libsql-ffi 0.9.30

// vsv extension by Keith Medcalf, Public Domain
// https://github.com/ncruces/kmedcalf-sqlite/blob/main/vsv.c

// Modified by Anton Zhiyanov, MIT License
// https://github.com/nalgeon/sqlean/

// CSV files as virtual tables in SQLite

/*
** 2020-02-08 modified by Keith Medcalf who also disclaims all copyright
** on the modifications and hereby places this code in the public domain
**
** This file contains the implementation of an SQLite virtual table for
** reading VSV (Variably Separated Values), which are like CSV files,
** but subtly different.  VSV supports a number of extensions to the
** CSV format as well as more processing options.
**
**
** Usage:
**
**  create virtual table temp.vsv using vsv(...);
**  select * from vsv;
**
** The parameters to the vsv module (the vsv(...) part) are as follows:
**
**  filename=STRING     the filename, passed to the Operating System
**  data=STRING         alternative data
**  schema=STRING       Alternate Schema to use
**  columns=N           columns parsed from the VSV file
**  header=BOOL         whether or not a header row is present
**  skip=N              number of leading data rows to skip
**  rsep=STRING         record separator
**  fsep=STRING         field separator
**  dsep=STRING         decimal separator
**  validatetext=BOOL   validate UTF-8 encoding of text fields
**  affinity=AFFINITY   affinity to apply to each returned value
**  nulls=BOOL          empty fields are returned as NULL
**
**
** Defaults:
**
**  filename / data     nothing.  You must provide one or the other
**                      it is an error to provide both or neither
**  schema              nothing.  If not provided then one will be
**                      generated for you from the header, or if no
**                      header is available then autogenerated using
**                      field names manufactured as cX where X is the
**                      column number
**  columns             nothing.  If not specified then the number of
**                      columns is determined by counting the fields
**                      in the first record of the VSV file (which
**                      will be the header row if header is specified),
**                      the number of columns is not parsed from the
**                      schema even if one is provided
**  header=no           no header row in the VSV file
**  skip=0              do not skip any data rows in the VSV file
**  fsep=','            default field separator is a comma
**  rsep='\n'           default record separator is a newline
**  dsep='.'            default decimal separator is a point
**  validatetext=no     do not validate text field encoding
**  affinity=none       do not apply affinity to each returned value
**  nulls=off           empty fields returned as zero-length
**
**
** Parameter types:
**
**  STRING              means a quoted string
**  N                   means a whole number not containing a sign
**  BOOL                means something that evaluates as true or false
**                          it is case insensitive
**                          yes, no, true, false, 1, 0
**  AFFINITY            means an SQLite3 type specification
**                          it is case insensitive
**                          none, blob, text, integer, real, numeric
**
** STRING means a quoted string.  The quote character may be either
** a single quote or a double quote.  Two quote characters in a row
** will be replaced with a single quote character.  STRINGS do not
** need to be quoted if it is obvious where they begin and end
** (that is, they do not contain a comma).  Leading and trailing
** spaces will be trimmed from unquoted strings.
**
**    filename =./this/filename.here, ...
**    filename =./this/filename.here , ...
**    filename = ./this/filename.here, ...
**    filename = ./this/filename.here , ...
**    filename = './this/filename.here', ...
**    filename = "./this/filename.here", ...
**
**  are all equivalent.
**
** BOOL defaults to true so the following specifications are all the
** same:
**
**  header = true
**  header = yes
**  header = 1
**  header
**
**
** Specific Parameters:
**
** The platform/compiler/OS fopen call is responsible for interpreting
** the filename.  It may contain anything recognized by the OS.
**
** The separator string containing exactly one character, or a valid
** escape sequence.  Recognized escape sequences are:
**
**  \t                  horizontal tab, ascii character 9 (0x09)
**  \n                  linefeed, ascii character 10 (0x0a)
**  \v                  vertical tab, ascii character 11 (0x0b)
**  \f                  form feed, ascii character 12 (0x0c)
**  \xhh                specific byte where hh is hexadecimal
**
** The validatetext setting will cause the validity of the field
** encoding (not its contents) to be verified.  It effects how
** fields that are supposed to contain text will be returned to
** the SQLite3 library in order to prevent invalid utf8 data from
** being stored or processed as if it were valid utf8 text.
**
** The nulls option will cause fields that do not contain anything
** to return NULL rather than an empty result.  Two separators
** side-by-each with no intervening characters at all will be
** returned as NULL if nulls is true and if nulls is false or
** the contents are explicity empty ("") then a 0 length blob
** (if affinity=blob) or 0 length text string.
**
** For the affinity setting, the following processing is applied to
** each value returned by the VSV virtual table:
**
**  none                no affinity is applied, all fields will be
**                      returned as text just like in the original
**                      csv module, embedded nulls will terminate
**                      the text.  if validatetext is in effect then
**                      an error will be thrown if the field does
**                      not contain validly encoded text or contains
**                      embedded nulls
**
**  blob                all fields will be returned as blobs
**                      validatetext has no effect
**
**  text                all fields will be returned as text just
**                      like in the original csv module, embedded
**                      nulls will terminate the text.
**                      if validatetext is in effect then a blob
**                      will be returned if the field does not
**                      contain validly encoded text or the field
**                      contains embedded nulls
**
**  integer             if the field data looks like an integer,
**                      (regex "^ *(\+|-)?\d+ *$"),
**                      then an integer will be returned as
**                      provided by the compiler and platform
**                      runtime strtoll function
**                      otherwise the field will be processed as
**                      text as defined above
**
**  real                if the field data looks like a number,
**                      (regex "^ *(\+|-)?(\d+\.?\d*|\d*\.?\d+)([eE](\+|-)?\d+)? *$")
**                      then a double will be returned as
**                      provided by the compiler and platform
**                      runtime strtold function otherwise the
**                      field will be processed as text as
**                      defined above
**
**  numeric             if the field looks like an integer
**                      (see integer above) that integer will be
**                      returned
**                      if the field looks like a number
**                      (see real above) then the number will
**                      returned as an integer if it has no
**                      fractional part and
**                      (a) your platform/compiler supports
**                      long double and the number will fit in
**                      a 64-bit integer; or,
**                      (b) your platform/compiler does not
**                      support long double (treats it as a double)
**                      then a 64-bit integer will only be returned
**                      if the value would fit in a 6-byte varint,
**                      otherwise a double will be returned
**
** The nulls option will cause fields that do not contain anything
** to return NULL rather than an empty result.  Two separators
** side-by-each with no intervening characters at all will be
** returned as NULL if nulls is true and if nulls is false or
** the contents are explicity empty ("") then a 0 length blob
** (if affinity=blob) or 0 length text string will be returned.
**
*/
/*
** 2016-05-28
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains the implementation of an SQLite virtual table for
** reading CSV files.
**
** Usage:
**
**    .load ./csv
**    CREATE VIRTUAL TABLE temp.csv USING csv(filename=FILENAME);
**    SELECT * FROM csv;
**
** The columns are named "c1", "c2", "c3", ... by default.  Or the
** application can define its own CREATE TABLE statement using the
** schema= parameter, like this:
**
**    CREATE VIRTUAL TABLE temp.csv2 USING csv(
**       filename = "../http.log",
**       schema = "CREATE TABLE x(date,ipaddr,url,referrer,userAgent)"
**    );
**
** Instead of specifying a file, the text of the CSV can be loaded using
** the data= parameter.
**
** If the columns=N parameter is supplied, then the CSV file is assumed to have
** N columns.  If both the columns= and schema= parameters are omitted, then
** the number and names of the columns is determined by the first line of
** the CSV input.
**
*/
#include <assert.h>
#include <ctype.h>
#include <math.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT3

