backend_startup.c

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/*-------------------------------------------------------------------------
 *
 * backend_startup.c
 *    Backend startup code
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/tcop/backend_startup.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <unistd.h>
 
#include "access/xlog.h"
#include "access/xlogrecovery.h"
#include "common/ip.h"
#include "common/string.h"
#include "libpq/libpq.h"
#include "libpq/libpq-be.h"
#include "libpq/pqformat.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "postmaster/postmaster.h"
#include "replication/walsender.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/procsignal.h"
#include "storage/proc.h"
#include "tcop/backend_startup.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/guc_hooks.h"
#include "utils/injection_point.h"
#include "utils/memutils.h"
#include "utils/ps_status.h"
#include "utils/timeout.h"
#include "utils/varlena.h"
 
/* GUCs */
bool        Trace_connection_negotiation = false;
uint32      log_connections = 0;
char       *log_connections_string = NULL;
 
/* Other globals */
 
/*
 * ConnectionTiming stores timestamps of various points in connection
 * establishment and setup.
 * ready_for_use is initialized to a special value here so we can check if
 * we've already set it before doing so in PostgresMain().
 */
ConnectionTiming conn_timing = {.ready_for_use = TIMESTAMP_MINUS_INFINITY};
 
static void BackendInitialize(ClientSocket *client_sock, CAC_state cac);
static int  ProcessSSLStartup(Port *port);
static int  ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done);
static void ProcessCancelRequestPacket(Port *port, void *pkt, int pktlen);
static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options);
static void process_startup_packet_die(SIGNAL_ARGS);
static void StartupPacketTimeoutHandler(void);
static bool validate_log_connections_options(List *elemlist, uint32 *flags);
 
/*
 * Entry point for a new backend process.
 *
 * Initialize the connection, read the startup packet, authenticate the
 * client, and start the main processing loop.
 */
void
BackendMain(const void *startup_data, size_t startup_data_len)
{
    const BackendStartupData *bsdata = startup_data;
 
    Assert(startup_data_len == sizeof(BackendStartupData));
    Assert(MyClientSocket != NULL);
 
#ifdef EXEC_BACKEND
 
    /*
     * Need to reinitialize the SSL library in the backend, since the context
     * structures contain function pointers and cannot be passed through the
     * parameter file.
     *
     * If for some reason reload fails (maybe the user installed broken key
     * files), soldier on without SSL; that's better than all connections
     * becoming impossible.
     *
     * XXX should we do this in all child processes?  For the moment it's
     * enough to do it in backend children.
     */
#ifdef USE_SSL
    if (EnableSSL)
    {
        if (secure_initialize(false) == 0)
            LoadedSSL = true;
        else
            ereport(LOG,
                    (errmsg("SSL configuration could not be loaded in child process")));
    }
#endif
#endif
 
    /* Perform additional initialization and collect startup packet */
    BackendInitialize(MyClientSocket, bsdata->canAcceptConnections);
 
    /*
     * Create a per-backend PGPROC struct in shared memory.  We must do this
     * before we can use LWLocks or access any shared memory.
     */
    InitProcess();
 
    /*
     * Make sure we aren't in PostmasterContext anymore.  (We can't delete it
     * just yet, though, because InitPostgres will need the HBA data.)
     */
    MemoryContextSwitchTo(TopMemoryContext);
 
    PostgresMain(MyProcPort->database_name, MyProcPort->user_name);
}
 
 
/*
 * BackendInitialize -- initialize an interactive (postmaster-child)
 *              backend process, and collect the client's startup packet.
 *
 * returns: nothing.  Will not return at all if there's any failure.
 *
 * Note: this code does not depend on having any access to shared memory.
 * Indeed, our approach to SIGTERM/timeout handling *requires* that
 * shared memory not have been touched yet; see comments within.
 * In the EXEC_BACKEND case, we are physically attached to shared memory
 * but have not yet set up most of our local pointers to shmem structures.
 */
static void
BackendInitialize(ClientSocket *client_sock, CAC_state cac)
{
    int         status;
    int         ret;
    Port       *port;
    char        remote_host[NI_MAXHOST];
    char        remote_port[NI_MAXSERV];
    StringInfoData ps_data;
    MemoryContext oldcontext;
 
    /* Tell fd.c about the long-lived FD associated with the client_sock */
    ReserveExternalFD();
 
