thodg/libgit2

diff --git a/include/git2/diff.h b/include/git2/diff.h
index 71a8b72..c989ba4 100644
--- a/include/git2/diff.h
+++ b/include/git2/diff.h
@@ -391,7 +391,7 @@ typedef enum {
 	 */
 	GIT_DIFF_LINE_FILE_HDR  = 'F',
 	GIT_DIFF_LINE_HUNK_HDR  = 'H',
-	GIT_DIFF_LINE_BINARY    = 'B'
+	GIT_DIFF_LINE_BINARY    = 'B' /**< For "Binary files x and y differ" */
 } git_diff_line_t;
 
 /**
@@ -943,6 +943,28 @@ GIT_EXTERN(int) git_diff_patch_get_line_in_hunk(
 	size_t line_of_hunk);
 
 /**
+ * Look up size of patch diff data in bytes
+ *
+ * This returns the raw size of the patch data.  This only includes the
+ * actual data from the lines of the diff, not the file or hunk headers.
+ *
+ * If you pass `include_context` as true (non-zero), this will be the size
+ * of all of the diff output; if you pass it as false (zero), this will
+ * only include the actual changed lines (as if `context_lines` was 0).
+ *
+ * @param patch A git_diff_patch representing changes to one file
+ * @param include_context Include context lines in size if non-zero
+ * @param include_hunk_headers Include hunk header lines if non-zero
+ * @param include_file_headers Include file header lines if non-zero
+ * @return The number of bytes of data
+ */
+GIT_EXTERN(size_t) git_diff_patch_size(
+	git_diff_patch *patch,
+	int include_context,
+	int include_hunk_headers,
+	int include_file_headers);
+
+/**
  * Serialize the patch to text via callback.
  *
  * Returning a non-zero value from the callback will terminate the iteration
diff --git a/src/diff.h b/src/diff.h
index d1bec00..bec7e27 100644
--- a/src/diff.h
+++ b/src/diff.h
@@ -82,6 +82,13 @@ extern const char *git_diff_delta__path(const git_diff_delta *delta);
 extern bool git_diff_delta__should_skip(
 	const git_diff_options *opts, const git_diff_delta *delta);
 
+extern int git_diff_delta__format_file_header(
+	git_buf *out,
+	const git_diff_delta *delta,
+	const char *oldpfx,
+	const char *newpfx,
+	int oid_strlen);
+
 extern int git_diff__oid_for_file(
 	git_repository *, const char *, uint16_t, git_off_t, git_oid *);
 
diff --git a/src/diff_patch.c b/src/diff_patch.c
index 69bb081..cc45b6d 100644
--- a/src/diff_patch.c
+++ b/src/diff_patch.c
@@ -42,7 +42,7 @@ struct git_diff_patch {
 	git_array_t(diff_patch_hunk) hunks;
 	git_array_t(diff_patch_line) lines;
 	size_t oldno, newno;
-	size_t content_size;
+	size_t content_size, context_size, header_size;
 	git_pool flattened;
 };
 
@@ -810,6 +810,39 @@ notfound:
 	return diff_error_outofrange(thing);
 }
 
+size_t git_diff_patch_size(
+	git_diff_patch *patch,
+	int include_context,
+	int include_hunk_headers,
+	int include_file_headers)
+{
+	size_t out;
+
+	assert(patch);
+
+	out = patch->content_size;
+
+	if (!include_context)
+		out -= patch->context_size;
+
+	if (include_hunk_headers)
+		out += patch->header_size;
+
+	if (include_file_headers) {
+		git_buf file_header = GIT_BUF_INIT;
+
+		if (git_diff_delta__format_file_header(
+				&file_header, patch->delta, NULL, NULL, 0) < 0)
+			giterr_clear();
+		else
+			out += git_buf_len(&file_header);
+
+		git_buf_free(&file_header);
+	}
+
+	return out;
+}
+
 git_diff_list *git_diff_patch__diff(git_diff_patch *patch)
 {
 	return patch->diff;
@@ -904,6 +937,8 @@ static int diff_patch_hunk_cb(
 	hunk->header[header_len] = '\0';
 	hunk->header_len = header_len;
 
