internal/fetch/fetch.go - pkgsite - Git at Google

 // Copyright 2019 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 fetch provides a way to fetch modules from a proxy.
 package fetch

 import (
 	"archive/zip"
 	"context"
 	"errors"
 	"fmt"
 	"net/http"
 	"path"
 	"sort"
 	"strconv"
 	"sync"
 	"time"

 	"go.opencensus.io/plugin/ochttp"
 	"go.opencensus.io/stats"
 	"go.opencensus.io/stats/view"
 	"go.opencensus.io/tag"
 	"go.opencensus.io/trace"
 	"golang.org/x/mod/modfile"
 	"golang.org/x/pkgsite/internal"
 	"golang.org/x/pkgsite/internal/dcensus"
 	"golang.org/x/pkgsite/internal/derrors"
 	"golang.org/x/pkgsite/internal/licenses"
 	"golang.org/x/pkgsite/internal/log"
 	"golang.org/x/pkgsite/internal/proxy"
 	"golang.org/x/pkgsite/internal/source"
 	"golang.org/x/pkgsite/internal/stdlib"
 )

 var (
 	errModuleContainsNoPackages = errors.New("module contains 0 packages")
 	errMalformedZip             = errors.New("module zip is malformed")
 )

 var (
 	fetchLatency = stats.Float64(
 		"go-discovery/worker/fetch-latency",
 		"Latency of a fetch request.",
 		stats.UnitSeconds,
 	)
 	fetchesShedded = stats.Int64(
 		"go-discovery/worker/fetch-shedded",
 		"Count of shedded fetches.",
 		stats.UnitDimensionless,
 	)
 	fetchedPackages = stats.Int64(
 		"go-discovery/worker/fetch-package-count",
 		"Count of successfully fetched packages.",
 		stats.UnitDimensionless,
 	)

 	// FetchLatencyDistribution aggregates frontend fetch request
 	// latency by status code. It does not count shedded requests.
 	FetchLatencyDistribution = &view.View{
 		Name:        "go-discovery/worker/fetch-latency",
 		Measure:     fetchLatency,
 		Aggregation: ochttp.DefaultLatencyDistribution,
 		Description: "Fetch latency by result status.",
 		TagKeys:     []tag.Key{dcensus.KeyStatus},
 	}
 	// FetchResponseCount counts fetch responses by status.
 	FetchResponseCount = &view.View{
 		Name:        "go-discovery/worker/fetch-count",
 		Measure:     fetchLatency,
 		Aggregation: view.Count(),
 		Description: "Fetch request count by result status",
 		TagKeys:     []tag.Key{dcensus.KeyStatus},
 	}
 	// FetchPackageCount counts how many packages were successfully fetched.
 	FetchPackageCount = &view.View{
 		Name:        "go-discovery/worker/fetch-package-count",
 		Measure:     fetchedPackages,
 		Aggregation: view.Count(),
 		Description: "Count of packages successfully fetched",
 	}
 	// SheddedFetchCount counts the number of fetches that were shedded.
 	SheddedFetchCount = &view.View{
 		Name:        "go-discovery/worker/fetch-shedded",
 		Measure:     fetchesShedded,
 		Aggregation: view.Count(),
 		Description: "Count of shedded fetches",
 	}
 )

 type FetchResult struct {
 	ModulePath           string
 	RequestedVersion     string
 	ResolvedVersion      string
 	GoModPath            string
 	Status               int
 	Error                error
 	Defer                func() // caller must defer this on all code paths
 	Module               *internal.Module
 	PackageVersionStates []*internal.PackageVersionState
 }

