os: do not assume syscall i/o funcs return n=0 on error

Fixes issue 9007.

LGTM=iant, r
R=r, iant
CC=golang-codereviews
https://codereview.appspot.com/160670043

1 files changed, 5 insertions, 5 deletions

diff --git a/src/os/file_unix.go b/src/os/file_unix.go
index bba0d9c0f..4e413fbe8 100644
--- a/src/os/file_unix.go
+++ b/src/os/file_unix.go
@@ -187,7 +187,7 @@ func (f *File) read(b []byte) (n int, err error) {
 	if needsMaxRW && len(b) > maxRW {
 		b = b[:maxRW]
 	}
-	return syscall.Read(f.fd, b)
+	return fixCount(syscall.Read(f.fd, b))
 }
 
 // pread reads len(b) bytes from the File starting at byte offset off.
@@ -197,7 +197,7 @@ func (f *File) pread(b []byte, off int64) (n int, err error) {
 	if needsMaxRW && len(b) > maxRW {
 		b = b[:maxRW]
 	}
-	return syscall.Pread(f.fd, b, off)
+	return fixCount(syscall.Pread(f.fd, b, off))
 }
 
 // write writes len(b) bytes to the File.
@@ -208,7 +208,7 @@ func (f *File) write(b []byte) (n int, err error) {
 		if needsMaxRW && len(bcap) > maxRW {
 			bcap = bcap[:maxRW]
 		}
-		m, err := syscall.Write(f.fd, bcap)
+		m, err := fixCount(syscall.Write(f.fd, bcap))
 		n += m
 
 		// If the syscall wrote some data but not all (short write)
@@ -234,7 +234,7 @@ func (f *File) pwrite(b []byte, off int64) (n int, err error) {
 	if needsMaxRW && len(b) > maxRW {
 		b = b[:maxRW]
 	}
-	return syscall.Pwrite(f.fd, b, off)
+	return fixCount(syscall.Pwrite(f.fd, b, off))
 }
 
 // seek sets the offset for the next Read or Write on file to offset, interpreted
@@ -242,7 +242,7 @@ func (f *File) pwrite(b []byte, off int64) (n int, err error) {
 // relative to the current offset, and 2 means relative to the end.
 // It returns the new offset and an error, if any.
 func (f *File) seek(offset int64, whence int) (ret int64, err error) {
-	return syscall.Seek(f.fd, offset, whence)
+	return fixCount(syscall.Seek(f.fd, offset, whence))
 }
 
 // Truncate changes the size of the named file.