SQLite

  "OPTIONS:\n"
  "\n"
  "   --exe PATH    Name of the sqlite3_rsync program on the remote side\n"
  "   --help        Show this help screen\n"
  "   --ssh PATH    Name of the SSH program used to reach the remote side\n"
  "   -v            Verbose.  Multiple v's for increasing output\n"
  "   --version     Show detailed version information\n"
  "   --wal-only    Do not sync unless both databases are in WAL mode\n"
;

typedef unsigned char u8;

/* Context for the run */
typedef struct SQLiteRsync SQLiteRsync;
struct SQLiteRsync {

  int nWrErr;              /* Number of failed attempts to write on the pipe */
  u8 eVerbose;             /* Bigger for more output.  0 means none. */
  u8 bCommCheck;           /* True to debug the communication protocol */
  u8 isRemote;             /* On the remote side of a connection */
  u8 isReplica;            /* True if running on the replica side */
  u8 iProtocol;            /* Protocol version number */
  u8 wrongEncoding;        /* ATTACH failed due to wrong encoding */
  u8 bWalOnly;             /* Require WAL mode */
  sqlite3_uint64 nOut;     /* Bytes transmitted */
  sqlite3_uint64 nIn;      /* Bytes received */
  unsigned int nPage;      /* Total number of pages in the database */
  unsigned int szPage;     /* Database page size */
  unsigned int nHashSent;  /* Hashes sent (replica to origin) */
  unsigned int nPageSent;  /* Page contents sent (origin to replica) */
};

      reportError(p, "cannot open origin \"%s\": %s",
                  p->zOrigin, sqlite3_errmsg(p->db));
      closeDb(p);
      return;
    }
    hashRegister(p->db);
    runSql(p, "BEGIN");
    if( p->bWalOnly ){
      runSqlReturnText(p, buf, "PRAGMA journal_mode");
      if( sqlite3_stricmp(buf,"wal")!=0 ){
        reportError(p, "Origin database is not in WAL mode");
      }
    }
    runSqlReturnUInt(p, &nPage, "PRAGMA page_count");
    runSqlReturnUInt(p, &szPg, "PRAGMA page_size");
  
    if( p->nErr==0 ){
      /* Send the ORIGIN_BEGIN message */
      writeByte(p, ORIGIN_BEGIN);

        }
        if( nRPage==0 ){
          runSql(p, "PRAGMA replica.page_size=%u", szOPage);
          runSql(p, "PRAGMA replica.journal_mode=WAL");
          runSql(p, "SELECT * FROM replica.sqlite_schema");
        }
        runSql(p, "BEGIN IMMEDIATE");
        if( p->bWalOnly ){
          runSqlReturnText(p, buf, "PRAGMA replica.journal_mode");
          if( strcmp(buf, "wal")!=0 ){
            reportError(p, "replica is not in WAL mode");
            break;
          }
        }
        runSqlReturnUInt(p, &nRPage, "PRAGMA replica.page_count");
        runSqlReturnUInt(p, &szRPage, "PRAGMA replica.page_size");
        if( szRPage!=szOPage ){
          reportError(p, "page size mismatch; origin is %d bytes and "
                         "replica is %d bytes", szOPage, szRPage);
          break;

  sqlite3_int64 tmElapse;
  const char *zRemoteErrFile = 0;

#define cli_opt_val cmdline_option_value(argc, argv, ++i)
  memset(&ctx, 0, sizeof(ctx));
  for(i=1; i<argc; i++){
    const char *z = argv[i];
    if( z[0]=='-' && z[1]=='-' && z[2]!=0 ) z++;
    if( strcmp(z,"-origin")==0 ){
      isOrigin = 1;
      continue;
    }
    if( strcmp(z,"-replica")==0 ){
      isReplica = 1;
      continue;
    }
    if( numVs(z) ){
      ctx.eVerbose += numVs(z);
      continue;
    }
    if( strcmp(z, "-ssh")==0 ){
      zSsh = cli_opt_val;
      continue;
    }
    if( strcmp(z, "-exe")==0 ){
      zExe = cli_opt_val;
      continue;
    }
    if( strcmp(z, "-logfile")==0 ){
      /* DEBUG OPTION:  --logfile FILENAME
      ** Cause all local output traffic to be duplicated in FILENAME */
      const char *zLog = cli_opt_val;
      if( ctx.pLog ) fclose(ctx.pLog);
      ctx.pLog = fopen(zLog, "wb");
      if( ctx.pLog==0 ){
        fprintf(stderr, "cannot open \"%s\" for writing\n", argv[i]);
        return 1;
      }
      continue;
    }
    if( strcmp(z, "-errorfile")==0 ){
      /* DEBUG OPTION:  --errorfile FILENAME
      ** Error messages on the local side are written into FILENAME */
      ctx.zErrFile = cli_opt_val;
      continue;
    }
    if( strcmp(z, "-remote-errorfile")==0 ){
      /* DEBUG OPTION:  --remote-errorfile FILENAME
      ** Error messages on the remote side are written into FILENAME on
      ** the remote side. */
      zRemoteErrFile = cli_opt_val;
      continue;
    }
    if( strcmp(z, "-wal-only")==0 ){
      ctx.bWalOnly = 1;
      continue;
    }
    if( strcmp(z, "-help")==0 || strcmp(z, "--help")==0
     || strcmp(z, "-?")==0
    ){
      printf("%s", zUsage);
      return 0;
    }
    if( strcmp(z, "-version")==0 ){
      printf("%s\n", sqlite3_sourceid());
      return 0;
    }
    if( z[0]=='-' ){
      if( strcmp(z,"-commcheck")==0 ){  /* DEBUG ONLY */
        /* Run a communication check with the remote side.  Do not attempt
        ** to exchange any database connection */
        ctx.bCommCheck = 1;
        continue;
      }
      if( strcmp(z,"-arg-escape-check")==0 ){  /* DEBUG ONLY */
        /* Test the append_escaped_arg() routine by using it to render a
        ** copy of the input command-line, assuming all arguments except
        ** this one are filenames. */
        sqlite3_str *pStr = sqlite3_str_new(0);
        int k;
        for(k=0; k<argc; k++){
          append_escaped_arg(pStr, argv[k], i!=k);

      append_escaped_arg(pStr, "--commcheck", 0);
      if( ctx.eVerbose==0 ) ctx.eVerbose = 1;
    }
    if( zRemoteErrFile ){
      append_escaped_arg(pStr, "--errorfile", 0);
      append_escaped_arg(pStr, zRemoteErrFile, 1);
    }
    if( ctx.bWalOnly ){
      append_escaped_arg(pStr, "--wal-only", 0);
    }
    append_escaped_arg(pStr, zDiv, 1);
    append_escaped_arg(pStr, file_tail(ctx.zReplica), 1);
    zCmd = sqlite3_str_finish(pStr);
    if( ctx.eVerbose>=2 ) printf("%s\n", zCmd);
    if( popen2(zCmd, &ctx.pIn, &ctx.pOut, &childPid, 0) ){
      fprintf(stderr, "Could not start auxiliary process: %s\n", zCmd);
      return 1;