    /*
     * PreAuthDelay is a debugging aid for investigating problems in the
     * authentication cycle: it can be set in postgresql.conf to allow time to
     * attach to the newly-forked backend with a debugger.  (See also
     * PostAuthDelay, which we allow clients to pass through PGOPTIONS, but it
     * is not honored until after authentication.)
     */
    if (PreAuthDelay > 0)
        pg_usleep(PreAuthDelay * 1000000L);
 
    /* This flag will remain set until InitPostgres finishes authentication */
    ClientAuthInProgress = true;    /* limit visibility of log messages */
 
    /*
     * Initialize libpq and enable reporting of ereport errors to the client.
     * Must do this now because authentication uses libpq to send messages.
     *
     * The Port structure and all data structures attached to it are allocated
     * in TopMemoryContext, so that they survive into PostgresMain execution.
     * We need not worry about leaking this storage on failure, since we
     * aren't in the postmaster process anymore.
     */
    oldcontext = MemoryContextSwitchTo(TopMemoryContext);
    port = MyProcPort = pq_init(client_sock);
    MemoryContextSwitchTo(oldcontext);
 
    whereToSendOutput = DestRemote; /* now safe to ereport to client */
 
    /* set these to empty in case they are needed before we set them up */
    port->remote_host = "";
    port->remote_port = "";
 
    /*
     * We arrange to do _exit(1) if we receive SIGTERM or timeout while trying
     * to collect the startup packet; while SIGQUIT results in _exit(2).
     * Otherwise the postmaster cannot shutdown the database FAST or IMMED
     * cleanly if a buggy client fails to send the packet promptly.
     *
     * Exiting with _exit(1) is only possible because we have not yet touched
     * shared memory; therefore no outside-the-process state needs to get
     * cleaned up.
     */
    pqsignal(SIGTERM, process_startup_packet_die);
    /* SIGQUIT handler was already set up by InitPostmasterChild */
    InitializeTimeouts();       /* establishes SIGALRM handler */
    sigprocmask(SIG_SETMASK, &StartupBlockSig, NULL);
 
    /*
     * Get the remote host name and port for logging and status display.
     */
    remote_host[0] = '\0';
    remote_port[0] = '\0';
    if ((ret = pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
                                  remote_host, sizeof(remote_host),
                                  remote_port, sizeof(remote_port),
                                  (log_hostname ? 0 : NI_NUMERICHOST) | NI_NUMERICSERV)) != 0)
        ereport(WARNING,
                (errmsg_internal("pg_getnameinfo_all() failed: %s",
                                 gai_strerror(ret))));
 
    /*
     * Save remote_host and remote_port in port structure (after this, they
     * will appear in log_line_prefix data for log messages).
     */
    port->remote_host = MemoryContextStrdup(TopMemoryContext, remote_host);
    port->remote_port = MemoryContextStrdup(TopMemoryContext, remote_port);
 
    /* And now we can log that the connection was received, if enabled */
    if (log_connections & LOG_CONNECTION_RECEIPT)
    {
        if (remote_port[0])
            ereport(LOG,
                    (errmsg("connection received: host=%s port=%s",
                            remote_host,
                            remote_port)));
        else
            ereport(LOG,
                    (errmsg("connection received: host=%s",
                            remote_host)));
    }
 
    /* For testing client error handling */
#ifdef USE_INJECTION_POINTS
    INJECTION_POINT("backend-initialize", NULL);
    if (IS_INJECTION_POINT_ATTACHED("backend-initialize-v2-error"))
    {
        /*
         * This simulates an early error from a pre-v14 server, which used the
         * version 2 protocol for any errors that occurred before processing
         * the startup packet.
         */
        FrontendProtocol = PG_PROTOCOL(2, 0);
        elog(FATAL, "protocol version 2 error triggered");
    }
#endif
 
    /*
     * If we did a reverse lookup to name, we might as well save the results
     * rather than possibly repeating the lookup during authentication.
     *
     * Note that we don't want to specify NI_NAMEREQD above, because then we'd
     * get nothing useful for a client without an rDNS entry.  Therefore, we
     * must check whether we got a numeric IPv4 or IPv6 address, and not save
     * it into remote_hostname if so.  (This test is conservative and might
     * sometimes classify a hostname as numeric, but an error in that
     * direction is safe; it only results in a possible extra lookup.)
     */
    if (log_hostname &&
        ret == 0 &&
        strspn(remote_host, "0123456789.") < strlen(remote_host) &&
        strspn(remote_host, "0123456789ABCDEFabcdef:") < strlen(remote_host))
    {
        port->remote_hostname = MemoryContextStrdup(TopMemoryContext, remote_host);
    }
 
