From: Timo Sirainen <timo.sirainen@open-xchange.com>
Date: Thu, 12 Mar 2020 10:57:41 +0000 (+0200)
Subject: lib: safe_sendfile() - clarify return value 0 handling
X-Git-Tag: 2.3.11.2~509
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f0a845736edf78c322630da24ba42c6571654787;p=thirdparty%2Fdovecot%2Fcore.git

lib: safe_sendfile() - clarify return value 0 handling
---

diff --git a/src/lib/sendfile-util.c b/src/lib/sendfile-util.c
index 83e420af3f..662285b14d 100644
--- a/src/lib/sendfile-util.c
+++ b/src/lib/sendfile-util.c
@@ -22,8 +22,7 @@ ssize_t safe_sendfile(int out_fd, int in_fd, uoff_t *offset, size_t count)
 	off_t safe_offset;
 	ssize_t ret;
 
-	if (count == 0)
-		return 0;
+	i_assert(count > 0);
 
 	/* make sure given offset fits into off_t */
 	if (sizeof(off_t) * CHAR_BIT == 32) {
@@ -49,7 +48,7 @@ ssize_t safe_sendfile(int out_fd, int in_fd, uoff_t *offset, size_t count)
 
 	safe_offset = (off_t)*offset;
 	ret = sendfile(out_fd, in_fd, &safe_offset, count);
-	/* ret=0 : trying to read past EOF, errno = EPIPE : remote is gone */
+	/* ret=0 : trying to read past EOF */
 	*offset = (uoff_t)safe_offset;
 	return ret;
 }
@@ -65,14 +64,11 @@ ssize_t safe_sendfile(int out_fd, int in_fd, uoff_t *offset, size_t count)
 	off_t sbytes;
 	int ret;
 
+	/* if count=0 is passed to sendfile(), it sends everything
+	   from in_fd until EOF. We don't want that. */
+	i_assert(count > 0);
 	i_assert(count <= SSIZE_T_MAX);
 
-	if (count == 0) {
-		/* if count=0 is passed to sendfile(), it sends everything
-		   from in_fd until EOF. We don't want that. */
-		return 0;
-	}
-
 	i_zero(&hdtr);
 	ret = sendfile(in_fd, out_fd, *offset, count, &hdtr, &sbytes, 0);
 
@@ -100,11 +96,9 @@ ssize_t safe_sendfile(int out_fd, int in_fd, uoff_t *offset, size_t count)
 	ssize_t ret;
 	off_t s_offset;
 
+	i_assert(count > 0);
 	i_assert(count <= SSIZE_T_MAX);
 
-	if (count == 0)
-		return 0;
-
 	/* NOTE: if outfd is not a socket, some Solaris versions will
 	   kernel panic */
 
diff --git a/src/lib/sendfile-util.h b/src/lib/sendfile-util.h
index 29ada6f605..3d7f14aa0a 100644
--- a/src/lib/sendfile-util.h
+++ b/src/lib/sendfile-util.h
@@ -1,9 +1,16 @@
 #ifndef SENDFILE_UTIL_H
 #define SENDFILE_UTIL_H
 
-/* Wrapper for various sendfile()-like calls. Returns -1 and errno=EINVAL if
-   it isn't supported for some reason (out_fd isn't a socket, offset is too
-   large, or there simply is no sendfile()). */
+/* Wrapper for various sendfile()-like calls. Read a maximum of count bytes
+   from the given offset in in_fd and write them to out_fd. The offset is
+   updated after the call. Note the call assert-crashes if count is 0.
+
+   Returns:
+   >0 number of bytes successfully written (maybe less than count)
+   0 if offset points to the input's EOF or past it
+   -1, errno=EINVAL if it isn't supported for some reason (out_fd isn't a
+       socket or there simply is no sendfile()).
+   -1, errno=EAGAIN if non-blocking write couldn't send anything */
 ssize_t safe_sendfile(int out_fd, int in_fd, uoff_t *offset, size_t count);
 
 #endif