internal/worker/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 worker

 import (
 	"context"
 	"errors"
 	"fmt"
 	"net/http"
 	"sort"
 	"strings"
 	"sync"
 	"time"
 	"unicode/utf8"

 	"go.opencensus.io/trace"
 	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/semver"
 	"golang.org/x/pkgsite/internal"
 	"golang.org/x/pkgsite/internal/cache"
 	"golang.org/x/pkgsite/internal/derrors"
 	"golang.org/x/pkgsite/internal/experiment"
 	"golang.org/x/pkgsite/internal/fetch"
 	"golang.org/x/pkgsite/internal/log"
 	"golang.org/x/pkgsite/internal/postgres"
 	"golang.org/x/pkgsite/internal/proxy"
 	"golang.org/x/pkgsite/internal/source"
 	"golang.org/x/pkgsite/internal/stdlib"
 )

 // ProxyRemoved is a set of module@version that have been removed from the proxy,
 // even though they are still in the index.
 var ProxyRemoved = map[string]bool{}

 // fetchTask represents the result of a fetch task that was processed.
 type fetchTask struct {
 	fetch.FetchResult
 	timings map[string]time.Duration
 }

 // A Fetcher holds state for fetching modules.
 type Fetcher struct {
 	ProxyClient  *proxy.Client
 	SourceClient *source.Client
 	DB           *postgres.DB
 	Cache        *cache.Cache
 }

 // FetchAndUpdateState fetches and processes a module version, and then updates
 // the module_version_states table according to the result. It returns an HTTP
 // status code representing the result of the fetch operation, and a non-nil
 // error if this status code is not 200.
 func (f *Fetcher) FetchAndUpdateState(ctx context.Context, modulePath, requestedVersion, appVersionLabel string) (_ int, resolvedVersion string, err error) {
 	defer derrors.Wrap(&err, "FetchAndUpdateState(%q, %q, %q)", modulePath, requestedVersion, appVersionLabel)
 	tctx, span := trace.StartSpan(ctx, "FetchAndUpdateState")
 	ctx = experiment.NewContext(tctx, experiment.FromContext(ctx).Active()...)
 	ctx = log.NewContextWithLabel(ctx, "fetch", modulePath+"@"+requestedVersion)
 	if !utf8.ValidString(modulePath) {
 		log.Errorf(ctx, "module path %q is not valid UTF-8", modulePath)
 	}
 	if !utf8.ValidString(requestedVersion) {
 		log.Errorf(ctx, "requested version %q is not valid UTF-8", requestedVersion)
 	}
 	span.AddAttributes(
 		trace.StringAttribute("modulePath", modulePath),
 		trace.StringAttribute("version", requestedVersion))
 	defer span.End()

 	// Whenever we fetch a module, make sure its raw latest information is up to
 	// date in the DB.
 	if err := f.fetchAndUpdateRawLatest(ctx, modulePath); err != nil {
 		// Do not fail the fetch just because we couldn't update the raw latest info.
 		log.Errorf(ctx, "updating raw latest: %v", err)
 		if isInternalError(err) {
 			derrors.Report(err)
 		}
 	}

 	ft := f.fetchAndInsertModule(ctx, modulePath, requestedVersion)
 	span.AddAttributes(trace.Int64Attribute("numPackages", int64(len(ft.PackageVersionStates))))

 	// If there were any errors processing the module then we didn't insert it.
 	// Delete it in case we are reprocessing an existing module.
 	// However, don't delete if the error was internal, or we are shedding load.
 	if ft.Status >= 400 && ft.Status < 500 {
 		if err := deleteModule(ctx, f.DB, ft); err != nil {
 			log.Error(ctx, err)
 			ft.Error = err
 			ft.Status = http.StatusInternalServerError
 		}
 		// Do not return an error here, because we want to insert into
 		// module_version_states below.
 	}
 	// Regardless of what the status code is, insert the result into
 	// version_map, so that a response can be returned for frontend_fetch.
 	if err := updateVersionMap(ctx, f.DB, ft); err != nil {
 		log.Error(ctx, err)
 		if ft.Status != http.StatusInternalServerError {
 			ft.Error = err
 			ft.Status = http.StatusInternalServerError
 		}
 		// Do not return an error here, because we want to insert into
 		// module_version_states below.
 	}
 	if !semver.IsValid(ft.ResolvedVersion) {
 		// If the requestedVersion was not successfully resolved to a semantic
 		// version, then at this point it will be the same as the
 		// resolvedVersion. This fetch request does not need to be recorded in
 		// module_version_states, since that table is only used to track
 		// modules that have been published to index.golang.org.
 		return ft.Status, ft.ResolvedVersion, ft.Error
 	}

