httpresponse.go

Documentation: golang.org/x/tools/go/analysis/passes/httpresponse

     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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