Merge branch 'db/delta-applier' into svn-fe

* db/delta-applier:
  vcs-svn: cap number of bytes read from sliding view
  test-svn-fe: split off "test-svn-fe -d" into a separate function
  vcs-svn: let deltas use data from preimage
  vcs-svn: let deltas use data from postimage
  vcs-svn: verify that deltas consume all inline data
  vcs-svn: implement copyfrom_data delta instruction
  vcs-svn: read instructions from deltas
  vcs-svn: read inline data from deltas
  vcs-svn: read the preimage when applying deltas
  vcs-svn: parse svndiff0 window header
  vcs-svn: skeleton of an svn delta parser
  vcs-svn: make buffer_read_binary API more convenient
  vcs-svn: learn to maintain a sliding view of a file
  Makefile: list one vcs-svn/xdiff object or header per line

Conflicts:
	Makefile
	vcs-svn/LICENSE

10 files changed, 753 insertions, 25 deletions

diff --git a/Makefile b/Makefile
index 91e20d29c6..e954dffa9e 100644
--- a/Makefile
+++ b/Makefile
@@ -342,6 +342,11 @@ BUILTIN_OBJS =
 BUILT_INS =
 COMPAT_CFLAGS =
 COMPAT_OBJS =
+XDIFF_H =
+XDIFF_OBJS =
+VCSSVN_H =
+VCSSVN_OBJS =
+VCSSVN_TEST_OBJS =
 EXTRA_CPPFLAGS =
 LIB_H =
 LIB_OBJS =
@@ -1832,11 +1837,23 @@ GIT_OBJS := $(LIB_OBJS) $(BUILTIN_OBJS) $(PROGRAM_OBJS) $(TEST_OBJS) \
 ifndef NO_CURL
 	GIT_OBJS += http.o http-walker.o remote-curl.o
 endif
-XDIFF_OBJS = xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o \
-	xdiff/xmerge.o xdiff/xpatience.o
-VCSSVN_OBJS = vcs-svn/line_buffer.o vcs-svn/repo_tree.o \
-	vcs-svn/fast_export.o vcs-svn/svndump.o
-VCSSVN_TEST_OBJS = test-line-buffer.o
+
+XDIFF_OBJS += xdiff/xdiffi.o
+XDIFF_OBJS += xdiff/xprepare.o
+XDIFF_OBJS += xdiff/xutils.o
+XDIFF_OBJS += xdiff/xemit.o
+XDIFF_OBJS += xdiff/xmerge.o
+XDIFF_OBJS += xdiff/xpatience.o
+
+VCSSVN_OBJS += vcs-svn/line_buffer.o
+VCSSVN_OBJS += vcs-svn/sliding_window.o
+VCSSVN_OBJS += vcs-svn/repo_tree.o
+VCSSVN_OBJS += vcs-svn/fast_export.o
+VCSSVN_OBJS += vcs-svn/svndiff.o
+VCSSVN_OBJS += vcs-svn/svndump.o
+
+VCSSVN_TEST_OBJS += test-line-buffer.o
+
 OBJECTS := $(GIT_OBJS) $(XDIFF_OBJS) $(VCSSVN_OBJS)
 
 dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
@@ -1955,15 +1972,25 @@ connect.o transport.o http-backend.o: url.h
 http-fetch.o http-walker.o remote-curl.o transport.o walker.o: walker.h
 http.o http-walker.o http-push.o http-fetch.o remote-curl.o: http.h url.h
 
-xdiff-interface.o $(XDIFF_OBJS): \
-	xdiff/xinclude.h xdiff/xmacros.h xdiff/xdiff.h xdiff/xtypes.h \
-	xdiff/xutils.h xdiff/xprepare.h xdiff/xdiffi.h xdiff/xemit.h
-
-$(VCSSVN_OBJS) $(VCSSVN_TEST_OBJS): $(LIB_H) \
-	vcs-svn/line_buffer.h vcs-svn/repo_tree.h vcs-svn/fast_export.h \
-	vcs-svn/svndump.h
-
-test-svn-fe.o: vcs-svn/svndump.h
+XDIFF_H += xdiff/xinclude.h
+XDIFF_H += xdiff/xmacros.h
+XDIFF_H += xdiff/xdiff.h
+XDIFF_H += xdiff/xtypes.h
+XDIFF_H += xdiff/xutils.h
+XDIFF_H += xdiff/xprepare.h
+XDIFF_H += xdiff/xdiffi.h
+XDIFF_H += xdiff/xemit.h
+
+xdiff-interface.o $(XDIFF_OBJS): $(XDIFF_H)
+
+VCSSVN_H += vcs-svn/line_buffer.h
+VCSSVN_H += vcs-svn/sliding_window.h
+VCSSVN_H += vcs-svn/repo_tree.h
+VCSSVN_H += vcs-svn/fast_export.h
+VCSSVN_H += vcs-svn/svndiff.h
+VCSSVN_H += vcs-svn/svndump.h
+
+$(VCSSVN_OBJS) $(VCSSVN_TEST_OBJS): $(LIB_H) $(VCSSVN_H)
 endif
 
 exec_cmd.s exec_cmd.o: EXTRA_CPPFLAGS = \
diff --git a/t/t9011-svn-da.sh b/t/t9011-svn-da.sh
new file mode 100755
index 0000000000..b38d16f9db
--- /dev/null
+++ b/t/t9011-svn-da.sh
@@ -0,0 +1,248 @@
+#!/bin/sh
+
+test_description='test parsing of svndiff0 files
+
+Using the "test-svn-fe -d" helper, check that svn-fe correctly
+interprets deltas using various facilities (some from the spec,
+some only learned from practice).