    /*
     * Ready to begin client interaction.  We will give up and _exit(1) after
     * a time delay, so that a broken client can't hog a connection
     * indefinitely.  PreAuthDelay and any DNS interactions above don't count
     * against the time limit.
     *
     * Note: AuthenticationTimeout is applied here while waiting for the
     * startup packet, and then again in InitPostgres for the duration of any
     * authentication operations.  So a hostile client could tie up the
     * process for nearly twice AuthenticationTimeout before we kick him off.
     *
     * Note: because PostgresMain will call InitializeTimeouts again, the
     * registration of STARTUP_PACKET_TIMEOUT will be lost.  This is okay
     * since we never use it again after this function.
     */
    RegisterTimeout(STARTUP_PACKET_TIMEOUT, StartupPacketTimeoutHandler);
    enable_timeout_after(STARTUP_PACKET_TIMEOUT, AuthenticationTimeout * 1000);
 
    /* Handle direct SSL handshake */
    status = ProcessSSLStartup(port);
 
    /*
     * Receive the startup packet (which might turn out to be a cancel request
     * packet).
     */
    if (status == STATUS_OK)
        status = ProcessStartupPacket(port, false, false);
 
    /*
     * If we're going to reject the connection due to database state, say so
     * now instead of wasting cycles on an authentication exchange. (This also
     * allows a pg_ping utility to be written.)
     */
    if (status == STATUS_OK)
    {
        switch (cac)
        {
            case CAC_STARTUP:
                ereport(FATAL,
                        (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                         errmsg("the database system is starting up")));
                break;
            case CAC_NOTHOTSTANDBY:
                if (!EnableHotStandby)
                    ereport(FATAL,
                            (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                             errmsg("the database system is not accepting connections"),
                             errdetail("Hot standby mode is disabled.")));
                else if (reachedConsistency)
                    ereport(FATAL,
                            (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                             errmsg("the database system is not yet accepting connections"),
                             errdetail("Recovery snapshot is not yet ready for hot standby."),
                             errhint("To enable hot standby, close write transactions with more than %d subtransactions on the primary server.",
                                     PGPROC_MAX_CACHED_SUBXIDS)));
                else
                    ereport(FATAL,
                            (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                             errmsg("the database system is not yet accepting connections"),
                             errdetail("Consistent recovery state has not been yet reached.")));
                break;
            case CAC_SHUTDOWN:
                ereport(FATAL,
                        (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                         errmsg("the database system is shutting down")));
                break;
            case CAC_RECOVERY:
                ereport(FATAL,
                        (errcode(ERRCODE_CANNOT_CONNECT_NOW),
                         errmsg("the database system is in recovery mode")));
                break;
            case CAC_TOOMANY:
                ereport(FATAL,
                        (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                         errmsg("sorry, too many clients already")));
                break;
            case CAC_OK:
                break;
        }
    }
 
    /*
     * Disable the timeout, and prevent SIGTERM again.
     */
    disable_timeout(STARTUP_PACKET_TIMEOUT, false);
    sigprocmask(SIG_SETMASK, &BlockSig, NULL);
 
    /*
     * As a safety check that nothing in startup has yet performed
     * shared-memory modifications that would need to be undone if we had
     * exited through SIGTERM or timeout above, check that no on_shmem_exit
     * handlers have been registered yet.  (This isn't terribly bulletproof,
     * since someone might misuse an on_proc_exit handler for shmem cleanup,
     * but it's a cheap and helpful check.  We cannot disallow on_proc_exit
     * handlers unfortunately, since pq_init() already registered one.)
     */
    check_on_shmem_exit_lists_are_empty();
 
    /*
     * Stop here if it was bad or a cancel packet.  ProcessStartupPacket
     * already did any appropriate error reporting.
     */
    if (status != STATUS_OK)
        proc_exit(0);
 
    /*
     * Now that we have the user and database name, we can set the process
     * title for ps.  It's good to do this as early as possible in startup.
     */
    initStringInfo(&ps_data);
    if (am_walsender)
        appendStringInfo(&ps_data, "%s ", GetBackendTypeDesc(B_WAL_SENDER));
    appendStringInfo(&ps_data, "%s ", port->user_name);
    if (port->database_name[0] != '\0')
        appendStringInfo(&ps_data, "%s ", port->database_name);
    appendStringInfoString(&ps_data, port->remote_host);
    if (port->remote_port[0] != '\0')
        appendStringInfo(&ps_data, "(%s)", port->remote_port);
 
    init_ps_display(ps_data.data);
    pfree(ps_data.data);
 
    set_ps_display("initializing");
}
 
/*
 * Check for a direct SSL connection.
 *
 * This happens before the startup packet so we are careful not to actually
 * read any bytes from the stream if it's not a direct SSL connection.
 */
static int
ProcessSSLStartup(Port *port)
{
    int         firstbyte;
 
