[PATCH 02/11] vcs-svn: Skeleton of an svn delta parser

[Jonathan Nieder <jrnieder@gmail.com>]

A delta in the subversion delta (svndiff0) format consists of the
magic bytes SVN\0 followed by a sequence of windows, each beginning
with a window header consisting of five integers (with variable-length
representation):

	source view offset
	source view length
	output length
	instructions length
	auxiliary data length

Add an svndiff0_apply() function and test-svn-fe -d commandline tool
to parse such a delta in the special case of not including any
instructions or auxiliary data.

Later patches will add features to turn this into a fully functional
delta applier, for use by svn-fe in parsing the streams produced by
"svnrdump dump" and "svnadmin dump --deltas".

Helped-by: Ramkumar Ramachandra <artagnon@gmail.com>
Helped-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 Makefile          |    4 +-
 t/t9011-svn-da.sh |   82 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 test-svn-fe.c     |   39 ++++++++++++++++++++----
 vcs-svn/svndiff.c |   64 +++++++++++++++++++++++++++++++++++++++++
 vcs-svn/svndiff.h |    9 ++++++
 5 files changed, 189 insertions(+), 9 deletions(-)
 create mode 100755 t/t9011-svn-da.sh
 create mode 100644 vcs-svn/svndiff.h

diff --git a/Makefile b/Makefile
index d99da33..966f5c7 100644
--- a/Makefile
+++ b/Makefile
@@ -1766,7 +1766,7 @@ XDIFF_OBJS = xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o \
 	xdiff/xmerge.o xdiff/xpatience.o
 VCSSVN_OBJS = vcs-svn/string_pool.o vcs-svn/line_buffer.o \
 	vcs-svn/repo_tree.o vcs-svn/fast_export.o vcs-svn/svndump.o \
-	vcs-svn/sliding_window.o
+	vcs-svn/sliding_window.o vcs-svn/svndiff.o
 OBJECTS := $(GIT_OBJS) $(XDIFF_OBJS) $(VCSSVN_OBJS)
 
 dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
@@ -1893,7 +1893,7 @@ xdiff-interface.o $(XDIFF_OBJS): \
 $(VCSSVN_OBJS): \
 	vcs-svn/obj_pool.h vcs-svn/trp.h vcs-svn/string_pool.h \
 	vcs-svn/line_buffer.h vcs-svn/repo_tree.h vcs-svn/fast_export.h \
-	vcs-svn/svndump.h vcs-svn/sliding_window.h
+	vcs-svn/sliding_window.h vcs-svn/svndump.h vcs-svn/svndiff.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 0000000..8dccd16
--- /dev/null
+++ b/t/t9011-svn-da.sh
@@ -0,0 +1,82 @@
+#!/bin/sh
+
+test_description='test handling of deltas by dumpfile importer'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	>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 '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 '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 '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 '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_done
diff --git a/test-svn-fe.c b/test-svn-fe.c
index 77cf78a..197a2c3 100644
--- a/test-svn-fe.c
+++ b/test-svn-fe.c
@@ -4,14 +4,39 @@
 
 #include "git-compat-util.h"
 #include "vcs-svn/svndump.h"
+#include "vcs-svn/svndiff.h"
+#include "vcs-svn/line_buffer.h"
 
 int main(int argc, char *argv[])
 {
-	if (argc != 2)
-		usage("test-svn-fe <file>");
-	svndump_init(argv[1]);
-	svndump_read(NULL);
-	svndump_deinit();
-	svndump_reset();
-	return 0;
+	static const char test_svnfe_usage[] =
+		"test-svn-fe (<dumpfile> | [-d] <preimage> <delta> <len>)";
+	if (argc < 2)
+		usage(test_svnfe_usage);
+	if (argc == 2) {
+		svndump_init(argv[1]);
+		svndump_read(NULL);
+		svndump_deinit();
+		svndump_reset();
+		return 0;
+	}
+	if (argc == 5 && !strcmp(argv[1], "-d")) {
+		struct line_buffer preimage = LINE_BUFFER_INIT;
+		struct line_buffer delta = LINE_BUFFER_INIT;
+		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, stdout))
+			return 1;
+		if (buffer_deinit(&preimage))
+			die_errno("cannot close preimage");
+		if (buffer_deinit(&delta))
+			die_errno("cannot close delta");
+		buffer_reset(&preimage);
+		buffer_reset(&delta);
+		return 0;
+	}
+	usage(test_svnfe_usage);
 }
diff --git a/vcs-svn/svndiff.c b/vcs-svn/svndiff.c
index 36d2b30..e572a93 100644
--- a/vcs-svn/svndiff.c
+++ b/vcs-svn/svndiff.c
@@ -12,6 +12,7 @@
  * See http://svn.apache.org/repos/asf/subversion/trunk/notes/svndiff.
  *
  * svndiff0 ::= 'SVN\0' window window*;
+ * window ::= int int int int int instructions inline_data;
  * int ::= highdigit* lowdigit;
  * highdigit ::= # binary 1000 0000 OR-ed with 7 bit value;
  * lowdigit ::= # 7 bit value;
@@ -76,3 +77,66 @@ static int parse_int(const char **buf, size_t *result, const char *end)
 	return error("Invalid instruction: incomplete integer %"PRIu64,
 		     (uint64_t) rv);
 }
+
+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: %"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: %"PRIuMAX, val);
+	*result = val;
+	return 0;
+}
+
+static int apply_one_window(struct line_buffer *delta, off_t *delta_len)
+{
+	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))
+		return -1;
+	if (instructions_len > 0)
+		return error("What do you think I am?  A delta applier?");
+	if (data_len > 0)
+		return error("No support for inline data yet");
+	return 0;
+}
+
+int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
+		   struct line_buffer *preimage, FILE *postimage)
+{
+	assert(delta && preimage && postimage);
+
+	if (read_magic(delta, &delta_len))
+		return -1;
+	while (delta_len > 0) {	/* 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) ||
+		    apply_one_window(delta, &delta_len))
+			return -1;
+		if (delta_len && buffer_at_eof(delta))
+			return error("Delta ends early! "
+				     "(%"PRIu64" bytes remaining)",
+				     (uint64_t) delta_len);
+	}
+	return 0;
+}
diff --git a/vcs-svn/svndiff.h b/vcs-svn/svndiff.h
new file mode 100644
index 0000000..a986099
--- /dev/null
+++ b/vcs-svn/svndiff.h
@@ -0,0 +1,9 @@
+#ifndef SVNDIFF_H_
+#define SVNDIFF_H_
+
+#include "line_buffer.h"
+
+extern int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
+			  struct line_buffer *preimage, FILE *postimage);
+
+#endif
-- 
1.7.2.3