forked from zserge/tojvm
-
Notifications
You must be signed in to change notification settings - Fork 0
/
loader.go
180 lines (164 loc) · 4.24 KB
/
loader.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
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
package tojvm
import (
"encoding/binary"
"fmt"
"io"
"math"
)
type Class struct {
ConstPool ConstPool
Name string
Super string
Flags uint16
Interfaces []string
Fields []Field
Methods []Field
Attributes []Attribute
}
type Tag byte
// From Table 4.4-A
const (
TagClass Tag = 7
TagFieldRef = 9
TagMethodRef = 10
TagInterfaceMethodRef = 11
TagString = 8
TagInteger = 3
TagFloat = 4
TagLong = 5
TagDouble = 6
TagNameAndType = 12
TagUTF8 = 1
TagMethodHandle = 15
TagMethodType = 16
TagInvokeDynamic = 18
)
type Const struct {
Tag Tag
NameIndex uint16
ClassIndex uint16
NameAndTypeIndex uint16
StringIndex uint16
DescIndex uint16
Integer int32
Long int64
Float float32
Double float64
String string
}
type Field struct {
Flags uint16
Name string
Descriptor string
Attributes []Attribute
}
type Attribute struct {
Name string
Data []byte
}
type ConstPool []Const
func (cp ConstPool) Resolve(index uint16) string {
if cp[index-1].Tag == TagUTF8 {
return cp[index-1].String
} else if cp[index-1].Tag == TagString {
return cp.Resolve(cp[index-1].StringIndex)
} else if cp[index-1].Tag == TagClass || cp[index-1].Tag == TagNameAndType {
return cp.Resolve(cp[index-1].NameIndex)
}
return ""
}
type loader struct {
r io.Reader
err error
}
func (l *loader) bytes(n int) []byte {
b := make([]byte, n, n)
if l.err == nil {
_, l.err = io.ReadFull(l.r, b)
}
return b
}
func (l *loader) u1() uint8 { return l.bytes(1)[0] }
func (l *loader) u2() uint16 { return binary.BigEndian.Uint16(l.bytes(2)) }
func (l *loader) u4() uint32 { return binary.BigEndian.Uint32(l.bytes(4)) }
func (l *loader) u8() uint64 { return binary.BigEndian.Uint64(l.bytes(8)) }
func (l *loader) cpinfo() (constPool ConstPool) {
constPoolCount := l.u2()
for i := uint16(1); i < constPoolCount; i++ {
c := Const{Tag: Tag(l.u1())}
switch c.Tag {
case TagClass:
c.NameIndex = l.u2()
case TagFieldRef, TagMethodRef, TagInterfaceMethodRef:
c.ClassIndex = l.u2()
c.NameAndTypeIndex = l.u2()
case TagString:
c.StringIndex = l.u2()
case TagInteger:
c.Integer = int32(l.u4())
case TagFloat:
c.Float = math.Float32frombits(l.u4())
case TagLong:
c.Long = int64(l.u8())
case TagDouble:
c.Double = math.Float64frombits(l.u8())
case TagNameAndType:
c.NameIndex, c.DescIndex = l.u2(), l.u2()
case TagUTF8:
c.String = string(l.bytes(int(l.u2())))
default:
l.err = fmt.Errorf("unsupported tag: %d", c.Tag)
}
constPool = append(constPool, c)
if c.Tag == TagDouble || c.Tag == TagLong {
// For 64-bit types an additional, valid, but unused const should be added
constPool = append(constPool, Const{Tag: TagInteger})
i++
}
}
return constPool
}
func (l *loader) interfaces(cp ConstPool) (interfaces []string) {
interfaceCount := l.u2()
for i := uint16(0); i < interfaceCount; i++ {
interfaces = append(interfaces, cp.Resolve(l.u2()))
}
return interfaces
}
func (l *loader) fields(cp ConstPool) (fields []Field) {
fieldsCount := l.u2()
for i := uint16(0); i < fieldsCount; i++ {
fields = append(fields, Field{
Flags: l.u2(),
Name: cp.Resolve(l.u2()),
Descriptor: cp.Resolve(l.u2()),
Attributes: l.attrs(cp),
})
}
return fields
}
func (l *loader) attrs(cp ConstPool) (attrs []Attribute) {
attributesCount := l.u2()
for i := uint16(0); i < attributesCount; i++ {
attrs = append(attrs, Attribute{
Name: cp.Resolve(l.u2()),
Data: l.bytes(int(l.u4())),
})
}
return attrs
}
func Load(r io.Reader) (Class, error) {
loader := &loader{r: r}
c := Class{}
loader.u8() // magic, minor, major
cp := loader.cpinfo() // const pool info
c.ConstPool = cp
c.Flags = loader.u2() // access flags
c.Name = cp.Resolve(loader.u2()) // this class
c.Super = cp.Resolve(loader.u2()) // super class
c.Interfaces = loader.interfaces(cp)
c.Fields = loader.fields(cp) // fields
c.Methods = loader.fields(cp) // methods
c.Attributes = loader.attrs(cp) // methods
return c, loader.err
}