odb: Direct writes are back

DIRECT WRITES ARE BACK AND FASTER THAN EVER. The streaming writer to the
ODB was an overkill for the smaller objects like Commit and Tags; most
of the streaming logic was taking too long.

This commit makes Commits, Tags and Trees to be built-up in memory, and
then written to disk in 2 pushes (header + data), instead of streaming
everything.

This is *always* faster, even for big files (since the git_filebuf class
still does streaming writes when the memory cache overflows). This is
also a gazillion lines of code smaller, because we don't have to
precompute the final size of the object before starting the stream (this
was kind of defeating the point of streaming, anyway).

Blobs are still written with full streaming instead of loading them in
memory, since this is still the fastest way.

A new `git_buf` class has been added. It's missing some features, but
it'll get there.

2 files changed, 61 insertions, 0 deletions

diff --git a/tests/t17-bufs.c b/tests/t17-bufs.c
new file mode 100644
index 000000000..b0269b790
--- /dev/null
+++ b/tests/t17-bufs.c
@@ -0,0 +1,59 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+#include "test_lib.h"
+#include "test_helpers.h"
+
+#include <git2.h>
+#include "buffer.h"
+
+const char *test_string = "Have you seen that? Have you seeeen that??";
+
+BEGIN_TEST(buf0, "check that resizing works properly")
+	git_buf buf = GIT_BUF_INIT;
+	git_buf_puts(&buf, test_string);
+
+	must_be_true(git_buf_oom(&buf) == 0);
+	must_be_true(strcmp(git_buf_cstr(&buf), test_string) == 0);
+
+	git_buf_puts(&buf, test_string);
+	must_be_true(strlen(git_buf_cstr(&buf)) == strlen(test_string) * 2);
+END_TEST
+
+BEGIN_TEST(buf1, "check that printf works properly")
+	git_buf buf = GIT_BUF_INIT;
+
+	git_buf_printf(&buf, "%s %s %d ", "shoop", "da", 23);
+	must_be_true(git_buf_oom(&buf) == 0);
+	must_be_true(strcmp(git_buf_cstr(&buf), "shoop da 23 ") == 0);
+
+	git_buf_printf(&buf, "%s %d", "woop", 42);
+	must_be_true(git_buf_oom(&buf) == 0);
+	must_be_true(strcmp(git_buf_cstr(&buf), "shoop da 23 woop 42") == 0);
+END_TEST
+
+BEGIN_SUITE(buffers)
+	 ADD_TEST(buf0)
+	 ADD_TEST(buf1)
+END_SUITE
diff --git a/tests/test_main.c b/tests/test_main.c
index aab6c068b..2d3e5f954 100644
--- a/tests/test_main.c
+++ b/tests/test_main.c
@@ -44,6 +44,7 @@ DECLARE_SUITE(repository);
 DECLARE_SUITE(threads);
 DECLARE_SUITE(config);
 DECLARE_SUITE(remotes);
+DECLARE_SUITE(buffers);
 
 static libgit2_suite suite_methods[]= {
 	SUITE_NAME(core),
@@ -61,6 +62,7 @@ static libgit2_suite suite_methods[]= {
 	SUITE_NAME(threads),
 	SUITE_NAME(config),
 	SUITE_NAME(remotes),
+	SUITE_NAME(buffers),
 };
 
 #define GIT_SUITE_COUNT (ARRAY_SIZE(suite_methods))