 // FetchModule queries the proxy or the Go repo for the requested module
 // version, downloads the module zip, and processes the contents to return an
 // *internal.Module and related information.
 //
 // Even if err is non-nil, the result may contain useful information, like the go.mod path.
 //
 // Callers of FetchModule must
 //   defer fr.Defer()
 // immediately after the call.
 func FetchModule(ctx context.Context, modulePath, requestedVersion string, proxyClient *proxy.Client, sourceClient *source.Client) (fr *FetchResult) {
 	start := time.Now()
 	fr = &FetchResult{
 		ModulePath:       modulePath,
 		RequestedVersion: requestedVersion,
 		Defer:            func() {},
 	}
 	var fi *FetchInfo
 	defer func() {
 		if fr.Error != nil {
 			derrors.Wrap(&fr.Error, "FetchModule(%q, %q)", modulePath, requestedVersion)
 			fr.Status = derrors.ToStatus(fr.Error)
 		}
 		if fr.Status == 0 {
 			fr.Status = http.StatusOK
 		}
 		latency := float64(time.Since(start).Seconds())
 		dcensus.RecordWithTag(ctx, dcensus.KeyStatus, strconv.Itoa(fr.Status), fetchLatency.M(latency))
 		if fr.Status < 300 {
 			stats.Record(ctx, fetchedPackages.M(int64(len(fr.PackageVersionStates))))
 		}
 		if fi != nil {
 			finishFetchInfo(fi, fr.Status, fr.Error)
 		}
 		log.Debugf(ctx, "memory after fetch of %s@%s: %dM", modulePath, requestedVersion, allocMeg())
 	}()

 	var (
 		commitTime time.Time
 		zipReader  *zip.Reader
 		zipSize    int64
 		err        error
 	)
 	// Get the just information we need to make a load-shedding decision.
 	if modulePath == stdlib.ModulePath {
 		var resolvedVersion string
 		resolvedVersion, zipSize, err = stdlib.ZipInfo(requestedVersion)
 		if err != nil {
 			fr.Error = err
 			return fr
 		}
 		fr.ResolvedVersion = resolvedVersion
 	} else {
 		info, err := proxyClient.GetInfo(ctx, modulePath, requestedVersion)
 		if err != nil {
 			fr.Error = err
 			return fr
 		}
 		fr.ResolvedVersion = info.Version
 		commitTime = info.Time
 		zipSize, err = proxyClient.GetZipSize(ctx, modulePath, fr.ResolvedVersion)
 		if err != nil {
 			fr.Error = err
 			return fr
 		}
 	}

 	// Load shed or mark module as too large.
 	// We treat zip size
 	// as a proxy for the total memory consumed by processing a module, and use
 	// it to decide whether we can currently afford to process a module.
 	shouldShed, deferFunc := zipLoadShedder.shouldShed(uint64(zipSize))
 	fr.Defer = deferFunc
 	if shouldShed {
 		fr.Error = fmt.Errorf("%w: size=%dMi", derrors.SheddingLoad, zipSize/mib)
 		stats.Record(ctx, fetchesShedded.M(1))
 		return fr
 	}

 	if zipSize > maxModuleZipSize {
 		log.Warningf(ctx, "FetchModule: %s@%s zip size %dMi exceeds max %dMi",
 			modulePath, fr.ResolvedVersion, zipSize/mib, maxModuleZipSize/mib)
 		fr.Error = derrors.ModuleTooLarge
 		return fr
 	}

 	// Proceed with the fetch.
 	fi = &FetchInfo{
 		ModulePath: modulePath,
 		Version:    fr.ResolvedVersion,
 		ZipSize:    uint64(zipSize),
 		Start:      time.Now(),
 	}
 	startFetchInfo(fi)