 	// Update the module_version_states table with the new status of
 	// module@version. This must happen last, because if it succeeds with a
 	// code < 500 but a later action fails, we will never retry the later
 	// action.
 	// TODO(golang/go#39628): Split UpsertModuleVersionState into
 	// InsertModuleVersionState and UpdateModuleVersionState.
 	start := time.Now()
 	err = f.DB.UpsertModuleVersionState(ctx, ft.ModulePath, ft.ResolvedVersion, appVersionLabel,
 		time.Time{}, ft.Status, ft.GoModPath, ft.Error, ft.PackageVersionStates)
 	ft.timings["db.UpsertModuleVersionState"] = time.Since(start)
 	if err != nil {
 		log.Error(ctx, err)
 		if ft.Error != nil {
 			ft.Status = http.StatusInternalServerError
 			ft.Error = fmt.Errorf("db.UpsertModuleVersionState: %v, original error: %v", err, ft.Error)
 		}
 		logTaskResult(ctx, ft, "Failed to update module version state")
 		return http.StatusInternalServerError, ft.ResolvedVersion, ft.Error
 	}
 	logTaskResult(ctx, ft, "Updated module version state")
 	return ft.Status, ft.ResolvedVersion, ft.Error
 }

 // isInternalError reports whether the error is a problem with the server, rather than
 // the incoming data.
 func isInternalError(err error) bool {
 	// Errors from modfile.ParseLax are user errors.
 	if e := (modfile.ErrorList{}); errors.As(err, &e) {
 		return false
 	}
 	if e := (&modfile.Error{}); errors.As(err, &e) {
 		return false
 	}
 	return true
 }

 // fetchAndInsertModule fetches the given module version from the module proxy
 // or (in the case of the standard library) from the Go repo and writes the
 // resulting data to the database.
 func (f *Fetcher) fetchAndInsertModule(ctx context.Context, modulePath, requestedVersion string) *fetchTask {
 	ft := &fetchTask{
 		FetchResult: fetch.FetchResult{
 			ModulePath:       modulePath,
 			RequestedVersion: requestedVersion,
 		},
 		timings: map[string]time.Duration{},
 	}
 	defer func() {
 		derrors.Wrap(&ft.Error, "fetchAndInsertModule(%q, %q)", modulePath, requestedVersion)
 		if ft.Error != nil {
 			ft.Status = derrors.ToStatus(ft.Error)
 			ft.ResolvedVersion = requestedVersion
 		}
 	}()

 	if ProxyRemoved[modulePath+"@"+requestedVersion] {
 		log.Infof(ctx, "not fetching %s@%s because it is on the ProxyRemoved list", modulePath, requestedVersion)
 		ft.Error = derrors.Excluded
 		return ft
 	}

 	exc, err := f.DB.IsExcluded(ctx, modulePath)
 	if err != nil {
 		ft.Error = err
 		return ft
 	}
 	if exc {
 		ft.Error = derrors.Excluded
 		return ft
 	}

 	// Fetch the module, and the current @main and @master version of this module.
 	// The @main and @master version will be used to update the version_map
 	// target if applicable.
 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
 		start := time.Now()
 		fr := fetch.FetchModule(ctx, modulePath, requestedVersion, f.ProxyClient, f.SourceClient)
 		if fr == nil {
 			panic("fetch.FetchModule should never return a nil FetchResult")
 		}
 		defer fr.Defer()
 		ft.FetchResult = *fr
 		ft.timings["fetch.FetchModule"] = time.Since(start)
 	}()
 	// Do not resolve the @main and @master version if proxy fetch is disabled.
 	var main string
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
 		if !f.ProxyClient.FetchDisabled() {
 			main = resolvedVersion(ctx, modulePath, internal.MainVersion, f.ProxyClient)
 		}
 	}()
 	var master string
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
 		if !f.ProxyClient.FetchDisabled() {
 			master = resolvedVersion(ctx, modulePath, internal.MasterVersion, f.ProxyClient)
 		}
 	}()
 	wg.Wait()
 	ft.MainVersion = main
 	ft.MasterVersion = master