/**A macro to hint to the compiler that a function should not be * *inlined.*/
#if defined(__GNUC__)
#define VSV_NOINLINE __attribute__((noinline))
#elif defined(_MSC_VER) && _MSC_VER >= 1310
#define VSV_NOINLINE __declspec(noinline)
#else
#define VSV_NOINLINE
#endif

/*
** Max size of the error message in a VsvReader
*/
#define VSV_MXERR 200

/*
** Size of the VsvReader input buffer
*/
#define VSV_INBUFSZ 1024

/*
** A context object used when read a VSV file.
*/
typedef struct VsvReader VsvReader;
struct VsvReader {
    FILE* in;             /* Read the VSV text from this input stream */
    char* z;              /* Accumulated text for a field */
    int n;                /* Number of bytes in z */
    int nAlloc;           /* Space allocated for z[] */
    int nLine;            /* Current line number */
    int bNotFirst;        /* True if prior text has been seen */
    int cTerm;            /* Character that terminated the most recent field */
    int fsep;             /* Field Seperator Character */
    int rsep;             /* Record Seperator Character */
    int dsep;             /* Decimal Seperator Character */
    int affinity;         /* Perform Affinity Conversions */
    int notNull;          /* Have we seen data for field */
    size_t iIn;           /* Next unread character in the input buffer */
    size_t nIn;           /* Number of characters in the input buffer */
    char* zIn;            /* The input buffer */
    char zErr[VSV_MXERR]; /* Error message */
};

/*
** Initialize a VsvReader object
*/
static void vsv_reader_init(VsvReader* p) {
    p->in = 0;
    p->z = 0;
    p->n = 0;
    p->nAlloc = 0;
    p->nLine = 0;
    p->bNotFirst = 0;
    p->nIn = 0;
    p->zIn = 0;
    p->notNull = 0;
    p->zErr[0] = 0;
}

/*
** Close and reset a VsvReader object
*/
static void vsv_reader_reset(VsvReader* p) {
    if (p->in) {
        fclose(p->in);
        sqlite3_free(p->zIn);
    }
    sqlite3_free(p->z);
    vsv_reader_init(p);
}

/*
** Report an error on a VsvReader
*/
static void vsv_errmsg(VsvReader* p, const char* zFormat, ...) {
    va_list ap;
    va_start(ap, zFormat);
    sqlite3_vsnprintf(VSV_MXERR, p->zErr, zFormat, ap);
    va_end(ap);
}

/*
** Open the file associated with a VsvReader
** Return the number of errors.
*/
static int vsv_reader_open(VsvReader* p,          /* The reader to open */
                           const char* zFilename, /* Read from this filename */
                           const char* zData      /*  ... or use this data */
) {
    if (zFilename) {
        p->zIn = sqlite3_malloc(VSV_INBUFSZ);
        if (p->zIn == 0) {
            vsv_errmsg(p, "out of memory");
            return 1;
        }
        p->in = fopen(zFilename, "rb");
        if (p->in == 0) {
            sqlite3_free(p->zIn);
            vsv_reader_reset(p);
            vsv_errmsg(p, "cannot open '%s' for reading", zFilename);
            return 1;
        }
    } else {
        assert(p->in == 0);
        p->zIn = (char*)zData;
        p->nIn = strlen(zData);
    }
    return 0;
}

/*
** The input buffer has overflowed.  Refill the input buffer, then
** return the next character
*/
static VSV_NOINLINE int vsv_getc_refill(VsvReader* p) {
    size_t got;

    assert(p->iIn >= p->nIn); /* Only called on an empty input buffer */
    assert(p->in != 0);       /* Only called if reading from a file */

    got = fread(p->zIn, 1, VSV_INBUFSZ, p->in);
    if (got == 0) {
        return EOF;
    }
    p->nIn = got;
    p->iIn = 1;
    return p->zIn[0];
}

/*
** Return the next character of input.  Return EOF at end of input.
*/
static int vsv_getc(VsvReader* p) {
    if (p->iIn >= p->nIn) {
        if (p->in != 0) {
            return vsv_getc_refill(p);
        }
        return EOF;
    }
    return ((unsigned char*)p->zIn)[p->iIn++];
}

/*
** Increase the size of p->z and append character c to the end.
** Return 0 on success and non-zero if there is an OOM error
*/
static VSV_NOINLINE int vsv_resize_and_append(VsvReader* p, char c) {
    char* zNew;
    int nNew = p->nAlloc * 2 + 100;
    zNew = sqlite3_realloc64(p->z, nNew);
    if (zNew) {
        p->z = zNew;
        p->nAlloc = nNew;
        p->z[p->n++] = c;
        return 0;
    } else {
        vsv_errmsg(p, "out of memory");
        return 1;
    }
}

/*
** Append a single character to the VsvReader.z[] array.
** Return 0 on success and non-zero if there is an OOM error
*/
static int vsv_append(VsvReader* p, char c) {
    if (p->n >= p->nAlloc - 1) {
        return vsv_resize_and_append(p, c);
    }
    p->z[p->n++] = c;
    return 0;
}