 	if modulePath == stdlib.ModulePath {
 		zipReader, commitTime, err = stdlib.Zip(requestedVersion)
 		if err != nil {
 			fr.Error = err
 			return fr
 		}
 		fr.GoModPath = stdlib.ModulePath
 	} else {
 		goModBytes, err := proxyClient.GetMod(ctx, modulePath, fr.ResolvedVersion)
 		if err != nil {
 			fr.Error = err
 			return fr
 		}
 		goModPath := modfile.ModulePath(goModBytes)
 		if goModPath == "" {
 			fr.Error = fmt.Errorf("go.mod has no module path: %w", derrors.BadModule)
 			return fr
 		}
 		fr.GoModPath = goModPath
 		if goModPath != modulePath {
 			// The module path in the go.mod file doesn't match the path of the
 			// zip file. Don't insert the module. Store an AlternativeModule
 			// status in module_version_states.
 			fr.Error = fmt.Errorf("module path=%s, go.mod path=%s: %w", modulePath, goModPath, derrors.AlternativeModule)
 			return fr
 		}
 		zipReader, err = proxyClient.GetZip(ctx, modulePath, fr.ResolvedVersion)
 		if err != nil {
 			fr.Error = err
 			return fr
 		}
 	}
 	mod, pvs, err := processZipFile(ctx, modulePath, fr.ResolvedVersion, commitTime, zipReader, sourceClient)
 	if err != nil {
 		fr.Error = err
 		return fr
 	}
 	fr.Module = mod
 	fr.PackageVersionStates = pvs
 	if modulePath == stdlib.ModulePath {
 		fr.Module.HasGoMod = true
 	}
 	for _, state := range fr.PackageVersionStates {
 		if state.Status != http.StatusOK {
 			fr.Status = derrors.ToStatus(derrors.HasIncompletePackages)
 		}
 	}
 	return fr
 }

 // processZipFile extracts information from the module version zip.
 func processZipFile(ctx context.Context, modulePath string, resolvedVersion string, commitTime time.Time, zipReader *zip.Reader, sourceClient *source.Client) (_ *internal.Module, _ []*internal.PackageVersionState, err error) {
 	defer derrors.Wrap(&err, "processZipFile(%q, %q)", modulePath, resolvedVersion)

 	ctx, span := trace.StartSpan(ctx, "fetch.processZipFile")
 	defer span.End()

 	sourceInfo, err := source.ModuleInfo(ctx, sourceClient, modulePath, resolvedVersion)
 	if err != nil {
 		log.Infof(ctx, "error getting source info: %v", err)
 	}
 	readmes, err := extractReadmesFromZip(modulePath, resolvedVersion, zipReader)
 	if err != nil {
 		return nil, nil, fmt.Errorf("extractReadmesFromZip(%q, %q, zipReader): %v", modulePath, resolvedVersion, err)
 	}
 	logf := func(format string, args ...interface{}) {
 		log.Infof(ctx, format, args...)
 	}
 	d := licenses.NewDetector(modulePath, resolvedVersion, zipReader, logf)
 	allLicenses := d.AllLicenses()
 	packages, packageVersionStates, err := extractPackagesFromZip(ctx, modulePath, resolvedVersion, zipReader, d, sourceInfo)
 	if errors.Is(err, errModuleContainsNoPackages) || errors.Is(err, errMalformedZip) {
 		return nil, nil, fmt.Errorf("%v: %w", err.Error(), derrors.BadModule)
 	}
 	if err != nil {
 		return nil, nil, fmt.Errorf("extractPackagesFromZip(%q, %q, zipReader, %v): %v", modulePath, resolvedVersion, allLicenses, err)
 	}
 	hasGoMod := zipContainsFilename(zipReader, path.Join(moduleVersionDir(modulePath, resolvedVersion), "go.mod"))

 	return &internal.Module{
 		ModuleInfo: internal.ModuleInfo{
 			ModulePath:        modulePath,
 			Version:           resolvedVersion,
 			CommitTime:        commitTime,
 			IsRedistributable: d.ModuleIsRedistributable(),
 			HasGoMod:          hasGoMod,
 			SourceInfo:        sourceInfo,
 		},
 		Licenses: allLicenses,
 		Units:    moduleUnits(modulePath, resolvedVersion, packages, readmes, d),
 	}, packageVersionStates, nil
 }