+	patch->header_size += header_len;
+
 	hunk->line_start = git_array_size(patch->lines);
 	hunk->line_count = 0;
 
@@ -924,6 +959,7 @@ static int diff_patch_line_cb(
 	git_diff_patch *patch = payload;
 	diff_patch_hunk *hunk;
 	diff_patch_line *line;
+	const char *content_end = content + content_len;
 
 	GIT_UNUSED(delta);
 	GIT_UNUSED(range);
@@ -938,34 +974,43 @@ static int diff_patch_line_cb(
 	line->len = content_len;
 	line->origin = line_origin;
 
-	patch->content_size += content_len;
-
 	/* do some bookkeeping so we can provide old/new line numbers */
 
-	for (line->lines = 0; content_len > 0; --content_len) {
+	line->lines = 0;
+	while (content < content_end)
 		if (*content++ == '\n')
 			++line->lines;
-	}
+
+	patch->content_size += content_len;
 
 	switch (line_origin) {
 	case GIT_DIFF_LINE_ADDITION:
+		patch->content_size += 1;
 	case GIT_DIFF_LINE_DEL_EOFNL:
 		line->oldno = -1;
 		line->newno = patch->newno;
 		patch->newno += line->lines;
 		break;
 	case GIT_DIFF_LINE_DELETION:
+		patch->content_size += 1;
 	case GIT_DIFF_LINE_ADD_EOFNL:
 		line->oldno = patch->oldno;
 		line->newno = -1;
 		patch->oldno += line->lines;
 		break;
-	default:
+	case GIT_DIFF_LINE_CONTEXT:
+		patch->content_size += 1;
+		patch->context_size += 1;
+	case GIT_DIFF_LINE_CONTEXT_EOFNL:
+		patch->context_size += content_len;
 		line->oldno = patch->oldno;
 		line->newno = patch->newno;
 		patch->oldno += line->lines;
 		patch->newno += line->lines;
 		break;
+	default:
+		assert(false);
+		break;
 	}
 
 	hunk->line_count++;
diff --git a/src/diff_print.c b/src/diff_print.c
index 0de5488..4ddd724 100644
--- a/src/diff_print.c
+++ b/src/diff_print.c
@@ -98,12 +98,12 @@ static int diff_print_one_compact(
 
 	if (delta->old_file.path != delta->new_file.path &&
 		strcomp(delta->old_file.path,delta->new_file.path) != 0)
-		git_buf_printf(out, "%c\t%s%c -> %s%c\n", code,
+		git_buf_printf(out, "%c\t%s%c %s%c\n", code,
 			delta->old_file.path, old_suffix, delta->new_file.path, new_suffix);
 	else if (delta->old_file.mode != delta->new_file.mode &&
 		delta->old_file.mode != 0 && delta->new_file.mode != 0)
-		git_buf_printf(out, "%c\t%s%c (%o -> %o)\n", code,
-			delta->old_file.path, new_suffix, delta->old_file.mode, delta->new_file.mode);
+		git_buf_printf(out, "%c\t%s%c %s%c\n", code,
+			delta->old_file.path, old_suffix, delta->new_file.path, new_suffix);
 	else if (old_suffix != ' ')
 		git_buf_printf(out, "%c\t%s%c\n", code, delta->old_file.path, old_suffix);
 	else
@@ -198,13 +198,13 @@ int git_diff_print_raw(
 	return error;
 }
 
-static int diff_print_oid_range(diff_print_info *pi, const git_diff_delta *delta)
+static int diff_print_oid_range(
+	git_buf *out, const git_diff_delta *delta, int oid_strlen)
 {
-	git_buf *out = pi->buf;
 	char start_oid[GIT_OID_HEXSZ+1], end_oid[GIT_OID_HEXSZ+1];
 