/*
** Read a single field of VSV text.  Compatible with rfc4180 and extended
** with the option of having a separator other than ",".
**
**   +  Input comes from p->in.
**   +  Store results in p->z of length p->n.  Space to hold p->z comes
**      from sqlite3_malloc64().
**   +  Keep track of the line number in p->nLine.
**   +  Store the character that terminates the field in p->cTerm.  Store
**      EOF on end-of-file.
**
** Return 0 at EOF or on OOM.  On EOF, the p->cTerm character will have
** been set to EOF.
*/
static char* vsv_read_one_field(VsvReader* p) {
    int c;
    p->notNull = 0;
    p->n = 0;
    c = vsv_getc(p);
    if (c == EOF) {
        p->cTerm = EOF;
        return 0;
    }
    if (c == '"') {
        int pc, ppc;
        int startLine = p->nLine;
        p->notNull = 1;
        pc = ppc = 0;
        while (1) {
            c = vsv_getc(p);
            if (c == '\n') {
                p->nLine++;
            }
            if (c == '"' && pc == '"') {
                pc = ppc;
                ppc = 0;
                continue;
            }
            if ((c == p->fsep && pc == '"') || (c == p->rsep && pc == '"') ||
                (p->rsep == '\n' && c == '\n' && pc == '\r' && ppc == '"') ||
                (c == EOF && pc == '"')) {
                do {
                    p->n--;
                } while (p->z[p->n] != '"');
                p->cTerm = (char)c;
                break;
            }
            if (pc == '"' && p->rsep == '\n' && c != '\r') {
                vsv_errmsg(p, "line %d: unescaped %c character", p->nLine, '"');
                break;
            }
            if (c == EOF) {
                vsv_errmsg(p, "line %d: unterminated %c-quoted field\n", startLine, '"');
                p->cTerm = (char)c;
                break;
            }
            if (vsv_append(p, (char)c)) {
                return 0;
            }
            ppc = pc;
            pc = c;
        }
    } else {
        /*
        ** If this is the first field being parsed and it begins with the
        ** UTF-8 BOM  (0xEF BB BF) then skip the BOM
        */
        if ((c & 0xff) == 0xef && p->bNotFirst == 0) {
            vsv_append(p, (char)c);
            c = vsv_getc(p);
            if ((c & 0xff) == 0xbb) {
                vsv_append(p, (char)c);
                c = vsv_getc(p);
                if ((c & 0xff) == 0xbf) {
                    p->bNotFirst = 1;
                    p->n = 0;
                    return vsv_read_one_field(p);
                }
            }
        }
        while (c != EOF && c != p->rsep && c != p->fsep) {
            if (c == '\n')
                p->nLine++;
            if (!p->notNull)
                p->notNull = 1;
            if (vsv_append(p, (char)c))
                return 0;
            c = vsv_getc(p);
        }
        if (c == '\n') {
            p->nLine++;
        }
        if (p->n > 0 && (p->rsep == '\n' || p->fsep == '\n') && p->z[p->n - 1] == '\r') {
            p->n--;
            if (p->n == 0) {
                p->notNull = 0;
            }
        }
        p->cTerm = (char)c;
    }
    if (p->z) {
        p->z[p->n] = 0;
    }
    p->bNotFirst = 1;
    return p->z;
}

/*
** Forward references to the various virtual table methods implemented
** in this file.
*/
static int vsvtabCreate(sqlite3*, void*, int, const char* const*, sqlite3_vtab**, char**);
static int vsvtabConnect(sqlite3*, void*, int, const char* const*, sqlite3_vtab**, char**);
static int vsvtabBestIndex(sqlite3_vtab*, sqlite3_index_info*);
static int vsvtabDisconnect(sqlite3_vtab*);
static int vsvtabOpen(sqlite3_vtab*, sqlite3_vtab_cursor**);
static int vsvtabClose(sqlite3_vtab_cursor*);
static int vsvtabFilter(sqlite3_vtab_cursor*,
                        int idxNum,
                        const char* idxStr,
                        int argc,
                        sqlite3_value** argv);
static int vsvtabNext(sqlite3_vtab_cursor*);
static int vsvtabEof(sqlite3_vtab_cursor*);
static int vsvtabColumn(sqlite3_vtab_cursor*, sqlite3_context*, int);
static int vsvtabRowid(sqlite3_vtab_cursor*, sqlite3_int64*);

/*
** An instance of the VSV virtual table
*/
typedef struct VsvTable {
    sqlite3_vtab base; /* Base class.  Must be first */
    char* zFilename;   /* Name of the VSV file */
    char* zData;       /* Raw VSV data in lieu of zFilename */
    long iStart;       /* Offset to start of data in zFilename */
    int nCol;          /* Number of columns in the VSV file */
    int fsep;          /* The field seperator for this VSV file */
    int rsep;          /* The record seperator for this VSV file */
    int dsep;          /* The record decimal for this VSV file */
    int affinity;      /* Perform affinity conversions */
    int nulls;         /* Process NULLs */
    int validateUTF8;  /* Validate UTF8 */
} VsvTable;

/*
** A cursor for the VSV virtual table
*/
typedef struct VsvCursor {
    sqlite3_vtab_cursor base; /* Base class.  Must be first */
    VsvReader rdr;            /* The VsvReader object */
    char** azVal;             /* Value of the current row */
    int* aLen;                /* Allocation Length of each entry */
    int* dLen;                /* Data Length of each entry */
    sqlite3_int64 iRowid;     /* The current rowid.  Negative for EOF */
} VsvCursor;

/*
** Transfer error message text from a reader into a VsvTable
*/
static void vsv_xfer_error(VsvTable* pTab, VsvReader* pRdr) {
    sqlite3_free(pTab->base.zErrMsg);
    pTab->base.zErrMsg = sqlite3_mprintf("%s", pRdr->zErr);
}

/*
** This method is the destructor for a VsvTable object.
*/
static int vsvtabDisconnect(sqlite3_vtab* pVtab) {
    VsvTable* p = (VsvTable*)pVtab;
    sqlite3_free(p->zFilename);
    sqlite3_free(p->zData);
    sqlite3_free(p);
    return SQLITE_OK;
}

/*
** Skip leading whitespace.  Return a pointer to the first non-whitespace
** character, or to the zero terminator if the string has only whitespace
*/
static const char* vsv_skip_whitespace(const char* z) {
    while (isspace((unsigned char)z[0])) {
        z++;
    }
    return z;
}

/*
** Remove trailing whitespace from the end of string z[]
*/
static void vsv_trim_whitespace(char* z) {
    size_t n = strlen(z);
    while (n > 0 && isspace((unsigned char)z[n])) {
        n--;
    }
    z[n] = 0;
}

