
/* Tokenizer implementation */

#include "Python.h"
#include "pgenheaders.h"

#include <ctype.h>
#include <assert.h>

#include "tokenizer.h"
#include "errcode.h"

#ifndef PGEN
#include "unicodeobject.h"
#include "bytesobject.h"
#include "fileobject.h"
#include "codecs.h"
#include "abstract.h"
#endif /* PGEN */

#define is_potential_identifier_start(c) (\
              (c >= 'a' && c <= 'z')\
               || (c >= 'A' && c <= 'Z')\
               || c == '_'\
               || (c >= 128))

#define is_potential_identifier_char(c) (\
              (c >= 'a' && c <= 'z')\
               || (c >= 'A' && c <= 'Z')\
               || (c >= '0' && c <= '9')\
               || c == '_'\
               || (c >= 128))

extern char *PyOS_Readline(FILE *, FILE *, const char *);
/* Return malloc'ed string including trailing \n;
   empty malloc'ed string for EOF;
   NULL if interrupted */

/* Don't ever change this -- it would break the portability of Python code */
#define TABSIZE 8

/* Forward */
static struct tok_state *tok_new(void);
static int tok_nextc(struct tok_state *tok);
static void tok_backup(struct tok_state *tok, int c);


/* Token names */

const char *_PyParser_TokenNames[] = {
    "ENDMARKER",
    "NAME",
    "NUMBER",
    "STRING",
    "NEWLINE",
    "INDENT",
    "DEDENT",
    "LPAR",
    "RPAR",
    "LSQB",
    "RSQB",
    "COLON",
    "COMMA",
    "SEMI",
    "PLUS",
    "MINUS",
    "STAR",
    "SLASH",
    "VBAR",
    "AMPER",
    "LESS",
    "GREATER",
    "EQUAL",
    "DOT",
    "PERCENT",
    "LBRACE",
    "RBRACE",
    "EQEQUAL",
    "NOTEQUAL",
    "LESSEQUAL",
    "GREATEREQUAL",
    "TILDE",
    "CIRCUMFLEX",
    "LEFTSHIFT",
    "RIGHTSHIFT",
    "DOUBLESTAR",
    "PLUSEQUAL",
    "MINEQUAL",
    "STAREQUAL",
    "SLASHEQUAL",
    "PERCENTEQUAL",
    "AMPEREQUAL",
    "VBAREQUAL",
    "CIRCUMFLEXEQUAL",
    "LEFTSHIFTEQUAL",
    "RIGHTSHIFTEQUAL",
    "DOUBLESTAREQUAL",
    "DOUBLESLASH",
    "DOUBLESLASHEQUAL",
    "AT",
    "ATEQUAL",
    "RARROW",
    "ELLIPSIS",
    /* This table must match the #defines in token.h! */
    "OP",
    "<ERRORTOKEN>",
    "COMMENT",
    "NL",
    "ENCODING",
    "<N_TOKENS>"
};


/* Create and initialize a new tok_state structure */

static struct tok_state *
tok_new(void)
{
    struct tok_state *tok = (struct tok_state *)PyMem_MALLOC(
                                            sizeof(struct tok_state));
    if (tok == NULL)
        return NULL;
    tok->buf = tok->cur = tok->end = tok->inp = tok->start = NULL;
    tok->done = E_OK;
    tok->fp = NULL;
    tok->input = NULL;
    tok->tabsize = TABSIZE;
    tok->indent = 0;
    tok->indstack[0] = 0;

    tok->atbol = 1;
    tok->pendin = 0;
    tok->prompt = tok->nextprompt = NULL;
    tok->lineno = 0;
    tok->level = 0;
    tok->altwarning = 1;
    tok->alterror = 1;
    tok->alttabsize = 1;
    tok->altindstack[0] = 0;
    tok->decoding_state = STATE_INIT;
    tok->decoding_erred = 0;
    tok->read_coding_spec = 0;
    tok->enc = NULL;
    tok->encoding = NULL;
    tok->cont_line = 0;
#ifndef PGEN
    tok->filename = NULL;
    tok->decoding_readline = NULL;
    tok->decoding_buffer = NULL;
#endif

    return tok;
}

static char *
new_string(const char *s, Py_ssize_t len, struct tok_state *tok)
{
    char* result = (char *)PyMem_MALLOC(len + 1);
    if (!result) {
        tok->done = E_NOMEM;
        return NULL;
    }
    memcpy(result, s, len);
    result[len] = '\0';
    return result;
}

#ifdef PGEN

static char *
decoding_fgets(char *s, int size, struct tok_state *tok)
{
    return fgets(s, size, tok->fp);
}

static int
decoding_feof(struct tok_state *tok)
{
    return feof(tok->fp);
}

static char *
decode_str(const char *str, int exec_input, struct tok_state *tok)
{
    return new_string(str, strlen(str), tok);
}

#else /* PGEN */

static char *
error_ret(struct tok_state *tok) /* XXX */
{
    tok->decoding_erred = 1;
    if (tok->fp != NULL && tok->buf != NULL) /* see PyTokenizer_Free */
        PyMem_FREE(tok->buf);
    tok->buf = tok->cur = tok->end = tok->inp = tok->start = NULL;
    tok->done = E_DECODE;
    return NULL;                /* as if it were EOF */
}


static const char *
get_normal_name(const char *s)  /* for utf-8 and latin-1 */
{
    char buf[13];
    int i;
    for (i = 0; i < 12; i++) {
        int c = s[i];
        if (c == '\0')
            break;
        else if (c == '_')
            buf[i] = '-';
        else
            buf[i] = tolower(c);
    }
    buf[i] = '\0';
    if (strcmp(buf, "utf-8") == 0 ||
        strncmp(buf, "utf-8-", 6) == 0)
        return "utf-8";
    else if (strcmp(buf, "latin-1") == 0 ||
             strcmp(buf, "iso-8859-1") == 0 ||
             strcmp(buf, "iso-latin-1") == 0 ||
             strncmp(buf, "latin-1-", 8) == 0 ||
             strncmp(buf, "iso-8859-1-", 11) == 0 ||
             strncmp(buf, "iso-latin-1-", 12) == 0)
        return "iso-8859-1";
    else
        return s;
}