+'
+. ./test-lib.sh
+
+>empty
+printf foo >preimage
+
+test_expect_success 'reject empty delta' '
+	test_must_fail test-svn-fe -d preimage empty 0
+'
+
+test_expect_success 'delta can empty file' '
+	printf "SVNQ" | q_to_nul >clear.delta &&
+	test-svn-fe -d preimage clear.delta 4 >actual &&
+	test_cmp empty actual
+'
+
+test_expect_success 'reject svndiff2' '
+	printf "SVN\002" >bad.filetype &&
+	test_must_fail test-svn-fe -d preimage bad.filetype 4
+'
+
+test_expect_success 'one-window empty delta' '
+	printf "SVNQ%s" "QQQQQ" | q_to_nul >clear.onewindow &&
+	test-svn-fe -d preimage clear.onewindow 9 >actual &&
+	test_cmp empty actual
+'
+
+test_expect_success 'reject incomplete window header' '
+	printf "SVNQ%s" "QQQQQ" | q_to_nul >clear.onewindow &&
+	printf "SVNQ%s" "QQ" | q_to_nul >clear.partialwindow &&
+	test_must_fail test-svn-fe -d preimage clear.onewindow 6 &&
+	test_must_fail test-svn-fe -d preimage clear.partialwindow 6
+'
+
+test_expect_success 'reject declared delta longer than actual delta' '
+	printf "SVNQ%s" "QQQQQ" | q_to_nul >clear.onewindow &&
+	printf "SVNQ%s" "QQ" | q_to_nul >clear.partialwindow &&
+	test_must_fail test-svn-fe -d preimage clear.onewindow 14 &&
+	test_must_fail test-svn-fe -d preimage clear.partialwindow 9
+'
+
+test_expect_success 'two-window empty delta' '
+	printf "SVNQ%s%s" "QQQQQ" "QQQQQ" | q_to_nul >clear.twowindow &&
+	test-svn-fe -d preimage clear.twowindow 14 >actual &&
+	test_must_fail test-svn-fe -d preimage clear.twowindow 13 &&
+	test_cmp empty actual
+'
+
+test_expect_success 'noisy zeroes' '
+	printf "SVNQ%s" \
+		"RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRQQQQQ" |
+		tr R "\200" |
+		q_to_nul >clear.noisy &&
+	len=$(wc -c <clear.noisy) &&
+	test-svn-fe -d preimage clear.noisy $len &&
+	test_cmp empty actual
+'
+
+test_expect_success 'reject variable-length int in magic' '
+	printf "SVNRQ" | tr R "\200" | q_to_nul >clear.badmagic &&
+	test_must_fail test-svn-fe -d preimage clear.badmagic 5
+'
+
+test_expect_success 'reject truncated integer' '
+	printf "SVNQ%s%s" "QQQQQ" "QQQQRRQ" |
+		tr R "\200" |
+		q_to_nul >clear.fullint &&
+	printf "SVNQ%s%s" "QQQQQ" "QQQQRR" |
+		tr RT "\201" |
+		q_to_nul >clear.partialint &&
+	test_must_fail test-svn-fe -d preimage clear.fullint 15 &&
+	test-svn-fe -d preimage clear.fullint 16 &&
+	test_must_fail test-svn-fe -d preimage clear.partialint 15
+'
+
+test_expect_success 'nonempty (but unused) preimage view' '
+	printf "SVNQ%b" "Q\003QQQ" | q_to_nul >clear.readpreimage &&
+	test-svn-fe -d preimage clear.readpreimage 9 >actual &&
+	test_cmp empty actual
+'
+
+test_expect_success 'preimage view: right endpoint cannot backtrack' '
+	printf "SVNQ%b%b" "Q\003QQQ" "Q\002QQQ" |
+		q_to_nul >clear.backtrack &&
+	test_must_fail test-svn-fe -d preimage clear.backtrack 14
+'
+
+test_expect_success 'preimage view: left endpoint can advance' '
+	printf "SVNQ%b%b" "Q\003QQQ" "\001\002QQQ" |
+		q_to_nul >clear.preshrink &&
+	printf "SVNQ%b%b" "Q\003QQQ" "\001\001QQQ" |
+		q_to_nul >clear.shrinkbacktrack &&
+	test-svn-fe -d preimage clear.preshrink 14 >actual &&
+	test_must_fail test-svn-fe -d preimage clear.shrinkbacktrack 14 &&
+	test_cmp empty actual
+'
+
+test_expect_success 'preimage view: offsets compared by value' '
+	printf "SVNQ%b%b" "\001\001QQQ" "\0200Q\003QQQ" |
+		q_to_nul >clear.noisybacktrack &&