 	// There was an error fetching this module.
 	if ft.Error != nil {
 		logf := log.Infof
 		if ft.Status == http.StatusServiceUnavailable {
 			logf = log.Warningf
 		} else if ft.Status >= 500 && ft.Status != derrors.ToStatus(derrors.ProxyTimedOut) {
 			logf = log.Errorf
 		}
 		logf(ctx, "Error executing fetch: %v (code %d)", ft.Error, ft.Status)
 		return ft
 	}

 	// The module was successfully fetched.
 	log.Infof(ctx, "fetch.FetchModule succeeded for %s@%s", ft.ModulePath, ft.RequestedVersion)
 	start := time.Now()
 	isLatest, err := f.DB.InsertModule(ctx, ft.Module)
 	ft.timings["db.InsertModule"] = time.Since(start)
 	if err != nil {
 		log.Error(ctx, err)

 		ft.Status = derrors.ToStatus(err)
 		ft.Error = err
 		return ft
 	}
 	log.Infof(ctx, "db.InsertModule succeeded for %s@%s", ft.ModulePath, ft.RequestedVersion)
 	// Invalidate the cache if we just processed the latest version of a module.
 	if isLatest {
 		if err := f.invalidateCache(ctx, ft.ModulePath); err != nil {
 			// Failure to invalidate the cache is not that serious; at worst it means some pages will be stale.
 			// (Cache TTLs for details pages configured in internal/frontend/server.go must not be too long,
 			// to account for this possibility.)
 			log.Errorf(ctx, "failed to invalidate cache for %s: %v", ft.ModulePath, err)
 		} else {
 			log.Infof(ctx, "invalidated cache for %s", ft.ModulePath)
 		}
 	}
 	return ft
 }

 // invalidateCache deletes the series path for modulePath, as well as any
 // possible URL path of which it is a componentwise prefix. That is, it deletes
 // example.com/mod, example.com/mod@v1.2.3 and example.com/mod/pkg, but not the
 // unrelated example.com/module.
 //
 // We delete the series path, not the module path, because adding a v2 module
 // can affect v1 pages. For example, the first v2 module will add a "higher
 // major version" banner to all v1 pages. While adding a v1 version won't
 // currently affect v2 pages, that could change some day (for instance, if we
 // decide to provide history). So it's better to be safe and delete all paths in
 // the series.
 func (f *Fetcher) invalidateCache(ctx context.Context, modulePath string) error {
 	if f.Cache == nil {
 		return nil
 	}
 	var errs []error
 	seriesPath := internal.SeriesPathForModule(modulePath)
 	// All cache keys are request URLs, so they begin with "/".
 	if err := f.Cache.Delete(ctx, "/"+seriesPath); err != nil {
 		errs = append(errs, err)
 	}
 	// Delete all suffixes of the series path followed by a character that marks its end.
 	for _, end := range "/@?#" {
 		if err := f.Cache.DeletePrefix(ctx, fmt.Sprintf("/%s%c", seriesPath, end)); err != nil {
 			errs = append(errs, err)
 		}
 	}
 	if len(errs) > 0 {
 		return fmt.Errorf("%d errors, first is %w", len(errs), errs[0])
 	}
 	return nil
 }

 func resolvedVersion(ctx context.Context, modulePath, requestedVersion string, proxyClient *proxy.Client) string {
 	if modulePath == stdlib.ModulePath && requestedVersion == internal.MainVersion {
 		return ""
 	}
 	info, err := fetch.GetInfo(ctx, modulePath, requestedVersion, proxyClient)
 	if err != nil {
 		if !errors.Is(err, derrors.NotFound) {
 			// If an error occurs, log it and insert the module as normal.
 			log.Errorf(ctx, "fetch.GetInfo(ctx, %q, %q, f.ProxyClient, false): %v", modulePath, requestedVersion, err)
 		}
 		return ""
 	}
 	return info.Version
 }

