| 1 | // Copyright 2016 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // Package httpresponse defines an Analyzer that checks for mistakes |
| 6 | // using HTTP responses. |
| 7 | package httpresponse |
| 8 | |
| 9 | import ( |
| 10 | "go/ast" |
| 11 | "go/types" |
| 12 | |
| 13 | "golang.org/x/tools/go/analysis" |
| 14 | "golang.org/x/tools/go/analysis/passes/inspect" |
| 15 | "golang.org/x/tools/go/analysis/passes/internal/analysisutil" |
| 16 | "golang.org/x/tools/go/ast/inspector" |
| 17 | ) |
| 18 | |
| 19 | const Doc = `check for mistakes using HTTP responses |
| 20 | |
| 21 | A common mistake when using the net/http package is to defer a function |
| 22 | call to close the http.Response Body before checking the error that |
| 23 | determines whether the response is valid: |
| 24 | |
| 25 | resp, err := http.Head(url) |
| 26 | defer resp.Body.Close() |
| 27 | if err != nil { |
| 28 | log.Fatal(err) |
| 29 | } |
| 30 | // (defer statement belongs here) |
| 31 | |
| 32 | This checker helps uncover latent nil dereference bugs by reporting a |
| 33 | diagnostic for such mistakes.` |
| 34 | |
| 35 | var Analyzer = &analysis.Analyzer{ |
| 36 | Name: "httpresponse", |
| 37 | Doc: Doc, |
| 38 | Requires: []*analysis.Analyzer{inspect.Analyzer}, |
| 39 | Run: run, |
| 40 | } |
| 41 | |
| 42 | func run(pass *analysis.Pass) (interface{}, error) { |
| 43 | inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector) |
| 44 | |
| 45 | // Fast path: if the package doesn't import net/http, |
| 46 | // skip the traversal. |
| 47 | if !analysisutil.Imports(pass.Pkg, "net/http") { |
| 48 | return nil, nil |
| 49 | } |
| 50 | |
| 51 | nodeFilter := []ast.Node{ |
| 52 | (*ast.CallExpr)(nil), |
| 53 | } |
| 54 | inspect.WithStack(nodeFilter, func(n ast.Node, push bool, stack []ast.Node) bool { |
| 55 | if !push { |
| 56 | return true |
| 57 | } |
| 58 | call := n.(*ast.CallExpr) |
| 59 | if !isHTTPFuncOrMethodOnClient(pass.TypesInfo, call) { |
| 60 | return true // the function call is not related to this check. |
| 61 | } |
| 62 | |
| 63 | // Find the innermost containing block, and get the list |
| 64 | // of statements starting with the one containing call. |
| 65 | stmts, ncalls := restOfBlock(stack) |
| 66 | if len(stmts) < 2 { |
| 67 | // The call to the http function is the last statement of the block. |
| 68 | return true |
| 69 | } |
| 70 | |
| 71 | // Skip cases in which the call is wrapped by another (#52661). |
| 72 | // Example: resp, err := checkError(http.Get(url)) |
| 73 | if ncalls > 1 { |
| 74 | return true |
| 75 | } |
| 76 | |
| 77 | asg, ok := stmts[0].(*ast.AssignStmt) |
| 78 | if !ok { |
| 79 | return true // the first statement is not assignment. |
| 80 | } |
| 81 | |
| 82 | resp := rootIdent(asg.Lhs[0]) |
| 83 | if resp == nil { |
| 84 | return true // could not find the http.Response in the assignment. |
| 85 | } |
| 86 | |
| 87 | def, ok := stmts[1].(*ast.DeferStmt) |
| 88 | if !ok { |
| 89 | return true // the following statement is not a defer. |
| 90 | } |
| 91 | root := rootIdent(def.Call.Fun) |
| 92 | if root == nil { |
| 93 | return true // could not find the receiver of the defer call. |
| 94 | } |
| 95 | |
| 96 | if resp.Obj == root.Obj { |