    Assert(!port->ssl_in_use);
 
    pq_startmsgread();
    firstbyte = pq_peekbyte();
    pq_endmsgread();
    if (firstbyte == EOF)
    {
        /*
         * Like in ProcessStartupPacket, if we get no data at all, don't
         * clutter the log with a complaint.
         */
        return STATUS_ERROR;
    }
 
    if (firstbyte != 0x16)
    {
        /* Not an SSL handshake message */
        return STATUS_OK;
    }
 
    /*
     * First byte indicates standard SSL handshake message
     *
     * (It can't be a Postgres startup length because in network byte order
     * that would be a startup packet hundreds of megabytes long)
     */
 
#ifdef USE_SSL
    if (!LoadedSSL || port->laddr.addr.ss_family == AF_UNIX)
    {
        /* SSL not supported */
        goto reject;
    }
 
    if (secure_open_server(port) == -1)
    {
        /*
         * we assume secure_open_server() sent an appropriate TLS alert
         * already
         */
        goto reject;
    }
    Assert(port->ssl_in_use);
 
    if (!port->alpn_used)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("received direct SSL connection request without ALPN protocol negotiation extension")));
        goto reject;
    }
 
    if (Trace_connection_negotiation)
        ereport(LOG,
                (errmsg("direct SSL connection accepted")));
    return STATUS_OK;
#else
    /* SSL not supported by this build */
    goto reject;
#endif
 
reject:
    if (Trace_connection_negotiation)
        ereport(LOG,
                (errmsg("direct SSL connection rejected")));
    return STATUS_ERROR;
}
 
/*
 * Read a client's startup packet and do something according to it.
 *
 * Returns STATUS_OK or STATUS_ERROR, or might call ereport(FATAL) and
 * not return at all.
 *
 * (Note that ereport(FATAL) stuff is sent to the client, so only use it
 * if that's what you want.  Return STATUS_ERROR if you don't want to
 * send anything to the client, which would typically be appropriate
 * if we detect a communications failure.)
 *
 * Set ssl_done and/or gss_done when negotiation of an encrypted layer
 * (currently, TLS or GSSAPI) is completed. A successful negotiation of either
 * encryption layer sets both flags, but a rejected negotiation sets only the
 * flag for that layer, since the client may wish to try the other one. We
 * should make no assumption here about the order in which the client may make
 * requests.
 */
static int
ProcessStartupPacket(Port *port, bool ssl_done, bool gss_done)
{
    int32       len;
    char       *buf = NULL;
    ProtocolVersion proto;
    MemoryContext oldcontext;
 
    pq_startmsgread();
 
    /*
     * Grab the first byte of the length word separately, so that we can tell
     * whether we have no data at all or an incomplete packet.  (This might
     * sound inefficient, but it's not really, because of buffering in
     * pqcomm.c.)
     */
    if (pq_getbytes(&len, 1) == EOF)
    {
        /*
         * If we get no data at all, don't clutter the log with a complaint;
         * such cases often occur for legitimate reasons.  An example is that
         * we might be here after responding to NEGOTIATE_SSL_CODE, and if the
         * client didn't like our response, it'll probably just drop the
         * connection.  Service-monitoring software also often just opens and
         * closes a connection without sending anything.  (So do port
         * scanners, which may be less benign, but it's not really our job to
         * notice those.)
         */
        goto fail;
    }
 
    if (pq_getbytes(((char *) &len) + 1, 3) == EOF)
    {
        /* Got a partial length word, so bleat about that */
        if (!ssl_done && !gss_done)
            ereport(COMMERROR,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("incomplete startup packet")));
        goto fail;
    }
 
    len = pg_ntoh32(len);
    len -= 4;
 
    if (len < (int32) sizeof(ProtocolVersion) ||
        len > MAX_STARTUP_PACKET_LENGTH)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid length of startup packet")));
        goto fail;
    }
 