/* Return the coding spec in S, or NULL if none is found.  */

static int
get_coding_spec(const char *s, char **spec, Py_ssize_t size, struct tok_state *tok)
{
    Py_ssize_t i;
    *spec = NULL;
    /* Coding spec must be in a comment, and that comment must be
     * the only statement on the source code line. */
    for (i = 0; i < size - 6; i++) {
        if (s[i] == '#')
            break;
        if (s[i] != ' ' && s[i] != '\t' && s[i] != '\014')
            return 1;
    }
    for (; i < size - 6; i++) { /* XXX inefficient search */
        const char* t = s + i;
        if (strncmp(t, "coding", 6) == 0) {
            const char* begin = NULL;
            t += 6;
            if (t[0] != ':' && t[0] != '=')
                continue;
            do {
                t++;
            } while (t[0] == '\x20' || t[0] == '\t');

            begin = t;
            while (Py_ISALNUM(t[0]) ||
                   t[0] == '-' || t[0] == '_' || t[0] == '.')
                t++;

            if (begin < t) {
                char* r = new_string(begin, t - begin, tok);
                const char* q;
                if (!r)
                    return 0;
                q = get_normal_name(r);
                if (r != q) {
                    PyMem_FREE(r);
                    r = new_string(q, strlen(q), tok);
                    if (!r)
                        return 0;
                }
                *spec = r;
                break;
            }
        }
    }
    return 1;
}

/* Check whether the line contains a coding spec. If it does,
   invoke the set_readline function for the new encoding.
   This function receives the tok_state and the new encoding.
   Return 1 on success, 0 on failure.  */

static int
check_coding_spec(const char* line, Py_ssize_t size, struct tok_state *tok,
                  int set_readline(struct tok_state *, const char *))
{
    char *cs;
    int r = 1;

    if (tok->cont_line) {
        /* It's a continuation line, so it can't be a coding spec. */
        tok->read_coding_spec = 1;
        return 1;
    }
    if (!get_coding_spec(line, &cs, size, tok))
        return 0;
    if (!cs) {
        Py_ssize_t i;
        for (i = 0; i < size; i++) {
            if (line[i] == '#' || line[i] == '\n' || line[i] == '\r')
                break;
            if (line[i] != ' ' && line[i] != '\t' && line[i] != '\014') {
                /* Stop checking coding spec after a line containing
                 * anything except a comment. */
                tok->read_coding_spec = 1;
                break;
            }
        }
        return 1;
    }
    tok->read_coding_spec = 1;
    if (tok->encoding == NULL) {
        assert(tok->decoding_state == STATE_RAW);
        if (strcmp(cs, "utf-8") == 0) {
            tok->encoding = cs;
        } else {
            r = set_readline(tok, cs);
            if (r) {
                tok->encoding = cs;
                tok->decoding_state = STATE_NORMAL;
            }
            else {
                PyErr_Format(PyExc_SyntaxError,
                             "encoding problem: %s", cs);
                PyMem_FREE(cs);
            }
        }
    } else {                /* then, compare cs with BOM */
        r = (strcmp(tok->encoding, cs) == 0);
        if (!r)
            PyErr_Format(PyExc_SyntaxError,
                         "encoding problem: %s with BOM", cs);
        PyMem_FREE(cs);
    }
    return r;
}

/* See whether the file starts with a BOM. If it does,
   invoke the set_readline function with the new encoding.
   Return 1 on success, 0 on failure.  */

static int
check_bom(int get_char(struct tok_state *),
          void unget_char(int, struct tok_state *),
          int set_readline(struct tok_state *, const char *),
          struct tok_state *tok)
{
    int ch1, ch2, ch3;
    ch1 = get_char(tok);
    tok->decoding_state = STATE_RAW;
    if (ch1 == EOF) {
        return 1;
    } else if (ch1 == 0xEF) {
        ch2 = get_char(tok);
        if (ch2 != 0xBB) {
            unget_char(ch2, tok);
            unget_char(ch1, tok);
            return 1;
        }
        ch3 = get_char(tok);
        if (ch3 != 0xBF) {
            unget_char(ch3, tok);
            unget_char(ch2, tok);
            unget_char(ch1, tok);
            return 1;
        }
#if 0
    /* Disable support for UTF-16 BOMs until a decision
       is made whether this needs to be supported.  */
    } else if (ch1 == 0xFE) {
        ch2 = get_char(tok);
        if (ch2 != 0xFF) {
            unget_char(ch2, tok);
            unget_char(ch1, tok);
            return 1;
        }
        if (!set_readline(tok, "utf-16-be"))
            return 0;
        tok->decoding_state = STATE_NORMAL;
    } else if (ch1 == 0xFF) {
        ch2 = get_char(tok);
        if (ch2 != 0xFE) {
            unget_char(ch2, tok);
            unget_char(ch1, tok);
            return 1;
        }
        if (!set_readline(tok, "utf-16-le"))
            return 0;
        tok->decoding_state = STATE_NORMAL;
#endif
    } else {
        unget_char(ch1, tok);
        return 1;
    }
    if (tok->encoding != NULL)
        PyMem_FREE(tok->encoding);
    tok->encoding = new_string("utf-8", 5, tok);
    if (!tok->encoding)
        return 0;
    /* No need to set_readline: input is already utf-8 */
    return 1;
}

/* Read a line of text from TOK into S, using the stream in TOK.
   Return NULL on failure, else S.

   On entry, tok->decoding_buffer will be one of:
     1) NULL: need to call tok->decoding_readline to get a new line
     2) PyUnicodeObject *: decoding_feof has called tok->decoding_readline and
       stored the result in tok->decoding_buffer
     3) PyByteArrayObject *: previous call to fp_readl did not have enough room
       (in the s buffer) to copy entire contents of the line read
       by tok->decoding_readline.  tok->decoding_buffer has the overflow.
       In this case, fp_readl is called in a loop (with an expanded buffer)
       until the buffer ends with a '\n' (or until the end of the file is
       reached): see tok_nextc and its calls to decoding_fgets.
*/

static char *
fp_readl(char *s, int size, struct tok_state *tok)
{
    PyObject* bufobj;
    const char *buf;
    Py_ssize_t buflen;

    /* Ask for one less byte so we can terminate it */
    assert(size > 0);
    size--;

    if (tok->decoding_buffer) {
        bufobj = tok->decoding_buffer;
        Py_INCREF(bufobj);
    }
    else
    {
        bufobj = _PyObject_CallNoArg(tok->decoding_readline);
        if (bufobj == NULL)
            goto error;
    }
    if (PyUnicode_CheckExact(bufobj))
    {
        buf = PyUnicode_AsUTF8AndSize(bufobj, &buflen);
        if (buf == NULL) {
            goto error;
        }
    }
    else
    {
        buf = PyByteArray_AsString(bufobj);
        if (buf == NULL) {
            goto error;
        }
        buflen = PyByteArray_GET_SIZE(bufobj);
    }

    Py_XDECREF(tok->decoding_buffer);
    if (buflen > size) {
        /* Too many chars, the rest goes into tok->decoding_buffer */
        tok->decoding_buffer = PyByteArray_FromStringAndSize(buf+size,
                                                         buflen-size);
        if (tok->decoding_buffer == NULL)
            goto error;
        buflen = size;
    }
    else
        tok->decoding_buffer = NULL;

    memcpy(s, buf, buflen);
    s[buflen] = '\0';
    if (buflen == 0) /* EOF */
        s = NULL;
    Py_DECREF(bufobj);
    return s;

error:
    Py_XDECREF(bufobj);
    return error_ret(tok);
}

/* Set the readline function for TOK to a StreamReader's
   readline function. The StreamReader is named ENC.

