On Wed, Feb 6, 2013 at 2:23 PM, Sage Weil <sage@xxxxxxxxxxx> wrote:
> On Wed, 6 Feb 2013, Yehuda Sadeh wrote:
>> The matter of json decoding was brought up as part of the discussion
>> of the ceph management api. I recently had to deal with it with the
>> rados gateway, as I wasn't too happy was the current mechanisms that
>> were used for this purpose. So I introduced a new decode_json()
>> functionality (now in common/ceph_json.* at the wip-json-decode
>> branch). It's very similar to the regular encode/decode stuff that we
>> use to encode/decode structures. Encoding is being done using the
>> already existing dump() method, and decoding will be done through the
>> new decode_json() method.
>>
>> As an example we'll define a new UserInfo structure:
>>
>> struct UserInfo {
>> string uid;
>> string display_name;
>> int max_buckets;
>> list<Key> keys;
>>
>> void dump(Formatter *f) const;
>> void decode_json(JSONObj *obj);
>> };
>>
>> The dump() method will look like this:
>>
>> void UserInfo::dump(Formatter *f) const
>> {
>> f->open_object_section("user_info");
>> f->dump_string("user_id", uid);
>> f->dump_string("display_name", display_name);
>> f->dump_int("max_buckets", (int)max_buckets);
>>
>> f->open_array_section("keys");
>> for (list<Key>::iterator iter = keys.begin(); siter != keys.end(); ++iter) {
>> iter->dump(f);
>> }
>> f->close_section();
>>
>> f->close_section();
>> }
>>
>> It is recommended that every dump() method opens an object section and
>> puts everything within, so that every object could be easily embedded
>> within other objects. We can also probably create some template that
>
> The current loose convention is that the dump objects do not define the
> container they dump into. It's a bit weird, but it lets you do things
> like:
>
> map<Key, Value> foo;
>
> f->open_array_section("keys");
> for (map<Key,Value>::iterator iter = keys.begin(); siter != keys.end(); ++iter) {
> f->open_object_section("thing");
> f->dump_string("key", iter->first);
> iter->second.dump(f);
> f->close_section();
> }
> f->close_section();
>
> Admittedly that doesn't come up *that* often, but it happened enough when
> we first started doing the dump stuff that all/most of the dumpers work
> that way.
>
> How should we deal with that?
>
Modify the dumpers to not work this way? It's a matter of conventions,
not set in stone. If we keep this form then we'd need to create
decoders for these records:
struct KeyRecord {
Key k;
Value v;
void decode_json(JSONObj *obj) {
JSONDecoder::decode_json("key", key, obj);
v.decode_json(obj);
}
};
This will work, assuming Value doesn't have any field indexed by "key".
Yehuda
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