    /*
     * Allocate space to hold the startup packet, plus one extra byte that's
     * initialized to be zero.  This ensures we will have null termination of
     * all strings inside the packet.
     */
    buf = palloc(len + 1);
    buf[len] = '\0';
 
    if (pq_getbytes(buf, len) == EOF)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("incomplete startup packet")));
        goto fail;
    }
    pq_endmsgread();
 
    /*
     * The first field is either a protocol version number or a special
     * request code.
     */
    port->proto = proto = pg_ntoh32(*((ProtocolVersion *) buf));
 
    if (proto == CANCEL_REQUEST_CODE)
    {
        ProcessCancelRequestPacket(port, buf, len);
        /* Not really an error, but we don't want to proceed further */
        goto fail;
    }
 
    if (proto == NEGOTIATE_SSL_CODE && !ssl_done)
    {
        char        SSLok;
 
#ifdef USE_SSL
 
        /*
         * No SSL when disabled or on Unix sockets.
         *
         * Also no SSL negotiation if we already have a direct SSL connection
         */
        if (!LoadedSSL || port->laddr.addr.ss_family == AF_UNIX || port->ssl_in_use)
            SSLok = 'N';
        else
            SSLok = 'S';        /* Support for SSL */
#else
        SSLok = 'N';            /* No support for SSL */
#endif
 
        if (Trace_connection_negotiation)
        {
            if (SSLok == 'S')
                ereport(LOG,
                        (errmsg("SSLRequest accepted")));
            else
                ereport(LOG,
                        (errmsg("SSLRequest rejected")));
        }
 
        while (secure_write(port, &SSLok, 1) != 1)
        {
            if (errno == EINTR)
                continue;       /* if interrupted, just retry */
            ereport(COMMERROR,
                    (errcode_for_socket_access(),
                     errmsg("failed to send SSL negotiation response: %m")));
            goto fail;          /* close the connection */
        }
 
#ifdef USE_SSL
        if (SSLok == 'S' && secure_open_server(port) == -1)
            goto fail;
#endif
 
        pfree(buf);
 
        /*
         * At this point we should have no data already buffered.  If we do,
         * it was received before we performed the SSL handshake, so it wasn't
         * encrypted and indeed may have been injected by a man-in-the-middle.
         * We report this case to the client.
         */
        if (pq_buffer_remaining_data() > 0)
            ereport(FATAL,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("received unencrypted data after SSL request"),
                     errdetail("This could be either a client-software bug or evidence of an attempted man-in-the-middle attack.")));
 
        /*
         * regular startup packet, cancel, etc packet should follow, but not
         * another SSL negotiation request, and a GSS request should only
         * follow if SSL was rejected (client may negotiate in either order)
         */
        return ProcessStartupPacket(port, true, SSLok == 'S');
    }
    else if (proto == NEGOTIATE_GSS_CODE && !gss_done)
    {
        char        GSSok = 'N';
 
#ifdef ENABLE_GSS
        /* No GSSAPI encryption when on Unix socket */
        if (port->laddr.addr.ss_family != AF_UNIX)
            GSSok = 'G';
#endif
 
        if (Trace_connection_negotiation)
        {
            if (GSSok == 'G')
                ereport(LOG,
                        (errmsg("GSSENCRequest accepted")));
            else
                ereport(LOG,
                        (errmsg("GSSENCRequest rejected")));
        }
 
        while (secure_write(port, &GSSok, 1) != 1)
        {
            if (errno == EINTR)
                continue;
            ereport(COMMERROR,
                    (errcode_for_socket_access(),
                     errmsg("failed to send GSSAPI negotiation response: %m")));
            goto fail;          /* close the connection */
        }
 
#ifdef ENABLE_GSS
        if (GSSok == 'G' && secure_open_gssapi(port) == -1)
            goto fail;
#endif
 
        pfree(buf);
 
        /*
         * At this point we should have no data already buffered.  If we do,
         * it was received before we performed the GSS handshake, so it wasn't
         * encrypted and indeed may have been injected by a man-in-the-middle.
         * We report this case to the client.
         */
        if (pq_buffer_remaining_data() > 0)
            ereport(FATAL,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("received unencrypted data after GSSAPI encryption request"),
                     errdetail("This could be either a client-software bug or evidence of an attempted man-in-the-middle attack.")));
 
        /*
         * regular startup packet, cancel, etc packet should follow, but not
         * another GSS negotiation request, and an SSL request should only
         * follow if GSS was rejected (client may negotiate in either order)
         */
        return ProcessStartupPacket(port, GSSok == 'G', true);
    }
 