   This function is called from check_bom and check_coding_spec.

   ENC is usually identical to the future value of tok->encoding,
   except for the (currently unsupported) case of UTF-16.

   Return 1 on success, 0 on failure. */

static int
fp_setreadl(struct tok_state *tok, const char* enc)
{
    PyObject *readline, *io, *stream;
    _Py_IDENTIFIER(open);
    _Py_IDENTIFIER(readline);
    int fd;
    long pos;

    fd = fileno(tok->fp);
    /* Due to buffering the file offset for fd can be different from the file
     * position of tok->fp.  If tok->fp was opened in text mode on Windows,
     * its file position counts CRLF as one char and can't be directly mapped
     * to the file offset for fd.  Instead we step back one byte and read to
     * the end of line.*/
    pos = ftell(tok->fp);
    if (pos == -1 ||
        lseek(fd, (off_t)(pos > 0 ? pos - 1 : pos), SEEK_SET) == (off_t)-1) {
        PyErr_SetFromErrnoWithFilename(PyExc_OSError, NULL);
        return 0;
    }

    io = PyImport_ImportModuleNoBlock("io");
    if (io == NULL)
        return 0;

    stream = _PyObject_CallMethodId(io, &PyId_open, "isisOOO",
                    fd, "r", -1, enc, Py_None, Py_None, Py_False);
    Py_DECREF(io);
    if (stream == NULL)
        return 0;

    readline = _PyObject_GetAttrId(stream, &PyId_readline);
    Py_DECREF(stream);
    if (readline == NULL)
        return 0;
    Py_XSETREF(tok->decoding_readline, readline);

    if (pos > 0) {
        PyObject *bufobj = _PyObject_CallNoArg(readline);
        if (bufobj == NULL)
            return 0;
        Py_DECREF(bufobj);
    }

    return 1;
}

/* Fetch the next byte from TOK. */

static int fp_getc(struct tok_state *tok) {
    return getc(tok->fp);
}

/* Unfetch the last byte back into TOK.  */

static void fp_ungetc(int c, struct tok_state *tok) {
    ungetc(c, tok->fp);
}

/* Check whether the characters at s start a valid
   UTF-8 sequence. Return the number of characters forming
   the sequence if yes, 0 if not.  */
static int valid_utf8(const unsigned char* s)
{
    int expected = 0;
    int length;
    if (*s < 0x80)
        /* single-byte code */
        return 1;
    if (*s < 0xc0)
        /* following byte */
        return 0;
    if (*s < 0xE0)
        expected = 1;
    else if (*s < 0xF0)
        expected = 2;
    else if (*s < 0xF8)
        expected = 3;
    else
        return 0;
    length = expected + 1;
    for (; expected; expected--)
        if (s[expected] < 0x80 || s[expected] >= 0xC0)
            return 0;
    return length;
}

/* Read a line of input from TOK. Determine encoding
   if necessary.  */

static char *
decoding_fgets(char *s, int size, struct tok_state *tok)
{
    char *line = NULL;
    int badchar = 0;
    for (;;) {
        if (tok->decoding_state == STATE_NORMAL) {
            /* We already have a codec associated with
               this input. */
            line = fp_readl(s, size, tok);
            break;
        } else if (tok->decoding_state == STATE_RAW) {
            /* We want a 'raw' read. */
            line = Py_UniversalNewlineFgets(s, size,
                                            tok->fp, NULL);
            break;
        } else {
            /* We have not yet determined the encoding.
               If an encoding is found, use the file-pointer
               reader functions from now on. */
            if (!check_bom(fp_getc, fp_ungetc, fp_setreadl, tok))
                return error_ret(tok);
            assert(tok->decoding_state != STATE_INIT);
        }
    }
    if (line != NULL && tok->lineno < 2 && !tok->read_coding_spec) {
        if (!check_coding_spec(line, strlen(line), tok, fp_setreadl)) {
            return error_ret(tok);
        }
    }
#ifndef PGEN
    /* The default encoding is UTF-8, so make sure we don't have any
       non-UTF-8 sequences in it. */
    if (line && !tok->encoding) {
        unsigned char *c;
        int length;
        for (c = (unsigned char *)line; *c; c += length)
            if (!(length = valid_utf8(c))) {
                badchar = *c;
                break;
            }
    }
    if (badchar) {
        /* Need to add 1 to the line number, since this line
           has not been counted, yet.  */
        PyErr_Format(PyExc_SyntaxError,
                "Non-UTF-8 code starting with '\\x%.2x' "
                "in file %U on line %i, "
                "but no encoding declared; "
                "see http://python.org/dev/peps/pep-0263/ for details",
                badchar, tok->filename, tok->lineno + 1);
        return error_ret(tok);
    }
#endif
    return line;
}

static int
decoding_feof(struct tok_state *tok)
{
    if (tok->decoding_state != STATE_NORMAL) {
        return feof(tok->fp);
    } else {
        PyObject* buf = tok->decoding_buffer;
        if (buf == NULL) {
            buf = _PyObject_CallNoArg(tok->decoding_readline);
            if (buf == NULL) {
                error_ret(tok);
                return 1;
            } else {
                tok->decoding_buffer = buf;
            }
        }
        return PyObject_Length(buf) == 0;
    }
}

/* Fetch a byte from TOK, using the string buffer. */

static int
buf_getc(struct tok_state *tok) {
    return Py_CHARMASK(*tok->str++);
}

/* Unfetch a byte from TOK, using the string buffer. */

static void
buf_ungetc(int c, struct tok_state *tok) {
    tok->str--;
    assert(Py_CHARMASK(*tok->str) == c);        /* tok->cur may point to read-only segment */
}

/* Set the readline function for TOK to ENC. For the string-based
   tokenizer, this means to just record the encoding. */

static int
buf_setreadl(struct tok_state *tok, const char* enc) {
    tok->enc = enc;
    return 1;
}

