--- /dev/null
+// 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 := restOfBlock(stack)
+ if len(stmts) < 2 {
+ return true // the call to the http function is the last statement of the block.
+ }
+
+ 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 (the last element of stack).
+func restOfBlock(stack []ast.Node) []ast.Stmt {
+ 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:]
+ }
+ }
+ break
+ }
+ }
+ return nil
+}
+
+// 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
+}
projects / dotfiles / .git / blobdiff