    /* Could add additional special packet types here */
 
    /*
     * Set FrontendProtocol now so that ereport() knows what format to send if
     * we fail during startup. We use the protocol version requested by the
     * client unless it's higher than the latest version we support. It's
     * possible that error message fields might look different in newer
     * protocol versions, but that's something those new clients should be
     * able to deal with.
     */
    FrontendProtocol = Min(proto, PG_PROTOCOL_LATEST);
 
    /* Check that the major protocol version is in range. */
    if (PG_PROTOCOL_MAJOR(proto) < PG_PROTOCOL_MAJOR(PG_PROTOCOL_EARLIEST) ||
        PG_PROTOCOL_MAJOR(proto) > PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST))
        ereport(FATAL,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("unsupported frontend protocol %u.%u: server supports %u.0 to %u.%u",
                        PG_PROTOCOL_MAJOR(proto), PG_PROTOCOL_MINOR(proto),
                        PG_PROTOCOL_MAJOR(PG_PROTOCOL_EARLIEST),
                        PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST),
                        PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST))));
 
    /*
     * Now fetch parameters out of startup packet and save them into the Port
     * structure.
     */
    oldcontext = MemoryContextSwitchTo(TopMemoryContext);
 
    /* Handle protocol version 3 startup packet */
    {
        int32       offset = sizeof(ProtocolVersion);
        List       *unrecognized_protocol_options = NIL;
 
        /*
         * Scan packet body for name/option pairs.  We can assume any string
         * beginning within the packet body is null-terminated, thanks to
         * zeroing extra byte above.
         */
        port->guc_options = NIL;
 
        while (offset < len)
        {
            char       *nameptr = buf + offset;
            int32       valoffset;
            char       *valptr;
 
            if (*nameptr == '\0')
                break;          /* found packet terminator */
            valoffset = offset + strlen(nameptr) + 1;
            if (valoffset >= len)
                break;          /* missing value, will complain below */
            valptr = buf + valoffset;
 
            if (strcmp(nameptr, "database") == 0)
                port->database_name = pstrdup(valptr);
            else if (strcmp(nameptr, "user") == 0)
                port->user_name = pstrdup(valptr);
            else if (strcmp(nameptr, "options") == 0)
                port->cmdline_options = pstrdup(valptr);
            else if (strcmp(nameptr, "replication") == 0)
            {
                /*
                 * Due to backward compatibility concerns the replication
                 * parameter is a hybrid beast which allows the value to be
                 * either boolean or the string 'database'. The latter
                 * connects to a specific database which is e.g. required for
                 * logical decoding while.
                 */
                if (strcmp(valptr, "database") == 0)
                {
                    am_walsender = true;
                    am_db_walsender = true;
                }
                else if (!parse_bool(valptr, &am_walsender))
                    ereport(FATAL,
                            (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                             errmsg("invalid value for parameter \"%s\": \"%s\"",
                                    "replication",
                                    valptr),
                             errhint("Valid values are: \"false\", 0, \"true\", 1, \"database\".")));
            }
            else if (strncmp(nameptr, "_pq_.", 5) == 0)
            {
                /*
                 * Any option beginning with _pq_. is reserved for use as a
                 * protocol-level option, but at present no such options are
                 * defined.
                 */
                unrecognized_protocol_options =
                    lappend(unrecognized_protocol_options, pstrdup(nameptr));
            }
            else
            {
                /* Assume it's a generic GUC option */
                port->guc_options = lappend(port->guc_options,
                                            pstrdup(nameptr));
                port->guc_options = lappend(port->guc_options,
                                            pstrdup(valptr));
 
                /*
                 * Copy application_name to port if we come across it.  This
                 * is done so we can log the application_name in the
                 * connection authorization message.  Note that the GUC would
                 * be used but we haven't gone through GUC setup yet.
                 */
                if (strcmp(nameptr, "application_name") == 0)
                {
                    port->application_name = pg_clean_ascii(valptr, 0);
                }
            }
            offset = valoffset + strlen(valptr) + 1;
        }
 
        /*
         * If we didn't find a packet terminator exactly at the end of the
         * given packet length, complain.
         */
        if (offset != len - 1)
            ereport(FATAL,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("invalid startup packet layout: expected terminator as last byte")));
 
        /*
         * If the client requested a newer protocol version or if the client
         * requested any protocol options we didn't recognize, let them know
         * the newest minor protocol version we do support and the names of
         * any unrecognized options.
         */
        if (PG_PROTOCOL_MINOR(proto) > PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST) ||
            unrecognized_protocol_options != NIL)
            SendNegotiateProtocolVersion(unrecognized_protocol_options);
    }
 