/* Return a UTF-8 encoding Python string object from the
   C byte string STR, which is encoded with ENC. */

static PyObject *
translate_into_utf8(const char* str, const char* enc) {
    PyObject *utf8;
    PyObject* buf = PyUnicode_Decode(str, strlen(str), enc, NULL);
    if (buf == NULL)
        return NULL;
    utf8 = PyUnicode_AsUTF8String(buf);
    Py_DECREF(buf);
    return utf8;
}


static char *
translate_newlines(const char *s, int exec_input, struct tok_state *tok) {
    int skip_next_lf = 0;
    size_t needed_length = strlen(s) + 2, final_length;
    char *buf, *current;
    char c = '\0';
    buf = PyMem_MALLOC(needed_length);
    if (buf == NULL) {
        tok->done = E_NOMEM;
        return NULL;
    }
    for (current = buf; *s; s++, current++) {
        c = *s;
        if (skip_next_lf) {
            skip_next_lf = 0;
            if (c == '\n') {
                c = *++s;
                if (!c)
                    break;
            }
        }
        if (c == '\r') {
            skip_next_lf = 1;
            c = '\n';
        }
        *current = c;
    }
    /* If this is exec input, add a newline to the end of the string if
       there isn't one already. */
    if (exec_input && c != '\n') {
        *current = '\n';
        current++;
    }
    *current = '\0';
    final_length = current - buf + 1;
    if (final_length < needed_length && final_length)
        /* should never fail */
        buf = PyMem_REALLOC(buf, final_length);
    return buf;
}

/* Decode a byte string STR for use as the buffer of TOK.
   Look for encoding declarations inside STR, and record them
   inside TOK.  */

static const char *
decode_str(const char *input, int single, struct tok_state *tok)
{
    PyObject* utf8 = NULL;
    const char *str;
    const char *s;
    const char *newl[2] = {NULL, NULL};
    int lineno = 0;
    tok->input = str = translate_newlines(input, single, tok);
    if (str == NULL)
        return NULL;
    tok->enc = NULL;
    tok->str = str;
    if (!check_bom(buf_getc, buf_ungetc, buf_setreadl, tok))
        return error_ret(tok);
    str = tok->str;             /* string after BOM if any */
    assert(str);
    if (tok->enc != NULL) {
        utf8 = translate_into_utf8(str, tok->enc);
        if (utf8 == NULL)
            return error_ret(tok);
        str = PyBytes_AsString(utf8);
    }
    for (s = str;; s++) {
        if (*s == '\0') break;
        else if (*s == '\n') {
            assert(lineno < 2);
            newl[lineno] = s;
            lineno++;
            if (lineno == 2) break;
        }
    }
    tok->enc = NULL;
    /* need to check line 1 and 2 separately since check_coding_spec
       assumes a single line as input */
    if (newl[0]) {
        if (!check_coding_spec(str, newl[0] - str, tok, buf_setreadl))
            return error_ret(tok);
        if (tok->enc == NULL && !tok->read_coding_spec && newl[1]) {
            if (!check_coding_spec(newl[0]+1, newl[1] - newl[0],
                                   tok, buf_setreadl))
                return error_ret(tok);
        }
    }
    if (tok->enc != NULL) {
        assert(utf8 == NULL);
        utf8 = translate_into_utf8(str, tok->enc);
        if (utf8 == NULL)
            return error_ret(tok);
        str = PyBytes_AS_STRING(utf8);
    }
    assert(tok->decoding_buffer == NULL);
    tok->decoding_buffer = utf8; /* CAUTION */
    return str;
}

#endif /* PGEN */

/* Set up tokenizer for string */

struct tok_state *
PyTokenizer_FromString(const char *str, int exec_input)
{
    struct tok_state *tok = tok_new();
    if (tok == NULL)
        return NULL;
    str = decode_str(str, exec_input, tok);
    if (str == NULL) {
        PyTokenizer_Free(tok);
        return NULL;
    }

    /* XXX: constify members. */
    tok->buf = tok->cur = tok->end = tok->inp = (char*)str;
    return tok;
}

struct tok_state *
PyTokenizer_FromUTF8(const char *str, int exec_input)
{
    struct tok_state *tok = tok_new();
    if (tok == NULL)
        return NULL;
#ifndef PGEN
    tok->input = str = translate_newlines(str, exec_input, tok);
#endif
    if (str == NULL) {
        PyTokenizer_Free(tok);
        return NULL;
    }
    tok->decoding_state = STATE_RAW;
    tok->read_coding_spec = 1;
    tok->enc = NULL;
    tok->str = str;
    tok->encoding = (char *)PyMem_MALLOC(6);
    if (!tok->encoding) {
        PyTokenizer_Free(tok);
        return NULL;
    }
    strcpy(tok->encoding, "utf-8");

    /* XXX: constify members. */
    tok->buf = tok->cur = tok->end = tok->inp = (char*)str;
    return tok;
}

/* Set up tokenizer for file */

struct tok_state *
PyTokenizer_FromFile(FILE *fp, const char* enc,
                     const char *ps1, const char *ps2)
{
    struct tok_state *tok = tok_new();
    if (tok == NULL)
        return NULL;
    if ((tok->buf = (char *)PyMem_MALLOC(BUFSIZ)) == NULL) {
        PyTokenizer_Free(tok);
        return NULL;
    }
    tok->cur = tok->inp = tok->buf;
    tok->end = tok->buf + BUFSIZ;
    tok->fp = fp;
    tok->prompt = ps1;
    tok->nextprompt = ps2;
    if (enc != NULL) {
        /* Must copy encoding declaration since it
           gets copied into the parse tree. */
        tok->encoding = PyMem_MALLOC(strlen(enc)+1);
        if (!tok->encoding) {
            PyTokenizer_Free(tok);
            return NULL;
        }
        strcpy(tok->encoding, enc);
        tok->decoding_state = STATE_NORMAL;
    }
    return tok;
}


/* Free a tok_state structure */

void
PyTokenizer_Free(struct tok_state *tok)
{
    if (tok->encoding != NULL)
        PyMem_FREE(tok->encoding);
#ifndef PGEN
    Py_XDECREF(tok->decoding_readline);
    Py_XDECREF(tok->decoding_buffer);
    Py_XDECREF(tok->filename);
#endif
    if (tok->fp != NULL && tok->buf != NULL)
        PyMem_FREE(tok->buf);
    if (tok->input)
        PyMem_FREE((char *)tok->input);
    PyMem_FREE(tok);
}