 // moduleVersionDir formats the content subdirectory for the given
 // modulePath and version.
 func moduleVersionDir(modulePath, version string) string {
 	return fmt.Sprintf("%s@%s", modulePath, version)
 }

 // zipContainsFilename reports whether there is a file with the given name in the zip.
 func zipContainsFilename(r *zip.Reader, name string) bool {
 	for _, f := range r.File {
 		if f.Name == name {
 			return true
 		}
 	}
 	return false
 }

 type FetchInfo struct {
 	ModulePath string
 	Version    string
 	ZipSize    uint64
 	Start      time.Time
 	Finish     time.Time
 	Status     int
 	Error      error
 }

 var (
 	fetchInfoMu  sync.Mutex
 	fetchInfoMap = map[*FetchInfo]struct{}{}
 )

 func init() {
 	const linger = time.Minute
 	go func() {
 		for {
 			now := time.Now()
 			fetchInfoMu.Lock()
 			for fi := range fetchInfoMap {
 				if !fi.Finish.IsZero() && now.Sub(fi.Finish) > linger {
 					delete(fetchInfoMap, fi)
 				}
 			}
 			fetchInfoMu.Unlock()
 			time.Sleep(linger)
 		}
 	}()
 }

 func startFetchInfo(fi *FetchInfo) {
 	fetchInfoMu.Lock()
 	defer fetchInfoMu.Unlock()
 	fetchInfoMap[fi] = struct{}{}
 }

 func finishFetchInfo(fi *FetchInfo, status int, err error) {
 	fetchInfoMu.Lock()
 	defer fetchInfoMu.Unlock()
 	fi.Finish = time.Now()
 	fi.Status = status
 	fi.Error = err
 }

 // FetchInfos returns information about all fetches in progress,
 // sorted by start time.
 func FetchInfos() []*FetchInfo {
 	var fis []*FetchInfo
 	fetchInfoMu.Lock()
 	for fi := range fetchInfoMap {
 		// Copy to avoid races on Status and Error when read by
 		// worker home page.
 		cfi := *fi
 		fis = append(fis, &cfi)
 	}
 	fetchInfoMu.Unlock()
 	// Order first by done-ness, then by age.
 	sort.Slice(fis, func(i, j int) bool {
 		if (fis[i].Status == 0) == (fis[j].Status == 0) {
 			return fis[i].Start.Before(fis[j].Start)
 		}
 		return fis[i].Status == 0
 	})
 	return fis
 }
	// Copyright 2019 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 fetch provides a way to fetch modules from a proxy.
	package fetch

	import (
	"archive/zip"
	"context"
	"errors"
	"fmt"
	"net/http"
	"path"
	"sort"
	"strconv"
	"sync"
	"time"

	"go.opencensus.io/plugin/ochttp"
	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
	"go.opencensus.io/tag"
	"go.opencensus.io/trace"
	"golang.org/x/mod/modfile"
	"golang.org/x/pkgsite/internal"
	"golang.org/x/pkgsite/internal/dcensus"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/licenses"
	"golang.org/x/pkgsite/internal/log"
	"golang.org/x/pkgsite/internal/proxy"
	"golang.org/x/pkgsite/internal/source"
	"golang.org/x/pkgsite/internal/stdlib"
	)

	var (
	errModuleContainsNoPackages = errors.New("module contains 0 packages")
	errMalformedZip = errors.New("module zip is malformed")
	)

	var (
	fetchLatency = stats.Float64(
	"go-discovery/worker/fetch-latency",
	"Latency of a fetch request.",
	stats.UnitSeconds,
	)
	fetchesShedded = stats.Int64(
	"go-discovery/worker/fetch-shedded",
	"Count of shedded fetches.",
	stats.UnitDimensionless,
	)
	fetchedPackages = stats.Int64(
	"go-discovery/worker/fetch-package-count",
	"Count of successfully fetched packages.",
	stats.UnitDimensionless,
	)

