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interp: improve handling of composed interfaces wrappers
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This change implements a workaround to better support composed
interfaces in yaegi and let the interpreter to define objects which
impletment multiple interfaces at once.

We use the existing MapTypes to store what possible composed interfaces
wrapper could be used for some interfaces. When generating an interface
wrapper, the wrapper with the highest number of implemented methods is
chosen.

This is still an imperfect solution but it improves the accuracy of
interpreter in some critical cases.

This workaround could be removed in future if/when golang/go#15924
is resolved.

Fixes traefik#1425.
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@mvertes
mvertes committed Aug 23, 2022
1 parent ab869c8 commit aa4f4a8
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44 changes: 44 additions & 0 deletions _test/issue-1425.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
package main

import (
"io"
"log"
"os"
"strings"
)

type WrappedReader struct {
reader io.Reader
}

func (wr WrappedReader) Read(p []byte) (n int, err error) {
return wr.reader.Read(p)
}

// Of course, this implementation is completely stupid because it does not write
// to the intended writer, as any honest WriteTo implementation should. its
// implemtion is just to make obvious the divergence of behaviour with yaegi.
func (wr WrappedReader) WriteTo(w io.Writer) (n int64, err error) {
// Ignore w, send to Stdout to prove whether this WriteTo is used.
data, err := io.ReadAll(wr)
if err != nil {
return 0, err
}
nn, err := os.Stdout.Write(data)
return int64(nn), err
}

func main() {
f := strings.NewReader("hello world")
wr := WrappedReader{reader: f}

// behind the scenes, io.Copy is supposed to use wr.WriteTo if the implementation exists.
// With Go, it works as expected, i.e. the output is sent to os.Stdout.
// With Yaegi, it doesn't, i.e. the output is sent to io.Discard.
if _, err := io.Copy(io.Discard, wr); err != nil {
log.Fatal(err)
}
}

// Output:
// hello world
221 changes: 0 additions & 221 deletions interp/interp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,16 +4,12 @@ import (
"bufio"
"context"
"errors"
"flag"
"fmt"
"go/build"
"go/constant"
"go/scanner"
"go/token"
"io"
"io/fs"
"log"
"math/bits"
"os"
"os/signal"
"path"
Expand Down Expand Up @@ -547,62 +543,6 @@ func (interp *Interpreter) EvalTest(path string) error {
return err
}

// Symbols returns a map of interpreter exported symbol values for the given
// import path. If the argument is the empty string, all known symbols are
// returned.
func (interp *Interpreter) Symbols(importPath string) Exports {
m := map[string]map[string]reflect.Value{}
interp.mutex.RLock()
defer interp.mutex.RUnlock()

for k, v := range interp.srcPkg {
if importPath != "" && k != importPath {
continue
}
syms := map[string]reflect.Value{}
for n, s := range v {
if !canExport(n) {
// Skip private non-exported symbols.
continue
}
switch s.kind {
case constSym:
syms[n] = s.rval
case funcSym:
syms[n] = genFunctionWrapper(s.node)(interp.frame)
case varSym:
syms[n] = interp.frame.data[s.index]
case typeSym:
syms[n] = reflect.New(s.typ.TypeOf())
}
}

if len(syms) > 0 {
m[k] = syms
}

if importPath != "" {
return m
}
}

if importPath != "" && len(m) > 0 {
return m
}

for k, v := range interp.binPkg {
if importPath != "" && k != importPath {
continue
}
m[k] = v
if importPath != "" {
return m
}
}

return m
}

func isFile(filesystem fs.FS, path string) bool {
fi, err := fs.Stat(filesystem, path)
return err == nil && fi.Mode().IsRegular()
Expand Down Expand Up @@ -664,167 +604,6 @@ func (interp *Interpreter) stop() {

func (interp *Interpreter) runid() uint64 { return atomic.LoadUint64(&interp.id) }

// getWrapper returns the wrapper type of the corresponding interface, or nil if not found.
func (interp *Interpreter) getWrapper(t reflect.Type) reflect.Type {
if p, ok := interp.binPkg[t.PkgPath()]; ok {
return p["_"+t.Name()].Type().Elem()
}
return nil
}

