endpoint: refactor, fix stale holds on initial replication, holds release subcmds

- endpoint abstractions now share an interface `Abstraction`
- pkg endpoint now has a query facitilty (`ListAbstractions`) which is
  used to find on-disk
    - step holds and bookmarks
    - replication cursors (v1, v2)
    - last-received-holds
- the `zrepl holds list` command consumes endpoint.ListAbstractions
- the new `zrepl holds release-{all,stale}` commands can be used
  to remove abstractions of package endpoint

Co-authored-by: InsanePrawn <insane.prawny@gmail.com>

supersedes #282
fixes #280
fixes #278

client/holds_release.go

@@ -0,0 +1,144 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"github.com/fatih/color"
+	"github.com/pkg/errors"
+	"github.com/spf13/pflag"
+	"github.com/zrepl/zrepl/cli"
+	"github.com/zrepl/zrepl/endpoint"
+)
+
+// shared between release-all and release-step
+var holdsReleaseFlags struct {
+	Filter holdsFilterFlags
+	Json   bool
+	DryRun bool
+}
+
+func registerHoldsReleaseFlags(s *pflag.FlagSet) {
+	holdsReleaseFlags.Filter.registerHoldsFilterFlags(s, "release")
+	s.BoolVar(&holdsReleaseFlags.Json, "json", false, "emit json instead of pretty-printed")
+	s.BoolVar(&holdsReleaseFlags.DryRun, "dry-run", false, "do a dry-run")
+}
+
+var holdsCmdReleaseAll = &cli.Subcommand{
+	Use:             "release-all",
+	Run:             doHoldsReleaseAll,
+	NoRequireConfig: true,
+	Short:           `(DANGEROUS) release all zrepl-managed holds and bookmarks, mostly useful for uninstalling zrepl`,
+	SetupFlags:      registerHoldsReleaseFlags,
+}
+
+var holdsCmdReleaseStale = &cli.Subcommand{
+	Use:             "release-stale",
+	Run:             doHoldsReleaseStale,
+	NoRequireConfig: true,
+	Short:           `release stale zrepl-managed holds and boomkarks (useful if zrepl has a bug and doesn't do it by itself)`,
+	SetupFlags:      registerHoldsReleaseFlags,
+}
+
+func doHoldsReleaseAll(sc *cli.Subcommand, args []string) error {
+	var err error
+	ctx := context.Background()
+
+	if len(args) > 0 {
+		return errors.New("this subcommand takes no positional arguments")
+	}
+
+	q, err := holdsReleaseFlags.Filter.Query()
+	if err != nil {
+		return errors.Wrap(err, "invalid filter specification on command line")
+	}
+
+	abstractions, listErrors, err := endpoint.ListAbstractions(ctx, q)
+	if err != nil {
+		return err // context clear by invocation of command
+	}
+	if len(listErrors) > 0 {
+		color.New(color.FgRed).Fprintf(os.Stderr, "there were errors in listing the abstractions:\n%s\n", listErrors)
+		// proceed anyways with rest of abstractions
+	}
+
+	return doHoldsRelease_Common(ctx, abstractions)
+}
+
+func doHoldsReleaseStale(sc *cli.Subcommand, args []string) error {
+
+	var err error
+	ctx := context.Background()
+
+	if len(args) > 0 {
+		return errors.New("this subcommand takes no positional arguments")
+	}
+
+	q, err := holdsReleaseFlags.Filter.Query()
+	if err != nil {
+		return errors.Wrap(err, "invalid filter specification on command line")
+	}
+
+	stalenessInfo, err := endpoint.ListStale(ctx, q)
+	if err != nil {
+		return err // context clear by invocation of command
+	}
+
+	return doHoldsRelease_Common(ctx, stalenessInfo.Stale)
+}
+
+func doHoldsRelease_Common(ctx context.Context, destroy []endpoint.Abstraction) error {
+
+	if holdsReleaseFlags.DryRun {
+		if holdsReleaseFlags.Json {
+			m, err := json.MarshalIndent(destroy, "", "  ")
+			if err != nil {
+				panic(err)
+			}
+			if _, err := os.Stdout.Write(m); err != nil {
+				panic(err)
+			}
+			fmt.Println()
+		} else {
+			for _, a := range destroy {
+				fmt.Printf("would destroy %s\n", a)
+			}
+		}
+		return nil
+	}
+
+	outcome := endpoint.BatchDestroy(ctx, destroy)
+	hadErr := false
+
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	colorErr := color.New(color.FgRed)
+	printfSuccess := color.New(color.FgGreen).FprintfFunc()
+	printfSection := color.New(color.Bold).FprintfFunc()
+
+	for res := range outcome {
+		hadErr = hadErr || res.DestroyErr != nil
+		if holdsReleaseFlags.Json {
+			err := enc.Encode(res)
+			if err != nil {
+				colorErr.Fprintf(os.Stderr, "cannot marshal there were errors in destroying the abstractions")
+			}
+		} else {
+			printfSection(os.Stdout, "destroy %s ...", res.Abstraction)
+			if res.DestroyErr != nil {
+				colorErr.Fprintf(os.Stdout, " failed:\n%s\n", res.DestroyErr)
+			} else {
+				printfSuccess(os.Stdout, " OK\n")
+			}
+		}
+	}
+
+	if hadErr {
+		colorErr.Add(color.Bold).Fprintf(os.Stderr, "there were errors in destroying the abstractions")
+		return fmt.Errorf("")
+	} else {
+		return nil
+	}
+}