+	printf "SVNQ%b%b" "\001\001QQQ" "\0200\001\002QQQ" |
+		q_to_nul >clear.noisyadvance &&
+	test_must_fail test-svn-fe -d preimage clear.noisybacktrack 15 &&
+	test-svn-fe -d preimage clear.noisyadvance 15 &&
+	test_cmp empty actual
+'
+
+test_expect_success 'preimage view: reject truncated preimage' '
+	printf "SVNQ%b" "\010QQQQ" | q_to_nul >clear.lateemptyread &&
+	printf "SVNQ%b" "\010\001QQQ" | q_to_nul >clear.latenonemptyread &&
+	printf "SVNQ%b" "\001\010QQQ" | q_to_nul >clear.longread &&
+	test_must_fail test-svn-fe -d preimage clear.lateemptyread 9 &&
+	test_must_fail test-svn-fe -d preimage clear.latenonemptyread 9 &&
+	test_must_fail test-svn-fe -d preimage clear.longread 9
+'
+
+test_expect_success 'forbid unconsumed inline data' '
+	printf "SVNQ%b%s%b%s" "QQQQ\003" "bar" "QQQQ\001" "x" |
+		q_to_nul >inline.clear &&
+	test_must_fail test-svn-fe -d preimage inline.clear 18 >actual
+'
+
+test_expect_success 'reject truncated inline data' '
+	printf "SVNQ%b%s" "QQQQ\003" "b" | q_to_nul >inline.trunc &&
+	test_must_fail test-svn-fe -d preimage inline.trunc 10
+'
+
+test_expect_success 'reject truncated inline data (after instruction section)' '
+	printf "SVNQ%b%b%s" "QQ\001\001\003" "\0201" "b" | q_to_nul >insn.trunc &&
+	test_must_fail test-svn-fe -d preimage insn.trunc 11
+'
+
+test_expect_success 'copyfrom_data' '
+	echo hi >expect &&
+	printf "SVNQ%b%b%b" "QQ\003\001\003" "\0203" "hi\n" | q_to_nul >copydat &&
+	test-svn-fe -d preimage copydat 13 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'multiple copyfrom_data' '
+	echo hi >expect &&
+	printf "SVNQ%b%b%b%b%b" "QQ\003\002\003" "\0201\0202" "hi\n" \
+		"QQQ\002Q" "\0200Q" | q_to_nul >copy.multi &&
+	len=$(wc -c <copy.multi) &&
+	test-svn-fe -d preimage copy.multi $len >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'incomplete multiple insn' '
+	printf "SVNQ%b%b%b" "QQ\003\002\003" "\0203\0200" "hi\n" |
+		q_to_nul >copy.partial &&
+	len=$(wc -c <copy.partial) &&
+	test_must_fail test-svn-fe -d preimage copy.partial $len
+'
+
+test_expect_success 'catch attempt to copy missing data' '
+	printf "SVNQ%b%b%s%b%s" "QQ\002\002\001" "\0201\0201" "X" \
+			"QQQQ\002" "YZ" |
+		q_to_nul >copy.incomplete &&
+	len=$(wc -c <copy.incomplete) &&
+	test_must_fail test-svn-fe -d preimage copy.incomplete $len
+'
+
+test_expect_success 'copyfrom target to repeat data' '
+	printf foofoo >expect &&
+	printf "SVNQ%b%b%s" "QQ\006\004\003" "\0203\0100\003Q" "foo" |
+		q_to_nul >copytarget.repeat &&
+	len=$(wc -c <copytarget.repeat) &&
+	test-svn-fe -d preimage copytarget.repeat $len >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'copyfrom target out of order' '
+	printf foooof >expect &&
+	printf "SVNQ%b%b%s" \
+		"QQ\006\007\003" "\0203\0101\002\0101\001\0101Q" "foo" |
+		q_to_nul >copytarget.reverse &&
+	len=$(wc -c <copytarget.reverse) &&
+	test-svn-fe -d preimage copytarget.reverse $len >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'catch copyfrom future' '
+	printf "SVNQ%b%b%s" "QQ\004\004\003" "\0202\0101\002\0201" "XYZ" |
+		q_to_nul >copytarget.infuture &&
+	len=$(wc -c <copytarget.infuture) &&
+	test_must_fail test-svn-fe -d preimage copytarget.infuture $len
+'
+
+test_expect_success 'copy to sustain' '
+	printf XYXYXYXYXYXZ >expect &&
+	printf "SVNQ%b%b%s" "QQ\014\004\003" "\0202\0111Q\0201" "XYZ" |