// Use loads binary runtime symbols in the interpreter context so
// they can be used in interpreted code.
func (interp *Interpreter) Use(values Exports) error {
for k, v := range values {
importPath := path.Dir(k)
packageName := path.Base(k)

if k == "." && v["MapTypes"].IsValid() {
// Use mapping for special interface wrappers.
for kk, vv := range v["MapTypes"].Interface().(map[reflect.Value][]reflect.Type) {
interp.mapTypes[kk] = vv
}
continue
}

if importPath == "." {
return fmt.Errorf("export path %[1]q is missing a package name; did you mean '%[1]s/%[1]s'?", k)
}

if importPath == selfPrefix {
interp.hooks.Parse(v)
continue
}

if interp.binPkg[importPath] == nil {
interp.binPkg[importPath] = make(map[string]reflect.Value)
interp.pkgNames[importPath] = packageName
}

for s, sym := range v {
interp.binPkg[importPath][s] = sym
}
if k == selfPath {
interp.binPkg[importPath]["Self"] = reflect.ValueOf(interp)
}
}

// Checks if input values correspond to stdlib packages by looking for one
// well known stdlib package path.
if _, ok := values["fmt/fmt"]; ok {
fixStdlib(interp)
}
return nil
}

// fixStdlib redefines interpreter stdlib symbols to use the standard input,
// output and errror assigned to the interpreter. The changes are limited to
// the interpreter only.
// Note that it is possible to escape the virtualized stdio by
// read/write directly to file descriptors 0, 1, 2.
func fixStdlib(interp *Interpreter) {
p := interp.binPkg["fmt"]
if p == nil {
return
}

stdin, stdout, stderr := interp.stdin, interp.stdout, interp.stderr

p["Print"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fprint(stdout, a...) })
p["Printf"] = reflect.ValueOf(func(f string, a ...interface{}) (n int, err error) { return fmt.Fprintf(stdout, f, a...) })
p["Println"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fprintln(stdout, a...) })

p["Scan"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fscan(stdin, a...) })
p["Scanf"] = reflect.ValueOf(func(f string, a ...interface{}) (n int, err error) { return fmt.Fscanf(stdin, f, a...) })
p["Scanln"] = reflect.ValueOf(func(a ...interface{}) (n int, err error) { return fmt.Fscanln(stdin, a...) })

// Update mapTypes to virtualized symbols as well.
interp.mapTypes[p["Print"]] = interp.mapTypes[reflect.ValueOf(fmt.Print)]
interp.mapTypes[p["Printf"]] = interp.mapTypes[reflect.ValueOf(fmt.Printf)]
interp.mapTypes[p["Println"]] = interp.mapTypes[reflect.ValueOf(fmt.Println)]
interp.mapTypes[p["Scan"]] = interp.mapTypes[reflect.ValueOf(fmt.Scan)]
interp.mapTypes[p["Scanf"]] = interp.mapTypes[reflect.ValueOf(fmt.Scanf)]
interp.mapTypes[p["Scanln"]] = interp.mapTypes[reflect.ValueOf(fmt.Scanln)]

if p = interp.binPkg["flag"]; p != nil {
c := flag.NewFlagSet(os.Args[0], flag.PanicOnError)
c.SetOutput(stderr)
p["CommandLine"] = reflect.ValueOf(&c).Elem()
}

if p = interp.binPkg["log"]; p != nil {
l := log.New(stderr, "", log.LstdFlags)
// Restrict Fatal symbols to panic instead of exit.
p["Fatal"] = reflect.ValueOf(l.Panic)
p["Fatalf"] = reflect.ValueOf(l.Panicf)
p["Fatalln"] = reflect.ValueOf(l.Panicln)

p["Flags"] = reflect.ValueOf(l.Flags)
p["Output"] = reflect.ValueOf(l.Output)
p["Panic"] = reflect.ValueOf(l.Panic)
p["Panicf"] = reflect.ValueOf(l.Panicf)
p["Panicln"] = reflect.ValueOf(l.Panicln)
p["Prefix"] = reflect.ValueOf(l.Prefix)
p["Print"] = reflect.ValueOf(l.Print)
p["Printf"] = reflect.ValueOf(l.Printf)
p["Println"] = reflect.ValueOf(l.Println)
p["SetFlags"] = reflect.ValueOf(l.SetFlags)
p["SetOutput"] = reflect.ValueOf(l.SetOutput)
p["SetPrefix"] = reflect.ValueOf(l.SetPrefix)
p["Writer"] = reflect.ValueOf(l.Writer)

