diff --git a/base/indented_stream.h b/base/indented_stream.h
new file mode 100644
index 0000000..b47bca2
--- /dev/null
+++ b/base/indented_stream.h
@@ -0,0 +1,48 @@
+#ifndef BASE_INDENTED_STREAM_H
+#define BASE_INDENTED_STREAM_H
+
+#include <iostream>
+
+//----------------------------------------------------------------
+
+namespace {
+	class indented_stream {
+	public:
+		indented_stream(std::ostream &out)
+		: out_(out),
+		  indent_(0) {
+		}
+
+		void indent() {
+			for (unsigned i = 0; i < indent_ * 2; i++)
+				out_ << ' ';
+		}
+
+		void inc() {
+			indent_++;
+		}
+
+		void dec() {
+			indent_--;
+		}
+
+		template <typename T>
+		indented_stream &operator <<(T const &t) {
+			out_ << t;
+			return *this;
+		}
+
+		indented_stream &operator <<(std::ostream &(*fp)(std::ostream &)) {
+			out_ << fp;
+			return *this;
+		}
+
+	private:
+		std::ostream &out_;
+		unsigned indent_;
+	};
+}
+
+//----------------------------------------------------------------
+
+#endif
diff --git a/caching/xml_format.cc b/caching/xml_format.cc
index b03e997..cb03018 100644
--- a/caching/xml_format.cc
+++ b/caching/xml_format.cc
@@ -1,4 +1,5 @@
 #include "base/base64.h"
+#include "base/indented_stream.h"
 #include "caching/xml_format.h"
 
 #include <boost/lexical_cast.hpp>
@@ -18,8 +19,7 @@ namespace {
 	class xml_emitter : public emitter {
 	public:
 		xml_emitter(ostream &out)
-		: out_(out),
-		  indent_(0) {
+		: out_(out) {
 		}
 
 		void begin_superblock(std::string const &uuid,
@@ -27,37 +27,37 @@ namespace {
 				      block_address nr_cache_blocks,
 				      std::string const &policy,
 				      size_t hint_width) {
-			indent();
+			out_.indent();
 			out_ << "<superblock uuid=\"" << uuid << "\""
 			     << " block_size=\"" << block_size << "\""
 			     << " nr_cache_blocks=\"" << nr_cache_blocks << "\""
 			     << " policy=\"" << policy << "\""
 			     << " hint_width=\"" << hint_width << "\">" << endl;
-			inc();
+			out_.inc();
 		}
 
 		virtual void end_superblock() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</superblock>" << endl;
 		}
 
 		virtual void begin_mappings() {
-			indent();
+			out_.indent();
 			out_ << "<mappings>" << endl;
-			inc();
+			out_.inc();
 		}
 
 		virtual void end_mappings() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</mappings>" << endl;
 		}
 
 		virtual void mapping(block_address cblock,
 				     block_address oblock,
 				     bool dirty) {
-			indent();
+			out_.indent();
 			out_ << "<mapping"
 			     << " cache_block=\"" << cblock << "\""
 			     << " origin_block=\"" << oblock << "\""
@@ -66,14 +66,14 @@ namespace {
 		}
 
 		virtual void begin_hints() {
-			indent();
+			out_.indent();
 			out_ << "<hints>" << endl;
-			inc();
+			out_.inc();
 		}
 
 		virtual void end_hints() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</hints>" << endl;
 		}
 
@@ -81,7 +81,7 @@ namespace {
 				  vector<unsigned char> const &data) {
 			using namespace base;
 
-			indent();
+			out_.indent();
 			out_ << "<hint"
 			     << " cache_block=\"" << cblock << "\""
 			     << " data=\"" << base64_encode(data) << "\""
@@ -89,19 +89,19 @@ namespace {
 		}
 
 		virtual void begin_discards() {
-			indent();
+			out_.indent();
 			out_ << "<discards>" << endl;
-			inc();
+			out_.inc();
 		}
 
 		virtual void end_discards() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</discards>" << endl;
 		}
 
 		virtual void discard(block_address dblock_b, block_address dblock_e) {
-			indent();
+			out_.indent();
 			out_ << "<discard dbegin=\"" << dblock_b << "\""
 			     << " dend=\"" << dblock_e << "\"/>" << endl;
 		}
@@ -111,22 +111,7 @@ namespace {
 			return v ? "true" : "false";
 		}
 
-		// FIXME: factor out a common class with the thin_provisioning emitter
-		void indent() {
-			for (unsigned i = 0; i < indent_ * 2; i++)
-				out_ << ' ';
-		}
-
-		void inc() {
-			indent_++;
-		}
-
-		void dec() {
-			indent_--;
-		}
-
-		ostream &out_;
-		unsigned indent_;
+		indented_stream out_;
 	};
 
 	//--------------------------------
diff --git a/era/xml_format.cc b/era/xml_format.cc
index 924a93b..0878410 100644
--- a/era/xml_format.cc
+++ b/era/xml_format.cc
@@ -1,5 +1,7 @@
 #include "era/xml_format.h"
 
