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As noted by Per Cederqvist, new_buffersize() sometimes returns the 

buffer increment, and sometimes the new buffer size.  Make it do what
its name says, and fix the one place where this matters to the caller.

Also add a comment explaining why we call lseek() and then ftell().
This commit is contained in:
Guido van Rossum 1998-12-11 20:44:56 +00:00
parent 68055ce6fe
commit cada2938f7
1 changed files with 11 additions and 2 deletions
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13
Objects/fileobject.c
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@ -422,13 +422,22 @@ new_buffersize(f, currentsize)
struct stat st;
if (fstat(fileno(f->f_fp), &st) == 0) {
end = st.st_size;
/* The following is not a bug: we really need to call lseek()
*and* ftell(). The reason is that some stdio libraries
mistakenly flush their buffer when ftell() is called and
the lseek() call it makes fails, thereby throwing away
data that cannot be recovered in any way. To avoid this,
we first test lseek(), and only call ftell() if lseek()
works. We can't use the lseek() value either, because we
need to take the amount of buffered data into account.
(Yet another reason why stdio stinks. :-) */
pos = lseek(fileno(f->f_fp), 0L, SEEK_CUR);
if (pos >= 0)
pos = ftell(f->f_fp);
if (pos < 0)
clearerr(f->f_fp);
if (end > pos && pos >= 0)
return end - pos + 1;
return currentsize + end - pos + 1;
/* Add 1 so if the file were to grow we'd notice. */
}
#endif
@ -482,7 +491,7 @@ file_read(f, args)
if (bytesread < buffersize)
break;
if (bytesrequested < 0) {
buffersize = bytesread + new_buffersize(f, buffersize);
buffersize = new_buffersize(f, buffersize);
if (_PyString_Resize(&v, buffersize) < 0)
return NULL;
}