forked from apache/beam
/
read.go
96 lines (86 loc) · 2.98 KB
/
read.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package ioutilx contains additional io utilities.
package ioutilx
import (
"io"
"unsafe"
"github.com/apache/beam/sdks/go/pkg/beam/internal/errors"
)
// ReadN reads exactly N bytes from the reader. Fails otherwise.
func ReadN(r io.Reader, n int) ([]byte, error) {
ret := make([]byte, n)
index := 0
for {
i, err := r.Read(ret[index:])
if i+index == n {
return ret, nil
}
if err != nil {
return nil, err
}
if i == 0 {
return nil, errors.New("No data")
}
index += i
}
}
// ReadNBufUnsafe reads exactly cap(buf) bytes from the reader. Fails otherwise.
// Uses the unsafe package unsafely to convince escape analysis that the passed
// in []byte doesn't escape this function through the io.Reader.
// Intended for use with small, fixed sized, stack allocated buffers that have
// no business being allocated to the heap.
// If the io.Reader somehow retains the passed in []byte, then this should not
// be used, and ReadN preferred.
func ReadNBufUnsafe(r io.Reader, b []byte) error {
// Use with parameter retaining readers at your own peril.
ret := *(*[]byte)(noescape(unsafe.Pointer(&b)))
index := 0
n := len(ret)
for {
i, err := r.Read(ret[index:])
if i+index == n {
return nil
}
if err != nil {
return err
}
if i == 0 {
return errors.New("No data")
}
index += i
}
}
// ReadUnsafe is an unsafe version of read that breaks escape analysis
// to allow the passed in []byte to be allocated to the stack.
// Intended for use with small, fixed sized, stack allocated buffers that have
// no business being allocated to the heap.
// If the io.Reader somehow retains the passed in []byte, then this should not
// be used, and ReadN preferred.
func ReadUnsafe(r io.Reader, b []byte) (int, error) {
ret := *(*[]byte)(noescape(unsafe.Pointer(&b)))
return r.Read(ret)
}
// noescape hides a pointer from escape analysis. noescape is
// the identity function but escape analysis doesn't think the
// output depends on the input. noescape is inlined and currently
// compiles down to zero instructions.
// USE CAREFULLY!
// This was copied from the runtime; see issues 23382 and 7921.
//go:nosplit
func noescape(p unsafe.Pointer) unsafe.Pointer {
x := uintptr(p)
return unsafe.Pointer(x ^ 0)
}