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.

1 files changed, 24 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
new file mode 100644
index 000000000..1209340a1
--- /dev/null
+++ b/src/buffer.h
@@ -0,0 +1,24 @@
+#ifndef INCLUDE_buffer_h__
+#define INCLUDE_buffer_h__
+
+#include "common.h"
+
+typedef struct {
+	char *ptr;
+	ssize_t asize, size;
+} git_buf;
+
+#define GIT_BUF_INIT {NULL, 0, 0}
+
+int git_buf_grow(git_buf *buf, size_t target_size);
+int git_buf_oom(const git_buf *buf);
+void git_buf_putc(git_buf *buf, char c);
+void git_buf_put(git_buf *buf, const char *data, size_t len);
+void git_buf_puts(git_buf *buf, const char *string);
+void git_buf_printf(git_buf *buf, const char *format, ...) GIT_FORMAT_PRINTF(2, 3);
+const char *git_buf_cstr(git_buf *buf);
+void git_buf_free(git_buf *buf);
+
+#define git_buf_PUTS(buf, str) git_buf_put(buf, str, sizeof(str) - 1)
+
+#endif