/*
** Dequote the string
*/
static void vsv_dequote(char* z) {
    int j;
    char cQuote = z[0];
    size_t i, n;

    if (cQuote != '\'' && cQuote != '"') {
        return;
    }
    n = strlen(z);
    if (n < 2 || z[n - 1] != z[0]) {
        return;
    }
    for (i = 1, j = 0; i < n - 1; i++) {
        if (z[i] == cQuote && z[i + 1] == cQuote) {
            i++;
        }
        z[j++] = z[i];
    }
    z[j] = 0;
}

/*
** Check to see if the string is of the form:  "TAG = VALUE" with optional
** whitespace before and around tokens.  If it is, return a pointer to the
** first character of VALUE.  If it is not, return NULL.
*/
static const char* vsv_parameter(const char* zTag, int nTag, const char* z) {
    z = vsv_skip_whitespace(z);
    if (strncmp(zTag, z, nTag) != 0) {
        return 0;
    }
    z = vsv_skip_whitespace(z + nTag);
    if (z[0] != '=') {
        return 0;
    }
    return vsv_skip_whitespace(z + 1);
}

/*
** Decode a parameter that requires a dequoted string.
**
** Return 1 if the parameter is seen, or 0 if not.  1 is returned
** even if there is an error.  If an error occurs, then an error message
** is left in p->zErr.  If there are no errors, p->zErr[0]==0.
*/
static int vsv_string_parameter(VsvReader* p, /* Leave the error message here, if there is one */
                                const char* zParam, /* Parameter we are checking for */
                                const char* zArg,   /* Raw text of the virtual table argment */
                                char** pzVal        /* Write the dequoted string value here */
) {
    const char* zValue;
    zValue = vsv_parameter(zParam, (int)strlen(zParam), zArg);
    if (zValue == 0) {
        return 0;
    }
    p->zErr[0] = 0;
    if (*pzVal) {
        vsv_errmsg(p, "more than one '%s' parameter", zParam);
        return 1;
    }
    *pzVal = sqlite3_mprintf("%s", zValue);
    if (*pzVal == 0) {
        vsv_errmsg(p, "out of memory");
        return 1;
    }
    vsv_trim_whitespace(*pzVal);
    vsv_dequote(*pzVal);
    return 1;
}

/*
** Return 0 if the argument is false and 1 if it is true.  Return -1 if
** we cannot really tell.
*/
static int vsv_boolean(const char* z) {
    if (sqlite3_stricmp("yes", z) == 0 || sqlite3_stricmp("on", z) == 0 ||
        sqlite3_stricmp("true", z) == 0 || (z[0] == '1' && z[1] == 0)) {
        return 1;
    }
    if (sqlite3_stricmp("no", z) == 0 || sqlite3_stricmp("off", z) == 0 ||
        sqlite3_stricmp("false", z) == 0 || (z[0] == '0' && z[1] == 0)) {
        return 0;
    }
    return -1;
}

/*
** Check to see if the string is of the form:  "TAG = BOOLEAN" or just "TAG".
** If it is, set *pValue to be the value of the boolean ("true" if there is
** not "= BOOLEAN" component) and return non-zero.  If the input string
** does not begin with TAG, return zero.
*/
static int vsv_boolean_parameter(const char* zTag, /* Tag we are looking for */
                                 int nTag,         /* Size of the tag in bytes */
                                 const char* z,    /* Input parameter */
                                 int* pValue       /* Write boolean value here */
) {
    int b;
    z = vsv_skip_whitespace(z);
    if (strncmp(zTag, z, nTag) != 0) {
        return 0;
    }
    z = vsv_skip_whitespace(z + nTag);
    if (z[0] == 0) {
        *pValue = 1;
        return 1;
    }
    if (z[0] != '=') {
        return 0;
    }
    z = vsv_skip_whitespace(z + 1);
    b = vsv_boolean(z);
    if (b >= 0) {
        *pValue = b;
        return 1;
    }
    return 0;
}

/*
** Convert the seperator character specification into the character code
** Return 1 signifies error, 0 for no error
**
** Recognized inputs:
**      any single character
**      escaped characters \f \n \t \v
**      escaped hex byte   \x1e \x1f etc (RS and US respectively)
**
*/
static int vsv_parse_sep_char(char* in, int dflt, int* out) {
    if (!in) {
        *out = dflt;
        return 0;
    }
    switch (strlen(in)) {
        case 0: {
            *out = dflt;
            return 0;
        }
        case 1: {
            *out = in[0];
            return 0;
        }
        case 2: {
            if (in[0] != '\\') {
                return 1;
            }
            switch (in[1]) {
                case 'f': {
                    *out = 12;
                    return 0;
                }
                case 'n': {
                    *out = 10;
                    return 0;
                }
                case 't': {
                    *out = 9;
                    return 0;
                }
                case 'v': {
                    *out = 11;
                    return 0;
                }
            }
            return 1;
        }
        case 4: {
            if (sqlite3_strnicmp(in, "\\x", 2) != 0) {
                return 1;
            }
            if (!isxdigit(in[2]) || !isxdigit(in[3])) {
                return 1;
            }
            *out = ((in[2] > '9' ? (in[2] & 0x0f) + 9 : in[2] & 0x0f) << 4) +
                   (in[3] > '9' ? (in[3] & 0x0f) + 9 : in[3] & 0x0f);
            return 0;
        }
    }
    return 0;
}

/*
** Parameters:
**    filename=FILENAME          Name of file containing VSV content
**    data=TEXT                  Direct VSV content.
**    schema=SCHEMA              Alternative VSV schema.
**    header=YES|NO              First row of VSV defines the names of
**                               columns if "yes".  Default "no".
**    columns=N                  Assume the VSV file contains N columns.
**    fsep=FSET                  Field Seperator
**    rsep=RSEP                  Record Seperator
**    dsep=RSEP                  Decimal Seperator
**    skip=N                     skip N records of file (default 0)
**    affinity=AFF               affinity to apply to ALL columns
**                               default:  none
**                               none text integer real numeric
**
** If schema= is omitted, then the columns are named "c0", "c1", "c2",
** and so forth.  If columns=N is omitted, then the file is opened and
** the number of columns in the first row is counted to determine the
** column count.  If header=YES, then the first row is skipped.
*/
static int vsvtabConnect(sqlite3* db,
                         void* pAux,
                         int argc,
                         const char* const* argv,
                         sqlite3_vtab** ppVtab,
                         char** pzErr) {
    VsvTable* pNew = 0;    /* The VsvTable object to construct */
    int affinity = -1;     /* Affinity coercion */
    int bHeader = -1;      /* header= flags.  -1 means not seen yet */
    int validateUTF8 = -1; /* validateUTF8 flag */
    int rc = SQLITE_OK;    /* Result code from this routine */
    size_t i, j;           /* Loop counters */
    int b;                 /* Value of a boolean parameter */
    int nCol = -99;        /* Value of the columns= parameter */
    int nSkip = -1;        /* Value of the skip= parameter */
    int bNulls = -1;       /* Process Nulls flag */
    VsvReader sRdr;        /* A VSV file reader used to store an error
                            ** message and/or to count the number of columns */
    static const char* azParam[] = {"filename", "data", "schema", "fsep", "rsep", "dsep"};
    char* azPValue[6]; /* Parameter values */
#define VSV_FILENAME (azPValue[0])
#define VSV_DATA (azPValue[1])
#define VSV_SCHEMA (azPValue[2])
#define VSV_FSEP (azPValue[3])
#define VSV_RSEP (azPValue[4])
#define VSV_DSEP (azPValue[5])