+#include "base/indented_stream.h"
+
 using namespace boost;
 using namespace era;
 using namespace persistent_data;
@@ -11,82 +13,67 @@ namespace {
 	class xml_emitter : public emitter {
 	public:
 		xml_emitter(ostream &out)
-		: out_(out),
-		  indent_(0) {
+		: out_(out) {
 		}
 
 		void begin_superblock(std::string const &uuid,
 				      uint32_t block_size,
 				      pd::block_address nr_blocks,
 				      uint32_t current_era) {
-			indent();
+			out_.indent();
 			out_ << "<superblock uuid=\"" << uuid << "\""
 			     << " block_size=\"" << block_size << "\""
 			     << " nr_blocks=\"" << nr_blocks << "\""
-			     << " current_era=\"" << current_era << "\">" << endl;
-			inc();
+			     << " current_era=\"" << current_era << "\">";
+			out_ << endl;
+			out_.inc();
 		}
 
 		void end_superblock() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</superblock>" << endl;
 		}
 
 		void begin_writeset(uint32_t era, uint32_t nr_bits) {
-			indent();
+			out_.indent();
 			out_ << "<writeset era=\"" << era << "\""
 			     << " nr_bits=\"" << nr_bits << "\">" << endl;
-			inc();
+			out_.inc();
 		}
 
 		void writeset_bit(uint32_t bit, bool value) {
-			indent();
+			out_.indent();
 			// FIXME: collect all the bits, then uuencode
 			out_ << "<bit bit=\"" << bit << "\" value=\"" << value << "\">" << endl;
 		}
 
 		void end_writeset() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</writeset>" << endl;
 		}
 
 		void begin_era_array() {
-			indent();
+			out_.indent();
 			out_ << "<era_array>" << endl;
-			inc();
+			out_.inc();
 		}
 
 		void era(pd::block_address block, uint32_t era) {
-			indent();
+			out_.indent();
 			out_ << "<era block=\"" << block
 			     << "\" era=\"" << era << "\">" << endl;
 		}
 
 		void end_era_array() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</era_array>" << endl;
 		}
 
 	private:
-		// FIXME: factor out a common class with the thin_provisioning emitter
-		void indent() {
-			for (unsigned i = 0; i < indent_ * 2; i++)
-				out_ << ' ';
-		}
-
-		void inc() {
-			indent_++;
-		}
-
-		void dec() {
-			indent_--;
-		}
-
-		ostream &out_;
-		unsigned indent_;
+		indented_stream out_;
 	};
 }
 
diff --git a/thin-provisioning/xml_format.cc b/thin-provisioning/xml_format.cc
index 55007ca..2767b9a 100644
--- a/thin-provisioning/xml_format.cc
+++ b/thin-provisioning/xml_format.cc
@@ -17,6 +17,7 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "xml_format.h"
+#include "base/indented_stream.h"
 
 #include <boost/lexical_cast.hpp>
 #include <boost/optional.hpp>
@@ -41,8 +42,7 @@ namespace {
 	class xml_emitter : public emitter {
 	public:
 		xml_emitter(ostream &out)
-			: out_(out),
-			  indent_(0) {
+		: out_(out) {
 		}
 
 		void begin_superblock(string const &uuid,
@@ -51,7 +51,7 @@ namespace {
 				      uint32_t data_block_size,
 				      uint64_t nr_data_blocks,
 				      boost::optional<uint64_t> metadata_snap) {
-			indent();
+			out_.indent();
 			out_ << "<superblock uuid=\"" << uuid << "\""
 			     << " time=\"" << time << "\""
 			     << " transaction=\"" << trans_id << "\""
@@ -61,14 +61,13 @@ namespace {
 			if (metadata_snap)
 				out_ << "\" metadata_snap=\"" << *metadata_snap;
 
-			out_ << "\">"
-			     << endl;
-			inc();
+			out_ << "\">" << endl;
+			out_.inc();
 		}
 
 		void end_superblock() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</superblock>" << endl;
 		}
 
@@ -77,40 +76,40 @@ namespace {
 				  uint64_t trans_id,
 				  uint64_t creation_time,
 				  uint64_t snap_time) {
-			indent();
+			out_.indent();
 			out_ << "<device dev_id=\"" << dev_id << "\""
 			     << " mapped_blocks=\"" << mapped_blocks << "\""
 			     << " transaction=\"" << trans_id << "\""
 			     << " creation_time=\"" << creation_time << "\""
 			     << " snap_time=\"" << snap_time << "\">" << endl;
-			inc();
+			out_.inc();
 		}
 
 		void end_device() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</device>" << endl;
 		}
 
 		void begin_named_mapping(string const &name) {
-			indent();
+			out_.indent();
 			out_ << "<named_mapping>" << endl;
-			inc();
+			out_.inc();
 		}
 
 		void end_named_mapping() {
-			dec();
-			indent();
+			out_.dec();
+			out_.indent();
 			out_ << "</named_mapping>" << endl;
 		}
 
 		void identifier(string const &name) {
-			indent();
+			out_.indent();
 			out_ << "<identifier name=\"" << name << "\"/>" << endl;
 		}
 
 		void range_map(uint64_t origin_begin, uint64_t data_begin, uint32_t time, uint64_t len) {
-			indent();
+			out_.indent();
 
 			out_ << "<range_mapping origin_begin=\"" << origin_begin << "\""
 			     << " data_begin=\"" << data_begin << "\""
@@ -120,7 +119,7 @@ namespace {
 		}
 
 		void single_map(uint64_t origin_block, uint64_t data_block, uint32_t time) {
-			indent();
+			out_.indent();
 
 			out_ << "<single_mapping origin_block=\"" << origin_block << "\""
 			     << " data_block=\"" << data_block << "\""
@@ -129,21 +128,7 @@ namespace {
 		}
 
 	private:
-		void indent() {
-			for (unsigned i = 0; i < indent_ * 2; i++)
-				out_ << ' ';
-		}
-
-		void inc() {
-			indent_++;
-		}
-
-		void dec() {
-			indent_--;
-		}
-
-		ostream &out_;
-		unsigned indent_;
+		indented_stream out_;
 	};
 
 	//------------------------------------------------