W3C home > Mailing lists > Public > public-device-apis@w3.org > September 2012

Re: Content of URL picked by Intent

From: Greg Billock <gbillock@google.com>
Date: Wed, 26 Sep 2012 10:44:26 -0700
Message-ID: <CAAxVY9fEJ6oXxkt4MQ+vgUaXk0xx8bUGRignCiZPkiW=yJdQ0Q@mail.gmail.com>
To: Alex Russell <slightlyoff@google.com>
Cc: Brett van Zuiden <brettcvz@filepicker.io>, Tobie Langel <tobie@fb.com>, Jungkee Song <jungkee.song@samsung.com>, Norifumi Kikkawa <Norifumi.Kikkawa@jp.sony.com>, Paul Kinlan <paulkinlan@google.com>, WebIntents <public-web-intents@w3.org>, "public-device-apis@w3.org" <public-device-apis@w3.org>, "Frederick.Hirsch@nokia.com" <Frederick.Hirsch@nokia.com>
I was just talking to Alex at the virtual water cooler, and here's a
proposal I think solves the issues we are wrestling with in an elegant
way.

1. All interchange through MIME type specifiers is done with array
types. That is, if I say "image/png" I will pass [ { ... }, { ... } ].
Formally, that's sequence<MimeTypeIntentData>. This goes for wildcards
as well, so "image/*" or "video/*".

2. We introduce a MIME type parameter indicating that the array will
contain a single value. So if a service will only produce a single
value, it can say "image/*;single=true". This explicitly marks a
client or service as only handling a single value. The harm to be
avoided is the mismatch of a service or client that will only handle a
single value, and the other party producing multiple values, which are
then ignored. For example, a "save" intent service which only saves
the first value, and then returns SUCCESS, would be very unexpected to
the client which sent it eight things to save and received that
SUCCESS response.

This approach achieves the following goals:

a. Keeps the types consistent across all uses -- that makes it easy to
explain and learn.
b. Puts the burden of annotation on the service, not the client. If
the client sends "image/*" with one value, then obviously a service
that accepts multiple values can handle that. If a client does a
"pick":"image/*" and the service returns multiple values, the client
may only use the first one, but that is out of the control of the
service. The user can learn the capability of the tool and accomodate
that.
c. Respect the MIME type semantics. The single=true parameter
qualifies the type for the service for no surprises, but does not
change the interchange format (an array).

The only worry I have remaining is that for single values, developers
may be tempted to use direct object indexing. But I think maintaining
type consistency is really important, and there are plenty of other
platform APIs that use a similar convention, so I think this is a
soluble problem.

Please speak up if there are any objections to this -- I'm planning on
modifying the web intents wiki document to reflect this [1], but if
the TF desires, we can draw up a more formal document about this.

[1] http://www.w3.org/wiki/WebIntents/MIME_Types


On Tue, Sep 25, 2012 at 9:30 AM, Alex Russell <slightlyoff@google.com> wrote:
> Sorry for the slow response here. Inline:
>
>
> On Thu, Sep 20, 2012 at 7:34 PM, Brett van Zuiden <brettcvz@filepicker.io>
> wrote:
>>
>> Hi there - I'm typically just an observer here, but felt like this was an
>> area where we can share a lot of what we have learned.
>>
>> I'm one of the founders of Filepicker.io, and our first product has strong
>> parallels to web intents. We've had thousands of developers use our product
>> over the last handful of months, so have some real-life experience in
>> interacting with developers around the api.
>>
>> Our initial approach was to treat multiple as a flag to the getFile call
>> (our equivalent of the "pick" intent). If multiple wasn't set, we would
>> return the url and data as an object, if it was we would return an array.
>> I'm convinced this is the wrong way to do multiple, and that the right way
>> is to have an explicit pickMultiple call.
>>
>> Rationale:
>> * a {"multiple": true} flag has poor discoverability. I'm fairly happy
>> with our documentation, but we still get on average one question a week from
>> people asking if they can/how to select multiple files
>
>
> Agreed.
>
>>
>> * The use cases for selecting multiple files are fairly distinct from
>> those asking for single files. We initially thought the flag would help
>> people switch between the two - in practice, this rarely happens.
>> * We've found that the user interface for selecting multiple files should
>> be reasonably distinct from selecting a single file. For instance, the
>> presence of a "shelf" where selected files are queued before being submitted
>> * Making single-file pick an array creates a significant boiler-plate
>> issue where every implementation needs the same blob of code. It also raises
>> questions about edge cases: what happens if the user closes without
>> selecting any file? Can an empty array ever be returned for a single-file
>> pick? Will the length of the array always be identically 1?
>
>
> I'm sympathetic to this, but the "boilerplate" is also what makes you
> automatically able to handle a SEND_MULTIPLE style of intent. The default,
> correct way to write a receiver in this world is also the way to implement
> both single and multiple item receipt. It's surely less overhead than
> writing the same thing in the SEND_MULTIPLE version and then having a
> single-item handler as well, isn't it?
>
>>
>> Happy to provide more insights into what we've learned from our customers.
>> We've recently spec'd out the next version of our API and so have aggregated
>> quite a bit of experience into that document.
>>
>> - Brett van Zuiden
>> Founder | Filepicker.io
>>
>>
>> On Thu, Sep 20, 2012 at 1:56 PM, Greg Billock <gbillock@google.com> wrote:
>>>
>>> On Thu, Sep 20, 2012 at 10:43 AM, Tobie Langel <tobie@fb..com> wrote:
>>> > On 9/20/12 7:27 PM, "Greg Billock" <gbillock@google.com> wrote:
>>> >
>>> >>The discomfort I'm estimating as the most acute
>>> >>is client developers wanting to get started. I'd like them to have as
>>> >>few problems as possible using the API, and so I'd like to make their
>>> >>path as clear as possible.
>>> >
>>> > That's actually easily mitigated by providing example code developers
>>> > can
>>> > copy. It also an issue during a relatively short period of time and is
>>> > relevant to that particular API only. It's also very possible that the
>>> > developers will be familiar with the pattern having seen it elsewhere.
>>> >
>>> > However, inconsistencies in the platform hurt the productivity of
>>> > beginner, intermediate and seasoned developers alike. Not only does it
>>> > hurt developers when they are using that particular API, but it also
>>> > hurts
>>> > them **every time they will use any other API where consistency with
>>> > that
>>> > particular API would have been expected.** In other words, coming up a
>>> > custom solution here diminishes the quality of the platform as a
>>> > whole..
>>>
>>> I completely agree, and that's a major source of discomfort I'd dearly
>>> like to avoid. :-) If we can document around early pitfalls and give
>>> developers touching a lot of the platform a consistent experience,
>>> that's definitely where the balance of intuition ends up lying. I
>>> definitely think using arrays for multiple MIME values is the way to
>>> go, and accords well with the rest of the platform. The question is
>>> how to best indicate that. Always using them is a good approach that
>>> will work fine.
>>>
>>
>
Received on Wednesday, 26 September 2012 17:44:55 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 26 September 2012 17:44:56 GMT