 func updateVersionMap(ctx context.Context, db *postgres.DB, ft *fetchTask) (err error) {
 	start := time.Now()
 	defer func() {
 		ft.timings["worker.updatedVersionMap"] = time.Since(start)
 		derrors.Wrap(&err, "updateVersionMap(%q, %q, %q, %d, %v)",
 			ft.ModulePath, ft.RequestedVersion, ft.ResolvedVersion, ft.Status, ft.Error)
 	}()
 	ctx, span := trace.StartSpan(ctx, "worker.updateVersionMap")
 	defer span.End()

 	var errMsg string
 	if ft.Error != nil {
 		errMsg = ft.Error.Error()
 	}

 	// If the resolved version for the this module version is also the resolved
 	// version for @main or @master, update version_map to match.
 	requestedVersions := []string{ft.RequestedVersion}
 	if ft.MainVersion == ft.ResolvedVersion {
 		requestedVersions = append(requestedVersions, internal.MainVersion)
 	}
 	if ft.MasterVersion == ft.ResolvedVersion {
 		requestedVersions = append(requestedVersions, internal.MasterVersion)
 	}
 	for _, v := range requestedVersions {
 		v := v
 		vm := &internal.VersionMap{
 			ModulePath:       ft.ModulePath,
 			RequestedVersion: v,
 			ResolvedVersion:  ft.ResolvedVersion,
 			Status:           ft.Status,
 			GoModPath:        ft.GoModPath,
 			Error:            errMsg,
 		}
 		if err := db.UpsertVersionMap(ctx, vm); err != nil {
 			return err
 		}
 	}
 	return nil
 }

 func deleteModule(ctx context.Context, db *postgres.DB, ft *fetchTask) (err error) {
 	start := time.Now()
 	defer func() {
 		ft.timings["worker.deleteModule"] = time.Since(start)
 		derrors.Wrap(&err, "deleteModule(%q, %q, %q, %d, %v)",
 			ft.ModulePath, ft.RequestedVersion, ft.ResolvedVersion, ft.Status, ft.Error)
 	}()
 	ctx, span := trace.StartSpan(ctx, "worker.deleteModule")
 	defer span.End()

 	log.Infof(ctx, "%s@%s: code=%d, deleting", ft.ModulePath, ft.ResolvedVersion, ft.Status)
 	if err := db.DeleteModule(ctx, ft.ModulePath, ft.ResolvedVersion); err != nil {
 		return err
 	}
 	// If this was an alternative path (ft.Status == 491) and there is an older
 	// version in search_documents, delete it. This is the case where a module's
 	// canonical path was changed by the addition of a go.mod file. For example,
 	// versions of logrus before it acquired a go.mod file could have the path
 	// github.com/Sirupsen/logrus, but once the go.mod file specifies that the
 	// path is all lower-case, the old versions should not show up in search. We
 	// still leave their pages in the database so users of those old versions
 	// can still view documentation.
 	if ft.Status == derrors.ToStatus(derrors.AlternativeModule) {
 		log.Infof(ctx, "%s@%s: code=491, deleting older version from search", ft.ModulePath, ft.ResolvedVersion)
 		if err := db.DeleteOlderVersionFromSearchDocuments(ctx, ft.ModulePath, ft.ResolvedVersion); err != nil {
 			return err
 		}
 	}
 	return nil
 }

 func logTaskResult(ctx context.Context, ft *fetchTask, prefix string) {
 	var times []string
 	for k, v := range ft.timings {
 		times = append(times, fmt.Sprintf("%s=%.3fs", k, v.Seconds()))
 	}
 	sort.Strings(times)
 	msg := strings.Join(times, ", ")
 	logf := log.Infof
 	if ft.Status == http.StatusInternalServerError {
 		logf = log.Errorf
 	}
 	logf(ctx, "%s for %s@%s: code=%d, num_packages=%d, err=%v; timings: %s",
 		prefix, ft.ModulePath, ft.ResolvedVersion, ft.Status, len(ft.PackageVersionStates), ft.Error, msg)
 }

