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fix encoding scanning for non-seekable ports

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* libguile/read.c (scm_i_scan_for_encoding): If possible, just use the
  read buffer for the encoding scan, and avoid seeking.  Fixes
  `(open-input-file "/dev/urandom")', because /dev/urandom can't be
  seeked backwards.
This commit is contained in:
Andy Wingo 2011-03-03 12:46:49 +01:00
parent 8d795c83d4
commit d900843c72
1 changed files with 41 additions and 7 deletions
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48
libguile/read.c
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@ -1650,6 +1650,7 @@ scm_get_hash_procedure (int c)
char *
scm_i_scan_for_encoding (SCM port)
{
scm_t_port *pt;
char header[SCM_ENCODING_SEARCH_SIZE+1];
size_t bytes_read, encoding_length, i;
char *encoding = NULL;
@ -1657,15 +1658,46 @@ scm_i_scan_for_encoding (SCM port)
char *pos, *encoding_start;
int in_comment;
if (SCM_FPORTP (port) && !SCM_FDES_RANDOM_P (SCM_FPORT_FDES (port)))
/* PORT is a non-seekable file port (e.g., as created by Bash when using
"guile <(echo '(display "hello")')") so bail out. */
return NULL;
pt = SCM_PTAB_ENTRY (port);
bytes_read = scm_c_read (port, header, SCM_ENCODING_SEARCH_SIZE);
header[bytes_read] = '\0';
if (pt->rw_active == SCM_PORT_WRITE)
scm_flush (port);
scm_seek (port, scm_from_int (0), scm_from_int (SEEK_SET));
if (pt->rw_random)
pt->rw_active = SCM_PORT_READ;
if (pt->read_pos == pt->read_end)
{
/* We can use the read buffer, and thus avoid a seek. */
if (scm_fill_input (port) == EOF)
return NULL;
bytes_read = pt->read_end - pt->read_pos;
if (bytes_read > SCM_ENCODING_SEARCH_SIZE)
bytes_read = SCM_ENCODING_SEARCH_SIZE;
if (bytes_read <= 1)
/* An unbuffered port -- don't scan. */
return NULL;
memcpy (header, pt->read_pos, bytes_read);
header[bytes_read] = '\0';
}
else
{
/* Try to read some bytes and then seek back. Not all ports
support seeking back; and indeed some file ports (like
/dev/urandom) will succeed on an lseek (fd, 0, SEEK_CUR)---the
check performed by SCM_FPORT_FDES---but fail to seek
backwards. Hence this block comes second. We prefer to use
the read buffer in-place. */
if (SCM_FPORTP (port) && !SCM_FDES_RANDOM_P (SCM_FPORT_FDES (port)))
return NULL;
bytes_read = scm_c_read (port, header, SCM_ENCODING_SEARCH_SIZE);
header[bytes_read] = '\0';
scm_seek (port, scm_from_int (0), scm_from_int (SEEK_SET));
}
if (bytes_read > 3
&& header[0] == '\xef' && header[1] == '\xbb' && header[2] == '\xbf')
@ -1757,6 +1789,8 @@ SCM_DEFINE (scm_file_encoding, "file-encoding", 1, 0, 0,
char *enc;
SCM s_enc;
SCM_VALIDATE_OPINPORT (SCM_ARG1, port);
enc = scm_i_scan_for_encoding (port);
if (enc == NULL)
return SCM_BOOL_F;