/* Get next char, updating state; error code goes into tok->done */

static int
tok_nextc(struct tok_state *tok)
{
    for (;;) {
        if (tok->cur != tok->inp) {
            return Py_CHARMASK(*tok->cur++); /* Fast path */
        }
        if (tok->done != E_OK)
            return EOF;
        if (tok->fp == NULL) {
            char *end = strchr(tok->inp, '\n');
            if (end != NULL)
                end++;
            else {
                end = strchr(tok->inp, '\0');
                if (end == tok->inp) {
                    tok->done = E_EOF;
                    return EOF;
                }
            }
            if (tok->start == NULL)
                tok->buf = tok->cur;
            tok->line_start = tok->cur;
            tok->lineno++;
            tok->inp = end;
            return Py_CHARMASK(*tok->cur++);
        }
        if (tok->prompt != NULL) {
            char *newtok = PyOS_Readline(stdin, stdout, tok->prompt);
#ifndef PGEN
            if (newtok != NULL) {
                char *translated = translate_newlines(newtok, 0, tok);
                PyMem_FREE(newtok);
                if (translated == NULL)
                    return EOF;
                newtok = translated;
            }
            if (tok->encoding && newtok && *newtok) {
                /* Recode to UTF-8 */
                Py_ssize_t buflen;
                const char* buf;
                PyObject *u = translate_into_utf8(newtok, tok->encoding);
                PyMem_FREE(newtok);
                if (!u) {
                    tok->done = E_DECODE;
                    return EOF;
                }
                buflen = PyBytes_GET_SIZE(u);
                buf = PyBytes_AS_STRING(u);
                newtok = PyMem_MALLOC(buflen+1);
                strcpy(newtok, buf);
                Py_DECREF(u);
            }
#endif
            if (tok->nextprompt != NULL)
                tok->prompt = tok->nextprompt;
            if (newtok == NULL)
                tok->done = E_INTR;
            else if (*newtok == '\0') {
                PyMem_FREE(newtok);
                tok->done = E_EOF;
            }
            else if (tok->start != NULL) {
                size_t start = tok->start - tok->buf;
                size_t oldlen = tok->cur - tok->buf;
                size_t newlen = oldlen + strlen(newtok);
                char *buf = tok->buf;
                buf = (char *)PyMem_REALLOC(buf, newlen+1);
                tok->lineno++;
                if (buf == NULL) {
                    PyMem_FREE(tok->buf);
                    tok->buf = NULL;
                    PyMem_FREE(newtok);
                    tok->done = E_NOMEM;
                    return EOF;
                }
                tok->buf = buf;
                tok->cur = tok->buf + oldlen;
                tok->line_start = tok->cur;
                strcpy(tok->buf + oldlen, newtok);
                PyMem_FREE(newtok);
                tok->inp = tok->buf + newlen;
                tok->end = tok->inp + 1;
                tok->start = tok->buf + start;
            }
            else {
                tok->lineno++;
                if (tok->buf != NULL)
                    PyMem_FREE(tok->buf);
                tok->buf = newtok;
                tok->cur = tok->buf;
                tok->line_start = tok->buf;
                tok->inp = strchr(tok->buf, '\0');
                tok->end = tok->inp + 1;
            }
        }
        else {
            int done = 0;
            Py_ssize_t cur = 0;
            char *pt;
            if (tok->start == NULL) {
                if (tok->buf == NULL) {
                    tok->buf = (char *)
                        PyMem_MALLOC(BUFSIZ);
                    if (tok->buf == NULL) {
                        tok->done = E_NOMEM;
                        return EOF;
                    }
                    tok->end = tok->buf + BUFSIZ;
                }
                if (decoding_fgets(tok->buf, (int)(tok->end - tok->buf),
                          tok) == NULL) {
                    if (!tok->decoding_erred)
                        tok->done = E_EOF;
                    done = 1;
                }
                else {
                    tok->done = E_OK;
                    tok->inp = strchr(tok->buf, '\0');
                    done = tok->inp == tok->buf || tok->inp[-1] == '\n';
                }
            }
            else {
                cur = tok->cur - tok->buf;
                if (decoding_feof(tok)) {
                    tok->done = E_EOF;
                    done = 1;
                }
                else
                    tok->done = E_OK;
            }
            tok->lineno++;
            /* Read until '\n' or EOF */
            while (!done) {
                Py_ssize_t curstart = tok->start == NULL ? -1 :
                          tok->start - tok->buf;
                Py_ssize_t curvalid = tok->inp - tok->buf;
                Py_ssize_t newsize = curvalid + BUFSIZ;
                char *newbuf = tok->buf;
                newbuf = (char *)PyMem_REALLOC(newbuf,
                                               newsize);
                if (newbuf == NULL) {
                    tok->done = E_NOMEM;
                    tok->cur = tok->inp;
                    return EOF;
                }
                tok->buf = newbuf;
                tok->cur = tok->buf + cur;
                tok->line_start = tok->cur;
                tok->inp = tok->buf + curvalid;
                tok->end = tok->buf + newsize;
                tok->start = curstart < 0 ? NULL :
                         tok->buf + curstart;
                if (decoding_fgets(tok->inp,
                               (int)(tok->end - tok->inp),
                               tok) == NULL) {
                    /* Break out early on decoding
                       errors, as tok->buf will be NULL
                     */
                    if (tok->decoding_erred)
                        return EOF;
                    /* Last line does not end in \n,
                       fake one */
                    strcpy(tok->inp, "\n");
                }
                tok->inp = strchr(tok->inp, '\0');
                done = tok->inp[-1] == '\n';
            }
            if (tok->buf != NULL) {
                tok->cur = tok->buf + cur;
                tok->line_start = tok->cur;
                /* replace "\r\n" with "\n" */
                /* For Mac leave the \r, giving a syntax error */
                pt = tok->inp - 2;
                if (pt >= tok->buf && *pt == '\r') {
                    *pt++ = '\n';
                    *pt = '\0';
                    tok->inp = pt;
                }
            }
        }
        if (tok->done != E_OK) {
            if (tok->prompt != NULL)
                PySys_WriteStderr("\n");
            tok->cur = tok->inp;
            return EOF;
        }
    }
    /*NOTREACHED*/
}


/* Back-up one character */

static void
tok_backup(struct tok_state *tok, int c)
{
    if (c != EOF) {
        if (--tok->cur < tok->buf)
            Py_FatalError("tok_backup: beginning of buffer");
        if (*tok->cur != c)
            *tok->cur = c;
    }
}


