[PATCH v6 09/40] Add initial external odb support

[Christian Couder <christian.couder@gmail.com>]

The external-odb.{c,h} files contains the functions that are
called by the rest of Git from "sha1_file.c".

The odb-helper.{c,h} files contains the functions to
actually implement communication with the external scripts or
processes that will manage external git objects.

For now only script mode is supported, and only the 'have' and
'get_git_obj' instructions are supported.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 Makefile                |   2 +
 cache.h                 |   1 +
 external-odb.c          | 113 ++++++++++++++++++++
 external-odb.h          |   8 ++
 odb-helper.c            | 269 ++++++++++++++++++++++++++++++++++++++++++++++++
 odb-helper.h            |  27 +++++
 sha1_file.c             |  31 +++++-
 t/t0400-external-odb.sh |  46 +++++++++
 8 files changed, 495 insertions(+), 2 deletions(-)
 create mode 100644 external-odb.c
 create mode 100644 external-odb.h
 create mode 100644 odb-helper.c
 create mode 100644 odb-helper.h
 create mode 100755 t/t0400-external-odb.sh

diff --git a/Makefile b/Makefile
index f2bb7f2f63..24aab8ace3 100644
--- a/Makefile
+++ b/Makefile
@@ -784,6 +784,7 @@ LIB_OBJS += ewah/ewah_bitmap.o
 LIB_OBJS += ewah/ewah_io.o
 LIB_OBJS += ewah/ewah_rlw.o
 LIB_OBJS += exec_cmd.o
+LIB_OBJS += external-odb.o
 LIB_OBJS += fetch-pack.o
 LIB_OBJS += fsck.o
 LIB_OBJS += gettext.o
@@ -816,6 +817,7 @@ LIB_OBJS += notes-cache.o
 LIB_OBJS += notes-merge.o
 LIB_OBJS += notes-utils.o
 LIB_OBJS += object.o
+LIB_OBJS += odb-helper.o
 LIB_OBJS += oidset.o
 LIB_OBJS += packfile.o
 LIB_OBJS += pack-bitmap.o
diff --git a/cache.h b/cache.h
index 00d89568f3..6c22bd0525 100644
--- a/cache.h
+++ b/cache.h
@@ -1534,6 +1534,7 @@ extern void prepare_alt_odb(void);
 extern char *compute_alternate_path(const char *path, struct strbuf *err);
 typedef int alt_odb_fn(struct alternate_object_database *, void *);
 extern int foreach_alt_odb(alt_odb_fn, void*);
+extern void prepare_external_alt_odb(void);
 