    assert(sizeof(azPValue) == sizeof(azParam));
    memset(&sRdr, 0, sizeof(sRdr));
    memset(azPValue, 0, sizeof(azPValue));
    for (i = 3; i < (size_t)argc; i++) {
        const char* z = argv[i];
        const char* zValue;
        for (j = 0; j < sizeof(azParam) / sizeof(azParam[0]); j++) {
            if (vsv_string_parameter(&sRdr, azParam[j], z, &azPValue[j])) {
                break;
            }
        }
        if (j < sizeof(azParam) / sizeof(azParam[0])) {
            if (sRdr.zErr[0]) {
                goto vsvtab_connect_error;
            }
        } else if (vsv_boolean_parameter("header", 6, z, &b)) {
            if (bHeader >= 0) {
                vsv_errmsg(&sRdr, "more than one 'header' parameter");
                goto vsvtab_connect_error;
            }
            bHeader = b;
        } else if (vsv_boolean_parameter("validatetext", 12, z, &b)) {
            if (validateUTF8 >= 0) {
                vsv_errmsg(&sRdr, "more than one 'validatetext' parameter");
                goto vsvtab_connect_error;
            }
            validateUTF8 = b;
        } else if (vsv_boolean_parameter("nulls", 5, z, &b)) {
            if (bNulls >= 0) {
                vsv_errmsg(&sRdr, "more than one 'nulls' parameter");
                goto vsvtab_connect_error;
            }
            bNulls = b;
        } else if ((zValue = vsv_parameter("columns", 7, z)) != 0) {
            if (nCol > 0) {
                vsv_errmsg(&sRdr, "more than one 'columns' parameter");
                goto vsvtab_connect_error;
            }
            nCol = atoi(zValue);
            if (nCol <= 0) {
                vsv_errmsg(&sRdr, "column= value must be positive");
                goto vsvtab_connect_error;
            }
        } else if ((zValue = vsv_parameter("skip", 4, z)) != 0) {
            if (nSkip > 0) {
                vsv_errmsg(&sRdr, "more than one 'skip' parameter");
                goto vsvtab_connect_error;
            }
            nSkip = atoi(zValue);
            if (nSkip <= 0) {
                vsv_errmsg(&sRdr, "skip= value must be positive");
                goto vsvtab_connect_error;
            }
        } else if ((zValue = vsv_parameter("affinity", 8, z)) != 0) {
            if (affinity > -1) {
                vsv_errmsg(&sRdr, "more than one 'affinity' parameter");
                goto vsvtab_connect_error;
            }
            if (sqlite3_strnicmp(zValue, "none", 4) == 0)
                affinity = 0;
            else if (sqlite3_strnicmp(zValue, "blob", 4) == 0)
                affinity = 1;
            else if (sqlite3_strnicmp(zValue, "text", 4) == 0)
                affinity = 2;
            else if (sqlite3_strnicmp(zValue, "integer", 7) == 0)
                affinity = 3;
            else if (sqlite3_strnicmp(zValue, "real", 4) == 0)
                affinity = 4;
            else if (sqlite3_strnicmp(zValue, "numeric", 7) == 0)
                affinity = 5;
            else {
                vsv_errmsg(&sRdr, "unknown affinity: '%s'", zValue);
                goto vsvtab_connect_error;
            }
        } else {
            vsv_errmsg(&sRdr, "bad parameter: '%s'", z);
            goto vsvtab_connect_error;
        }
    }
    if (affinity == -1) {
        affinity = 0;
    }
    if (bNulls == -1) {
        bNulls = 0;
    }
    if (validateUTF8 == -1) {
        validateUTF8 = 0;
    }
    if ((VSV_FILENAME == 0) == (VSV_DATA == 0)) {
        vsv_errmsg(&sRdr, "must specify either filename= or data= but not both");
        goto vsvtab_connect_error;
    }
    if (vsv_parse_sep_char(VSV_FSEP, ',', &(sRdr.fsep))) {
        vsv_errmsg(&sRdr, "cannot parse fsep: '%s'", VSV_FSEP);
        goto vsvtab_connect_error;
    }
    if (vsv_parse_sep_char(VSV_RSEP, '\n', &(sRdr.rsep))) {
        vsv_errmsg(&sRdr, "cannot parse rsep: '%s'", VSV_RSEP);
        goto vsvtab_connect_error;
    }
    if (vsv_parse_sep_char(VSV_DSEP, '.', &(sRdr.dsep))) {
        vsv_errmsg(&sRdr, "cannot parse dsep: '%s'", VSV_DSEP);
        goto vsvtab_connect_error;
    }
    if ((nCol <= 0 || bHeader == 1) && vsv_reader_open(&sRdr, VSV_FILENAME, VSV_DATA)) {
        goto vsvtab_connect_error;
    }
    pNew = sqlite3_malloc(sizeof(*pNew));
    *ppVtab = (sqlite3_vtab*)pNew;
    if (pNew == 0) {
        goto vsvtab_connect_oom;
    }
    memset(pNew, 0, sizeof(*pNew));
    pNew->fsep = sRdr.fsep;
    pNew->rsep = sRdr.rsep;
    pNew->dsep = sRdr.dsep;
    pNew->affinity = affinity;
    pNew->validateUTF8 = validateUTF8;
    pNew->nulls = bNulls;
    if (VSV_SCHEMA == 0) {
        sqlite3_str* pStr = sqlite3_str_new(0);
        char* zSep = "";
        int iCol = 0;
        sqlite3_str_appendf(pStr, "CREATE TABLE x(");
        if (nCol < 0 && bHeader < 1) {
            nCol = 0;
            do {
                vsv_read_one_field(&sRdr);
                nCol++;
            } while (sRdr.cTerm == sRdr.fsep);
        }
        if (nCol > 0 && bHeader < 1) {
            for (iCol = 0; iCol < nCol; iCol++) {
                sqlite3_str_appendf(pStr, "%sc%d", zSep, iCol);
                zSep = ",";
            }
        } else {
            do {
                char* z = vsv_read_one_field(&sRdr);
                if ((nCol > 0 && iCol < nCol) || (nCol < 0 && bHeader)) {
                    sqlite3_str_appendf(pStr, "%s\"%w\"", zSep, z);
                    zSep = ",";
                    iCol++;
                }
            } while (sRdr.cTerm == sRdr.fsep);
            if (nCol < 0) {
                nCol = iCol;
            } else {
                while (iCol < nCol) {
                    sqlite3_str_appendf(pStr, "%sc%d", zSep, ++iCol);
                    zSep = ",";
                }
            }
        }
        sqlite3_str_appendf(pStr, ")");
        VSV_SCHEMA = sqlite3_str_finish(pStr);
        if (VSV_SCHEMA == 0) {
            goto vsvtab_connect_oom;
        }
    } else if (nCol < 0) {
        do {
            vsv_read_one_field(&sRdr);
            nCol++;
        } while (sRdr.cTerm == sRdr.fsep);
    } else if (nSkip < 1 && bHeader == 1) {
        do {
            vsv_read_one_field(&sRdr);
        } while (sRdr.cTerm == sRdr.fsep);
    }
    pNew->nCol = nCol;
    if (nSkip > 0) {
        int tskip = nSkip + (bHeader == 1);
        vsv_reader_reset(&sRdr);
        if (vsv_reader_open(&sRdr, VSV_FILENAME, VSV_DATA)) {
            goto vsvtab_connect_error;
        }
        do {
            do {
                if (!vsv_read_one_field(&sRdr))
                    goto vsvtab_connect_error;
            } while (sRdr.cTerm == sRdr.fsep);
            tskip--;
        } while (tskip > 0 && sRdr.cTerm == sRdr.rsep);
        if (tskip > 0) {
            vsv_errmsg(&sRdr, "premature end of file during skip");
            goto vsvtab_connect_error;
        }
    }
    pNew->zFilename = VSV_FILENAME;
    VSV_FILENAME = 0;
    pNew->zData = VSV_DATA;
    VSV_DATA = 0;
    if (bHeader != 1 && nSkip < 1) {
        pNew->iStart = 0;
    } else if (pNew->zData) {
        pNew->iStart = (int)sRdr.iIn;
    } else {
        pNew->iStart = (int)(ftell(sRdr.in) - sRdr.nIn + sRdr.iIn);
    }
    vsv_reader_reset(&sRdr);
    rc = sqlite3_declare_vtab(db, VSV_SCHEMA);
    if (rc) {
        vsv_errmsg(&sRdr, "bad schema: '%s' - %s", VSV_SCHEMA, sqlite3_errmsg(db));
        goto vsvtab_connect_error;
    }
    for (i = 0; i < sizeof(azPValue) / sizeof(azPValue[0]); i++) {
        sqlite3_free(azPValue[i]);
    }
    /*
    ** Rationale for DIRECTONLY:
    ** An attacker who controls a database schema could use this vtab
    ** to exfiltrate sensitive data from other files in the filesystem.
    ** And, recommended practice is to put all VSV virtual tables in the
    ** TEMP namespace, so they should still be usable from within TEMP
    ** views, so there shouldn't be a serious loss of functionality by
    ** prohibiting the use of this vtab from persistent triggers and views.
    */
    sqlite3_vtab_config(db, SQLITE_VTAB_DIRECTONLY);
    return SQLITE_OK;