	// FetchLatencyDistribution aggregates frontend fetch request
	// latency by status code. It does not count shedded requests.
	FetchLatencyDistribution = &view.View{
	Name: "go-discovery/worker/fetch-latency",
	Measure: fetchLatency,
	Aggregation: ochttp.DefaultLatencyDistribution,
	Description: "Fetch latency by result status.",
	TagKeys: []tag.Key{dcensus.KeyStatus},
	}
	// FetchResponseCount counts fetch responses by status.
	FetchResponseCount = &view.View{
	Name: "go-discovery/worker/fetch-count",
	Measure: fetchLatency,
	Aggregation: view.Count(),
	Description: "Fetch request count by result status",
	TagKeys: []tag.Key{dcensus.KeyStatus},
	}
	// FetchPackageCount counts how many packages were successfully fetched.
	FetchPackageCount = &view.View{
	Name: "go-discovery/worker/fetch-package-count",
	Measure: fetchedPackages,
	Aggregation: view.Count(),
	Description: "Count of packages successfully fetched",
	}
	// SheddedFetchCount counts the number of fetches that were shedded.
	SheddedFetchCount = &view.View{
	Name: "go-discovery/worker/fetch-shedded",
	Measure: fetchesShedded,
	Aggregation: view.Count(),
	Description: "Count of shedded fetches",
	}
	)

	type FetchResult struct {
	ModulePath string
	RequestedVersion string
	ResolvedVersion string
	GoModPath string
	Status int
	Error error
	Defer func() // caller must defer this on all code paths
	Module *internal.Module
	PackageVersionStates []*internal.PackageVersionState
	}

	// FetchModule queries the proxy or the Go repo for the requested module
	// version, downloads the module zip, and processes the contents to return an
	// *internal.Module and related information.
	//
	// Even if err is non-nil, the result may contain useful information, like the go.mod path.
	//
	// Callers of FetchModule must
	// defer fr.Defer()
	// immediately after the call.
	func FetchModule(ctx context.Context, modulePath, requestedVersion string, proxyClient proxy.Client, sourceClient source.Client) (fr *FetchResult) {
	start := time.Now()
	fr = &FetchResult{
	ModulePath: modulePath,
	RequestedVersion: requestedVersion,
	Defer: func() {},
	}
	var fi *FetchInfo
	defer func() {
	if fr.Error != nil {
	derrors.Wrap(&fr.Error, "FetchModule(%q, %q)", modulePath, requestedVersion)
	fr.Status = derrors.ToStatus(fr.Error)
	}
	if fr.Status == 0 {
	fr.Status = http.StatusOK
	}
	latency := float64(time.Since(start).Seconds())
	dcensus.RecordWithTag(ctx, dcensus.KeyStatus, strconv.Itoa(fr.Status), fetchLatency.M(latency))
	if fr.Status < 300 {
	stats.Record(ctx, fetchedPackages.M(int64(len(fr.PackageVersionStates))))
	}
	if fi != nil {
	finishFetchInfo(fi, fr.Status, fr.Error)
	}
	log.Debugf(ctx, "memory after fetch of %s@%s: %dM", modulePath, requestedVersion, allocMeg())
	}()

	var (
	commitTime time.Time
	zipReader *zip.Reader
	zipSize int64
	err error
	)
	// Get the just information we need to make a load-shedding decision.
	if modulePath == stdlib.ModulePath {
	var resolvedVersion string
	resolvedVersion, zipSize, err = stdlib.ZipInfo(requestedVersion)
	if err != nil {
	fr.Error = err
	return fr
	}
	fr.ResolvedVersion = resolvedVersion
	} else {
	info, err := proxyClient.GetInfo(ctx, modulePath, requestedVersion)
	if err != nil {
	fr.Error = err
	return fr
	}
	fr.ResolvedVersion = info.Version
	commitTime = info.Time
	zipSize, err = proxyClient.GetZipSize(ctx, modulePath, fr.ResolvedVersion)
	if err != nil {
	fr.Error = err
	return fr
	}
	}