+		q_to_nul >copytarget.sustain &&
+	len=$(wc -c <copytarget.sustain) &&
+	test-svn-fe -d preimage copytarget.sustain $len >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'catch copy that overflows' '
+	printf "SVNQ%b%b%s" "QQ\003\003\001" "\0201\0177Q" X |
+		q_to_nul >copytarget.overflow &&
+	len=$(wc -c <copytarget.overflow) &&
+	test_must_fail test-svn-fe -d preimage copytarget.overflow $len
+'
+
+test_expect_success 'copyfrom source' '
+	printf foo >expect &&
+	printf "SVNQ%b%b" "Q\003\003\002Q" "\003Q" | q_to_nul >copysource.all &&
+	test-svn-fe -d preimage copysource.all 11 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'copy backwards' '
+	printf oof >expect &&
+	printf "SVNQ%b%b" "Q\003\003\006Q" "\001\002\001\001\001Q" |
+		q_to_nul >copysource.rev &&
+	test-svn-fe -d preimage copysource.rev 15 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'offsets are relative to window' '
+	printf fo >expect &&
+	printf "SVNQ%b%b%b%b" "Q\003\001\002Q" "\001Q" \
+		"\002\001\001\002Q" "\001Q" |
+		q_to_nul >copysource.two &&
+	test-svn-fe -d preimage copysource.two 18 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'example from notes/svndiff' '
+	printf aaaaccccdddddddd >expect &&
+	printf aaaabbbbcccc >source &&
+	printf "SVNQ%b%b%s" "Q\014\020\007\001" \
+		"\004Q\004\010\0201\0107\010" d |
+		q_to_nul >delta.example &&
+	len=$(wc -c <delta.example) &&
+	test-svn-fe -d source delta.example $len >actual &&
+	test_cmp expect actual
+'
+
+test_done
diff --git a/test-svn-fe.c b/test-svn-fe.c
index b42ba789b1..332a5f711d 100644
--- a/test-svn-fe.c
+++ b/test-svn-fe.c
@@ -4,15 +4,51 @@
 
 #include "git-compat-util.h"
 #include "vcs-svn/svndump.h"
+#include "vcs-svn/svndiff.h"
+#include "vcs-svn/sliding_window.h"
+#include "vcs-svn/line_buffer.h"
 
-int main(int argc, char *argv[])
+static const char test_svnfe_usage[] =
+	"test-svn-fe (<dumpfile> | [-d] <preimage> <delta> <len>)";
+
+static int apply_delta(int argc, char *argv[])
 {
-	if (argc != 2)
-		usage("test-svn-fe <file>");
-	if (svndump_init(argv[1]))
+	struct line_buffer preimage = LINE_BUFFER_INIT;
+	struct line_buffer delta = LINE_BUFFER_INIT;
+	struct sliding_view preimage_view = SLIDING_VIEW_INIT(&preimage, -1);
+
+	if (argc != 5)
+		usage(test_svnfe_usage);
+
+	if (buffer_init(&preimage, argv[2]))
+		die_errno("cannot open preimage");
+	if (buffer_init(&delta, argv[3]))
+		die_errno("cannot open delta");
+	if (svndiff0_apply(&delta, (off_t) strtoull(argv[4], NULL, 0),
+					&preimage_view, stdout))
 		return 1;
-	svndump_read(NULL);
-	svndump_deinit();
-	svndump_reset();
+	if (buffer_deinit(&preimage))
+		die_errno("cannot close preimage");
+	if (buffer_deinit(&delta))
+		die_errno("cannot close delta");
+	buffer_reset(&preimage);
+	strbuf_release(&preimage_view.buf);
+	buffer_reset(&delta);
 	return 0;
 }
+
+int main(int argc, char *argv[])
+{
+	if (argc == 2) {
+		if (svndump_init(argv[1]))
+			return 1;
+		svndump_read(NULL);
+		svndump_deinit();
+		svndump_reset();
+		return 0;
+	}
+
+	if (argc >= 2 && !strcmp(argv[1], "-d"))
+		return apply_delta(argc, argv);
+	usage(test_svnfe_usage);
+}
diff --git a/vcs-svn/LICENSE b/vcs-svn/LICENSE
index 533f585ebf..eb91858b82 100644
--- a/vcs-svn/LICENSE
+++ b/vcs-svn/LICENSE
@@ -1,6 +1,8 @@
 Copyright (C) 2010 David Barr <david.barr@cordelta.com>.