vsvtab_connect_oom:
    rc = SQLITE_NOMEM;
    vsv_errmsg(&sRdr, "out of memory");

vsvtab_connect_error:
    if (pNew) {
        vsvtabDisconnect(&pNew->base);
    }
    for (i = 0; i < sizeof(azPValue) / sizeof(azPValue[0]); i++) {
        sqlite3_free(azPValue[i]);
    }
    if (sRdr.zErr[0]) {
        sqlite3_free(*pzErr);
        *pzErr = sqlite3_mprintf("%s", sRdr.zErr);
    }
    vsv_reader_reset(&sRdr);
    if (rc == SQLITE_OK) {
        rc = SQLITE_ERROR;
    }
    return rc;
}

/*
** Reset the current row content held by a VsvCursor.
*/
static void vsvtabCursorRowReset(VsvCursor* pCur) {
    VsvTable* pTab = (VsvTable*)pCur->base.pVtab;
    int i;
    for (i = 0; i < pTab->nCol; i++) {
        sqlite3_free(pCur->azVal[i]);
        pCur->azVal[i] = 0;
        pCur->aLen[i] = 0;
        pCur->dLen[i] = -1;
    }
}

/*
** The xConnect and xCreate methods do the same thing, but they must be
** different so that the virtual table is not an eponymous virtual table.
*/
static int vsvtabCreate(sqlite3* db,
                        void* pAux,
                        int argc,
                        const char* const* argv,
                        sqlite3_vtab** ppVtab,
                        char** pzErr) {
    return vsvtabConnect(db, pAux, argc, argv, ppVtab, pzErr);
}

/*
** Destructor for a VsvCursor.
*/
static int vsvtabClose(sqlite3_vtab_cursor* cur) {
    VsvCursor* pCur = (VsvCursor*)cur;
    vsvtabCursorRowReset(pCur);
    vsv_reader_reset(&pCur->rdr);
    sqlite3_free(cur);
    return SQLITE_OK;
}

/*
** Constructor for a new VsvTable cursor object.
*/
static int vsvtabOpen(sqlite3_vtab* p, sqlite3_vtab_cursor** ppCursor) {
    VsvTable* pTab = (VsvTable*)p;
    VsvCursor* pCur;
    size_t nByte;
    nByte = sizeof(*pCur) + (sizeof(char*) + (2 * sizeof(int))) * pTab->nCol;
    pCur = sqlite3_malloc64(nByte);
    if (pCur == 0)
        return SQLITE_NOMEM;
    memset(pCur, 0, nByte);
    pCur->azVal = (char**)&pCur[1];
    pCur->aLen = (int*)&pCur->azVal[pTab->nCol];
    pCur->dLen = (int*)&pCur->aLen[pTab->nCol];
    pCur->rdr.fsep = pTab->fsep;
    pCur->rdr.rsep = pTab->rsep;
    pCur->rdr.dsep = pTab->dsep;
    pCur->rdr.affinity = pTab->affinity;
    *ppCursor = &pCur->base;
    if (vsv_reader_open(&pCur->rdr, pTab->zFilename, pTab->zData)) {
        vsv_xfer_error(pTab, &pCur->rdr);
        return SQLITE_ERROR;
    }
    return SQLITE_OK;
}