	// Load shed or mark module as too large.
	// We treat zip size
	// as a proxy for the total memory consumed by processing a module, and use
	// it to decide whether we can currently afford to process a module.
	shouldShed, deferFunc := zipLoadShedder.shouldShed(uint64(zipSize))
	fr.Defer = deferFunc
	if shouldShed {
	fr.Error = fmt.Errorf("%w: size=%dMi", derrors.SheddingLoad, zipSize/mib)
	stats.Record(ctx, fetchesShedded.M(1))
	return fr
	}

	if zipSize > maxModuleZipSize {
	log.Warningf(ctx, "FetchModule: %s@%s zip size %dMi exceeds max %dMi",
	modulePath, fr.ResolvedVersion, zipSize/mib, maxModuleZipSize/mib)
	fr.Error = derrors.ModuleTooLarge
	return fr
	}

	// Proceed with the fetch.
	fi = &FetchInfo{
	ModulePath: modulePath,
	Version: fr.ResolvedVersion,
	ZipSize: uint64(zipSize),
	Start: time.Now(),
	}
	startFetchInfo(fi)

	if modulePath == stdlib.ModulePath {
	zipReader, commitTime, err = stdlib.Zip(requestedVersion)
	if err != nil {
	fr.Error = err
	return fr
	}
	fr.GoModPath = stdlib.ModulePath
	} else {
	goModBytes, err := proxyClient.GetMod(ctx, modulePath, fr.ResolvedVersion)
	if err != nil {
	fr.Error = err
	return fr
	}
	goModPath := modfile.ModulePath(goModBytes)
	if goModPath == "" {
	fr.Error = fmt.Errorf("go.mod has no module path: %w", derrors.BadModule)
	return fr
	}
	fr.GoModPath = goModPath
	if goModPath != modulePath {
	// The module path in the go.mod file doesn't match the path of the
	// zip file. Don't insert the module. Store an AlternativeModule
	// status in module_version_states.
	fr.Error = fmt.Errorf("module path=%s, go.mod path=%s: %w", modulePath, goModPath, derrors.AlternativeModule)
	return fr
	}
	zipReader, err = proxyClient.GetZip(ctx, modulePath, fr.ResolvedVersion)
	if err != nil {
	fr.Error = err
	return fr
	}
	}
	mod, pvs, err := processZipFile(ctx, modulePath, fr.ResolvedVersion, commitTime, zipReader, sourceClient)
	if err != nil {
	fr.Error = err
	return fr
	}
	fr.Module = mod
	fr.PackageVersionStates = pvs
	if modulePath == stdlib.ModulePath {
	fr.Module.HasGoMod = true
	}
	for _, state := range fr.PackageVersionStates {
	if state.Status != http.StatusOK {
	fr.Status = derrors.ToStatus(derrors.HasIncompletePackages)
	}
	}
	return fr
	}

	// processZipFile extracts information from the module version zip.
	func processZipFile(ctx context.Context, modulePath string, resolvedVersion string, commitTime time.Time, zipReader zip.Reader, sourceClient source.Client) (_ internal.Module, _ []internal.PackageVersionState, err error) {
	defer derrors.Wrap(&err, "processZipFile(%q, %q)", modulePath, resolvedVersion)

	ctx, span := trace.StartSpan(ctx, "fetch.processZipFile")
	defer span.End()