 All rights reserved.
 
+Copyright (C) 2010 Jonathan Nieder <jrnieder@gmail.com>.
+
 Copyright (C) 2005 Stefan Hegny, hydrografix Consulting GmbH,
 Frankfurt/Main, Germany
 and others, see http://svn2cc.sarovar.org
diff --git a/vcs-svn/line_buffer.c b/vcs-svn/line_buffer.c
index c39038723e..01fcb842f1 100644
--- a/vcs-svn/line_buffer.c
+++ b/vcs-svn/line_buffer.c
@@ -91,10 +91,10 @@ char *buffer_read_line(struct line_buffer *buf)
 	return buf->line_buffer;
 }
 
-void buffer_read_binary(struct line_buffer *buf,
-				struct strbuf *sb, uint32_t size)
+size_t buffer_read_binary(struct line_buffer *buf,
+				struct strbuf *sb, size_t size)
 {
-	strbuf_fread(sb, size, buf->infile);
+	return strbuf_fread(sb, size, buf->infile);
 }
 
 off_t buffer_copy_bytes(struct line_buffer *buf, off_t nbytes)
diff --git a/vcs-svn/line_buffer.h b/vcs-svn/line_buffer.h
index d0b22dda76..8901f214ba 100644
--- a/vcs-svn/line_buffer.h
+++ b/vcs-svn/line_buffer.h
@@ -23,7 +23,7 @@ long buffer_tmpfile_prepare_to_read(struct line_buffer *buf);
 int buffer_ferror(struct line_buffer *buf);
 char *buffer_read_line(struct line_buffer *buf);
 int buffer_read_char(struct line_buffer *buf);
-void buffer_read_binary(struct line_buffer *buf, struct strbuf *sb, uint32_t len);
+size_t buffer_read_binary(struct line_buffer *buf, struct strbuf *sb, size_t len);
 /* Returns number of bytes read (not necessarily written). */
 off_t buffer_copy_bytes(struct line_buffer *buf, off_t len);
 off_t buffer_skip_bytes(struct line_buffer *buf, off_t len);
diff --git a/vcs-svn/sliding_window.c b/vcs-svn/sliding_window.c
new file mode 100644
index 0000000000..1bac7a4c7f
--- /dev/null
+++ b/vcs-svn/sliding_window.c
@@ -0,0 +1,79 @@
+/*
+ * Licensed under a two-clause BSD-style license.
+ * See LICENSE for details.