| 97 | pass.ReportRangef(root, "using %s before checking for errors", resp.Name) |
| 98 | } |
| 99 | return true |
| 100 | }) |
| 101 | return nil, nil |
| 102 | } |
| 103 | |
| 104 | // isHTTPFuncOrMethodOnClient checks whether the given call expression is on |
| 105 | // either a function of the net/http package or a method of http.Client that |
| 106 | // returns (*http.Response, error). |
| 107 | func isHTTPFuncOrMethodOnClient(info *types.Info, expr *ast.CallExpr) bool { |
| 108 | fun, _ := expr.Fun.(*ast.SelectorExpr) |
| 109 | sig, _ := info.Types[fun].Type.(*types.Signature) |
| 110 | if sig == nil { |
| 111 | return false // the call is not of the form x.f() |
| 112 | } |
| 113 | |
| 114 | res := sig.Results() |
| 115 | if res.Len() != 2 { |
| 116 | return false // the function called does not return two values. |
| 117 | } |
| 118 | if ptr, ok := res.At(0).Type().(*types.Pointer); !ok || !isNamedType(ptr.Elem(), "net/http", "Response") { |
| 119 | return false // the first return type is not *http.Response. |
| 120 | } |
| 121 | |
| 122 | errorType := types.Universe.Lookup("error").Type() |
| 123 | if !types.Identical(res.At(1).Type(), errorType) { |
| 124 | return false // the second return type is not error |
| 125 | } |
| 126 | |
| 127 | typ := info.Types[fun.X].Type |
| 128 | if typ == nil { |
| 129 | id, ok := fun.X.(*ast.Ident) |
| 130 | return ok && id.Name == "http" // function in net/http package. |
| 131 | } |
| 132 | |
| 133 | if isNamedType(typ, "net/http", "Client") { |
| 134 | return true // method on http.Client. |
| 135 | } |
| 136 | ptr, ok := typ.(*types.Pointer) |
| 137 | return ok && isNamedType(ptr.Elem(), "net/http", "Client") // method on *http.Client. |
| 138 | } |
| 139 | |
| 140 | // restOfBlock, given a traversal stack, finds the innermost containing |
| 141 | // block and returns the suffix of its statements starting with the current |
| 142 | // node, along with the number of call expressions encountered. |
| 143 | func restOfBlock(stack []ast.Node) ([]ast.Stmt, int) { |
| 144 | var ncalls int |
| 145 | for i := len(stack) - 1; i >= 0; i-- { |
| 146 | if b, ok := stack[i].(*ast.BlockStmt); ok { |
| 147 | for j, v := range b.List { |
| 148 | if v == stack[i+1] { |
| 149 | return b.List[j:], ncalls |
| 150 | } |
| 151 | } |
| 152 | break |
| 153 | } |
| 154 | |
| 155 | if _, ok := stack[i].(*ast.CallExpr); ok { |
| 156 | ncalls++ |
| 157 | } |
| 158 | } |
| 159 | return nil, 0 |
| 160 | } |
| 161 | |
| 162 | // rootIdent finds the root identifier x in a chain of selections x.y.z, or nil if not found. |
| 163 | func rootIdent(n ast.Node) *ast.Ident { |
| 164 | switch n := n.(type) { |
| 165 | case *ast.SelectorExpr: |
| 166 | return rootIdent(n.X) |
| 167 | case *ast.Ident: |
| 168 | return n |
| 169 | default: |
| 170 | return nil |
| 171 | } |
| 172 | } |
| 173 | |
| 174 | // isNamedType reports whether t is the named type path.name. |
| 175 | func isNamedType(t types.Type, path, name string) bool { |
| 176 | n, ok := t.(*types.Named) |
| 177 | if !ok { |
| 178 | return false |
| 179 | } |
| 180 | obj := n.Obj() |
| 181 | return obj.Name() == name && obj.Pkg() != nil && obj.Pkg().Path() == path |
| 182 | } |
| 183 |
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