/*
** Advance a VsvCursor to its next row of input.
** Set the EOF marker if we reach the end of input.
*/
static int vsvtabNext(sqlite3_vtab_cursor* cur) {
    VsvCursor* pCur = (VsvCursor*)cur;
    VsvTable* pTab = (VsvTable*)cur->pVtab;
    int i = 0;
    char* z;
    do {
        z = vsv_read_one_field(&pCur->rdr);
        if (z == 0) {
            if (i < pTab->nCol)
                pCur->dLen[i] = -1;
        } else if (i < pTab->nCol) {
            if (pCur->aLen[i] < pCur->rdr.n + 1) {
                char* zNew = sqlite3_realloc64(pCur->azVal[i], pCur->rdr.n + 1);
                if (zNew == 0) {
                    z = 0;
                    vsv_errmsg(&pCur->rdr, "out of memory");
                    vsv_xfer_error(pTab, &pCur->rdr);
                    break;
                }
                pCur->azVal[i] = zNew;
                pCur->aLen[i] = pCur->rdr.n + 1;
            }
            if (!pCur->rdr.notNull && pTab->nulls) {
                pCur->dLen[i] = -1;
            } else {
                pCur->dLen[i] = pCur->rdr.n;
                memcpy(pCur->azVal[i], z, pCur->rdr.n + 1);
            }
            i++;
        }
    } while (pCur->rdr.cTerm == pCur->rdr.fsep);
    if ((pCur->rdr.cTerm == EOF && i == 0)) {
        pCur->iRowid = -1;
    } else {
        pCur->iRowid++;
        while (i < pTab->nCol) {
            pCur->dLen[i] = -1;
            i++;
        }
    }
    return SQLITE_OK;
}

/*
**
** Determine affinity of field
**
** ignore leading space
** then may have + or -
** then may have digits or . (if . found then type=real)
** then may have digits (if another . then not number)
** then may have e (if found then type=real)
** then may have + or -
** then may have digits
** then may have trailing space
*/
static int vsv_isValidNumber(int dsep, char* arg) {
    char* start;
    char* stop;
    int isValid = 0;
    int hasDigit = 0;

    start = arg;
    stop = arg + strlen(arg) - 1;
    while (start <= stop && *start == ' ')  // strip spaces from begining
    {
        start++;
    }
    while (start <= stop && *stop == ' ')  // strip spaces from end
    {
        stop--;
    }
    if (start > stop) {
        goto vsv_end_isValidNumber;
    }
    if (start <= stop && (*start == '+' || *start == '-'))  // may have + or -
    {
        start++;
    }
    if (start <= stop && isdigit(*start))  // must have a digit to be valid
    {
        hasDigit = 1;
        isValid = 1;
    }
    while (start <= stop && isdigit(*start))  // bunch of digits
    {
        start++;
    }
    if (start <= stop && *start == dsep)  // may have decimal separator
    {
        isValid = 2;
        if (*start != '.') {
            *start = '.';
        }
        start++;
    }
    if (start <= stop && isdigit(*start)) {
        hasDigit = 1;
    }
    while (start <= stop && isdigit(*start))  // bunch of digits
    {
        start++;
    }
    if (!hasDigit)  // no digits then invalid
    {
        isValid = 0;
        goto vsv_end_isValidNumber;
    }
    if (start <= stop && (*start == 'e' || *start == 'E'))  // may have 'e' or 'E'
    {
        isValid = 3;
        start++;
    }
    if (start <= stop && isValid == 3 && (*start == '+' || *start == '-')) {
        start++;
    }
    if (start <= stop && isValid == 3 && isdigit(*start)) {
        isValid = 2;
    }
    while (start <= stop && isdigit(*start))  // bunch of digits
    {
        start++;
    }
    if (isValid == 3) {
        isValid = 0;
    }
vsv_end_isValidNumber:
    if (start <= stop) {
        isValid = 0;
    }
    return isValid;
}

/*
** Validate UTF-8
** Return -1 if invalid else length
*/
static long long vsv_utf8IsValid(char* string) {
    long long length = 0;
    unsigned char* start;
    int trailing = 0;
    unsigned char c;

    start = (unsigned char*)string;
    while ((c = *start)) {
        if (trailing) {
            if ((c & 0xC0) == 0x80) {
                trailing--;
                start++;
                length++;
                continue;
            } else {
                length = -1;
                break;
            }
        }
        if ((c & 0x80) == 0) {
            start++;
            length++;
            continue;
        }
        if ((c & 0xE0) == 0xC0) {
            trailing = 1;
            start++;
            length++;
            continue;
        }
        if ((c & 0xF0) == 0xE0) {
            trailing = 2;
            start++;
            length++;
            continue;
        }
        if ((c & 0xF8) == 0xF0) {
            trailing = 3;
            start++;
            length++;
            continue;
        }
        length = -1;
        break;
    }
    return length;
}

/*
** Return values of columns for the row at which the VsvCursor
** is currently pointing.
*/
static int vsvtabColumn(sqlite3_vtab_cursor* cur, /* The cursor */
                        sqlite3_context* ctx,     /* First argument to sqlite3_result_...() */
                        int i                     /* Which column to return */
) {
    VsvCursor* pCur = (VsvCursor*)cur;
    VsvTable* pTab = (VsvTable*)cur->pVtab;
    long long dLen = pCur->dLen[i];
    long long length = 0;