+ */
+
+#include "git-compat-util.h"
+#include "sliding_window.h"
+#include "line_buffer.h"
+#include "strbuf.h"
+
+static int input_error(struct line_buffer *file)
+{
+	if (!buffer_ferror(file))
+		return error("delta preimage ends early");
+	return error("cannot read delta preimage: %s", strerror(errno));
+}
+
+static int skip_or_whine(struct line_buffer *file, off_t gap)
+{
+	if (buffer_skip_bytes(file, gap) != gap)
+		return input_error(file);
+	return 0;
+}
+
+static int read_to_fill_or_whine(struct line_buffer *file,
+				struct strbuf *buf, size_t width)
+{
+	buffer_read_binary(file, buf, width - buf->len);
+	if (buf->len != width)
+		return input_error(file);
+	return 0;
+}
+
+static int check_overflow(off_t a, size_t b)
+{
+	if (b > maximum_signed_value_of_type(off_t))
+		return error("unrepresentable length in delta: "
+				"%"PRIuMAX" > OFF_MAX", (uintmax_t) b);
+	if (signed_add_overflows(a, (off_t) b))
+		return error("unrepresentable offset in delta: "
+				"%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
+				(uintmax_t) a, (uintmax_t) b);
+	return 0;
+}
+
+int move_window(struct sliding_view *view, off_t off, size_t width)
+{
+	off_t file_offset;
+	assert(view);
+	assert(view->width <= view->buf.len);
+	assert(!check_overflow(view->off, view->buf.len));
+
+	if (check_overflow(off, width))
+		return -1;
+	if (off < view->off || off + width < view->off + view->width)
+		return error("invalid delta: window slides left");
+	if (view->max_off >= 0 && view->max_off < off + width)
+		return error("delta preimage ends early");
+
+	file_offset = view->off + view->buf.len;
+	if (off < file_offset) {
+		/* Move the overlapping region into place. */
+		strbuf_remove(&view->buf, 0, off - view->off);
+	} else {
+		/* Seek ahead to skip the gap. */
+		if (skip_or_whine(view->file, off - file_offset))
+			return -1;
+		strbuf_setlen(&view->buf, 0);
+	}
+
+	if (view->buf.len > width)
+		; /* Already read. */
+	else if (read_to_fill_or_whine(view->file, &view->buf, width))
+		return -1;
+
+	view->off = off;
+	view->width = width;
+	return 0;
+}
diff --git a/vcs-svn/sliding_window.h b/vcs-svn/sliding_window.h
new file mode 100644
index 0000000000..b43a825cba
--- /dev/null
+++ b/vcs-svn/sliding_window.h
@@ -0,0 +1,18 @@
+#ifndef SLIDING_WINDOW_H_
+#define SLIDING_WINDOW_H_
+
+#include "strbuf.h"
+
+struct sliding_view {
+	struct line_buffer *file;
+	off_t off;
+	size_t width;
+	off_t max_off;	/* -1 means unlimited */
+	struct strbuf buf;
+};
+
+#define SLIDING_VIEW_INIT(input, len)	{ (input), 0, 0, (len), STRBUF_INIT }
+
+extern int move_window(struct sliding_view *view, off_t off, size_t width);
+
+#endif
diff --git a/vcs-svn/svndiff.c b/vcs-svn/svndiff.c
new file mode 100644
index 0000000000..9ee41bbc90
--- /dev/null
+++ b/vcs-svn/svndiff.c
@@ -0,0 +1,308 @@
+/*
+ * Licensed under a two-clause BSD-style license.
+ * See LICENSE for details.
+ */
+
+#include "git-compat-util.h"
+#include "sliding_window.h"
+#include "line_buffer.h"
+#include "svndiff.h"
+
+/*
+ * svndiff0 applier
+ *
+ * See http://svn.apache.org/repos/asf/subversion/trunk/notes/svndiff.
+ *
+ * svndiff0 ::= 'SVN\0' window*
+ * window ::= int int int int int instructions inline_data;
+ * instructions ::= instruction*;
+ * instruction ::= view_selector int int
+ *   | copyfrom_data int
+ *   | packed_view_selector int
+ *   | packed_copyfrom_data
+ *   ;
+ * view_selector ::= copyfrom_source
+ *   | copyfrom_target
+ *   ;
+ * copyfrom_source ::= # binary 00 000000;
+ * copyfrom_target ::= # binary 01 000000;
+ * copyfrom_data ::= # binary 10 000000;
+ * packed_view_selector ::= # view_selector OR-ed with 6 bit value;
+ * packed_copyfrom_data ::= # copyfrom_data OR-ed with 6 bit value;
+ * int ::= highdigit* lowdigit;
+ * highdigit ::= # binary 1000 0000 OR-ed with 7 bit value;
+ * lowdigit ::= # 7 bit value;
+ */
+
+#define INSN_MASK	0xc0