-	git_oid_tostr(start_oid, pi->oid_strlen, &delta->old_file.oid);
-	git_oid_tostr(end_oid, pi->oid_strlen, &delta->new_file.oid);
+	git_oid_tostr(start_oid, oid_strlen, &delta->old_file.oid);
+	git_oid_tostr(end_oid, oid_strlen, &delta->new_file.oid);
 
 	/* TODO: Match git diff more closely */
 	if (delta->old_file.mode == delta->new_file.mode) {
@@ -228,52 +228,78 @@ static int diff_print_oid_range(diff_print_info *pi, const git_diff_delta *delta
 	return 0;
 }
 
-static int diff_print_patch_file(
-	const git_diff_delta *delta, float progress, void *data)
+static int diff_delta_format_with_paths(
+	git_buf *out,
+	const git_diff_delta *delta,
+	const char *oldpfx,
+	const char *newpfx,
+	const char *template)
 {
-	diff_print_info *pi = data;
-	const char *oldpfx = pi->diff ? pi->diff->opts.old_prefix : NULL;
 	const char *oldpath = delta->old_file.path;
-	const char *newpfx = pi->diff ? pi->diff->opts.new_prefix : NULL;
 	const char *newpath = delta->new_file.path;
-	uint32_t opts_flags = pi->diff ? pi->diff->opts.flags : GIT_DIFF_NORMAL;
 
-	GIT_UNUSED(progress);
+	if (git_oid_iszero(&delta->old_file.oid)) {
+		oldpfx = "";
+		oldpath = "/dev/null";
+	}
+	if (git_oid_iszero(&delta->new_file.oid)) {
+		newpfx = "";
+		newpath = "/dev/null";
+	}
 
-	if (S_ISDIR(delta->new_file.mode) ||
-		delta->status == GIT_DELTA_UNMODIFIED ||
-		delta->status == GIT_DELTA_IGNORED ||
-		(delta->status == GIT_DELTA_UNTRACKED &&
-		 (opts_flags & GIT_DIFF_INCLUDE_UNTRACKED_CONTENT) == 0))
-		return 0;
+	return git_buf_printf(out, template, oldpfx, oldpath, newpfx, newpath);
+}
 
+int git_diff_delta__format_file_header(
+	git_buf *out,
+	const git_diff_delta *delta,
+	const char *oldpfx,
+	const char *newpfx,
+	int oid_strlen)
+{
 	if (!oldpfx)
 		oldpfx = DIFF_OLD_PREFIX_DEFAULT;
 	if (!newpfx)
 		newpfx = DIFF_NEW_PREFIX_DEFAULT;
+	if (!oid_strlen)
+		oid_strlen = GIT_ABBREV_DEFAULT + 1;
 
-	git_buf_clear(pi->buf);
-	git_buf_printf(pi->buf, "diff --git %s%s %s%s\n",
+	git_buf_clear(out);
+
+	git_buf_printf(out, "diff --git %s%s %s%s\n",
 		oldpfx, delta->old_file.path, newpfx, delta->new_file.path);
 
-	if (diff_print_oid_range(pi, delta) < 0)
+	if (diff_print_oid_range(out, delta, oid_strlen) < 0)
 		return -1;
 
-	if (git_oid_iszero(&delta->old_file.oid)) {
-		oldpfx = "";
-		oldpath = "/dev/null";
-	}
-	if (git_oid_iszero(&delta->new_file.oid)) {
-		newpfx = "";
-		newpath = "/dev/null";
-	}
+	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0)
+		diff_delta_format_with_paths(
+			out, delta, oldpfx, newpfx, "--- %s%s\n+++ %s%s\n");
 
-	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0) {
-		git_buf_printf(pi->buf, "--- %s%s\n", oldpfx, oldpath);
-		git_buf_printf(pi->buf, "+++ %s%s\n", newpfx, newpath);
-	}
+	return git_buf_oom(out) ? -1 : 0;
+}
 