 /*
  * Allocate a "struct alternate_object_database" but do _not_ actually
diff --git a/external-odb.c b/external-odb.c
new file mode 100644
index 0000000000..e9c3f11666
--- /dev/null
+++ b/external-odb.c
@@ -0,0 +1,113 @@
+#include "cache.h"
+#include "external-odb.h"
+#include "odb-helper.h"
+
+static struct odb_helper *helpers;
+static struct odb_helper **helpers_tail = &helpers;
+
+static struct odb_helper *find_or_create_helper(const char *name, int len)
+{
+	struct odb_helper *o;
+
+	for (o = helpers; o; o = o->next)
+		if (!strncmp(o->name, name, len) && !o->name[len])
+			return o;
+
+	o = odb_helper_new(name, len);
+	*helpers_tail = o;
+	helpers_tail = &o->next;
+
+	return o;
+}
+
+static int external_odb_config(const char *var, const char *value, void *data)
+{
+	struct odb_helper *o;
+	const char *name;
+	int namelen;
+	const char *subkey;
+
+	if (parse_config_key(var, "odb", &name, &namelen, &subkey) < 0)
+		return 0;
+
+	o = find_or_create_helper(name, namelen);
+
+	if (!strcmp(subkey, "scriptcommand"))
+		return git_config_string(&o->cmd, var, value);
+
+	return 0;
+}
+
+static void external_odb_init(void)
+{
+	static int initialized;
+
+	if (initialized)
+		return;
+	initialized = 1;
+
+	git_config(external_odb_config, NULL);
+}
+
+const char *external_odb_root(void)
+{
+	static const char *root;
+	if (!root)
+		root = git_pathdup("objects/external");
+	return root;
+}
+
+int external_odb_has_object(const unsigned char *sha1)
+{
+	struct odb_helper *o;
+
+	external_odb_init();
+
+	for (o = helpers; o; o = o->next)
+		if (odb_helper_has_object(o, sha1))
+			return 1;
+	return 0;
+}
+
+int external_odb_get_object(const unsigned char *sha1)
+{
+	struct odb_helper *o;
+	const char *path;
+
+	if (!external_odb_has_object(sha1))
+		return -1;
+
+	path = sha1_file_name_alt(external_odb_root(), sha1);
+	safe_create_leading_directories_const(path);
+	prepare_external_alt_odb();
+
+	for (o = helpers; o; o = o->next) {
+		struct strbuf tmpfile = STRBUF_INIT;
+		int ret;
+		int fd;
+
+		if (!odb_helper_has_object(o, sha1))
+			continue;
+
+		fd = create_object_tmpfile(&tmpfile, path);
+		if (fd < 0) {
+			strbuf_release(&tmpfile);
+			return -1;
+		}
+
+		if (odb_helper_get_object(o, sha1, fd) < 0) {
+			close(fd);
+			unlink(tmpfile.buf);
+			strbuf_release(&tmpfile);
+			continue;
+		}
+
+		close_sha1_file(fd);
+		ret = finalize_object_file(tmpfile.buf, path);
+		strbuf_release(&tmpfile);
+		if (!ret)
+			return 0;
+	}
+
+	return -1;
+}
diff --git a/external-odb.h b/external-odb.h
new file mode 100644
index 0000000000..dc5635f452
--- /dev/null
+++ b/external-odb.h
@@ -0,0 +1,8 @@
+#ifndef EXTERNAL_ODB_H
+#define EXTERNAL_ODB_H
+
+extern const char *external_odb_root(void);
+extern int external_odb_has_object(const unsigned char *sha1);
+extern int external_odb_get_object(const unsigned char *sha1);
+
+#endif /* EXTERNAL_ODB_H */
diff --git a/odb-helper.c b/odb-helper.c
new file mode 100644
index 0000000000..5e91044872
--- /dev/null
+++ b/odb-helper.c
@@ -0,0 +1,269 @@
+#include "cache.h"
+#include "object.h"
+#include "argv-array.h"
+#include "odb-helper.h"
+#include "run-command.h"
+#include "sha1-lookup.h"
+
+struct odb_helper *odb_helper_new(const char *name, int namelen)
+{
+	struct odb_helper *o;
+
+	o = xcalloc(1, sizeof(*o));
+	o->name = xmemdupz(name, namelen);
+
+	return o;
+}
+
+struct odb_helper_cmd {
+	struct argv_array argv;
+	struct child_process child;