/* Return the token corresponding to a single character */

int
PyToken_OneChar(int c)
{
    switch (c) {
    case '(':           return LPAR;
    case ')':           return RPAR;
    case '[':           return LSQB;
    case ']':           return RSQB;
    case ':':           return COLON;
    case ',':           return COMMA;
    case ';':           return SEMI;
    case '+':           return PLUS;
    case '-':           return MINUS;
    case '*':           return STAR;
    case '/':           return SLASH;
    case '|':           return VBAR;
    case '&':           return AMPER;
    case '<':           return LESS;
    case '>':           return GREATER;
    case '=':           return EQUAL;
    case '.':           return DOT;
    case '%':           return PERCENT;
    case '{':           return LBRACE;
    case '}':           return RBRACE;
    case '^':           return CIRCUMFLEX;
    case '~':           return TILDE;
    case '@':           return AT;
    default:            return OP;
    }
}


int
PyToken_TwoChars(int c1, int c2)
{
    switch (c1) {
    case '=':
        switch (c2) {
        case '=':               return EQEQUAL;
        }
        break;
    case '!':
        switch (c2) {
        case '=':               return NOTEQUAL;
        }
        break;
    case '<':
        switch (c2) {
        case '>':               return NOTEQUAL;
        case '=':               return LESSEQUAL;
        case '<':               return LEFTSHIFT;
        }
        break;
    case '>':
        switch (c2) {
        case '=':               return GREATEREQUAL;
        case '>':               return RIGHTSHIFT;
        }
        break;
    case '+':
        switch (c2) {
        case '=':               return PLUSEQUAL;
        }
        break;
    case '-':
        switch (c2) {
        case '=':               return MINEQUAL;
        case '>':               return RARROW;
        }
        break;
    case '*':
        switch (c2) {
        case '*':               return DOUBLESTAR;
        case '=':               return STAREQUAL;
        }
        break;
    case '/':
        switch (c2) {
        case '/':               return DOUBLESLASH;
        case '=':               return SLASHEQUAL;
        }
        break;
    case '|':
        switch (c2) {
        case '=':               return VBAREQUAL;
        }
        break;
    case '%':
        switch (c2) {
        case '=':               return PERCENTEQUAL;
        }
        break;
    case '&':
        switch (c2) {
        case '=':               return AMPEREQUAL;
        }
        break;
    case '^':
        switch (c2) {
        case '=':               return CIRCUMFLEXEQUAL;
        }
        break;
    case '@':
        switch (c2) {
        case '=':               return ATEQUAL;
        }
        break;
    }
    return OP;
}

int
PyToken_ThreeChars(int c1, int c2, int c3)
{
    switch (c1) {
    case '<':
        switch (c2) {
        case '<':
            switch (c3) {
            case '=':
                return LEFTSHIFTEQUAL;
            }
            break;
        }
        break;
    case '>':
        switch (c2) {
        case '>':
            switch (c3) {
            case '=':
                return RIGHTSHIFTEQUAL;
            }
            break;
        }
        break;
    case '*':
        switch (c2) {
        case '*':
            switch (c3) {
            case '=':
                return DOUBLESTAREQUAL;
            }
            break;
        }
        break;
    case '/':
        switch (c2) {
        case '/':
            switch (c3) {
            case '=':
                return DOUBLESLASHEQUAL;
            }
            break;
        }
        break;
    case '.':
        switch (c2) {
        case '.':
            switch (c3) {
            case '.':
                return ELLIPSIS;
            }
            break;
        }
        break;
    }
    return OP;
}

static int
indenterror(struct tok_state *tok)
{
    if (tok->alterror) {
        tok->done = E_TABSPACE;
        tok->cur = tok->inp;
        return 1;
    }
    if (tok->altwarning) {
#ifdef PGEN
        PySys_WriteStderr("inconsistent use of tabs and spaces "
                          "in indentation\n");
#else
        PySys_FormatStderr("%U: inconsistent use of tabs and spaces "
                          "in indentation\n", tok->filename);
#endif
        tok->altwarning = 0;
    }
    return 0;
}

#ifdef PGEN
#define verify_identifier(tok) 1
#else
/* Verify that the identifier follows PEP 3131.
   All identifier strings are guaranteed to be "ready" unicode objects.
 */
static int
verify_identifier(struct tok_state *tok)
{
    PyObject *s;
    int result;
    if (tok->decoding_erred)
        return 0;
    s = PyUnicode_DecodeUTF8(tok->start, tok->cur - tok->start, NULL);
    if (s == NULL || PyUnicode_READY(s) == -1) {
        if (PyErr_ExceptionMatches(PyExc_UnicodeDecodeError)) {
            PyErr_Clear();
            tok->done = E_IDENTIFIER;
        } else {
            tok->done = E_ERROR;
        }
        return 0;
    }
    result = PyUnicode_IsIdentifier(s);
    Py_DECREF(s);
    if (result == 0)
        tok->done = E_IDENTIFIER;
    return result;
}
#endif

static int
tok_decimal_tail(struct tok_state *tok)
{
    int c;

    while (1) {
        do {
            c = tok_nextc(tok);
        } while (isdigit(c));
        if (c != '_') {
            break;
        }
        c = tok_nextc(tok);
        if (!isdigit(c)) {
            tok->done = E_TOKEN;
            tok_backup(tok, c);
            return 0;
        }
    }
    return c;
}

/* Get next token, after space stripping etc. */

static int
tok_get(struct tok_state *tok, char **p_start, char **p_end)
{
    int c;
    int blankline, nonascii;

    *p_start = *p_end = NULL;
  nextline:
    tok->start = NULL;
    blankline = 0;

    /* Get indentation level */
    if (tok->atbol) {
        int col = 0;
        int altcol = 0;
        tok->atbol = 0;
        for (;;) {
            c = tok_nextc(tok);
            if (c == ' ') {
                col++, altcol++;
            }
            else if (c == '\t') {
                col = (col/tok->tabsize + 1) * tok->tabsize;
                altcol = (altcol/tok->alttabsize + 1)
                    * tok->alttabsize;
            }
            else if (c == '\014')  {/* Control-L (formfeed) */
                col = altcol = 0; /* For Emacs users */
            }
            else {
                break;
            }
        }
        tok_backup(tok, c);
        if (c == '#' || c == '\n') {
            /* Lines with only whitespace and/or comments
               shouldn't affect the indentation and are
               not passed to the parser as NEWLINE tokens,
               except *totally* empty lines in interactive
               mode, which signal the end of a command group. */
            if (col == 0 && c == '\n' && tok->prompt != NULL) {
                blankline = 0; /* Let it through */
            }
            else {
                blankline = 1; /* Ignore completely */
            }
            /* We can't jump back right here since we still
               may need to skip to the end of a comment */
        }
        if (!blankline && tok->level == 0) {
            if (col == tok->indstack[tok->indent]) {
                /* No change */
                if (altcol != tok->altindstack[tok->indent]) {
                    if (indenterror(tok)) {
                        return ERRORTOKEN;
                    }
                }
            }
            else if (col > tok->indstack[tok->indent]) {
                /* Indent -- always one */
                if (tok->indent+1 >= MAXINDENT) {
                    tok->done = E_TOODEEP;
                    tok->cur = tok->inp;
                    return ERRORTOKEN;
                }
                if (altcol <= tok->altindstack[tok->indent]) {
                    if (indenterror(tok)) {
                        return ERRORTOKEN;
                    }
                }
                tok->pendin++;
                tok->indstack[++tok->indent] = col;
                tok->altindstack[tok->indent] = altcol;
            }
            else /* col < tok->indstack[tok->indent] */ {
                /* Dedent -- any number, must be consistent */
                while (tok->indent > 0 &&
                    col < tok->indstack[tok->indent]) {
                    tok->pendin--;
                    tok->indent--;
                }
                if (col != tok->indstack[tok->indent]) {
                    tok->done = E_DEDENT;
                    tok->cur = tok->inp;
                    return ERRORTOKEN;
                }
                if (altcol != tok->altindstack[tok->indent]) {
                    if (indenterror(tok)) {
                        return ERRORTOKEN;
                    }
                }
            }
        }
    }

