container: add support for uploading to registries

Add a new generic container registry client via a new `container`
package. Use this to create a command line utility as well as a
new upload target for container registries.

The code uses the github.com/containers/* project and packages to
interact with container registires that is also used by skopeo,
podman et al. One if the dependencies is `proglottis/gpgme` that
is using cgo to bind libgpgme, so we have to add the corresponding
devel package to the BuildRequires as well as installing it on CI.

Checks will follow later via an integration test.

vendor/github.com/containers/common/pkg/retry/retry.go

@@ -0,0 +1,108 @@
+package retry
+
+import (
+	"context"
+	"io"
+	"math"
+	"net"
+	"net/url"
+	"syscall"
+	"time"
+
+	"github.com/docker/distribution/registry/api/errcode"
+	errcodev2 "github.com/docker/distribution/registry/api/v2"
+	"github.com/hashicorp/go-multierror"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// RetryOptions defines the option to retry
+type RetryOptions struct {
+	MaxRetry int           // The number of times to possibly retry
+	Delay    time.Duration // The delay to use between retries, if set
+}
+
+// RetryIfNecessary retries the operation in exponential backoff with the retryOptions
+func RetryIfNecessary(ctx context.Context, operation func() error, retryOptions *RetryOptions) error {
+	err := operation()
+	for attempt := 0; err != nil && isRetryable(err) && attempt < retryOptions.MaxRetry; attempt++ {
+		delay := time.Duration(int(math.Pow(2, float64(attempt)))) * time.Second
+		if retryOptions.Delay != 0 {
+			delay = retryOptions.Delay
+		}
+		logrus.Warnf("Failed, retrying in %s ... (%d/%d). Error: %v", delay, attempt+1, retryOptions.MaxRetry, err)
+		select {
+		case <-time.After(delay):
+			break
+		case <-ctx.Done():
+			return err
+		}
+		err = operation()
+	}
+	return err
+}
+
+func isRetryable(err error) bool {
+	err = errors.Cause(err)
+
+	switch err {
+	case nil:
+		return false
+	case context.Canceled, context.DeadlineExceeded:
+		return false
+	default: // continue
+	}
+
+	type unwrapper interface {
+		Unwrap() error
+	}
+
+	switch e := err.(type) {
+
+	case errcode.Error:
+		switch e.Code {
+		case errcode.ErrorCodeUnauthorized, errcode.ErrorCodeDenied,
+			errcodev2.ErrorCodeNameUnknown, errcodev2.ErrorCodeManifestUnknown:
+			return false
+		}
+		return true
+	case *net.OpError:
+		return isRetryable(e.Err)
+	case *url.Error: // This includes errors returned by the net/http client.
+		if e.Err == io.EOF { // Happens when a server accepts a HTTP connection and sends EOF
+			return true
+		}
+		return isRetryable(e.Err)
+	case syscall.Errno:
+		return isErrnoRetryable(e)
+	case errcode.Errors:
+		// if this error is a group of errors, process them all in turn
+		for i := range e {
+			if !isRetryable(e[i]) {
+				return false
+			}
+		}
+		return true
+	case *multierror.Error:
+		// if this error is a group of errors, process them all in turn
+		for i := range e.Errors {
+			if !isRetryable(e.Errors[i]) {
+				return false
+			}
+		}
+		return true
+	case unwrapper: // Test this last, because various error types might implement .Unwrap()
+		err = e.Unwrap()
+		return isRetryable(err)
+	}
+
+	return false
+}
+
+func isErrnoRetryable(e error) bool {
+	switch e {
+	case syscall.ECONNREFUSED, syscall.EINTR, syscall.EAGAIN, syscall.EBUSY, syscall.ENETDOWN, syscall.ENETUNREACH, syscall.ENETRESET, syscall.ECONNABORTED, syscall.ECONNRESET, syscall.ETIMEDOUT, syscall.EHOSTDOWN, syscall.EHOSTUNREACH:
+		return true
+	}
+	return isErrnoERESTART(e)
+}

vendor/github.com/containers/common/pkg/retry/retry_linux.go

@@ -0,0 +1,9 @@
+package retry
+
+import (
+	"syscall"
+)
+
+func isErrnoERESTART(e error) bool {
+	return e == syscall.ERESTART
+}

vendor/github.com/containers/common/pkg/retry/retry_unsupported.go

@@ -0,0 +1,8 @@
+//go:build !linux
+// +build !linux
+
+package retry
+
+func isErrnoERESTART(e error) bool {
+	return false
+}