    /* Check a user name was given. */
    if (port->user_name == NULL || port->user_name[0] == '\0')
        ereport(FATAL,
                (errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
                 errmsg("no PostgreSQL user name specified in startup packet")));
 
    /* The database defaults to the user name. */
    if (port->database_name == NULL || port->database_name[0] == '\0')
        port->database_name = pstrdup(port->user_name);
 
    /*
     * Truncate given database and user names to length of a Postgres name.
     * This avoids lookup failures when overlength names are given.
     */
    if (strlen(port->database_name) >= NAMEDATALEN)
        port->database_name[NAMEDATALEN - 1] = '\0';
    if (strlen(port->user_name) >= NAMEDATALEN)
        port->user_name[NAMEDATALEN - 1] = '\0';
 
    if (am_walsender)
        MyBackendType = B_WAL_SENDER;
    else
        MyBackendType = B_BACKEND;
 
    /*
     * Normal walsender backends, e.g. for streaming replication, are not
     * connected to a particular database. But walsenders used for logical
     * replication need to connect to a specific database. We allow streaming
     * replication commands to be issued even if connected to a database as it
     * can make sense to first make a basebackup and then stream changes
     * starting from that.
     */
    if (am_walsender && !am_db_walsender)
        port->database_name[0] = '\0';
 
    /*
     * Done filling the Port structure
     */
    MemoryContextSwitchTo(oldcontext);
 
    pfree(buf);
 
    return STATUS_OK;
 
fail:
    /* be tidy, just to avoid Valgrind complaints */
    if (buf)
        pfree(buf);
 
    return STATUS_ERROR;
}
 
/*
 * The client has sent a cancel request packet, not a normal
 * start-a-new-connection packet.  Perform the necessary processing.  Nothing
 * is sent back to the client.
 */
static void
ProcessCancelRequestPacket(Port *port, void *pkt, int pktlen)
{
    CancelRequestPacket *canc;
    int         len;
 
    if (pktlen < offsetof(CancelRequestPacket, cancelAuthCode))
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid length of cancel request packet")));
        return;
    }
    len = pktlen - offsetof(CancelRequestPacket, cancelAuthCode);
    if (len == 0 || len > 256)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid length of cancel key in cancel request packet")));
        return;
    }
 
    canc = (CancelRequestPacket *) pkt;
    SendCancelRequest(pg_ntoh32(canc->backendPID), canc->cancelAuthCode, len);
}
 
/*
 * Send a NegotiateProtocolVersion to the client.  This lets the client know
 * that they have either requested a newer minor protocol version than we are
 * able to speak, or at least one protocol option that we don't understand, or
 * possibly both. FrontendProtocol has already been set to the version
 * requested by the client or the highest version we know how to speak,
 * whichever is older. If the highest version that we know how to speak is too
 * old for the client, it can abandon the connection.
 *
 * We also include in the response a list of protocol options we didn't
 * understand.  This allows clients to include optional parameters that might
 * be present either in newer protocol versions or third-party protocol
 * extensions without fear of having to reconnect if those options are not
 * understood, while at the same time making certain that the client is aware
 * of which options were actually accepted.
 */
static void
SendNegotiateProtocolVersion(List *unrecognized_protocol_options)
{
    StringInfoData buf;
    ListCell   *lc;
 
    pq_beginmessage(&buf, PqMsg_NegotiateProtocolVersion);
    pq_sendint32(&buf, FrontendProtocol);
    pq_sendint32(&buf, list_length(unrecognized_protocol_options));
    foreach(lc, unrecognized_protocol_options)
        pq_sendstring(&buf, lfirst(lc));
    pq_endmessage(&buf);
 
    /* no need to flush, some other message will follow */
}
 
 
/*
 * SIGTERM while processing startup packet.
 *
 * Running proc_exit() from a signal handler would be quite unsafe.
 * However, since we have not yet touched shared memory, we can just
 * pull the plug and exit without running any atexit handlers.
 *
 * One might be tempted to try to send a message, or log one, indicating
 * why we are disconnecting.  However, that would be quite unsafe in itself.
 * Also, it seems undesirable to provide clues about the database's state
 * to a client that has not yet completed authentication, or even sent us
 * a startup packet.
 */
static void
process_startup_packet_die(SIGNAL_ARGS)
{
    _exit(1);
}
 