+#define INSN_COPYFROM_SOURCE	0x00
+#define INSN_COPYFROM_TARGET	0x40
+#define INSN_COPYFROM_DATA	0x80
+#define OPERAND_MASK	0x3f
+
+#define VLI_CONTINUE	0x80
+#define VLI_DIGIT_MASK	0x7f
+#define VLI_BITS_PER_DIGIT 7
+
+struct window {
+	struct sliding_view *in;
+	struct strbuf out;
+	struct strbuf instructions;
+	struct strbuf data;
+};
+
+#define WINDOW_INIT(w)	{ (w), STRBUF_INIT, STRBUF_INIT, STRBUF_INIT }
+
+static void window_release(struct window *ctx)
+{
+	strbuf_release(&ctx->out);
+	strbuf_release(&ctx->instructions);
+	strbuf_release(&ctx->data);
+}
+
+static int write_strbuf(struct strbuf *sb, FILE *out)
+{
+	if (fwrite(sb->buf, 1, sb->len, out) == sb->len)	/* Success. */
+		return 0;
+	return error("cannot write delta postimage: %s", strerror(errno));
+}
+
+static int error_short_read(struct line_buffer *input)
+{
+	if (buffer_ferror(input))
+		return error("error reading delta: %s", strerror(errno));
+	return error("invalid delta: unexpected end of file");
+}
+
+static int read_chunk(struct line_buffer *delta, off_t *delta_len,
+		      struct strbuf *buf, size_t len)
+{
+	strbuf_reset(buf);
+	if (len > *delta_len ||
+	    buffer_read_binary(delta, buf, len) != len)
+		return error_short_read(delta);
+	*delta_len -= buf->len;
+	return 0;
+}
+
+static int read_magic(struct line_buffer *in, off_t *len)
+{
+	static const char magic[] = {'S', 'V', 'N', '\0'};
+	struct strbuf sb = STRBUF_INIT;
+
+	if (read_chunk(in, len, &sb, sizeof(magic))) {
+		strbuf_release(&sb);
+		return -1;
+	}
+	if (memcmp(sb.buf, magic, sizeof(magic))) {
+		strbuf_release(&sb);
+		return error("invalid delta: unrecognized file type");
+	}
+	strbuf_release(&sb);
+	return 0;
+}
+
+static int read_int(struct line_buffer *in, uintmax_t *result, off_t *len)
+{
+	uintmax_t rv = 0;
+	off_t sz;
+	for (sz = *len; sz; sz--) {
+		const int ch = buffer_read_char(in);
+		if (ch == EOF)
+			break;
+
+		rv <<= VLI_BITS_PER_DIGIT;
+		rv += (ch & VLI_DIGIT_MASK);
+		if (ch & VLI_CONTINUE)
+			continue;
+
+		*result = rv;
+		*len = sz - 1;
+		return 0;
+	}
+	return error_short_read(in);
+}
+
+static int parse_int(const char **buf, size_t *result, const char *end)
+{
+	size_t rv = 0;
+	const char *pos;
+	for (pos = *buf; pos != end; pos++) {
+		unsigned char ch = *pos;
+
+		rv <<= VLI_BITS_PER_DIGIT;
+		rv += (ch & VLI_DIGIT_MASK);
+		if (ch & VLI_CONTINUE)
+			continue;
+
+		*result = rv;
+		*buf = pos + 1;
+		return 0;
+	}
+	return error("invalid delta: unexpected end of instructions section");
+}
+
+static int read_offset(struct line_buffer *in, off_t *result, off_t *len)
+{
+	uintmax_t val;
+	if (read_int(in, &val, len))
+		return -1;
+	if (val > maximum_signed_value_of_type(off_t))
+		return error("unrepresentable offset in delta: %"PRIuMAX"", val);
+	*result = val;
+	return 0;
+}
+
+static int read_length(struct line_buffer *in, size_t *result, off_t *len)
+{
+	uintmax_t val;
+	if (read_int(in, &val, len))
+		return -1;
+	if (val > SIZE_MAX)
+		return error("unrepresentable length in delta: %"PRIuMAX"", val);
+	*result = val;
+	return 0;
+}
+
+static int copyfrom_source(struct window *ctx, const char **instructions,
+			   size_t nbytes, const char *insns_end)
+{
+	size_t offset;
+	if (parse_int(instructions, &offset, insns_end))
+		return -1;
+	if (unsigned_add_overflows(offset, nbytes) ||
+	    offset + nbytes > ctx->in->width)
+		return error("invalid delta: copies source data outside view");
+	strbuf_add(&ctx->out, ctx->in->buf.buf + offset, nbytes);
+	return 0;
+}
+
+static int copyfrom_target(struct window *ctx, const char **instructions,
+			   size_t nbytes, const char *instructions_end)
+{
+	size_t offset;
+	if (parse_int(instructions, &offset, instructions_end))
+		return -1;
+	if (offset >= ctx->out.len)
+		return error("invalid delta: copies from the future");
+	for (; nbytes > 0; nbytes--)
