blobmsg-ex

記錄libubox裡面blobmsg使用範例

更新記錄

item	note
20160812	第一版

BLOB

二進位大型物件（英语：binary large object ，或英语：basic large object，縮寫為Blob、BLOB、BLOb）

BlobMsg

blobmsg裡面的是是由許多組(name+data)
所以name是唯一的
若設定相同的iname,此時還是以第一次設定為主

1 2	blobmsg_add_string(buf, "message", "Hello, world!"); blobmsg_add_string(buf, "message", "Test Data");

圖片出處：BLOB二进制对象

example

example
blobmsg-example.c
解析blob資料

static const struct blobmsg_policy pol[] = {
	[FOO_MESSAGE] = {
		.name = "message",
		.type = BLOBMSG_TYPE_STRING,
	},
	[FOO_LIST] = {
		.name = "list",
		.type = BLOBMSG_TYPE_ARRAY,
	},
	[FOO_TESTDATA] = {
		.name = "testdata",
		.type = BLOBMSG_TYPE_TABLE,
	},
};


static void dump_message(struct blob_buf *buf)
{
	struct blob_attr *tb[ARRAY_SIZE(pol)];

	if (blobmsg_parse(pol, ARRAY_SIZE(pol), tb, blob_data(buf->head), blob_len(buf->head)) != 0) {
		fprintf(stderr, "Parse failed\n");
		return;
	}
	if (tb[FOO_MESSAGE])
		fprintf(stderr, "Message: %s\n", (char *) blobmsg_data(tb[FOO_MESSAGE]));

	if (tb[FOO_LIST]) {
		fprintf(stderr, "List: ");
		dump_table(blobmsg_data(tb[FOO_LIST]), blobmsg_data_len(tb[FOO_LIST]), 0, true);
	}
	if (tb[FOO_TESTDATA]) {
		fprintf(stderr, "Testdata: ");
		dump_table(blobmsg_data(tb[FOO_TESTDATA]), blobmsg_data_len(tb[FOO_TESTDATA]), 0, false);
	}
}

建立blob資料

static void
fill_message(struct blob_buf *buf)
{
	void *tbl;

	blobmsg_add_string(buf, "message", "Hello, world!");

	tbl = blobmsg_open_table(buf, "testdata");
	blobmsg_add_u32(buf, "hello", 1);
	blobmsg_add_string(buf, "world", "2");
	blobmsg_close_table(buf, tbl);

	tbl = blobmsg_open_array(buf, "list");
	blobmsg_add_u32(buf, NULL, 0);
	blobmsg_add_u32(buf, NULL, 1);
	blobmsg_add_u32(buf, NULL, 2);
	blobmsg_close_table(buf, tbl);
}

int main(int argc, char **argv)
{
	static struct blob_buf buf;

	blobmsg_buf_init(&buf);
	fill_message(&buf);
	dump_message(&buf);	
..
}

測試

gk350a :[~]# ./blobmsg-example 
Message: Hello, world!
List: {
0
1
2
}
Testdata: {
        hello : 1
        world : 2
}
json: {"message":"Hello, world!","testdata":{"hello":1,"world":"2"},"list":[0,1,2]}
gk350a :[~]#

struct blob

blobmsg_buf_init(struct blob_buf *buf)
- blob_buf_init(buf, BLOBMSG_TYPE_TABLE)

1
2
3

buf->grow = blob_buffer_grow
buf->head = buf->buf;
blob_add(buf, buf->buf, id, 0)                  // id = BLOBMSG_TYPE_TABLE

blob_buffer_grow(struct blob_buf *buf, int minlen)
是realloc

new = realloc(buf->buf, buf->buflen + delta);
在buf->buf指標位置去要新的空間(大小由buf len決定) 對齊256byte
memset(buf->buf + buf->buflen, 0, delta);
buf->buflen += delta;

blob_add(struct blob_buf buf, struct blob_attr pos, int id, int payload)

1 2	blob_buf_grow(buf, required) // buf->grow(buf, required) blob_init(attr, id, payload + sizeof(struct blob_attr)); // 初始padload為0數值

blobmsg_add_string

blobmsg_add_string(struct blob_buf buf, const char name, const char *string)

blobmsg_add_field(buf, BLOBMSG_TYPE_STRING, name, string, strlen(string) + 1);

1 2	attr = blobmsg_new(buf, type, name, len, &data_dest); // struct blob_attr *attr; memcpy(data_dest, data, len);

blobmsg_open_table

blobmsg_open_table(struct blob_buf buf, const char name)

blobmsg_open_nested(buf, name, false);

1
2
3

struct blob_attr *head;
int type = array ? BLOBMSG_TYPE_ARRAY : BLOBMSG_TYPE_TABLE;
head = blobmsg_new(buf, type, name, 0, &data);

blobmsg_add_u32

blobmsg_add_u32(struct blob_buf buf, const char name, uint32_t val)

1 2	val = cpu_to_be32(val); return blobmsg_add_field(buf, BLOBMSG_TYPE_INT32, name, &val, 4);

blobmsg_parse

int blobmsg_parse(const struct blobmsg_policy policy, int policy_len,
struct blob_attr **tb, void data, unsigned int len)

參考來源

BLOB二进制对象