+};
+
+/*
+ * Callers are responsible to ensure that the result of vaddf(fmt, ap)
+ * is properly shell-quoted.
+ */
+static void prepare_helper_command(struct argv_array *argv, const char *cmd,
+				   const char *fmt, va_list ap)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_addstr(&buf, cmd);
+	strbuf_addch(&buf, ' ');
+	strbuf_vaddf(&buf, fmt, ap);
+
+	argv_array_push(argv, buf.buf);
+	strbuf_release(&buf);
+}
+
+__attribute__((format (printf,3,4)))
+static int odb_helper_start(struct odb_helper *o,
+			    struct odb_helper_cmd *cmd,
+			    const char *fmt, ...)
+{
+	va_list ap;
+
+	memset(cmd, 0, sizeof(*cmd));
+	argv_array_init(&cmd->argv);
+
+	if (!o->cmd)
+		return -1;
+
+	va_start(ap, fmt);
+	prepare_helper_command(&cmd->argv, o->cmd, fmt, ap);
+	va_end(ap);
+
+	cmd->child.argv = cmd->argv.argv;
+	cmd->child.use_shell = 1;
+	cmd->child.no_stdin = 1;
+	cmd->child.out = -1;
+
+	if (start_command(&cmd->child) < 0) {
+		argv_array_clear(&cmd->argv);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int odb_helper_finish(struct odb_helper *o,
+			     struct odb_helper_cmd *cmd)
+{
+	int ret = finish_command(&cmd->child);
+	argv_array_clear(&cmd->argv);
+	if (ret) {
+		warning("odb helper '%s' reported failure", o->name);
+		return -1;
+	}
+	return 0;
+}
+
+static int parse_object_line(struct odb_helper_object *o, const char *line)
+{
+	char *end;
+	if (get_sha1_hex(line, o->sha1) < 0)
+		return -1;
+
+	line += 40;
+	if (*line++ != ' ')
+		return -1;
+
+	o->size = strtoul(line, &end, 10);
+	if (line == end || *end++ != ' ')
+		return -1;
+
+	o->type = type_from_string(end);
+	return 0;
+}
+
+static int add_have_entry(struct odb_helper *o, const char *line)
+{
+	ALLOC_GROW(o->have, o->have_nr+1, o->have_alloc);
+	if (parse_object_line(&o->have[o->have_nr], line) < 0) {
+		warning("bad 'have' input from odb helper '%s': %s",
+			o->name, line);
+		return 1;
+	}
+	o->have_nr++;
+	return 0;
+}
+
+static int odb_helper_object_cmp(const void *va, const void *vb)
+{
+	const struct odb_helper_object *a = va, *b = vb;
+	return hashcmp(a->sha1, b->sha1);
+}
+
+static void odb_helper_load_have(struct odb_helper *o)
+{
+	struct odb_helper_cmd cmd;
+	FILE *fh;
+	struct strbuf line = STRBUF_INIT;
+
+	if (o->have_valid)
+		return;
+	o->have_valid = 1;
+
+	if (odb_helper_start(o, &cmd, "have") < 0)
+		return;
+
+	fh = xfdopen(cmd.child.out, "r");
+	while (strbuf_getline(&line, fh) != EOF)
+		if (add_have_entry(o, line.buf))
+			break;
+
+	strbuf_release(&line);
+	fclose(fh);
+	odb_helper_finish(o, &cmd);
+
+	qsort(o->have, o->have_nr, sizeof(*o->have), odb_helper_object_cmp);
+}
+
+static const unsigned char *have_sha1_access(size_t index, void *table)
+{
+	struct odb_helper_object *have = table;
+	return have[index].sha1;
+}
+
+static struct odb_helper_object *odb_helper_lookup(struct odb_helper *o,
+						   const unsigned char *sha1)
+{
+	int idx;
+
+	odb_helper_load_have(o);
+	idx = sha1_pos(sha1, o->have, o->have_nr, have_sha1_access);
+	if (idx < 0)
+		return NULL;
+	return &o->have[idx];
+}
+
+int odb_helper_has_object(struct odb_helper *o, const unsigned char *sha1)
+{
+	return !!odb_helper_lookup(o, sha1);
+}
+
+int odb_helper_get_object(struct odb_helper *o, const unsigned char *sha1,
+			    int fd)
+{
+	struct odb_helper_object *obj;
+	struct odb_helper_cmd cmd;
+	unsigned long total_got;
+	git_zstream stream;
+	int zret = Z_STREAM_END;
+	git_SHA_CTX hash;