/*
 * Timeout while processing startup packet.
 * As for process_startup_packet_die(), we exit via _exit(1).
 */
static void
StartupPacketTimeoutHandler(void)
{
    _exit(1);
}
 
/*
 * Helper for the log_connections GUC check hook.
 *
 * `elemlist` is a listified version of the string input passed to the
 * log_connections GUC check hook, check_log_connections().
 * check_log_connections() is responsible for cleaning up `elemlist`.
 *
 * validate_log_connections_options() returns false if an error was
 * encountered and the GUC input could not be validated and true otherwise.
 *
 * `flags` returns the flags that should be stored in the log_connections GUC
 * by its assign hook.
 */
static bool
validate_log_connections_options(List *elemlist, uint32 *flags)
{
    ListCell   *l;
    char       *item;
 
    /*
     * For backwards compatibility, we accept these tokens by themselves.
     *
     * Prior to PostgreSQL 18, log_connections was a boolean GUC that accepted
     * any unambiguous substring of 'true', 'false', 'yes', 'no', 'on', and
     * 'off'. Since log_connections became a list of strings in 18, we only
     * accept complete option strings.
     */
    static const struct config_enum_entry compat_options[] = {
        {"off", 0},
        {"false", 0},
        {"no", 0},
        {"0", 0},
        {"on", LOG_CONNECTION_ON},
        {"true", LOG_CONNECTION_ON},
        {"yes", LOG_CONNECTION_ON},
        {"1", LOG_CONNECTION_ON},
    };
 
    *flags = 0;
 
    /* If an empty string was passed, we're done */
    if (list_length(elemlist) == 0)
        return true;
 
    /*
     * Now check for the backwards compatibility options. They must always be
     * specified on their own, so we error out if the first option is a
     * backwards compatibility option and other options are also specified.
     */
    item = linitial(elemlist);
 
    for (size_t i = 0; i < lengthof(compat_options); i++)
    {
        struct config_enum_entry option = compat_options[i];
 
        if (pg_strcasecmp(item, option.name) != 0)
            continue;
 
        if (list_length(elemlist) > 1)
        {
            GUC_check_errdetail("Cannot specify log_connections option \"%s\" in a list with other options.",
                                item);
            return false;
        }
 
        *flags = option.val;
        return true;
    }
 
    /* Now check the aspect options. The empty string was already handled */
    foreach(l, elemlist)
    {
        static const struct config_enum_entry options[] = {
            {"receipt", LOG_CONNECTION_RECEIPT},
            {"authentication", LOG_CONNECTION_AUTHENTICATION},
            {"authorization", LOG_CONNECTION_AUTHORIZATION},
            {"setup_durations", LOG_CONNECTION_SETUP_DURATIONS},
            {"all", LOG_CONNECTION_ALL},
        };
 
        item = lfirst(l);
        for (size_t i = 0; i < lengthof(options); i++)
        {
            struct config_enum_entry option = options[i];
 
            if (pg_strcasecmp(item, option.name) == 0)
            {
                *flags |= option.val;
                goto next;
            }
        }
 
        GUC_check_errdetail("Invalid option \"%s\".", item);
        return false;
 
next:   ;
    }
 
    return true;
}
 
 
/*
 * GUC check hook for log_connections
 */
bool
check_log_connections(char **newval, void **extra, GucSource source)
{
    uint32      flags;
    char       *rawstring;
    List       *elemlist;
    bool        success;
 
    /* Need a modifiable copy of string */
    rawstring = pstrdup(*newval);
 
    if (!SplitIdentifierString(rawstring, ',', &elemlist))
    {
        GUC_check_errdetail("Invalid list syntax in parameter \"%s\".", "log_connections");
        pfree(rawstring);
        list_free(elemlist);
        return false;
    }
 
    /* Validation logic is all in the helper */
    success = validate_log_connections_options(elemlist, &flags);
 
    /* Time for cleanup */
    pfree(rawstring);
    list_free(elemlist);
 
    if (!success)
        return false;
 
    /*
     * We succeeded, so allocate `extra` and save the flags there for use by
     * assign_log_connections().
     */
    *extra = guc_malloc(LOG, sizeof(int));
    if (!*extra)
        return false;
    *((int *) *extra) = flags;
 
    return true;
}
 
/*
 * GUC assign hook for log_connections
 */
void
assign_log_connections(const char *newval, void *extra)
{
    log_connections = *((int *) extra);
}