-	if (git_buf_oom(pi->buf))
+static int diff_print_patch_file(
+	const git_diff_delta *delta, float progress, void *data)
+{
+	diff_print_info *pi = data;
+	const char *oldpfx =
+		pi->diff ? pi->diff->opts.old_prefix : DIFF_OLD_PREFIX_DEFAULT;
+	const char *newpfx =
+		pi->diff ? pi->diff->opts.new_prefix : DIFF_NEW_PREFIX_DEFAULT;
+	uint32_t opts_flags = pi->diff ? pi->diff->opts.flags : GIT_DIFF_NORMAL;
+
+	GIT_UNUSED(progress);
+
+	if (S_ISDIR(delta->new_file.mode) ||
+		delta->status == GIT_DELTA_UNMODIFIED ||
+		delta->status == GIT_DELTA_IGNORED ||
+		(delta->status == GIT_DELTA_UNTRACKED &&
+		 (opts_flags & GIT_DIFF_INCLUDE_UNTRACKED_CONTENT) == 0))
+		return 0;
+
+	if (git_diff_delta__format_file_header(
+			pi->buf, delta, oldpfx, newpfx, pi->oid_strlen) < 0)
 		return -1;
 
 	if (pi->print_cb(delta, NULL, GIT_DIFF_LINE_FILE_HDR,
@@ -284,10 +310,10 @@ static int diff_print_patch_file(
 		return 0;
 
 	git_buf_clear(pi->buf);
-	git_buf_printf(
-		pi->buf, "Binary files %s%s and %s%s differ\n",
-		oldpfx, oldpath, newpfx, newpath);
-	if (git_buf_oom(pi->buf))
+
+	if (diff_delta_format_with_paths(
+			pi->buf, delta, oldpfx, newpfx,
+			"Binary files %s%s and %s%s differ\n") < 0)
 		return -1;
 
 	if (pi->print_cb(delta, NULL, GIT_DIFF_LINE_BINARY,
diff --git a/tests-clar/diff/patch.c b/tests-clar/diff/patch.c
index 3f14a0d..6a33fa9 100644
--- a/tests-clar/diff/patch.c
+++ b/tests-clar/diff/patch.c
@@ -128,6 +128,11 @@ void test_diff_patch__to_string(void)
 
 	cl_assert_equal_s(expected, text);
 
+	cl_assert_equal_sz(31, git_diff_patch_size(patch, 0, 0, 0));
+	cl_assert_equal_sz(31, git_diff_patch_size(patch, 1, 0, 0));
+	cl_assert_equal_sz(31 + 16, git_diff_patch_size(patch, 1, 1, 0));
+	cl_assert_equal_sz(strlen(expected), git_diff_patch_size(patch, 1, 1, 1));
+
 	git__free(text);
 	git_diff_patch_free(patch);
 	git_diff_list_free(diff);
@@ -408,7 +413,7 @@ void test_diff_patch__hunks_have_correct_line_numbers(void)
 
 static void check_single_patch_stats(
 	git_repository *repo, size_t hunks,
-	size_t adds, size_t dels, size_t ctxt,
+	size_t adds, size_t dels, size_t ctxt, size_t *sizes,
 	const char *expected)
 {
 	git_diff_list *diff;
@@ -437,6 +442,18 @@ static void check_single_patch_stats(
 		cl_git_pass(git_diff_patch_to_str(&text, patch));
 		cl_assert_equal_s(expected, text);
 		git__free(text);
+
+		cl_assert_equal_sz(
+			strlen(expected), git_diff_patch_size(patch, 1, 1, 1));
+	}
+
+	if (sizes) {
+		if (sizes[0])
+			cl_assert_equal_sz(sizes[0], git_diff_patch_size(patch, 0, 0, 0));
+		if (sizes[1])
+			cl_assert_equal_sz(sizes[1], git_diff_patch_size(patch, 1, 0, 0));
+		if (sizes[2])
+			cl_assert_equal_sz(sizes[2], git_diff_patch_size(patch, 1, 1, 0));
 	}
 