    tok->start = tok->cur;

    /* Return pending indents/dedents */
    if (tok->pendin != 0) {
        if (tok->pendin < 0) {
            tok->pendin++;
            return DEDENT;
        }
        else {
            tok->pendin--;
            return INDENT;
        }
    }

 again:
    tok->start = NULL;
    /* Skip spaces */
    do {
        c = tok_nextc(tok);
    } while (c == ' ' || c == '\t' || c == '\014');

    /* Set start of current token */
    tok->start = tok->cur - 1;

    /* Skip comment */
    if (c == '#') {
        while (c != EOF && c != '\n') {
            c = tok_nextc(tok);
        }
    }

    /* Check for EOF and errors now */
    if (c == EOF) {
        return tok->done == E_EOF ? ENDMARKER : ERRORTOKEN;
    }

    /* Identifier (most frequent token!) */
    nonascii = 0;
    if (is_potential_identifier_start(c)) {
        /* Process the various legal combinations of b"", r"", u"", and f"". */
        int saw_b = 0, saw_r = 0, saw_u = 0, saw_f = 0;
        while (1) {
            if (!(saw_b || saw_u || saw_f) && (c == 'b' || c == 'B'))
                saw_b = 1;
            /* Since this is a backwards compatibility support literal we don't
               want to support it in arbitrary order like byte literals. */
            else if (!(saw_b || saw_u || saw_r || saw_f)
                     && (c == 'u'|| c == 'U')) {
                saw_u = 1;
            }
            /* ur"" and ru"" are not supported */
            else if (!(saw_r || saw_u) && (c == 'r' || c == 'R')) {
                saw_r = 1;
            }
            else if (!(saw_f || saw_b || saw_u) && (c == 'f' || c == 'F')) {
                saw_f = 1;
            }
            else {
                break;
            }
            c = tok_nextc(tok);
            if (c == '"' || c == '\'') {
                goto letter_quote;
            }
        }
        while (is_potential_identifier_char(c)) {
            if (c >= 128) {
                nonascii = 1;
            }
            c = tok_nextc(tok);
        }
        tok_backup(tok, c);
        if (nonascii && !verify_identifier(tok)) {
            return ERRORTOKEN;
        }
        *p_start = tok->start;
        *p_end = tok->cur;

        return NAME;
    }

    /* Newline */
    if (c == '\n') {
        tok->atbol = 1;
        if (blankline || tok->level > 0) {
            goto nextline;
        }
        *p_start = tok->start;
        *p_end = tok->cur - 1; /* Leave '\n' out of the string */
        tok->cont_line = 0;
        return NEWLINE;
    }

    /* Period or number starting with period? */
    if (c == '.') {
        c = tok_nextc(tok);
        if (isdigit(c)) {
            goto fraction;
        } else if (c == '.') {
            c = tok_nextc(tok);
            if (c == '.') {
                *p_start = tok->start;
                *p_end = tok->cur;
                return ELLIPSIS;
            }
            else {
                tok_backup(tok, c);
            }
            tok_backup(tok, '.');
        }
        else {
            tok_backup(tok, c);
        }
        *p_start = tok->start;
        *p_end = tok->cur;
        return DOT;
    }

    /* Number */
    if (isdigit(c)) {
        if (c == '0') {
            /* Hex, octal or binary -- maybe. */
            c = tok_nextc(tok);
            if (c == 'x' || c == 'X') {
                /* Hex */
                c = tok_nextc(tok);
                do {
                    if (c == '_') {
                        c = tok_nextc(tok);
                    }
                    if (!isxdigit(c)) {
                        tok->done = E_TOKEN;
                        tok_backup(tok, c);
                        return ERRORTOKEN;
                    }
                    do {
                        c = tok_nextc(tok);
                    } while (isxdigit(c));
                } while (c == '_');
            }
            else if (c == 'o' || c == 'O') {
                /* Octal */
                c = tok_nextc(tok);
                do {
                    if (c == '_') {
                        c = tok_nextc(tok);
                    }
                    if (c < '0' || c >= '8') {
                        tok->done = E_TOKEN;
                        tok_backup(tok, c);
                        return ERRORTOKEN;
                    }
                    do {
                        c = tok_nextc(tok);
                    } while ('0' <= c && c < '8');
                } while (c == '_');
            }
            else if (c == 'b' || c == 'B') {
                /* Binary */
                c = tok_nextc(tok);
                do {
                    if (c == '_') {
                        c = tok_nextc(tok);
                    }
                    if (c != '0' && c != '1') {
                        tok->done = E_TOKEN;
                        tok_backup(tok, c);
                        return ERRORTOKEN;
                    }
                    do {
                        c = tok_nextc(tok);
                    } while (c == '0' || c == '1');
                } while (c == '_');
            }
            else {
                int nonzero = 0;
                /* maybe old-style octal; c is first char of it */
                /* in any case, allow '0' as a literal */
                while (1) {
                    if (c == '_') {
                        c = tok_nextc(tok);
                        if (!isdigit(c)) {
                            tok->done = E_TOKEN;
                            tok_backup(tok, c);
                            return ERRORTOKEN;
                        }
                    }
                    if (c != '0') {
                        break;
                    }
                    c = tok_nextc(tok);
                }
                if (isdigit(c)) {
                    nonzero = 1;
                    c = tok_decimal_tail(tok);
                    if (c == 0) {
                        return ERRORTOKEN;
                    }
                }
                if (c == '.') {
                    c = tok_nextc(tok);
                    goto fraction;
                }
                else if (c == 'e' || c == 'E') {
                    goto exponent;
                }
                else if (c == 'j' || c == 'J') {
                    goto imaginary;
                }
                else if (nonzero) {
                    /* Old-style octal: now disallowed. */
                    tok->done = E_TOKEN;
                    tok_backup(tok, c);
                    return ERRORTOKEN;
                }
            }
        }
        else {
            /* Decimal */
            c = tok_decimal_tail(tok);
            if (c == 0) {
                return ERRORTOKEN;
            }
            {
                /* Accept floating point numbers. */
                if (c == '.') {
                    c = tok_nextc(tok);
        fraction:
                    /* Fraction */
                    if (isdigit(c)) {
                        c = tok_decimal_tail(tok);
                        if (c == 0) {
                            return ERRORTOKEN;
                        }
                    }
                }
                if (c == 'e' || c == 'E') {
                    int e;
                  exponent:
                    e = c;
                    /* Exponent part */
                    c = tok_nextc(tok);
                    if (c == '+' || c == '-') {
                        c = tok_nextc(tok);
                        if (!isdigit(c)) {
                            tok->done = E_TOKEN;
                            tok_backup(tok, c);
                            return ERRORTOKEN;
                        }
                    } else if (!isdigit(c)) {
                        tok_backup(tok, c);
                        tok_backup(tok, e);
                        *p_start = tok->start;
                        *p_end = tok->cur;
                        return NUMBER;
                    }
                    c = tok_decimal_tail(tok);
                    if (c == 0) {
                        return ERRORTOKEN;
                    }
                }
                if (c == 'j' || c == 'J') {
                    /* Imaginary part */
        imaginary:
                    c = tok_nextc(tok);
                }
            }
        }
        tok_backup(tok, c);
        *p_start = tok->start;
        *p_end = tok->cur;
        return NUMBER;
    }

