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
181
182
|
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package httpresponse defines an Analyzer that checks for mistakes
// using HTTP responses.
package httpresponse
import (
"go/ast"
"go/types"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
"golang.org/x/tools/go/ast/inspector"
)
const Doc = `check for mistakes using HTTP responses
A common mistake when using the net/http package is to defer a function
call to close the http.Response Body before checking the error that
determines whether the response is valid:
resp, err := http.Head(url)
defer resp.Body.Close()
if err != nil {
log.Fatal(err)
}
// (defer statement belongs here)
This checker helps uncover latent nil dereference bugs by reporting a
diagnostic for such mistakes.`
var Analyzer = &analysis.Analyzer{
Name: "httpresponse",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
}
func run(pass *analysis.Pass) (interface{}, error) {
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
// Fast path: if the package doesn't import net/http,
// skip the traversal.
if !analysisutil.Imports(pass.Pkg, "net/http") {
return nil, nil
}
nodeFilter := []ast.Node{
(*ast.CallExpr)(nil),
}
inspect.WithStack(nodeFilter, func(n ast.Node, push bool, stack []ast.Node) bool {
if !push {
return true
}
call := n.(*ast.CallExpr)
if !isHTTPFuncOrMethodOnClient(pass.TypesInfo, call) {
return true // the function call is not related to this check.
}
// Find the innermost containing block, and get the list
// of statements starting with the one containing call.
stmts, ncalls := restOfBlock(stack)
if len(stmts) < 2 {
// The call to the http function is the last statement of the block.
return true
}
// Skip cases in which the call is wrapped by another (#52661).
// Example: resp, err := checkError(http.Get(url))
if ncalls > 1 {
return true
}
asg, ok := stmts[0].(*ast.AssignStmt)
if !ok {
return true // the first statement is not assignment.
}
resp := rootIdent(asg.Lhs[0])
if resp == nil {
return true // could not find the http.Response in the assignment.
}
def, ok := stmts[1].(*ast.DeferStmt)
if !ok {
return true // the following statement is not a defer.
}
root := rootIdent(def.Call.Fun)
if root == nil {
return true // could not find the receiver of the defer call.
}
if resp.Obj == root.Obj {
pass.ReportRangef(root, "using %s before checking for errors", resp.Name)
}
return true
})
return nil, nil
}
// isHTTPFuncOrMethodOnClient checks whether the given call expression is on
// either a function of the net/http package or a method of http.Client that
// returns (*http.Response, error).
func isHTTPFuncOrMethodOnClient(info *types.Info, expr *ast.CallExpr) bool {
fun, _ := expr.Fun.(*ast.SelectorExpr)
sig, _ := info.Types[fun].Type.(*types.Signature)
if sig == nil {
return false // the call is not of the form x.f()
}
res := sig.Results()
if res.Len() != 2 {
return false // the function called does not return two values.
}
if ptr, ok := res.At(0).Type().(*types.Pointer); !ok || !isNamedType(ptr.Elem(), "net/http", "Response") {
return false // the first return type is not *http.Response.
}
errorType := types.Universe.Lookup("error").Type()
if !types.Identical(res.At(1).Type(), errorType) {
return false // the second return type is not error
}
typ := info.Types[fun.X].Type
if typ == nil {
id, ok := fun.X.(*ast.Ident)
return ok && id.Name == "http" // function in net/http package.
}
if isNamedType(typ, "net/http", "Client") {
return true // method on http.Client.
}
ptr, ok := typ.(*types.Pointer)
return ok && isNamedType(ptr.Elem(), "net/http", "Client") // method on *http.Client.
}
// restOfBlock, given a traversal stack, finds the innermost containing
// block and returns the suffix of its statements starting with the current
// node, along with the number of call expressions encountered.
func restOfBlock(stack []ast.Node) ([]ast.Stmt, int) {
var ncalls int
for i := len(stack) - 1; i >= 0; i-- {
if b, ok := stack[i].(*ast.BlockStmt); ok {
for j, v := range b.List {
if v == stack[i+1] {
return b.List[j:], ncalls
}
}
break
}
if _, ok := stack[i].(*ast.CallExpr); ok {
ncalls++
}
}
return nil, 0
}
// rootIdent finds the root identifier x in a chain of selections x.y.z, or nil if not found.
func rootIdent(n ast.Node) *ast.Ident {
switch n := n.(type) {
case *ast.SelectorExpr:
return rootIdent(n.X)
case *ast.Ident:
return n
default:
return nil
}
}
// isNamedType reports whether t is the named type path.name.
func isNamedType(t types.Type, path, name string) bool {
n, ok := t.(*types.Named)
if !ok {
return false
}
obj := n.Obj()
return obj.Name() == name && obj.Pkg() != nil && obj.Pkg().Path() == path
}
|