 // fetchAndUpdateRawLatest fetches information about the raw latest version from the proxy,
 // and updates the database if the version has changed.
 func (f *Fetcher) fetchAndUpdateRawLatest(ctx context.Context, modulePath string) (err error) {
 	defer derrors.Wrap(&err, "fetchAndUpdateRawLatest(%q)", modulePath)
 	info, err := fetch.RawLatestInfo(ctx, modulePath, f.ProxyClient, func(v string) (bool, error) {
 		modinfo, err := f.DB.GetModuleInfo(ctx, modulePath, v)
 		if err != nil {
 			return false, err
 		}
 		return modinfo.HasGoMod, nil
 	})
 	if err != nil {
 		return err
 	}
 	return f.DB.UpdateRawLatestInfo(ctx, info)
 }
	// 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 worker

	import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"sort"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"go.opencensus.io/trace"
	"golang.org/x/mod/modfile"
	"golang.org/x/mod/semver"
	"golang.org/x/pkgsite/internal"
	"golang.org/x/pkgsite/internal/cache"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/experiment"
	"golang.org/x/pkgsite/internal/fetch"
	"golang.org/x/pkgsite/internal/log"
	"golang.org/x/pkgsite/internal/postgres"
	"golang.org/x/pkgsite/internal/proxy"
	"golang.org/x/pkgsite/internal/source"
	"golang.org/x/pkgsite/internal/stdlib"
	)

	// ProxyRemoved is a set of module@version that have been removed from the proxy,
	// even though they are still in the index.
	var ProxyRemoved = map[string]bool{}

	// fetchTask represents the result of a fetch task that was processed.
	type fetchTask struct {
	fetch.FetchResult
	timings map[string]time.Duration
	}

	// A Fetcher holds state for fetching modules.
	type Fetcher struct {
	ProxyClient *proxy.Client
	SourceClient *source.Client
	DB *postgres.DB
	Cache *cache.Cache
	}

	// FetchAndUpdateState fetches and processes a module version, and then updates
	// the module_version_states table according to the result. It returns an HTTP
	// status code representing the result of the fetch operation, and a non-nil
	// error if this status code is not 200.
	func (f *Fetcher) FetchAndUpdateState(ctx context.Context, modulePath, requestedVersion, appVersionLabel string) (_ int, resolvedVersion string, err error) {
	defer derrors.Wrap(&err, "FetchAndUpdateState(%q, %q, %q)", modulePath, requestedVersion, appVersionLabel)
	tctx, span := trace.StartSpan(ctx, "FetchAndUpdateState")
	ctx = experiment.NewContext(tctx, experiment.FromContext(ctx).Active()...)
	ctx = log.NewContextWithLabel(ctx, "fetch", modulePath+"@"+requestedVersion)
	if !utf8.ValidString(modulePath) {
	log.Errorf(ctx, "module path %q is not valid UTF-8", modulePath)
	}
	if !utf8.ValidString(requestedVersion) {
	log.Errorf(ctx, "requested version %q is not valid UTF-8", requestedVersion)
	}
	span.AddAttributes(
	trace.StringAttribute("modulePath", modulePath),
	trace.StringAttribute("version", requestedVersion))
	defer span.End()

	// Whenever we fetch a module, make sure its raw latest information is up to
	// date in the DB.
	if err := f.fetchAndUpdateRawLatest(ctx, modulePath); err != nil {
	// Do not fail the fetch just because we couldn't update the raw latest info.
	log.Errorf(ctx, "updating raw latest: %v", err)
	if isInternalError(err) {
	derrors.Report(err)
	}
	}

	ft := f.fetchAndInsertModule(ctx, modulePath, requestedVersion)
	span.AddAttributes(trace.Int64Attribute("numPackages", int64(len(ft.PackageVersionStates))))

	// If there were any errors processing the module then we didn't insert it.
	// Delete it in case we are reprocessing an existing module.
	// However, don't delete if the error was internal, or we are shedding load.
	if ft.Status >= 400 && ft.Status < 500 {
	if err := deleteModule(ctx, f.DB, ft); err != nil {
	log.Error(ctx, err)
	ft.Error = err
	ft.Status = http.StatusInternalServerError
	}
	// Do not return an error here, because we want to insert into
	// module_version_states below.
	}
	// Regardless of what the status code is, insert the result into
	// version_map, so that a response can be returned for frontend_fetch.
	if err := updateVersionMap(ctx, f.DB, ft); err != nil {
	log.Error(ctx, err)
	if ft.Status != http.StatusInternalServerError {
	ft.Error = err
	ft.Status = http.StatusInternalServerError
	}
	// Do not return an error here, because we want to insert into
	// module_version_states below.
	}
	if !semver.IsValid(ft.ResolvedVersion) {
	// If the requestedVersion was not successfully resolved to a semantic
	// version, then at this point it will be the same as the
	// resolvedVersion. This fetch request does not need to be recorded in
	// module_version_states, since that table is only used to track
	// modules that have been published to index.golang.org.
	return ft.Status, ft.ResolvedVersion, ft.Error
	}

