go/zodb/zodbtools: Catobj

`zodb catobj` command to dump content of an object - similarly to `git
cat-file`. Two modes: raw and verbose with `zodb dump` like headers for
the object present.

There is no such command currently in zodbtools/py.

go/zodb/zodbtools/catobj.go

+// Copyright (C) 2017  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+package zodbtools
+// Catobj - dump content of a database object
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+
+	"lab.nexedi.com/kirr/go123/prog"
+	"lab.nexedi.com/kirr/neo/go/zodb"
+)
+
+
+// Catobj dumps content of one ZODB object.
+//
+// The object is printed in raw form without any headers (see Dumpobj)
+func Catobj(ctx context.Context, w io.Writer, stor zodb.IStorage, xid zodb.Xid) error {
+	buf, _, err := stor.Load(ctx, xid)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write(buf.Data) // NOTE deleted data are returned as err by Load
+	buf.Release()
+	if err != nil {
+		err = fmt.Errorf("%s: catobj %s: %s", stor.URL(), xid, err)
+	}
+	return err
+}
+
+// Dumpobj dumps content of one ZODB object with zodbdump-like header
+func Dumpobj(ctx context.Context, w io.Writer, stor zodb.IStorage, xid zodb.Xid, hashOnly bool) error {
+	var objInfo zodb.DataInfo
+
+	buf, serial, err := stor.Load(ctx, xid)
+	if err != nil {
+		return err
+	}
+
+	objInfo.Oid = xid.Oid
+	objInfo.Tid = serial
+	objInfo.Data = buf.Data
+	objInfo.DataTidHint = 0 // no copy detection at catobj - just dump raw content
+
+	d := dumper{W: w, HashOnly: hashOnly}
+	err = d.DumpData(&objInfo)
+	buf.Release()
+	return err
+}
+
+// ----------------------------------------
+const catobjSummary = "dump content of a database object"
+
+func catobjUsage(w io.Writer) {
+	fmt.Fprintf(w,
+`Usage: zodb catobj [OPTIONS] <storage> xid...
+Dump content of a ZODB database object.
+
+<storage> is an URL (see 'zodb help zurl') of a ZODB-storage.
+xid is object address (see 'zodb help xid').
+
+Options:
+
+	-h --help       this help text.
+	-hashonly	dump only hashes of objects without content.
+	-raw		dump object data without any headers. Only one object allowed.
+`)
+}
+
+func catobjMain(argv []string) {
+	hashOnly := false
+	raw := false
+
+	flags := flag.FlagSet{Usage: func() { catobjUsage(os.Stderr) }}
+	flags.Init("", flag.ExitOnError)
+	flags.BoolVar(&hashOnly, "hashonly", hashOnly, "dump only hashes of objects")
+	flags.BoolVar(&raw, "raw", hashOnly, "dump object data without any headers. Only one object allowed.")
+	// TODO also -batch to serve objects a-la `git cat-file --batch` ?
+	flags.Parse(argv[1:])
+
+	argv = flags.Args()
+	if len(argv) < 2 {
+		flags.Usage()
+		prog.Exit(2)
+	}
+	storUrl := argv[0]
+
+	if hashOnly && raw {
+		prog.Fatal("-hashonly & -raw are incompatible")
+	}
+
+	xidv := []zodb.Xid{}
+	for _, arg := range argv[1:] {
+		xid, err := zodb.ParseXid(arg)
+		if err != nil {
+			prog.Fatal(err)
+		}
+
+		xidv = append(xidv, xid)
+	}
+
+	if raw && len(xidv) > 1 {
+		prog.Fatal("only 1 object allowed with -raw")
+	}
+
+	ctx := context.Background()
+
+	stor, err := zodb.OpenStorage(ctx, storUrl, &zodb.OpenOptions{ReadOnly: true})
+	if err != nil {
+		prog.Fatal(err)
+	}
+	// TODO defer stor.Close()
+
+	catobj := func(xid zodb.Xid) error {
+		if raw {
+			return Catobj(ctx, os.Stdout, stor, xid)
+		} else {
+			return Dumpobj(ctx, os.Stdout, stor, xid, hashOnly)
+		}
+	}
+
+	for _, xid := range xidv {
+		err = catobj(xid)
+		if err != nil {
+			prog.Fatal(err)
+		}
+	}
+}

go/zodb/zodbtools/main.go

@@ -27,6 +27,7 @@ var commands = prog.CommandRegistry{
 	// NOTE the order commands are listed here is the order how they will appear in help
 	{"info", infoSummary, infoUsage, infoMain},
 	{"dump", dumpSummary, dumpUsage, dumpMain},
+	{"catobj", catobjSummary, catobjUsage, catobjMain},
 }
 
 // main zodbtools driver