// Update mapTypes to virtualized symbols as well.
interp.mapTypes[p["Print"]] = interp.mapTypes[reflect.ValueOf(log.Print)]
interp.mapTypes[p["Printf"]] = interp.mapTypes[reflect.ValueOf(log.Printf)]
interp.mapTypes[p["Println"]] = interp.mapTypes[reflect.ValueOf(log.Println)]
interp.mapTypes[p["Panic"]] = interp.mapTypes[reflect.ValueOf(log.Panic)]
interp.mapTypes[p["Panicf"]] = interp.mapTypes[reflect.ValueOf(log.Panicf)]
interp.mapTypes[p["Panicln"]] = interp.mapTypes[reflect.ValueOf(log.Panicln)]
}

if p = interp.binPkg["os"]; p != nil {
p["Args"] = reflect.ValueOf(&interp.args).Elem()
if interp.specialStdio {
// Inherit streams from interpreter even if they do not have a file descriptor.
p["Stdin"] = reflect.ValueOf(&stdin).Elem()
p["Stdout"] = reflect.ValueOf(&stdout).Elem()
p["Stderr"] = reflect.ValueOf(&stderr).Elem()
} else {
// Inherits streams from interpreter only if they have a file descriptor and preserve original type.
if s, ok := stdin.(*os.File); ok {
p["Stdin"] = reflect.ValueOf(&s).Elem()
}
if s, ok := stdout.(*os.File); ok {
p["Stdout"] = reflect.ValueOf(&s).Elem()
}
if s, ok := stderr.(*os.File); ok {
p["Stderr"] = reflect.ValueOf(&s).Elem()
}
}
if !interp.unrestricted {
// In restricted mode, scripts can only access to a passed virtualized env, and can not write the real one.
getenv := func(key string) string { return interp.env[key] }
p["Clearenv"] = reflect.ValueOf(func() { interp.env = map[string]string{} })
p["ExpandEnv"] = reflect.ValueOf(func(s string) string { return os.Expand(s, getenv) })
p["Getenv"] = reflect.ValueOf(getenv)
p["LookupEnv"] = reflect.ValueOf(func(key string) (s string, ok bool) { s, ok = interp.env[key]; return })
p["Setenv"] = reflect.ValueOf(func(key, value string) error { interp.env[key] = value; return nil })
p["Unsetenv"] = reflect.ValueOf(func(key string) error { delete(interp.env, key); return nil })
p["Environ"] = reflect.ValueOf(func() (a []string) {
for k, v := range interp.env {
a = append(a, k+"="+v)
}
return
})
}
}

if p = interp.binPkg["math/bits"]; p != nil {
// Do not trust extracted value maybe from another arch.
p["UintSize"] = reflect.ValueOf(constant.MakeInt64(bits.UintSize))
}
}

// ignoreScannerError returns true if the error from Go scanner can be safely ignored
// to let the caller grab one more line before retrying to parse its input.
func ignoreScannerError(e *scanner.Error, s string) bool {
Expand Down
10 changes: 7 additions & 3 deletions interp/run.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1050,19 +1050,23 @@ func genInterfaceWrapper(n *node, typ reflect.Type) func(*frame) reflect.Value {
return value
}
}
mn := typ.NumMethod()

// Retrieve methods from the interface wrapper, which is a struct where all fields
// except the first define the methods to implement.
// The first character of the field name must always be ignored.
wrap := getWrapper(n, typ)
mn := wrap.NumField() - 1
names := make([]string, mn)
methods := make([]*node, mn)
indexes := make([][]int, mn)
for i := 0; i < mn; i++ {
names[i] = typ.Method(i).Name
names[i] = wrap.Field(i + 1).Name[1:]
methods[i], indexes[i] = n.typ.lookupMethod(names[i])
if methods[i] == nil && n.typ.cat != nilT {
// interpreted method not found, look for binary method, possibly embedded
_, indexes[i], _, _ = n.typ.lookupBinMethod(names[i])
}
}
wrap := n.interp.getWrapper(typ)

return func(f *frame) reflect.Value {
v := value(f)
Expand Down
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