	// Update the module_version_states table with the new status of
	// module@version. This must happen last, because if it succeeds with a
	// code < 500 but a later action fails, we will never retry the later
	// action.
	// TODO(golang/go#39628): Split UpsertModuleVersionState into
	// InsertModuleVersionState and UpdateModuleVersionState.
	start := time.Now()
	err = f.DB.UpsertModuleVersionState(ctx, ft.ModulePath, ft.ResolvedVersion, appVersionLabel,
	time.Time{}, ft.Status, ft.GoModPath, ft.Error, ft.PackageVersionStates)
	ft.timings["db.UpsertModuleVersionState"] = time.Since(start)
	if err != nil {
	log.Error(ctx, err)
	if ft.Error != nil {
	ft.Status = http.StatusInternalServerError
	ft.Error = fmt.Errorf("db.UpsertModuleVersionState: %v, original error: %v", err, ft.Error)
	}
	logTaskResult(ctx, ft, "Failed to update module version state")
	return http.StatusInternalServerError, ft.ResolvedVersion, ft.Error
	}
	logTaskResult(ctx, ft, "Updated module version state")
	return ft.Status, ft.ResolvedVersion, ft.Error
	}

	// isInternalError reports whether the error is a problem with the server, rather than
	// the incoming data.
	func isInternalError(err error) bool {
	// Errors from modfile.ParseLax are user errors.
	if e := (modfile.ErrorList{}); errors.As(err, &e) {
	return false
	}
	if e := (&modfile.Error{}); errors.As(err, &e) {
	return false
	}
	return true
	}

	// fetchAndInsertModule fetches the given module version from the module proxy
	// or (in the case of the standard library) from the Go repo and writes the
	// resulting data to the database.
	func (f Fetcher) fetchAndInsertModule(ctx context.Context, modulePath, requestedVersion string) fetchTask {
	ft := &fetchTask{
	FetchResult: fetch.FetchResult{
	ModulePath: modulePath,
	RequestedVersion: requestedVersion,
	},
	timings: map[string]time.Duration{},
	}
	defer func() {
	derrors.Wrap(&ft.Error, "fetchAndInsertModule(%q, %q)", modulePath, requestedVersion)
	if ft.Error != nil {
	ft.Status = derrors.ToStatus(ft.Error)
	ft.ResolvedVersion = requestedVersion
	}
	}()

	if ProxyRemoved[modulePath+"@"+requestedVersion] {
	log.Infof(ctx, "not fetching %s@%s because it is on the ProxyRemoved list", modulePath, requestedVersion)
	ft.Error = derrors.Excluded
	return ft
	}

	exc, err := f.DB.IsExcluded(ctx, modulePath)
	if err != nil {
	ft.Error = err
	return ft
	}
	if exc {
	ft.Error = derrors.Excluded
	return ft
	}

	// Fetch the module, and the current @main and @master version of this module.
	// The @main and @master version will be used to update the version_map
	// target if applicable.
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
	defer wg.Done()
	start := time.Now()
	fr := fetch.FetchModule(ctx, modulePath, requestedVersion, f.ProxyClient, f.SourceClient)
	if fr == nil {
	panic("fetch.FetchModule should never return a nil FetchResult")
	}
	defer fr.Defer()
	ft.FetchResult = *fr
	ft.timings["fetch.FetchModule"] = time.Since(start)
	}()
	// Do not resolve the @main and @master version if proxy fetch is disabled.
	var main string
	wg.Add(1)
	go func() {
	defer wg.Done()
	if !f.ProxyClient.FetchDisabled() {
	main = resolvedVersion(ctx, modulePath, internal.MainVersion, f.ProxyClient)
	}
	}()
	var master string
	wg.Add(1)
	go func() {
	defer wg.Done()
	if !f.ProxyClient.FetchDisabled() {
	master = resolvedVersion(ctx, modulePath, internal.MasterVersion, f.ProxyClient)
	}
	}()
	wg.Wait()
	ft.MainVersion = main
	ft.MasterVersion = master

