get_default_nno_list(struct name_num_obj *nno, char *to_buf, int to_buf_len, char dup_markup)
{
        struct name_num_item *nni;
        int len = 0, cnt = 0;
        char pre_char = '\0', post_char = '\0';

        init_nno_saw(nno, 0);

        for (nni = nno->list, len = 0; nni->name; nni++) {
                if (nni->main_name) {
                        if (!dup_markup)
                                continue;
                        pre_char = dup_markup;
                        switch (pre_char) {
                        case '(': post_char = ')'; break;
                        case '[': post_char = ']'; break;
                        case '{': post_char = '}'; break;
                        default: break;
                        }
                }
                if (len)
                        to_buf[len++]= ' ';
                if (pre_char) {
                        to_buf[len++]= pre_char;
                        pre_char = '\0';
                }
                len += strlcpy(to_buf+len, nni->name, to_buf_len - len);
                if (len >= to_buf_len - 3)
                        exit_cleanup(RERR_UNSUPPORTED); /* IMPOSSIBLE... */
                if (post_char) {
                        to_buf[len++]= post_char;
                        post_char = '\0';
                }
                nno->saw[nni->num] = ++cnt;
        }

        return len;
}

static void send_negotiate_str(int f_out, struct name_num_obj *nno, const char *env_name)
{
        char tmpbuf[MAX_NSTR_STRLEN];
        const char *list_str = getenv(env_name);
        int len, fail_if_empty = list_str && strstr(list_str, "FAIL");

        if (!do_negotiated_strings) {
                if (!am_server && fail_if_empty) {
                        rprintf(FERROR, "Remote rsync is too old for %s negotation\n", nno->type);
                        exit_cleanup(RERR_UNSUPPORTED);
                }
                return;
        }

        if (list_str && *list_str && (!am_server || local_server)) {
                init_nno_saw(nno, 0);
                len = parse_nni_str(nno, list_str, tmpbuf, MAX_NSTR_STRLEN);
                if (fail_if_empty && !len)
                        len = strlcpy(tmpbuf, "FAIL", MAX_NSTR_STRLEN);
                list_str = tmpbuf;
        } else
                list_str = NULL;

        if (!list_str || !*list_str) {
                len = get_default_nno_list(nno, tmpbuf, sizeof tmpbuf, '\0');
        }

        if (DEBUG_GTE(NSTR, am_server ? 3 : 2)) {
                if (am_server)
                        rprintf(FINFO, "Server %s list (on server): %s\n", nno->type, tmpbuf);
                else
                        rprintf(FINFO, "Client %s list (on client): %s\n", nno->type, tmpbuf);
        }

        if (local_server) {
                /* A local server doesn't bother to send/recv the strings, it just constructs
                 * and parses the same string on both sides. */
                if (!read_batch)
                        recv_negotiate_str(-1, nno, tmpbuf, len);
        } else {
                /* Each side sends their list of valid names to the other side and then both sides
                 * pick the first name in the client's list that is also in the server's list. */
                write_vstring(f_out, tmpbuf, len);
        }
}

static void negotiate_the_strings(int f_in, int f_out)
{
        /* We send all the negotiation strings before we start to read them to help avoid a slow startup. */

        if (!checksum_choice)
                send_negotiate_str(f_out, &valid_checksums, "RSYNC_CHECKSUM_LIST");

        if (do_compression && !compress_choice)
                send_negotiate_str(f_out, &valid_compressions, "RSYNC_COMPRESS_LIST");

        if (valid_checksums.saw) {
                char tmpbuf[MAX_NSTR_STRLEN];
                recv_negotiate_str(f_in, &valid_checksums, tmpbuf, -1);
        }

        if (valid_compressions.saw) {
                char tmpbuf[MAX_NSTR_STRLEN];
                recv_negotiate_str(f_in, &valid_compressions, tmpbuf, -1);
        }
}

void setup_protocol(int f_out,int f_in)
{
        assert(file_extra_cnt == 0);
        assert(EXTRA64_CNT == 2 || EXTRA64_CNT == 1);