  letter_quote:
    /* String */
    if (c == '\'' || c == '"') {
        int quote = c;
        int quote_size = 1;             /* 1 or 3 */
        int end_quote_size = 0;

        /* Find the quote size and start of string */
        c = tok_nextc(tok);
        if (c == quote) {
            c = tok_nextc(tok);
            if (c == quote) {
                quote_size = 3;
            }
            else {
                end_quote_size = 1;     /* empty string found */
            }
        }
        if (c != quote) {
            tok_backup(tok, c);
        }

        /* Get rest of string */
        while (end_quote_size != quote_size) {
            c = tok_nextc(tok);
            if (c == EOF) {
                if (quote_size == 3) {
                    tok->done = E_EOFS;
                }
                else {
                    tok->done = E_EOLS;
                }
                tok->cur = tok->inp;
                return ERRORTOKEN;
            }
            if (quote_size == 1 && c == '\n') {
                tok->done = E_EOLS;
                tok->cur = tok->inp;
                return ERRORTOKEN;
            }
            if (c == quote) {
                end_quote_size += 1;
            }
            else {
                end_quote_size = 0;
                if (c == '\\') {
                    tok_nextc(tok);  /* skip escaped char */
                }
            }
        }

        *p_start = tok->start;
        *p_end = tok->cur;
        return STRING;
    }

    /* Line continuation */
    if (c == '\\') {
        c = tok_nextc(tok);
        if (c != '\n') {
            tok->done = E_LINECONT;
            tok->cur = tok->inp;
            return ERRORTOKEN;
        }
        tok->cont_line = 1;
        goto again; /* Read next line */
    }

    /* Check for two-character token */
    {
        int c2 = tok_nextc(tok);
        int token = PyToken_TwoChars(c, c2);
        if (token != OP) {
            int c3 = tok_nextc(tok);
            int token3 = PyToken_ThreeChars(c, c2, c3);
            if (token3 != OP) {
                token = token3;
            }
            else {
                tok_backup(tok, c3);
            }
            *p_start = tok->start;
            *p_end = tok->cur;
            return token;
        }
        tok_backup(tok, c2);
    }

    /* Keep track of parentheses nesting level */
    switch (c) {
    case '(':
    case '[':
    case '{':
        tok->level++;
        break;
    case ')':
    case ']':
    case '}':
        tok->level--;
        break;
    }

    /* Punctuation character */
    *p_start = tok->start;
    *p_end = tok->cur;
    return PyToken_OneChar(c);
}

int
PyTokenizer_Get(struct tok_state *tok, char **p_start, char **p_end)
{
    int result = tok_get(tok, p_start, p_end);
    if (tok->decoding_erred) {
        result = ERRORTOKEN;
        tok->done = E_DECODE;
    }
    return result;
}

/* Get the encoding of a Python file. Check for the coding cookie and check if
   the file starts with a BOM.

   PyTokenizer_FindEncodingFilename() returns NULL when it can't find the
   encoding in the first or second line of the file (in which case the encoding
   should be assumed to be UTF-8).

   The char* returned is malloc'ed via PyMem_MALLOC() and thus must be freed
   by the caller. */

char *
PyTokenizer_FindEncodingFilename(int fd, PyObject *filename)
{
    struct tok_state *tok;
    FILE *fp;
    char *p_start =NULL , *p_end =NULL , *encoding = NULL;

#ifndef PGEN
    fd = _Py_dup(fd);
#else
    fd = dup(fd);
#endif
    if (fd < 0) {
        return NULL;
    }

    fp = fdopen(fd, "r");
    if (fp == NULL) {
        return NULL;
    }
    tok = PyTokenizer_FromFile(fp, NULL, NULL, NULL);
    if (tok == NULL) {
        fclose(fp);
        return NULL;
    }
#ifndef PGEN
    if (filename != NULL) {
        Py_INCREF(filename);
        tok->filename = filename;
    }
    else {
        tok->filename = PyUnicode_FromString("<string>");
        if (tok->filename == NULL) {
            fclose(fp);
            PyTokenizer_Free(tok);
            return encoding;
        }
    }
#endif
    while (tok->lineno < 2 && tok->done == E_OK) {
        PyTokenizer_Get(tok, &p_start, &p_end);
    }
    fclose(fp);
    if (tok->encoding) {
        encoding = (char *)PyMem_MALLOC(strlen(tok->encoding) + 1);
        if (encoding)
        strcpy(encoding, tok->encoding);
    }
    PyTokenizer_Free(tok);
    return encoding;
}

char *
PyTokenizer_FindEncoding(int fd)
{
    return PyTokenizer_FindEncodingFilename(fd, NULL);
}

#ifdef Py_DEBUG

void
tok_dump(int type, char *start, char *end)
{
    printf("%s", _PyParser_TokenNames[type]);
    if (type == NAME || type == NUMBER || type == STRING || type == OP)
        printf("(%.*s)", (int)(end - start), start);
}

#endif