Support for saving pointers to fields in the state package.

Previously, it was not possible to encode/decode an object graph which
contained a pointer to a field within another type. This was because the
encoder was previously unable to disambiguate a pointer to an object and a
pointer within the object.

This CL remedies this by constructing an address map tracking the full memory
range object occupy. The encoded Refvalue message has been extended to allow
references to children objects within another object. Because the encoding
process may learn about object structure over time, we cannot encode any
objects under the entire graph has been generated.

This CL also updates the state package to use standard interfaces intead of
reflection-based dispatch in order to improve performance overall. This
includes a custom wire protocol to significantly reduce the number of
allocations and take advantage of structure packing.

As part of these changes, there are a small number of minor changes in other
places of the code base:

* The lists used during encoding are changed to use intrusive lists with the
  objectEncodeState directly, which required that the ilist Len() method is
  updated to work properly with the ElementMapper mechanism.

* A bug is fixed in the list code wherein Remove() called on an element that is
  already removed can corrupt the list (removing the element if there's only a
  single element). Now the behavior is correct.

* Standard error wrapping is introduced.

* Compressio was updated to implement the new wire.Reader and wire.Writer
  inteface methods directly. The lack of a ReadByte and WriteByte caused issues
  not due to interface dispatch, but because underlying slices for a Read or
  Write call through an interface would always escape to the heap!

* Statify has been updated to support the new APIs.

See README.md for a description of how the new mechanism works.