	sourceInfo, err := source.ModuleInfo(ctx, sourceClient, modulePath, resolvedVersion)
	if err != nil {
	log.Infof(ctx, "error getting source info: %v", err)
	}
	readmes, err := extractReadmesFromZip(modulePath, resolvedVersion, zipReader)
	if err != nil {
	return nil, nil, fmt.Errorf("extractReadmesFromZip(%q, %q, zipReader): %v", modulePath, resolvedVersion, err)
	}
	logf := func(format string, args ...interface{}) {
	log.Infof(ctx, format, args...)
	}
	d := licenses.NewDetector(modulePath, resolvedVersion, zipReader, logf)
	allLicenses := d.AllLicenses()
	packages, packageVersionStates, err := extractPackagesFromZip(ctx, modulePath, resolvedVersion, zipReader, d, sourceInfo)
	if errors.Is(err, errModuleContainsNoPackages) \|\| errors.Is(err, errMalformedZip) {
	return nil, nil, fmt.Errorf("%v: %w", err.Error(), derrors.BadModule)
	}
	if err != nil {
	return nil, nil, fmt.Errorf("extractPackagesFromZip(%q, %q, zipReader, %v): %v", modulePath, resolvedVersion, allLicenses, err)
	}
	hasGoMod := zipContainsFilename(zipReader, path.Join(moduleVersionDir(modulePath, resolvedVersion), "go.mod"))

	return &internal.Module{
	ModuleInfo: internal.ModuleInfo{
	ModulePath: modulePath,
	Version: resolvedVersion,
	CommitTime: commitTime,
	IsRedistributable: d.ModuleIsRedistributable(),
	HasGoMod: hasGoMod,
	SourceInfo: sourceInfo,
	},
	Licenses: allLicenses,
	Units: moduleUnits(modulePath, resolvedVersion, packages, readmes, d),
	}, packageVersionStates, nil
	}

	// moduleVersionDir formats the content subdirectory for the given
	// modulePath and version.
	func moduleVersionDir(modulePath, version string) string {
	return fmt.Sprintf("%s@%s", modulePath, version)
	}

	// zipContainsFilename reports whether there is a file with the given name in the zip.
	func zipContainsFilename(r *zip.Reader, name string) bool {
	for _, f := range r.File {
	if f.Name == name {
	return true
	}
	}
	return false
	}

	type FetchInfo struct {
	ModulePath string
	Version string
	ZipSize uint64
	Start time.Time
	Finish time.Time
	Status int
	Error error
	}

	var (
	fetchInfoMu sync.Mutex
	fetchInfoMap = map[*FetchInfo]struct{}{}
	)

	func init() {
	const linger = time.Minute
	go func() {
	for {
	now := time.Now()
	fetchInfoMu.Lock()
	for fi := range fetchInfoMap {
	if !fi.Finish.IsZero() && now.Sub(fi.Finish) > linger {
	delete(fetchInfoMap, fi)
	}
	}
	fetchInfoMu.Unlock()
	time.Sleep(linger)
	}
	}()
	}

	func startFetchInfo(fi *FetchInfo) {
	fetchInfoMu.Lock()
	defer fetchInfoMu.Unlock()
	fetchInfoMap[fi] = struct{}{}
	}

	func finishFetchInfo(fi *FetchInfo, status int, err error) {
	fetchInfoMu.Lock()
	defer fetchInfoMu.Unlock()
	fi.Finish = time.Now()
	fi.Status = status
	fi.Error = err
	}

	// FetchInfos returns information about all fetches in progress,
	// sorted by start time.
	func FetchInfos() []*FetchInfo {
	var fis []*FetchInfo
	fetchInfoMu.Lock()
	for fi := range fetchInfoMap {
	// Copy to avoid races on Status and Error when read by
	// worker home page.
	cfi := *fi
	fis = append(fis, &cfi)
	}
	fetchInfoMu.Unlock()
	// Order first by done-ness, then by age.
	sort.Slice(fis, func(i, j int) bool {
	if (fis[i].Status == 0) == (fis[j].Status == 0) {
	return fis[i].Start.Before(fis[j].Start)
	}
	return fis[i].Status == 0
	})
	return fis
	}