+	unsigned char real_sha1[20];
+	struct strbuf header = STRBUF_INIT;
+	unsigned long hdr_size;
+
+	obj = odb_helper_lookup(o, sha1);
+	if (!obj)
+		return -1;
+
+	if (odb_helper_start(o, &cmd, "get_git_obj %s", sha1_to_hex(sha1)) < 0)
+		return -1;
+
+	memset(&stream, 0, sizeof(stream));
+	git_inflate_init(&stream);
+	git_SHA1_Init(&hash);
+	total_got = 0;
+
+	for (;;) {
+		unsigned char buf[4096];
+		int r;
+
+		r = xread(cmd.child.out, buf, sizeof(buf));
+		if (r < 0) {
+			error("unable to read from odb helper '%s': %s",
+			      o->name, strerror(errno));
+			close(cmd.child.out);
+			odb_helper_finish(o, &cmd);
+			git_inflate_end(&stream);
+			return -1;
+		}
+		if (r == 0)
+			break;
+
+		write_or_die(fd, buf, r);
+
+		stream.next_in = buf;
+		stream.avail_in = r;
+		do {
+			unsigned char inflated[4096];
+			unsigned long got;
+
+			stream.next_out = inflated;
+			stream.avail_out = sizeof(inflated);
+			zret = git_inflate(&stream, Z_SYNC_FLUSH);
+			got = sizeof(inflated) - stream.avail_out;
+
+			git_SHA1_Update(&hash, inflated, got);
+			/* skip header when counting size */
+			if (!total_got) {
+				const unsigned char *p = memchr(inflated, '\0', got);
+				if (p) {
+					unsigned long hdr_last = p - inflated + 1;
+					strbuf_add(&header, inflated, hdr_last);
+					got -= hdr_last;
+				} else {
+					strbuf_add(&header, inflated, got);
+					got = 0;
+				}
+			}
+			total_got += got;
+		} while (stream.avail_in && zret == Z_OK);
+	}
+
+	close(cmd.child.out);
+	git_inflate_end(&stream);
+	git_SHA1_Final(real_sha1, &hash);
+	if (odb_helper_finish(o, &cmd))
+		return -1;
+	if (zret != Z_STREAM_END) {
+		warning("bad zlib data from odb helper '%s' for %s",
+			o->name, sha1_to_hex(sha1));
+		return -1;
+	}
+	if (total_got != obj->size) {
+		warning("size mismatch from odb helper '%s' for %s (%lu != %lu)",
+			o->name, sha1_to_hex(sha1), total_got, obj->size);
+		return -1;
+	}
+	if (hashcmp(real_sha1, sha1)) {
+		warning("sha1 mismatch from odb helper '%s' for %s (got %s)",
+			o->name, sha1_to_hex(sha1), sha1_to_hex(real_sha1));
+		return -1;
+	}
+	if (parse_sha1_header(header.buf, &hdr_size) < 0) {
+		warning("could not parse header from odb helper '%s' for %s",
+			o->name, sha1_to_hex(sha1));
+		return -1;
+	}
+	if (total_got != hdr_size) {
+		warning("size mismatch from odb helper '%s' for %s (%lu != %lu)",
+			o->name, sha1_to_hex(sha1), total_got, hdr_size);
+		return -1;
+	}
+
+	return 0;
+}
diff --git a/odb-helper.h b/odb-helper.h
new file mode 100644
index 0000000000..fb25ad579e
--- /dev/null
+++ b/odb-helper.h
@@ -0,0 +1,27 @@
+#ifndef ODB_HELPER_H
+#define ODB_HELPER_H
+
+struct odb_helper {
+	const char *name;
+	const char *cmd;
+
+	struct odb_helper_object {
+		unsigned char sha1[20];
+		unsigned long size;
+		enum object_type type;
+	} *have;
+	int have_nr;
+	int have_alloc;
+	int have_valid;
+
+	struct odb_helper *next;
+};
+
+extern struct odb_helper *odb_helper_new(const char *name, int namelen);
+extern int odb_helper_has_object(struct odb_helper *o,
+				 const unsigned char *sha1);
+extern int odb_helper_get_object(struct odb_helper *o,
+				 const unsigned char *sha1,
+				 int fd);
+
+#endif /* ODB_HELPER_H */
diff --git a/sha1_file.c b/sha1_file.c
index bea1ae6afb..4a4f5df5ec 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -29,6 +29,7 @@
 #include "mergesort.h"
 #include "quote.h"
 #include "packfile.h"
+#include "external-odb.h"
 
