feeds/: Allow for per package/feed error handling when polling

When errors occur but package data can still be processed then
the system should continue where possible. This is particularly
beneficial in feeds where data is fetched on a per package basis,
as a singular failure shouldn't immediately lead to data loss
for the whole session.

This also removes `errUnpublished` as a 'hard' error when polling
npm for critical packages. `feeds.PackagePollError{}` could be
extended to further feeds to provide more granular error
reporting where applicable.

feeds/crates/crates.go

@@ -80,11 +80,11 @@ func New(feedOptions feeds.FeedOptions, eventHandler *events.Handler) (*Feed, er
 	}, nil
 }
 
-func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, error) {
+func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, []error) {
 	pkgs := []*feeds.Package{}
 	packages, err := fetchPackages(feed.baseURL)
 	if err != nil {
-		return pkgs, err
+		return pkgs, []error{err}
 	}
 	for _, pkg := range packages {
 		pkg := feeds.NewPackage(pkg.UpdatedAt, pkg.Name, pkg.NewestVersion, FeedName)
@@ -93,7 +93,7 @@ func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, error) {
 	feed.lossyFeedAlerter.ProcessPackages(FeedName, pkgs)
 
 	pkgs = feeds.ApplyCutoff(pkgs, cutoff)
-	return pkgs, nil
+	return pkgs, []error{}
 }
 
 func (feed Feed) GetName() string {

feeds/crates/crates_test.go

@@ -27,8 +27,8 @@ func TestCratesLatest(t *testing.T) {
 	}
 
 	cutoff := time.Date(1970, 1, 1, 0, 0, 0, 0, time.UTC)
-	pkgs, err := feed.Latest(cutoff)
-	if err != nil {
+	pkgs, errs := feed.Latest(cutoff)
+	if len(errs) != 0 {
 		t.Fatalf("feed.Latest returned error: %v", err)
 	}
 
@@ -67,11 +67,11 @@ func TestCratesNotFound(t *testing.T) {
 	}
 
 	cutoff := time.Date(1970, 1, 1, 0, 0, 0, 0, time.UTC)
-	_, err = feed.Latest(cutoff)
-	if err == nil {
+	_, errs := feed.Latest(cutoff)
+	if len(errs) == 0 {
 		t.Fatalf("feed.Latest() was successful when an error was expected")
 	}
-	if !errors.Is(err, utils.ErrUnsuccessfulRequest) {
+	if !errors.Is(errs[len(errs)-1], utils.ErrUnsuccessfulRequest) {
 		t.Fatalf("feed.Latest() returned an error which did not match the expected error")
 	}
 }

feeds/feed.go

@@ -1,19 +1,22 @@
 package feeds
 
 import (
+	"errors"
 	"fmt"
 	"time"
 )
 
 const schemaVer = "1.0"
 
+var ErrNoPackagesPolled = errors.New("no packages were successfully polled")
+
 type UnsupportedOptionError struct {
 	Option string
 	Feed   string
 }
 
 type ScheduledFeed interface {
-	Latest(cutoff time.Time) ([]*Package, error)
+	Latest(cutoff time.Time) ([]*Package, []error)
 	GetFeedOptions() FeedOptions
 	GetName() string
 }
@@ -37,6 +40,15 @@ type Package struct {
 	SchemaVer   string    `json:"schema_ver"`
 }
 
+type PackagePollError struct {
+	Err  error
+	Name string
+}
+
+func (err PackagePollError) Error() string {
+	return fmt.Sprintf("Polling for package %s returned error: %v", err.Name, err.Err)
+}
+
 func NewPackage(created time.Time, name, version, feed string) *Package {
 	return &Package{
 		Name:        name,

feeds/goproxy/goproxy.go

@@ -100,18 +100,18 @@ func New(feedOptions feeds.FeedOptions) (*Feed, error) {
 	}, nil
 }
 
-func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, error) {
+func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, []error) {
 	pkgs := []*feeds.Package{}
 	packages, err := fetchPackages(feed.baseURL, cutoff)
 	if err != nil {
-		return pkgs, err
+		return pkgs, []error{err}
 	}
 	for _, pkg := range packages {
 		pkg := feeds.NewPackage(pkg.ModifiedDate, pkg.Title, pkg.Version, FeedName)
 		pkgs = append(pkgs, pkg)
 	}
 	pkgs = feeds.ApplyCutoff(pkgs, cutoff)
-	return pkgs, nil
+	return pkgs, []error{}
 }
 
 func (feed Feed) GetName() string {

feeds/goproxy/goproxy_test.go

@@ -26,8 +26,8 @@ func TestGoProxyLatest(t *testing.T) {
 	feed.baseURL = srv.URL
 
 	cutoff := time.Date(1970, 1, 1, 0, 0, 0, 0, time.UTC)
-	pkgs, err := feed.Latest(cutoff)
-	if err != nil {
+	pkgs, errs := feed.Latest(cutoff)
+	if len(errs) != 0 {
 		t.Fatalf("feed.Latest returned error: %v", err)
 	}
 