+		strbuf_addch(&ctx->out, ctx->out.buf[offset++]);
+	return 0;
+}
+
+static int copyfrom_data(struct window *ctx, size_t *data_pos, size_t nbytes)
+{
+	const size_t pos = *data_pos;
+	if (unsigned_add_overflows(pos, nbytes) ||
+	    pos + nbytes > ctx->data.len)
+		return error("invalid delta: copies unavailable inline data");
+	strbuf_add(&ctx->out, ctx->data.buf + pos, nbytes);
+	*data_pos += nbytes;
+	return 0;
+}
+
+static int parse_first_operand(const char **buf, size_t *out, const char *end)
+{
+	size_t result = (unsigned char) *(*buf)++ & OPERAND_MASK;
+	if (result) {	/* immediate operand */
+		*out = result;
+		return 0;
+	}
+	return parse_int(buf, out, end);
+}
+
+static int execute_one_instruction(struct window *ctx,
+				const char **instructions, size_t *data_pos)
+{
+	unsigned int instruction;
+	const char *insns_end = ctx->instructions.buf + ctx->instructions.len;
+	size_t nbytes;
+	assert(ctx);
+	assert(instructions && *instructions);
+	assert(data_pos);
+
+	instruction = (unsigned char) **instructions;
+	if (parse_first_operand(instructions, &nbytes, insns_end))
+		return -1;
+	switch (instruction & INSN_MASK) {
+	case INSN_COPYFROM_SOURCE:
+		return copyfrom_source(ctx, instructions, nbytes, insns_end);
+	case INSN_COPYFROM_TARGET:
+		return copyfrom_target(ctx, instructions, nbytes, insns_end);
+	case INSN_COPYFROM_DATA:
+		return copyfrom_data(ctx, data_pos, nbytes);
+	default:
+		return error("invalid delta: unrecognized instruction");
+	}
+}
+
+static int apply_window_in_core(struct window *ctx)
+{
+	const char *instructions;
+	size_t data_pos = 0;
+
+	/*
+	 * Fill ctx->out.buf using data from the source, target,
+	 * and inline data views.
+	 */
+	for (instructions = ctx->instructions.buf;
+	     instructions != ctx->instructions.buf + ctx->instructions.len;
+	     )
+		if (execute_one_instruction(ctx, &instructions, &data_pos))
+			return -1;
+	if (data_pos != ctx->data.len)
+		return error("invalid delta: does not copy all inline data");
+	return 0;
+}
+
+static int apply_one_window(struct line_buffer *delta, off_t *delta_len,
+			    struct sliding_view *preimage, FILE *out)
+{
+	struct window ctx = WINDOW_INIT(preimage);
+	size_t out_len;
+	size_t instructions_len;
+	size_t data_len;
+	assert(delta_len);
+
+	/* "source view" offset and length already handled; */
+	if (read_length(delta, &out_len, delta_len) ||
+	    read_length(delta, &instructions_len, delta_len) ||
+	    read_length(delta, &data_len, delta_len) ||
+	    read_chunk(delta, delta_len, &ctx.instructions, instructions_len) ||
+	    read_chunk(delta, delta_len, &ctx.data, data_len))
+		goto error_out;
+	strbuf_grow(&ctx.out, out_len);
+	if (apply_window_in_core(&ctx))
+		goto error_out;
+	if (ctx.out.len != out_len) {
+		error("invalid delta: incorrect postimage length");
+		goto error_out;
+	}
+	if (write_strbuf(&ctx.out, out))
+		goto error_out;
+	window_release(&ctx);
+	return 0;
+error_out:
+	window_release(&ctx);
+	return -1;
+}
+
+int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
+			struct sliding_view *preimage, FILE *postimage)
+{
+	assert(delta && preimage && postimage);
+
+	if (read_magic(delta, &delta_len))
+		return -1;
+	while (delta_len) {	/* For each window: */
+		off_t pre_off;
+		size_t pre_len;
+
+		if (read_offset(delta, &pre_off, &delta_len) ||
+		    read_length(delta, &pre_len, &delta_len) ||
+		    move_window(preimage, pre_off, pre_len) ||
+		    apply_one_window(delta, &delta_len, preimage, postimage))
+			return -1;
+	}
+	return 0;
+}
diff --git a/vcs-svn/svndiff.h b/vcs-svn/svndiff.h
new file mode 100644
index 0000000000..74eb464bab
--- /dev/null
+++ b/vcs-svn/svndiff.h
@@ -0,0 +1,10 @@
+#ifndef SVNDIFF_H_
+#define SVNDIFF_H_
+
+struct line_buffer;
+struct sliding_view;
+
+extern int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
+		struct sliding_view *preimage, FILE *postimage);
+
+#endif