        /* All int64 values must be set first so that they are guaranteed to be
         * aligned for direct int64-pointer memory access. */
        if (preserve_atimes)
                atimes_ndx = (file_extra_cnt += EXTRA64_CNT);
        if (am_sender) /* This is most likely in the in64 union as well. */
                pathname_ndx = (file_extra_cnt += PTR_EXTRA_CNT);
        else
                depth_ndx = ++file_extra_cnt;
        if (preserve_uid)
                uid_ndx = ++file_extra_cnt;
        if (preserve_gid)
                gid_ndx = ++file_extra_cnt;
        if (preserve_acls && !am_sender)
                acls_ndx = ++file_extra_cnt;
        if (preserve_xattrs)
                xattrs_ndx = ++file_extra_cnt;

        if (am_server)
                set_allow_inc_recurse();

        if (remote_protocol == 0) {
                if (am_server && !local_server)
                        check_sub_protocol();
                if (!read_batch)
                        write_int(f_out, protocol_version);
                remote_protocol = read_int(f_in);
                if (protocol_version > remote_protocol)
                        protocol_version = remote_protocol;
        }
        if (read_batch && remote_protocol > protocol_version) {
                rprintf(FERROR, "The protocol version in the batch file is too new (%d > %d).\n",
                        remote_protocol, protocol_version);
                exit_cleanup(RERR_PROTOCOL);
        }

        if (DEBUG_GTE(PROTO, 1)) {
                rprintf(FINFO, "(%s) Protocol versions: remote=%d, negotiated=%d\n",
                        am_server? "Server" : "Client", remote_protocol, protocol_version);
        }
        if (remote_protocol < MIN_PROTOCOL_VERSION
         || remote_protocol > MAX_PROTOCOL_VERSION) {
                rprintf(FERROR,"protocol version mismatch -- is your shell clean?\n");
                rprintf(FERROR,"(see the rsync man page for an explanation)\n");
                exit_cleanup(RERR_PROTOCOL);
        }
        if (remote_protocol < OLD_PROTOCOL_VERSION) {
                rprintf(FINFO,"%s is very old version of rsync, upgrade recommended.\n",
                        am_server? "Client" : "Server");
        }
        if (protocol_version < MIN_PROTOCOL_VERSION) {
                rprintf(FERROR, "--protocol must be at least %d on the %s.\n",
                        MIN_PROTOCOL_VERSION, am_server? "Server" : "Client");
                exit_cleanup(RERR_PROTOCOL);
        }
        if (protocol_version > PROTOCOL_VERSION) {
                rprintf(FERROR, "--protocol must be no more than %d on the %s.\n",
                        PROTOCOL_VERSION, am_server? "Server" : "Client");
                exit_cleanup(RERR_PROTOCOL);
        }
        if (read_batch)
                check_batch_flags();

#ifndef SUPPORT_PREALLOCATION
        if (preallocate_files && !am_sender) {
                rprintf(FERROR, "preallocation is not supported on this %s\n",
                        am_server ? "Server" : "Client");
                exit_cleanup(RERR_SYNTAX);
        }
#endif

        if (protocol_version < 30) {
                if (append_mode == 1)
                        append_mode = 2;
                if (preserve_acls && !local_server) {
                        rprintf(FERROR,
                            "--acls requires protocol 30 or higher"
                            " (negotiated %d).\n",
                            protocol_version);
                        exit_cleanup(RERR_PROTOCOL);
                }
                if (preserve_xattrs && !local_server) {
                        rprintf(FERROR,
                            "--xattrs requires protocol 30 or higher"
                            " (negotiated %d).\n",
                            protocol_version);
                        exit_cleanup(RERR_PROTOCOL);
                }
        }

        if (delete_mode && !(delete_before+delete_during+delete_after)) {
                if (protocol_version < 30)
                        delete_before = 1;
                else
                        delete_during = 1;
        }

        if (protocol_version < 29) {
                if (fuzzy_basis) {
                        rprintf(FERROR,
                            "--fuzzy requires protocol 29 or higher"
                            " (negotiated %d).\n",
                            protocol_version);
                        exit_cleanup(RERR_PROTOCOL);
                }

                if (basis_dir_cnt && inplace) {
                        rprintf(FERROR,
                            "%s with --inplace requires protocol 29 or higher"
                            " (negotiated %d).\n",
                            dest_option, protocol_version);
                        exit_cleanup(RERR_PROTOCOL);
                }

                if (basis_dir_cnt > 1) {
                        rprintf(FERROR,
                            "Using more than one %s option requires protocol"
                            " 29 or higher (negotiated %d).\n",
                            dest_option, protocol_version);
                        exit_cleanup(RERR_PROTOCOL);
                }