	// There was an error fetching this module.
	if ft.Error != nil {
	logf := log.Infof
	if ft.Status == http.StatusServiceUnavailable {
	logf = log.Warningf
	} else if ft.Status >= 500 && ft.Status != derrors.ToStatus(derrors.ProxyTimedOut) {
	logf = log.Errorf
	}
	logf(ctx, "Error executing fetch: %v (code %d)", ft.Error, ft.Status)
	return ft
	}

	// The module was successfully fetched.
	log.Infof(ctx, "fetch.FetchModule succeeded for %s@%s", ft.ModulePath, ft.RequestedVersion)
	start := time.Now()
	isLatest, err := f.DB.InsertModule(ctx, ft.Module)
	ft.timings["db.InsertModule"] = time.Since(start)
	if err != nil {
	log.Error(ctx, err)

	ft.Status = derrors.ToStatus(err)
	ft.Error = err
	return ft
	}
	log.Infof(ctx, "db.InsertModule succeeded for %s@%s", ft.ModulePath, ft.RequestedVersion)
	// Invalidate the cache if we just processed the latest version of a module.
	if isLatest {
	if err := f.invalidateCache(ctx, ft.ModulePath); err != nil {
	// Failure to invalidate the cache is not that serious; at worst it means some pages will be stale.
	// (Cache TTLs for details pages configured in internal/frontend/server.go must not be too long,
	// to account for this possibility.)
	log.Errorf(ctx, "failed to invalidate cache for %s: %v", ft.ModulePath, err)
	} else {
	log.Infof(ctx, "invalidated cache for %s", ft.ModulePath)
	}
	}
	return ft
	}

	// invalidateCache deletes the series path for modulePath, as well as any
	// possible URL path of which it is a componentwise prefix. That is, it deletes
	// example.com/mod, example.com/mod@v1.2.3 and example.com/mod/pkg, but not the
	// unrelated example.com/module.
	//
	// We delete the series path, not the module path, because adding a v2 module
	// can affect v1 pages. For example, the first v2 module will add a "higher
	// major version" banner to all v1 pages. While adding a v1 version won't
	// currently affect v2 pages, that could change some day (for instance, if we
	// decide to provide history). So it's better to be safe and delete all paths in
	// the series.
	func (f *Fetcher) invalidateCache(ctx context.Context, modulePath string) error {
	if f.Cache == nil {
	return nil
	}
	var errs []error
	seriesPath := internal.SeriesPathForModule(modulePath)
	// All cache keys are request URLs, so they begin with "/".
	if err := f.Cache.Delete(ctx, "/"+seriesPath); err != nil {
	errs = append(errs, err)
	}
	// Delete all suffixes of the series path followed by a character that marks its end.
	for _, end := range "/@?#" {
	if err := f.Cache.DeletePrefix(ctx, fmt.Sprintf("/%s%c", seriesPath, end)); err != nil {
	errs = append(errs, err)
	}
	}
	if len(errs) > 0 {
	return fmt.Errorf("%d errors, first is %w", len(errs), errs[0])
	}
	return nil
	}

	func resolvedVersion(ctx context.Context, modulePath, requestedVersion string, proxyClient *proxy.Client) string {
	if modulePath == stdlib.ModulePath && requestedVersion == internal.MainVersion {
	return ""
	}
	info, err := fetch.GetInfo(ctx, modulePath, requestedVersion, proxyClient)
	if err != nil {
	if !errors.Is(err, derrors.NotFound) {
	// If an error occurs, log it and insert the module as normal.
	log.Errorf(ctx, "fetch.GetInfo(ctx, %q, %q, f.ProxyClient, false): %v", modulePath, requestedVersion, err)
	}
	return ""
	}
	return info.Version
	}

	func updateVersionMap(ctx context.Context, db postgres.DB, ft fetchTask) (err error) {
	start := time.Now()
	defer func() {
	ft.timings["worker.updatedVersionMap"] = time.Since(start)
	derrors.Wrap(&err, "updateVersionMap(%q, %q, %q, %d, %v)",
	ft.ModulePath, ft.RequestedVersion, ft.ResolvedVersion, ft.Status, ft.Error)
	}()
	ctx, span := trace.StartSpan(ctx, "worker.updateVersionMap")
	defer span.End()