@@ -66,11 +66,11 @@ func TestGoproxyNotFound(t *testing.T) {
 	feed.baseURL = srv.URL
 
 	cutoff := time.Date(1970, 1, 1, 0, 0, 0, 0, time.UTC)
-	_, err = feed.Latest(cutoff)
-	if err == nil {
+	_, errs := feed.Latest(cutoff)
+	if len(errs) == 0 {
 		t.Fatalf("feed.Latest() was successful when an error was expected")
 	}
-	if !errors.Is(err, utils.ErrUnsuccessfulRequest) {
+	if !errors.Is(errs[len(errs)-1], utils.ErrUnsuccessfulRequest) {
 		t.Fatalf("feed.Latest() returned an error which did not match the expected error")
 	}
 }

feeds/npm/npm.go

@@ -138,13 +138,15 @@ func fetchPackage(baseURL, pkgTitle string) ([]*Package, error) {
 	return versionSlice, nil
 }
 
-func fetchAllPackages(url string) ([]*feeds.Package, error) {
+func fetchAllPackages(url string) ([]*feeds.Package, []error) {
 	pkgs := []*feeds.Package{}
+	errs := []error{}
 	packageChannel := make(chan []*Package)
-	errs := make(chan error)
+	errChannel := make(chan error)
 	packageEvents, err := fetchPackageEvents(url)
 	if err != nil {
-		return pkgs, err
+		// If we can't generate package events then return early.
+		return pkgs, append(errs, err)
 	}
 	// Handle the possibility of multiple releases of the same package
 	// within the polled `packages` slice.
@@ -157,7 +159,10 @@ func fetchAllPackages(url string) ([]*feeds.Package, error) {
 		go func(pkgTitle string, count int) {
 			pkgs, err := fetchPackage(url, pkgTitle)
 			if err != nil {
-				errs <- err
+				if !errors.Is(err, errUnpublished) {
+					err = feeds.PackagePollError{Name: pkgTitle, Err: err}
+				}
+				errChannel <- err
 				return
 			}
 			// Apply count slice
@@ -173,27 +178,31 @@ func fetchAllPackages(url string) ([]*feeds.Package, error) {
 					pkg.Version, FeedName)
 				pkgs = append(pkgs, feedPkg)
 			}
-		case err := <-errs:
-			// TODO: Add an event for unpublished package? This shouldn't
-			// be a hard error for the 'firehose'.
+		case err := <-errChannel:
+			// When polling the 'firehose' unpublished packages
+			// don't need to be logged as an error.
 			if !errors.Is(err, errUnpublished) {
-				return pkgs, fmt.Errorf("error in fetching version information: %w", err)
+				errs = append(errs, err)
 			}
 		}
 	}
-	return pkgs, nil
+	return pkgs, errs
 }
 
-func fetchCriticalPackages(url string, packages []string) ([]*feeds.Package, error) {
+func fetchCriticalPackages(url string, packages []string) ([]*feeds.Package, []error) {
 	pkgs := []*feeds.Package{}
+	errs := []error{}
 	packageChannel := make(chan []*Package)
-	errs := make(chan error)
+	errChannel := make(chan error)
 
 	for _, pkgTitle := range packages {
 		go func(pkgTitle string) {
 			pkgs, err := fetchPackage(url, pkgTitle)
 			if err != nil {
-				errs <- err
+				if !errors.Is(err, errUnpublished) {
+					err = feeds.PackagePollError{Name: pkgTitle, Err: err}
+				}
+				errChannel <- err
 				return
 			}
 			packageChannel <- pkgs
@@ -208,13 +217,15 @@ func fetchCriticalPackages(url string, packages []string) ([]*feeds.Package, err
 					pkg.Version, FeedName)
 				pkgs = append(pkgs, feedPkg)
 			}
-		case err := <-errs:
-			// Assume if a package has been unpublished that it is a valid hard
-			// error when polling for 'critical' packages.
-			return pkgs, fmt.Errorf("error in fetching version information: %w", err)
+		case err := <-errChannel:
+			// Assume if a package has been unpublished that it is a valid reason
+			// to log the error when polling for 'critical' packages. This could
+			// be changed for a 'lossy' type event instead. Further packages should
+			// be proccessed.
+			errs = append(errs, err)
 		}
 	}
-	return pkgs, nil
+	return pkgs, errs
 }
 
 type Feed struct {
@@ -233,18 +244,19 @@ func New(feedOptions feeds.FeedOptions, eventHandler *events.Handler) (*Feed, er
 	}, nil
 }
 
-func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, error) {
+func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, []error) {
 	pkgs := []*feeds.Package{}
-	var err error
+	var errs []error
 
 	if feed.packages == nil {
-		pkgs, err = fetchAllPackages(feed.baseURL)
+		pkgs, errs = fetchAllPackages(feed.baseURL)
 	} else {
-		pkgs, err = fetchCriticalPackages(feed.baseURL, *feed.packages)
+		pkgs, errs = fetchCriticalPackages(feed.baseURL, *feed.packages)
 	}
 
-	if err != nil {
-		return nil, err
+	if len(pkgs) == 0 {
+		// If none of the packages were successfully polled for, return early.
+		return nil, append(errs, feeds.ErrNoPackagesPolled)
 	}
 
 	// Ensure packages are sorted by CreatedDate in order of most recent, as goroutine
@@ -261,7 +273,7 @@ func (feed Feed) Latest(cutoff time.Time) ([]*feeds.Package, error) {
 	}
 
 	pkgs = feeds.ApplyCutoff(pkgs, cutoff)
-	return pkgs, nil
+	return pkgs, errs
 }
 
 func (feed Feed) GetName() string {