From: Gustavo Niemeyer <gustavo@niemeyer.net>
Date: Tue, 4 Mar 2003 00:50:24 +0000 (+0000)
Subject: Backported fix to [521782] unreliable file.read() error handling.
X-Git-Tag: v2.2.3c1~117
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fac559c5334afc8e44cf45555082be1f165a02e6;p=thirdparty%2FPython%2Fcpython.git

Backported fix to [521782] unreliable file.read() error handling.
---

diff --git a/Doc/lib/libstdtypes.tex b/Doc/lib/libstdtypes.tex
index fcc3361593b4..eff8ff40b8cc 100644
--- a/Doc/lib/libstdtypes.tex
+++ b/Doc/lib/libstdtypes.tex
@@ -1163,7 +1163,9 @@ Files have the following methods:
   certain files, like ttys, it makes sense to continue reading after
   an \EOF{} is hit.)  Note that this method may call the underlying
   C function \cfunction{fread()} more than once in an effort to
-  acquire as close to \var{size} bytes as possible.
+  acquire as close to \var{size} bytes as possible. Also note that
+  when in non-blocking mode, less data than what was requested may
+  be returned, even if no \var{size} parameter was given.
 \end{methoddesc}
 
 \begin{methoddesc}[file]{readline}{\optional{size}}
diff --git a/Misc/NEWS b/Misc/NEWS
index e81e87a2f716..aaecd01d9e1e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -295,6 +295,9 @@ Core and builtins
   supply a __doc__ descriptor that returns something different for a
   class than for instances of that class.
 
+- Fixed bug #521782: when a file was in non-blocking mode, file.read()
+  could silently lose data or wrongly throw an unknown error.
+
 Extension modules
 
 - In readline.c: change completion to avoid appending a space
diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index 58af9ce8b28f..b38dbb5c4d4d 100644
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -568,6 +568,20 @@ new_buffersize(PyFileObject *f, size_t currentsize)
 	return currentsize + SMALLCHUNK;
 }
 
+#if defined(EWOULDBLOCK) && defined(EAGAIN) && EWOULDBLOCK != EAGAIN
+#define BLOCKED_ERRNO(x) ((x) == EWOULDBLOCK || (x) == EAGAIN)
+#else
+#ifdef EWOULDBLOCK
+#define BLOCKED_ERRNO(x) ((x) == EWOULDBLOCK)
+#else
+#ifdef EAGAIN
+#define BLOCKED_ERRNO(x) ((x) == EAGAIN)
+#else
+#define BLOCKED_ERRNO(x) 0
+#endif
+#endif
+#endif
+
 static PyObject *
 file_read(PyFileObject *f, PyObject *args)
 {
@@ -601,18 +615,29 @@ file_read(PyFileObject *f, PyObject *args)
 		if (chunksize == 0) {
 			if (!ferror(f->f_fp))
 				break;
-			PyErr_SetFromErrno(PyExc_IOError);
 			clearerr(f->f_fp);
+			/* When in non-blocking mode, data shouldn't
+			 * be discarded if a blocking signal was
+			 * received. That will also happen if
+			 * chunksize != 0, but bytesread < buffersize. */
+			if (bytesread > 0 && BLOCKED_ERRNO(errno))
+				break;
+			PyErr_SetFromErrno(PyExc_IOError);
 			Py_DECREF(v);
 			return NULL;
 		}
 		bytesread += chunksize;
-		if (bytesread < buffersize)
+		if (bytesread < buffersize) {
+			clearerr(f->f_fp);
 			break;
+		}
 		if (bytesrequested < 0) {
 			buffersize = new_buffersize(f, buffersize);
 			if (_PyString_Resize(&v, buffersize) < 0)
 				return NULL;
+		} else {
+			/* Got what was requested. */
+			break;
 		}
 	}
 	if (bytesread != buffersize)
@@ -1321,7 +1346,9 @@ static char readline_doc[] =
 static char read_doc[] =
 "read([size]) -> read at most size bytes, returned as a string.\n"
 "\n"
-"If the size argument is negative or omitted, read until EOF is reached.";
+"If the size argument is negative or omitted, read until EOF is reached.\n"
+"Notice that when in non-blocking mode, less data than what was requested\n"
+"may be returned, even if no size parameter was given.";
 
 static char write_doc[] =
 "write(str) -> None.  Write string str to file.\n"