Subject: [PATCH 06/11] vcs-svn: Implement copyfrom_data delta instruction

From: Jonathan Nieder <[email-masked]>
Date: Wed, 13 Oct 2010 04:39:44 -0500

The copyfrom_data instruction copies a few bytes verbatim from the
auxiliary data section of a window to the postimage.

Signed-off-by: Jonathan Nieder <[email-masked]>
---
 t/t9011-svn-da.sh |   31 +++++++++++++++++++
 vcs-svn/svndiff.c |   86 +++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 112 insertions(+), 5 deletions(-)

diff --git a/t/t9011-svn-da.sh b/t/t9011-svn-da.sh
index 1383263..9279924 100755
--- a/t/t9011-svn-da.sh
+++ b/t/t9011-svn-da.sh
@@ -134,4 +134,35 @@ test_expect_success 'truncated inline data (after instruction section)' '
 	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_done
diff --git a/vcs-svn/svndiff.c b/vcs-svn/svndiff.c
index 72fe716..ac776e0 100644
--- a/vcs-svn/svndiff.c
+++ b/vcs-svn/svndiff.c
@@ -14,20 +14,40 @@
  *
  * svndiff0 ::= 'SVN\0' window 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
+ *   ;
+ * copyfrom_data ::= # binary 10 000000;
+ * 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_DATA	0x80
+#define OPERAND_MASK	0x3f
+
 #define VLI_CONTINUE	0x80
 #define VLI_DIGIT_MASK	0x7f
 #define VLI_BITS_PER_DIGIT 7
 
 struct window {
+	struct strbuf out;
 	struct strbuf instructions;
 	struct strbuf 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: %s\n", strerror(errno));
+}
+
 static int read_magic(struct line_buffer *in, off_t *len)
 {
 	static const char magic[] = {'S', 'V', 'N', '\0'};
@@ -118,9 +138,63 @@ static int read_chunk(struct line_buffer *delta, off_t *delta_len,
 	return 0;
 }
 
-static int apply_one_window(struct line_buffer *delta, off_t *delta_len)
+static int copyfrom_data(struct window *ctx, size_t *data_pos, size_t nbytes)
 {
-	struct window ctx = {STRBUF_INIT, STRBUF_INIT};
+	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) {
+		*out = result;
+		return 0;
+	}
+	return parse_int(buf, out, end);
+}
+
+static int step(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;
+	if ((instruction & INSN_MASK) != INSN_COPYFROM_DATA)
+		return error("Unknown instruction %x", instruction);
+	return copyfrom_data(ctx, data_pos, nbytes);
+}
+
+static int apply_window_in_core(struct window *ctx)
+{
+	const char *insn = ctx->instructions.buf;
+	size_t data_pos = 0;
+
+	/*
+	 * Populate ctx->out.buf using data from the source, target,
+	 * and inline data views.
+	 */
+	while (insn != ctx->instructions.buf + ctx->instructions.len)
+		if (step(ctx, &insn, &data_pos))
+			return -1;
+	return 0;
+}
+
+static int apply_one_window(struct line_buffer *delta, off_t *delta_len,
+			    FILE *out)
+{
+	struct window ctx = {STRBUF_INIT, STRBUF_INIT, STRBUF_INIT};
 	size_t out_len;
 	size_t instructions_len;
 	size_t data_len;
@@ -146,8 +220,10 @@ static int apply_one_window(struct line_buffer *delta, off_t *delta_len)
 		rv = error("Cannot read delta: %s", strerror(errno));
 		goto done;
 	}
-	if (instructions_len > 0)
-		return error("What do you think I am?  A delta applier?");
+	if (apply_window_in_core(&ctx) || write_strbuf(&ctx.out, out)) {
+		rv = -1;
+		goto done;
+	}
  done:
 	strbuf_release(&ctx.data);
 	strbuf_release(&ctx.instructions);
@@ -168,7 +244,7 @@ int svndiff0_apply(struct line_buffer *delta, off_t delta_len,
 		if (read_offset(delta, &pre_off, &delta_len) ||
 		    read_length(delta, &pre_len, &delta_len) ||
 		    move_window(&preimage_view, pre_off, pre_len) ||
-		    apply_one_window(delta, &delta_len))
+		    apply_one_window(delta, &delta_len, postimage))
 			goto fail;
 		if (delta_len && buffer_at_eof(delta)) {
 			error("Delta ends early! (%"PRIu64" bytes remaining)",
-- 
1.7.2.3