                if (prune_empty_dirs) {
                        rprintf(FERROR,
                            "--prune-empty-dirs requires protocol 29 or higher"
                            " (negotiated %d).\n",
                            protocol_version);
                        exit_cleanup(RERR_PROTOCOL);
                }
        } else if (protocol_version >= 30) {
                if (am_server) {
                        compat_flags = allow_inc_recurse ? CF_INC_RECURSE : 0;
#ifdef CAN_SET_SYMLINK_TIMES
                        compat_flags |= CF_SYMLINK_TIMES;
#endif
#ifdef ICONV_OPTION
                        compat_flags |= CF_SYMLINK_ICONV;
#endif
                        if (local_server || strchr(client_info, 'f') != NULL)
                                compat_flags |= CF_SAFE_FLIST;
                        if (local_server || strchr(client_info, 'x') != NULL)
                                compat_flags |= CF_AVOID_XATTR_OPTIM;
                        if (local_server || strchr(client_info, 'C') != NULL)
                                compat_flags |= CF_CHKSUM_SEED_FIX;
                        if (local_server || strchr(client_info, 'I') != NULL)
                                compat_flags |= CF_INPLACE_PARTIAL_DIR;
                        if (local_server || strchr(client_info, 'v') != NULL) {
                                if (!write_batch || protocol_version >= 30) {
                                        do_negotiated_strings = 1;
                                        compat_flags |= CF_VARINT_FLIST_FLAGS;
                                }
                        }
                        if (strchr(client_info, 'V') != NULL) { /* Support a pre-release 'V' that got superseded */
                                if (!write_batch)
                                        compat_flags |= CF_VARINT_FLIST_FLAGS;
                                write_byte(f_out, compat_flags);
                        } else
                                write_varint(f_out, compat_flags);
                } else { /* read_varint() is compatible with the older write_byte() when the 0x80 bit isn't on. */
                        compat_flags = read_varint(f_in);
                        if  (compat_flags & CF_VARINT_FLIST_FLAGS)
                                do_negotiated_strings = 1;
                }
                /* The inc_recurse var MUST be set to 0 or 1. */
                inc_recurse = compat_flags & CF_INC_RECURSE ? 1 : 0;
                want_xattr_optim = protocol_version >= 31 && !(compat_flags & CF_AVOID_XATTR_OPTIM);
                proper_seed_order = compat_flags & CF_CHKSUM_SEED_FIX ? 1 : 0;
                xfer_flags_as_varint = compat_flags & CF_VARINT_FLIST_FLAGS ? 1 : 0;
                if (am_sender) {
                        receiver_symlink_times = am_server
                            ? strchr(client_info, 'L') != NULL
                            : !!(compat_flags & CF_SYMLINK_TIMES);
                }
#ifdef CAN_SET_SYMLINK_TIMES
                else
                        receiver_symlink_times = 1;
#endif
#ifdef ICONV_OPTION
                sender_symlink_iconv = iconv_opt && (am_server
                    ? local_server || strchr(client_info, 's') != NULL
                    : !!(compat_flags & CF_SYMLINK_ICONV));
#endif
                if (inc_recurse && !allow_inc_recurse) {
                        /* This should only be able to happen in a batch. */
                        fprintf(stderr,
                            "Incompatible options specified for inc-recursive %s.\n",
                            read_batch ? "batch file" : "connection");
                        exit_cleanup(RERR_SYNTAX);
                }
                use_safe_inc_flist = (compat_flags & CF_SAFE_FLIST) || protocol_version >= 31;
                need_messages_from_generator = 1;
                if (compat_flags & CF_INPLACE_PARTIAL_DIR)
                        inplace_partial = 1;
#ifdef CAN_SET_SYMLINK_TIMES
        } else if (!am_sender) {
                receiver_symlink_times = 1;
#endif
        }

        if (need_unsorted_flist && (!am_sender || inc_recurse))
                unsort_ndx = ++file_extra_cnt;

        if (partial_dir && *partial_dir != '/' && (!am_server || local_server)) {
                int rflags = FILTRULE_NO_PREFIXES | FILTRULE_DIRECTORY;
                if (!am_sender || protocol_version >= 30)
                        rflags |= FILTRULE_PERISHABLE;
                parse_filter_str(&filter_list, partial_dir, rule_template(rflags), 0);
        }


#ifdef ICONV_OPTION
        if (protect_args && files_from) {
                if (am_sender)
                        filesfrom_convert = filesfrom_host && ic_send != (iconv_t)-1;
                else
                        filesfrom_convert = !filesfrom_host && ic_recv != (iconv_t)-1;
        }
#endif

        negotiate_the_strings(f_in, f_out);

        if (am_server) {
                if (!checksum_seed)
                        checksum_seed = time(NULL) ^ (getpid() << 6);
                write_int(f_out, checksum_seed);
        } else {
                checksum_seed = read_int(f_in);
        }

        init_flist();
}

void maybe_write_negotiated_strings(int batch_fd)
{
        if (valid_checksums.negotiated_name)
                write_vstring(batch_fd, valid_checksums.negotiated_name, strlen(valid_checksums.negotiated_name));

        if (valid_compressions.negotiated_name)
                write_vstring(batch_fd, valid_compressions.negotiated_name, strlen(valid_compressions.negotiated_name));
}