PiperOrigin-RevId: 318010298

1 files changed, 215 insertions, 0 deletions

diff --git a/pkg/state/tests/tests.go b/pkg/state/tests/tests.go
new file mode 100644
index 000000000..435a0e9db
--- /dev/null
+++ b/pkg/state/tests/tests.go
@@ -0,0 +1,215 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package tests tests the state packages.
+package tests
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"math"
+	"reflect"
+	"testing"
+
+	"gvisor.dev/gvisor/pkg/state"
+	"gvisor.dev/gvisor/pkg/state/pretty"
+)
+
+// discard is an implementation of wire.Writer.
+type discard struct{}
+
+// Write implements wire.Writer.Write.
+func (discard) Write(p []byte) (int, error) { return len(p), nil }
+
+// WriteByte implements wire.Writer.WriteByte.
+func (discard) WriteByte(byte) error { return nil }
+
+// checkEqual checks if two objects are equal.
+//
+// N.B. This only handles one level of dereferences for NaN. Otherwise we
+// would need to fork the entire implementation of reflect.DeepEqual.
+func checkEqual(root, loadedValue interface{}) bool {
+	if reflect.DeepEqual(root, loadedValue) {
+		return true
+	}
+
+	// NaN is not equal to itself. We handle the case of raw floating point
+	// primitives here, but don't handle this case nested.
+	rf32, ok1 := root.(float32)
+	lf32, ok2 := loadedValue.(float32)
+	if ok1 && ok2 && math.IsNaN(float64(rf32)) && math.IsNaN(float64(lf32)) {
+		return true
+	}
+	rf64, ok1 := root.(float64)
+	lf64, ok2 := loadedValue.(float64)
+	if ok1 && ok2 && math.IsNaN(rf64) && math.IsNaN(lf64) {
+		return true
+	}
+
+	// Same real for complex numbers.
+	rc64, ok1 := root.(complex64)
+	lc64, ok2 := root.(complex64)
+	if ok1 && ok2 {
+		return checkEqual(real(rc64), real(lc64)) && checkEqual(imag(rc64), imag(lc64))
+	}
+	rc128, ok1 := root.(complex128)
+	lc128, ok2 := root.(complex128)
+	if ok1 && ok2 {
+		return checkEqual(real(rc128), real(lc128)) && checkEqual(imag(rc128), imag(lc128))
+	}
+
+	return false
+}
+
+// runTestCases runs a test for each object in objects.
+func runTestCases(t *testing.T, shouldFail bool, prefix string, objects []interface{}) {
+	t.Helper()
+	for i, root := range objects {
+		t.Run(fmt.Sprintf("%s%d", prefix, i), func(t *testing.T) {
+			t.Logf("Original object:\n%#v", root)
+
+			// Save the passed object.
+			saveBuffer := &bytes.Buffer{}
+			saveObjectPtr := reflect.New(reflect.TypeOf(root))
+			saveObjectPtr.Elem().Set(reflect.ValueOf(root))
+			saveStats, err := state.Save(context.Background(), saveBuffer, saveObjectPtr.Interface())
+			if err != nil {
+				if shouldFail {
+					return
+				}
+				t.Fatalf("Save failed unexpectedly: %v", err)
+			}
+
+			// Dump the serialized proto to aid with debugging.
+			var ppBuf bytes.Buffer
+			t.Logf("Raw state:\n%v", saveBuffer.Bytes())
+			if err := pretty.PrintText(&ppBuf, bytes.NewReader(saveBuffer.Bytes())); err != nil {
+				// We don't count this as a test failure if we
+				// have shouldFail set, but we will count as a
+				// failure if we were not expecting to fail.
+				if !shouldFail {
+					t.Errorf("PrettyPrint(html=false) failed unexpected: %v", err)
+				}
+			}
+			if err := pretty.PrintHTML(discard{}, bytes.NewReader(saveBuffer.Bytes())); err != nil {
+				// See above.
+				if !shouldFail {
+					t.Errorf("PrettyPrint(html=true) failed unexpected: %v", err)
+				}
+			}
+			t.Logf("Encoded state:\n%s", ppBuf.String())
+			t.Logf("Save stats:\n%s", saveStats.String())
+
+			// Load a new copy of the object.
+			loadObjectPtr := reflect.New(reflect.TypeOf(root))
+			loadStats, err := state.Load(context.Background(), bytes.NewReader(saveBuffer.Bytes()), loadObjectPtr.Interface())
+			if err != nil {
+				if shouldFail {
+					return
+				}
+				t.Fatalf("Load failed unexpectedly: %v", err)
+			}
+
+			// Compare the values.
+			loadedValue := loadObjectPtr.Elem().Interface()
+			if !checkEqual(root, loadedValue) {
+				if shouldFail {
+					return
+				}
+				t.Fatalf("Objects differ:\n\toriginal: %#v\n\tloaded:   %#v\n", root, loadedValue)
+			}
+
+			// Everything went okay. Is that good?
+			if shouldFail {
+				t.Fatalf("This test was expected to fail, but didn't.")
+			}
+			t.Logf("Load stats:\n%s", loadStats.String())
+
+			// Truncate half the bytes in the byte stream,
+			// and ensure that we can't restore. Then
+			// truncate only the final byte and ensure that
+			// we can't restore.
+			l := saveBuffer.Len()
+			halfReader := bytes.NewReader(saveBuffer.Bytes()[:l/2])
+			if _, err := state.Load(context.Background(), halfReader, loadObjectPtr.Interface()); err == nil {
+				t.Errorf("Load with half bytes succeeded unexpectedly.")
+			}
+			missingByteReader := bytes.NewReader(saveBuffer.Bytes()[:l-1])
+			if _, err := state.Load(context.Background(), missingByteReader, loadObjectPtr.Interface()); err == nil {
+				t.Errorf("Load with missing byte succeeded unexpectedly.")
+			}
+		})
+	}
+}
+
+// convert converts the slice to an []interface{}.
+func convert(v interface{}) (r []interface{}) {
+	s := reflect.ValueOf(v) // Must be slice.
+	for i := 0; i < s.Len(); i++ {
+		r = append(r, s.Index(i).Interface())
+	}
+	return r
+}
+
+// flatten flattens multiple slices.
+func flatten(vs ...interface{}) (r []interface{}) {
+	for _, v := range vs {
+		r = append(r, convert(v)...)
+	}
+	return r
+}
+
+// filter maps from one slice to another.
+func filter(vs interface{}, fn func(interface{}) (interface{}, bool)) (r []interface{}) {
+	s := reflect.ValueOf(vs)
+	for i := 0; i < s.Len(); i++ {
+		v, ok := fn(s.Index(i).Interface())
+		if ok {
+			r = append(r, v)
+		}
+	}
+	return r
+}
+
+// combine combines objects in two slices as specified.
+func combine(v1, v2 interface{}, fn func(_, _ interface{}) interface{}) (r []interface{}) {
+	s1 := reflect.ValueOf(v1)
+	s2 := reflect.ValueOf(v2)
+	for i := 0; i < s1.Len(); i++ {
+		for j := 0; j < s2.Len(); j++ {
+			// Combine using the given function.
+			r = append(r, fn(s1.Index(i).Interface(), s2.Index(j).Interface()))
+		}
+	}
+	return r
+}
+
+// pointersTo is a filter function that returns pointers.
+func pointersTo(vs interface{}) []interface{} {
+	return filter(vs, func(o interface{}) (interface{}, bool) {
+		v := reflect.New(reflect.TypeOf(o))
+		v.Elem().Set(reflect.ValueOf(o))
+		return v.Interface(), true
+	})
+}
+
+// interfacesTo is a filter function that returns interface objects.
+func interfacesTo(vs interface{}) []interface{} {
+	return filter(vs, func(o interface{}) (interface{}, bool) {
+		var v [1]interface{}
+		v[0] = o
+		return v, true
+	})
+}