    if (i >= 0 && i < pTab->nCol && pCur->azVal[i] != 0 && dLen > -1) {
        switch (pTab->affinity) {
            case 0: {
                if (pTab->validateUTF8) {
                    length = vsv_utf8IsValid(pCur->azVal[i]);
                    if (length == dLen) {
                        sqlite3_result_text(ctx, pCur->azVal[i], dLen, SQLITE_TRANSIENT);
                    } else {
                        sqlite3_result_error(ctx, "Invalid UTF8 Data", -1);
                    }
                } else {
                    sqlite3_result_text(ctx, pCur->azVal[i], -1, SQLITE_TRANSIENT);
                }
                break;
            }
            case 1: {
                sqlite3_result_blob(ctx, pCur->azVal[i], dLen, SQLITE_TRANSIENT);
                break;
            }
            case 2: {
                if (pTab->validateUTF8) {
                    length = vsv_utf8IsValid(pCur->azVal[i]);
                    if (length < dLen) {
                        sqlite3_result_blob(ctx, pCur->azVal[i], dLen, SQLITE_TRANSIENT);
                    } else {
                        sqlite3_result_text(ctx, pCur->azVal[i], length, SQLITE_TRANSIENT);
                    }
                } else {
                    sqlite3_result_text(ctx, pCur->azVal[i], -1, SQLITE_TRANSIENT);
                }
                break;
            }
            case 3: {
                switch (vsv_isValidNumber(pCur->rdr.dsep, pCur->azVal[i])) {
                    case 1: {
                        sqlite3_result_int64(ctx, strtoll(pCur->azVal[i], 0, 10));
                        break;
                    }
                    default: {
                        if (pTab->validateUTF8) {
                            length = vsv_utf8IsValid(pCur->azVal[i]);
                            if (length < dLen) {
                                sqlite3_result_blob(ctx, pCur->azVal[i], dLen, SQLITE_TRANSIENT);
                            } else {
                                sqlite3_result_text(ctx, pCur->azVal[i], length, SQLITE_TRANSIENT);
                            }
                        } else {
                            sqlite3_result_text(ctx, pCur->azVal[i], -1, SQLITE_TRANSIENT);
                        }
                        break;
                    }
                }
                break;
            }
            case 4: {
                switch (vsv_isValidNumber(pCur->rdr.dsep, pCur->azVal[i])) {
                    case 1:
                    case 2: {
                        sqlite3_result_double(ctx, strtod(pCur->azVal[i], 0));
                        break;
                    }
                    default: {
                        if (pTab->validateUTF8) {
                            length = vsv_utf8IsValid(pCur->azVal[i]);
                            if (length < dLen) {
                                sqlite3_result_blob(ctx, pCur->azVal[i], dLen, SQLITE_TRANSIENT);
                            } else {
                                sqlite3_result_text(ctx, pCur->azVal[i], length, SQLITE_TRANSIENT);
                            }
                        } else {
                            sqlite3_result_text(ctx, pCur->azVal[i], -1, SQLITE_TRANSIENT);
                        }
                        break;
                    }
                }
                break;
            }
            case 5: {
                switch (vsv_isValidNumber(pCur->rdr.dsep, pCur->azVal[i])) {
                    case 1: {
                        sqlite3_result_int64(ctx, strtoll(pCur->azVal[i], 0, 10));
                        break;
                    }
                    case 2: {
                        long double dv, fp, ip;

                        dv = strtold(pCur->azVal[i], 0);
                        fp = modfl(dv, &ip);
                        if (sizeof(long double) > sizeof(double)) {
                            if (fp == 0.0L && dv >= -9223372036854775808.0L &&
                                dv <= 9223372036854775807.0L) {
                                sqlite3_result_int64(ctx, (long long)dv);
                            } else {
                                sqlite3_result_double(ctx, (double)dv);
                            }
                        } else {
                            // Only convert if it will fit in a 6-byte varint
                            if (fp == 0.0L && dv >= -140737488355328.0L &&
                                dv <= 140737488355328.0L) {
                                sqlite3_result_int64(ctx, (long long)dv);
                            } else {
                                sqlite3_result_double(ctx, (double)dv);
                            }
                        }
                        break;
                    }
                    default: {
                        if (pTab->validateUTF8) {
                            length = vsv_utf8IsValid(pCur->azVal[i]);
                            if (length < dLen) {
                                sqlite3_result_blob(ctx, pCur->azVal[i], dLen, SQLITE_TRANSIENT);
                            } else {
                                sqlite3_result_text(ctx, pCur->azVal[i], length, SQLITE_TRANSIENT);
                            }
                        } else {
                            sqlite3_result_text(ctx, pCur->azVal[i], -1, SQLITE_TRANSIENT);
                        }
                        break;
                    }
                }
            }
        }
    }
    return SQLITE_OK;
}

/*
** Return the rowid for the current row.
*/
static int vsvtabRowid(sqlite3_vtab_cursor* cur, sqlite_int64* pRowid) {
    VsvCursor* pCur = (VsvCursor*)cur;
    *pRowid = pCur->iRowid;
    return SQLITE_OK;
}

/*
** Return TRUE if the cursor has been moved off of the last
** row of output.
*/
static int vsvtabEof(sqlite3_vtab_cursor* cur) {
    VsvCursor* pCur = (VsvCursor*)cur;
    return pCur->iRowid < 0;
}

/*
** Only a full table scan is supported.  So xFilter simply rewinds to
** the beginning.
*/
static int vsvtabFilter(sqlite3_vtab_cursor* pVtabCursor,
                        int idxNum,
                        const char* idxStr,
                        int argc,
                        sqlite3_value** argv) {
    VsvCursor* pCur = (VsvCursor*)pVtabCursor;
    VsvTable* pTab = (VsvTable*)pVtabCursor->pVtab;
    pCur->iRowid = 0;
    if (pCur->rdr.in == 0) {
        assert(pCur->rdr.zIn == pTab->zData);
        assert(pTab->iStart >= 0);
        assert((size_t)pTab->iStart <= pCur->rdr.nIn);
        pCur->rdr.iIn = pTab->iStart;
    } else {
        fseek(pCur->rdr.in, pTab->iStart, SEEK_SET);
        pCur->rdr.iIn = 0;
        pCur->rdr.nIn = 0;
    }
    return vsvtabNext(pVtabCursor);
}

/*
** Only a forward full table scan is supported.  xBestIndex is mostly
** a no-op.
*/
static int vsvtabBestIndex(sqlite3_vtab* tab, sqlite3_index_info* pIdxInfo) {
    pIdxInfo->estimatedCost = 1000000;
    return SQLITE_OK;
}

static sqlite3_module vsv_module = {
    .xCreate = vsvtabCreate,
    .xConnect = vsvtabConnect,
    .xBestIndex = vsvtabBestIndex,
    .xDisconnect = vsvtabDisconnect,
    .xDestroy = vsvtabDisconnect,
    .xOpen = vsvtabOpen,
    .xClose = vsvtabClose,
    .xFilter = vsvtabFilter,
    .xNext = vsvtabNext,
    .xEof = vsvtabEof,
    .xColumn = vsvtabColumn,
    .xRowid = vsvtabRowid,
};

int vsv_init(sqlite3* db) {
    sqlite3_create_module(db, "vsv", &vsv_module, 0);
    return SQLITE_OK;
}