 	/* walk lines in hunk with basic sanity checks */
@@ -481,6 +498,23 @@ void test_diff_patch__line_counts_with_eofnl(void)
 	git_buf content = GIT_BUF_INIT;
 	const char *end;
 	git_index *index;
+	const char *expected =
+		/* below is pasted output of 'git diff' with fn context removed */
+		"diff --git a/songof7cities.txt b/songof7cities.txt\n"
+		"index 378a7d9..3d0154e 100644\n"
+		"--- a/songof7cities.txt\n"
+		"+++ b/songof7cities.txt\n"
+		"@@ -42,7 +42,7 @@ With peoples undefeated of the dark, enduring blood.\n"
+		" \n"
+		" To the sound of trumpets shall their seed restore my Cities\n"
+		" Wealthy and well-weaponed, that once more may I behold\n"
+		"-All the world go softly when it walks before my Cities,\n"
+		"+#All the world go softly when it walks before my Cities,\n"
+		" And the horses and the chariots fleeing from them as of old!\n"
+		" \n"
+		"   -- Rudyard Kipling\n"
+		"\\ No newline at end of file\n";
+	size_t expected_sizes[3] = { 115, 119 + 115 + 114, 119 + 115 + 114 + 71 };
 
 	g_repo = cl_git_sandbox_init("renames");
 
@@ -495,14 +529,14 @@ void test_diff_patch__line_counts_with_eofnl(void)
 	git_buf_consume(&content, end);
 	cl_git_rewritefile("renames/songof7cities.txt", content.ptr);
 
-	check_single_patch_stats(g_repo, 1, 0, 1, 3, NULL);
+	check_single_patch_stats(g_repo, 1, 0, 1, 3, NULL, NULL);
 
 	/* remove trailing whitespace */
 
 	git_buf_rtrim(&content);
 	cl_git_rewritefile("renames/songof7cities.txt", content.ptr);
 
-	check_single_patch_stats(g_repo, 2, 1, 2, 6, NULL);
+	check_single_patch_stats(g_repo, 2, 1, 2, 6, NULL, NULL);
 
 	/* add trailing whitespace */
 
@@ -514,7 +548,7 @@ void test_diff_patch__line_counts_with_eofnl(void)
 	cl_git_pass(git_buf_putc(&content, '\n'));
 	cl_git_rewritefile("renames/songof7cities.txt", content.ptr);
 
-	check_single_patch_stats(g_repo, 1, 1, 1, 3, NULL);
+	check_single_patch_stats(g_repo, 1, 1, 1, 3, NULL, NULL);
 
 	/* no trailing whitespace as context line */
 
@@ -537,22 +571,7 @@ void test_diff_patch__line_counts_with_eofnl(void)
 	cl_git_rewritefile("renames/songof7cities.txt", content.ptr);
 
 	check_single_patch_stats(
-		g_repo, 1, 1, 1, 6,
-		/* below is pasted output of 'git diff' with fn context removed */
-		"diff --git a/songof7cities.txt b/songof7cities.txt\n"
-		"index 378a7d9..3d0154e 100644\n"
-		"--- a/songof7cities.txt\n"
-		"+++ b/songof7cities.txt\n"
-		"@@ -42,7 +42,7 @@ With peoples undefeated of the dark, enduring blood.\n"
-		" \n"
-		" To the sound of trumpets shall their seed restore my Cities\n"
-		" Wealthy and well-weaponed, that once more may I behold\n"
-		"-All the world go softly when it walks before my Cities,\n"
-		"+#All the world go softly when it walks before my Cities,\n"
-		" And the horses and the chariots fleeing from them as of old!\n"
-		" \n"
-		"   -- Rudyard Kipling\n"
-		"\\ No newline at end of file\n");
+		g_repo, 1, 1, 1, 6, expected_sizes, expected);
 
 	git_buf_free(&content);
 	git_config_free(cfg);