	var errMsg string
	if ft.Error != nil {
	errMsg = ft.Error.Error()
	}

	// If the resolved version for the this module version is also the resolved
	// version for @main or @master, update version_map to match.
	requestedVersions := []string{ft.RequestedVersion}
	if ft.MainVersion == ft.ResolvedVersion {
	requestedVersions = append(requestedVersions, internal.MainVersion)
	}
	if ft.MasterVersion == ft.ResolvedVersion {
	requestedVersions = append(requestedVersions, internal.MasterVersion)
	}
	for _, v := range requestedVersions {
	v := v
	vm := &internal.VersionMap{
	ModulePath: ft.ModulePath,
	RequestedVersion: v,
	ResolvedVersion: ft.ResolvedVersion,
	Status: ft.Status,
	GoModPath: ft.GoModPath,
	Error: errMsg,
	}
	if err := db.UpsertVersionMap(ctx, vm); err != nil {
	return err
	}
	}
	return nil
	}

	func deleteModule(ctx context.Context, db postgres.DB, ft fetchTask) (err error) {
	start := time.Now()
	defer func() {
	ft.timings["worker.deleteModule"] = time.Since(start)
	derrors.Wrap(&err, "deleteModule(%q, %q, %q, %d, %v)",
	ft.ModulePath, ft.RequestedVersion, ft.ResolvedVersion, ft.Status, ft.Error)
	}()
	ctx, span := trace.StartSpan(ctx, "worker.deleteModule")
	defer span.End()

	log.Infof(ctx, "%s@%s: code=%d, deleting", ft.ModulePath, ft.ResolvedVersion, ft.Status)
	if err := db.DeleteModule(ctx, ft.ModulePath, ft.ResolvedVersion); err != nil {
	return err
	}
	// If this was an alternative path (ft.Status == 491) and there is an older
	// version in search_documents, delete it. This is the case where a module's
	// canonical path was changed by the addition of a go.mod file. For example,
	// versions of logrus before it acquired a go.mod file could have the path
	// github.com/Sirupsen/logrus, but once the go.mod file specifies that the
	// path is all lower-case, the old versions should not show up in search. We
	// still leave their pages in the database so users of those old versions
	// can still view documentation.
	if ft.Status == derrors.ToStatus(derrors.AlternativeModule) {
	log.Infof(ctx, "%s@%s: code=491, deleting older version from search", ft.ModulePath, ft.ResolvedVersion)
	if err := db.DeleteOlderVersionFromSearchDocuments(ctx, ft.ModulePath, ft.ResolvedVersion); err != nil {
	return err
	}
	}
	return nil
	}

	func logTaskResult(ctx context.Context, ft *fetchTask, prefix string) {
	var times []string
	for k, v := range ft.timings {
	times = append(times, fmt.Sprintf("%s=%.3fs", k, v.Seconds()))
	}
	sort.Strings(times)
	msg := strings.Join(times, ", ")
	logf := log.Infof
	if ft.Status == http.StatusInternalServerError {
	logf = log.Errorf
	}
	logf(ctx, "%s for %s@%s: code=%d, num_packages=%d, err=%v; timings: %s",
	prefix, ft.ModulePath, ft.ResolvedVersion, ft.Status, len(ft.PackageVersionStates), ft.Error, msg)
	}

	// fetchAndUpdateRawLatest fetches information about the raw latest version from the proxy,
	// and updates the database if the version has changed.
	func (f *Fetcher) fetchAndUpdateRawLatest(ctx context.Context, modulePath string) (err error) {
	defer derrors.Wrap(&err, "fetchAndUpdateRawLatest(%q)", modulePath)
	info, err := fetch.RawLatestInfo(ctx, modulePath, f.ProxyClient, func(v string) (bool, error) {
	modinfo, err := f.DB.GetModuleInfo(ctx, modulePath, v)
	if err != nil {
	return false, err
	}
	return modinfo.HasGoMod, nil
	})
	if err != nil {
	return err
	}
	return f.DB.UpdateRawLatestInfo(ctx, info)
	}