3 files changed, 55 insertions, 5 deletions

diff --git a/cmd/geth/chaincmd.go b/cmd/geth/chaincmd.go
index 947532f40..8586e3b81 100644
--- a/cmd/geth/chaincmd.go
+++ b/cmd/geth/chaincmd.go
@@ -26,6 +26,12 @@ var (
 		Action: exportChain,
 		Name:   "export",
 		Usage:  `export blockchain into file`,
+		Description: `
+Requires a first argument of the file to write to.
+Optional second and third arguments control the first and
+last block to write. In this mode, the file will be appended
+if already existing.
+		`,
 	}
 	upgradedbCommand = cli.Command{
 		Action: upgradeDB,
@@ -63,12 +69,30 @@ func importChain(ctx *cli.Context) {
 }
 
 func exportChain(ctx *cli.Context) {
-	if len(ctx.Args()) != 1 {
+	if len(ctx.Args()) < 1 {
 		utils.Fatalf("This command requires an argument.")
 	}
 	chain, _, _, _ := utils.MakeChain(ctx)
 	start := time.Now()
-	if err := utils.ExportChain(chain, ctx.Args().First()); err != nil {
+
+	var err error
+	fp := ctx.Args().First()
+	if len(ctx.Args()) < 3 {
+		err = utils.ExportChain(chain, fp)
+	} else {
+		// This can be improved to allow for numbers larger than 9223372036854775807
+		first, ferr := strconv.ParseInt(ctx.Args().Get(1), 10, 64)
+		last, lerr := strconv.ParseInt(ctx.Args().Get(2), 10, 64)
+		if ferr != nil || lerr != nil {
+			utils.Fatalf("Export error in parsing parameters: block number not an integer\n")
+		}
+		if first < 0 || last < 0 {
+			utils.Fatalf("Export error: block number must be greater than 0\n")
+		}
+		err = utils.ExportAppendChain(chain, fp, uint64(first), uint64(last))
+	}
+
+	if err != nil {
 		utils.Fatalf("Export error: %v\n", err)
 	}
 	fmt.Printf("Export done in %v", time.Since(start))
diff --git a/cmd/utils/cmd.go b/cmd/utils/cmd.go
index e5413973d..f7520a8e4 100644
--- a/cmd/utils/cmd.go
+++ b/cmd/utils/cmd.go
@@ -268,3 +268,18 @@ func ExportChain(chainmgr *core.ChainManager, fn string) error {
 	glog.Infoln("Exported blockchain to", fn)
 	return nil
 }
+
+func ExportAppendChain(chainmgr *core.ChainManager, fn string, first uint64, last uint64) error {
+	glog.Infoln("Exporting blockchain to", fn)
+	// TODO verify mode perms
+	fh, err := os.OpenFile(fn, os.O_CREATE|os.O_APPEND|os.O_WRONLY, os.ModePerm)
+	if err != nil {
+		return err
+	}
+	defer fh.Close()
+	if err := chainmgr.ExportN(fh, first, last); err != nil {
+		return err
+	}
+	glog.Infoln("Exported blockchain to", fn)
+	return nil
+}
diff --git a/core/chain_manager.go b/core/chain_manager.go
index edd1cc742..e87253304 100644
--- a/core/chain_manager.go
+++ b/core/chain_manager.go
@@ -347,13 +347,24 @@ func (bc *ChainManager) ResetWithGenesisBlock(gb *types.Block) {
 
 // Export writes the active chain to the given writer.
 func (self *ChainManager) Export(w io.Writer) error {
+	if err := self.ExportN(w, uint64(0), self.currentBlock.NumberU64()); err != nil {
+		return err
+	}
+	return nil
+}
+
+// ExportN writes a subset of the active chain to the given writer.
+func (self *ChainManager) ExportN(w io.Writer, first uint64, last uint64) error {
 	self.mu.RLock()
 	defer self.mu.RUnlock()
-	glog.V(logger.Info).Infof("exporting %v blocks...\n", self.currentBlock.Header().Number)
 
-	last := self.currentBlock.NumberU64()
+	if first > last {
+		return fmt.Errorf("export failed: first (%d) is greater than last (%d)", first, last)
+	}
+
+	glog.V(logger.Info).Infof("exporting %d blocks...\n", last-first+1)
 
-	for nr := uint64(1); nr <= last; nr++ {
+	for nr := first; nr <= last; nr++ {
 		block := self.GetBlockByNumber(nr)
 		if block == nil {
 			return fmt.Errorf("export failed on #%d: not found", nr)