 const unsigned char null_sha1[GIT_MAX_RAWSZ];
 const struct object_id null_oid;
@@ -613,6 +614,21 @@ int foreach_alt_odb(alt_odb_fn fn, void *cb)
 	return r;
 }
 
+void prepare_external_alt_odb(void)
+{
+	static int linked_external;
+	const char *path;
+
+	if (linked_external)
+		return;
+
+	path = external_odb_root();
+	if (!access(path, F_OK)) {
+		link_alt_odb_entry(path, NULL, 0, "");
+		linked_external = 1;
+	}
+}
+
 void prepare_alt_odb(void)
 {
 	const char *alt;
@@ -627,6 +643,7 @@ void prepare_alt_odb(void)
 	link_alt_odb_entries(alt, strlen(alt), PATH_SEP, NULL, 0);
 
 	read_info_alternates(get_object_directory(), 0);
+	prepare_external_alt_odb();
 }
 
 /* Returns 1 if we have successfully freshened the file, 0 otherwise. */
@@ -667,7 +684,7 @@ static int check_and_freshen_nonlocal(const unsigned char *sha1, int freshen)
 		if (check_and_freshen_file(path, freshen))
 			return 1;
 	}
-	return 0;
+	return external_odb_has_object(sha1);
 }
 
 static int check_and_freshen(const unsigned char *sha1, int freshen)
@@ -824,6 +841,9 @@ static int stat_sha1_file(const unsigned char *sha1, struct stat *st,
 			return 0;
 	}
 
+	if (!external_odb_get_object(sha1) && !lstat(*path, st))
+		return 0;
+
 	return -1;
 }
 
@@ -859,7 +879,14 @@ static int open_sha1_file(const unsigned char *sha1, const char **path)
 	if (fd >= 0)
 		return fd;
 
-	return open_sha1_file_alt(sha1, path);
+	fd = open_sha1_file_alt(sha1, path);
+	if (fd >= 0)
+		return fd;
+
+	if (!external_odb_get_object(sha1))
+		fd = open_sha1_file_alt(sha1, path);
+
+	return fd;
 }
 
 /*
diff --git a/t/t0400-external-odb.sh b/t/t0400-external-odb.sh
new file mode 100755
index 0000000000..2f4749fab1
--- /dev/null
+++ b/t/t0400-external-odb.sh
@@ -0,0 +1,46 @@
+#!/bin/sh
+
+test_description='basic tests for external object databases'
+
+. ./test-lib.sh
+
+ALT_SOURCE="$PWD/alt-repo/.git"
+export ALT_SOURCE
+write_script odb-helper <<\EOF
+GIT_DIR=$ALT_SOURCE; export GIT_DIR
+case "$1" in
+have)
+	git cat-file --batch-check --batch-all-objects |
+	awk '{print $1 " " $3 " " $2}'
+	;;
+get_git_obj)
+	cat "$GIT_DIR"/objects/$(echo $2 | sed 's#..#&/#')
+	;;
+esac
+EOF
+HELPER="\"$PWD\"/odb-helper"
+
+test_expect_success 'setup alternate repo' '
+	git init alt-repo &&
+	(cd alt-repo &&
+	 test_commit one &&
+	 test_commit two
+	) &&
+	alt_head=`cd alt-repo && git rev-parse HEAD`
+'
+
+test_expect_success 'alt objects are missing' '
+	test_must_fail git log --format=%s $alt_head
+'
+
+test_expect_success 'helper can retrieve alt objects' '
+	test_config odb.magic.scriptCommand "$HELPER" &&
+	cat >expect <<-\EOF &&
+	two
+	one
+	EOF
+	git log --format=%s $alt_head >actual &&
+	test_cmp expect actual
+'
+
+test_done
-- 
2.14.1.576.g3f707d88cd