Split layerCache into separate file

This makes things a little cleaner by having a single place that calls
buildLayer and passing a thunk down into the cache logic to call that on
a cache miss.

Also, remove the debug logging to make the code easier to follow (if you
need to recompile anyway, it's easy enough to add log lines).

pkg/build/cache.go

@@ -0,0 +1,212 @@
+/*
+Copyright 2021 Google LLC All Rights Reserved.
+
+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 build
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+)
+
+type diffIDToDescriptor map[v1.Hash]v1.Descriptor
+type buildIDToDiffID map[string]v1.Hash
+
+type layerCache struct {
+	buildToDiff map[string]buildIDToDiffID
+	diffToDesc  map[string]diffIDToDescriptor
+	sync.Mutex
+}
+
+type layerFactory func() (v1.Layer, error)
+
+func (c *layerCache) get(ctx context.Context, file string, platform *v1.Platform, miss layerFactory) (v1.Layer, error) {
+	if os.Getenv("KOCACHE") == "" {
+		return miss()
+	}
+
+	// Cache hit.
+	if diffid, desc, err := c.getMeta(ctx, file); err == nil {
+		return &lazyLayer{
+			diffid:     *diffid,
+			desc:       *desc,
+			buildLayer: miss,
+		}, nil
+	}
+
+	// Cache miss.
+	layer, err := miss()
+	if err != nil {
+		return nil, err
+	}
+	if err := c.put(ctx, file, layer); err != nil {
+		log.Printf("failed to cache metadata %s: %v", file, err)
+	}
+	return layer, nil
+}
+
+func (c *layerCache) getMeta(ctx context.Context, file string) (*v1.Hash, *v1.Descriptor, error) {
+	buildid, err := getBuildID(ctx, file)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if buildid == "" {
+		return nil, nil, fmt.Errorf("no buildid for %s", file)
+	}
+
+	btod, err := c.readBuildToDiff(file)
+	if err != nil {
+		return nil, nil, err
+	}
+	dtod, err := c.readDiffToDesc(file)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	diffid, ok := btod[buildid]
+	if !ok {
+		return nil, nil, fmt.Errorf("no diffid for %q", buildid)
+	}
+
+	desc, ok := dtod[diffid]
+	if !ok {
+		return nil, nil, fmt.Errorf("no desc for %q", diffid)
+	}
+
+	return &diffid, &desc, nil
+}
+
+// Compute new layer metadata and cache it in-mem and on-disk.
+func (c *layerCache) put(ctx context.Context, file string, layer v1.Layer) error {
+	buildid, err := getBuildID(ctx, file)
+	if err != nil {
+		return err
+	}
+
+	desc, err := partial.Descriptor(layer)
+	if err != nil {
+		return err
+	}
+
+	diffid, err := layer.DiffID()
+	if err != nil {
+		return err
+	}
+
+	btod, ok := c.buildToDiff[file]
+	if !ok {
+		btod = buildIDToDiffID{}
+	}
+	btod[buildid] = diffid
+
+	dtod, ok := c.diffToDesc[file]
+	if !ok {
+		dtod = diffIDToDescriptor{}
+	}
+	dtod[diffid] = *desc
+
+	// TODO: Implement better per-file locking.
+	c.Lock()
+	defer c.Unlock()
+
+	btodf, err := os.OpenFile(filepath.Join(filepath.Dir(file), "buildid-to-diffid"), os.O_RDWR|os.O_CREATE, 0755)
+	if err != nil {
+		return err
+	}
+	defer btodf.Close()
+
+	dtodf, err := os.OpenFile(filepath.Join(filepath.Dir(file), "diffid-to-descriptor"), os.O_RDWR|os.O_CREATE, 0755)
+	if err != nil {
+		return err
+	}
+	defer dtodf.Close()
+
+	enc := json.NewEncoder(btodf)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(&btod); err != nil {
+		return err
+	}
+
+	enc = json.NewEncoder(dtodf)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(&dtod); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c *layerCache) readDiffToDesc(file string) (diffIDToDescriptor, error) {
+	if dtod, ok := c.diffToDesc[file]; ok {
+		return dtod, nil
+	}
+
+	dtodf, err := os.Open(filepath.Join(filepath.Dir(file), "diffid-to-descriptor"))
+	if err != nil {
+		return nil, err
+	}
+	defer dtodf.Close()
+
+	var dtod diffIDToDescriptor
+	if err := json.NewDecoder(dtodf).Decode(&dtod); err != nil {
+		return nil, err
+	}
+	c.diffToDesc[file] = dtod
+	return dtod, nil
+}
+
+func (c *layerCache) readBuildToDiff(file string) (buildIDToDiffID, error) {
+	if btod, ok := c.buildToDiff[file]; ok {
+		return btod, nil
+	}
+
+	btodf, err := os.Open(filepath.Join(filepath.Dir(file), "buildid-to-diffid"))
+	if err != nil {
+		return nil, err
+	}
+	defer btodf.Close()
+
+	var btod buildIDToDiffID
+	if err := json.NewDecoder(btodf).Decode(&btod); err != nil {
+		return nil, err
+	}
+	c.buildToDiff[file] = btod
+	return btod, nil
+}
+
+func getBuildID(ctx context.Context, file string) (string, error) {
+	cmd := exec.CommandContext(ctx, "go", "tool", "buildid", file)
+	var output bytes.Buffer
+	cmd.Stderr = &output
+	cmd.Stdout = &output
+
+	if err := cmd.Run(); err != nil {
+		log.Printf("Unexpected error running \"go tool buildid %s\": %v\n%v", err, file, output.String())
+		return "", err
+	}
+	return strings.TrimSpace(output.String()), nil
+}