Open gregsdennis opened 2 weeks ago
FWIW I am of like mind.
(Corvus.JsonSchema does pass all the optional format tests, so that's easy for me to say!)
I agree that users expect that format
will assert and it's probably best that the expected behavior is the default. I say that reluctantly considering that my implementation currently doesn't support format-assertion at all and I'm not excited about the effect that a requirement will have on my bundle size.
I also agree users expect format
to perform assertions and are almost always confused when they first see they don't. However, if we bring back format
as an assertion, how do we prevent the issues that caused it to become an annotation by default?
As described in https://json-schema.org/draft/2019-09/release-notes#format-vocabulary, it was very hard to make implementations interoperable on the validation they should perform and at which degree, and these inconsistencies sometimes ended up being more painful and confusing than format
not being an assertion. Keep in mind that some formats are specifications on their own that can be very tricky to validate (like URIs?).
Sounds like if we go in this direction, we should not only make the currently optional tests required, but also extend them a lot more, which might be tricky given that some formats don't even have an "official" test suite of their own (again like URIs?)
Maybe a middle ground would be to make format
an assertion while also being a bit more prescriptive about i.e. the expected regular expressions that implementations should use as a minimum bar?
how do we prevent the issues that caused it to become an annotation by default
It was always an annotation (or before annotations were a thing, it just wasn't validated).
I agree having some minimal requirement set for each format is probably warranted.
Another question this raises (as highlighted by @jdesrosiers' https://github.com/json-schema-org/json-schema-spec/pull/1510#discussion_r1646587826) is how we want implementations to handle formats they don't understand. Should implementations automatically pass validation for these or fail them?
I think an implementation failing validation (or maybe even refusing to process the schema) gives a more expected outcome when compared with an implementation that does support the format. Getting a pass from an implementation that doesn't know the format when one that does fails feel more wrong to me.
Thoughts?
Sounds like if we go in this direction, we should not only make the currently optional tests required, but also extend them a lot more
Agreed. I think the biggest concern was the inconsistency between implementations. The test suite can address that issue. Maybe it's not perfect, but it can get better over time as we find edge cases. I think the only way making format
assert by default is a viable option is if we're fairly strict about what that validation behavior has to be. If we keep the lax requirements of the past, we'll just end up with the same problems.
Should implementations automatically pass validation for these or fail them?
I have different opinions depending on how we end up defining what asserting on format
requires. If we're strict about how each format must validate (within reason), then I think implementations should refuse to process a schema with a format it doesn't know. To be clear, I mean it should be considered an invalid schema, it should not evaluate to false. But, if we stick with the current anything-goes requirements, then an unknown format should return true.
IMO format
should exist in both states all the time, not enabled by some sort of config or vocabulary. The reason for this is because there are plenty of situations when we need both in the same schema! As it stands now, draft 2020 has format as annotation and schemas may use pattern
to validate a format, so it may use both states of format, but if you are going to make format
to validate by default this option goes away!
When I analyzed about 700 schemas from schemastore I noticed that surprisingly format
was rarely used, probably due to ambiguity around this keyword. Making format
to validate by default would rise the ambiguity around the keyword to highest level. Moreover, making format
to validate by default would be a massive breaking change for plenty of schemas that didn't expect the format
to be validated. And, json-schema
has defined patterns for format
validation, but those formats are not the same across various languages which are supporting different standards. Since json-schema
advertises that is a language agnostic standard I consider that json-schema
should not decide which patterns should be used to validate formats. All these being said, I consider that format-validation should be completly removed, format
keyword should stay as annotation and users should be encouraged to use pattern
! This approach would eliminate the ambiguity for ever.
But, if you won't accept the above solution I think at least you should create a second keyword for format
:
formatName
or formatStandard
, and the meta-schema validation for this keyword should be an enum limited to the names defined here hasFormat
or formatted
if you are going to make format to validate by default this option goes away
No, it doesn't. People can still use x-format
(or any x-
keyword) if they must have an annotation.
Making format to validate by default would rise the ambiguity around the keyword to highest level.
Making it always behave either way would definitively remove ambiguity. Making it validate would align with users' expectations.
If you're referring to the level of support for each format offered by different implementations, other comments in this issue address that by saying we need more rigorous (and non-optional) testing.
making format to validate by default would be a massive breaking change for plenty of schemas
It probably would be a breaking change for many schemas that don't declare $schema
, yes. This is why we recommend using it.
On the other hand, it will fix the multitude of schemas that exist in the wild which expect format validation.
It's also going to be a burden for many tooling maintainers because a lot of them don't support these formats fully. (I'm one of them.)
those formats are not the same across various languages which are supporting different standards. Since json-schema advertises that is a language agnostic standard I consider that json-schema should not decide which patterns should be used to validate formats.
JSON Schema very clearly defines the specifications for each format, and they're all language-agnostic (except maybe regex
which declares ECMA-262). If tools are implementing other specifications, then they are not conforming to JSON Schema and need to be fixed anyway.
format
keyword should stay as annotation and users should be encouraged to usepattern
Not all formats can be well-represented with regex, which is the only validation pattern
provides. Further, not everyone agrees on the regexes to use for each format. IMO forcing people to use pattern
doesn't fix anything and may actually make the problem worse.
@Julian what would it take to get Bowtie to report on formats, maybe even just locally, so we can get some rough numbers?
Indeed there's a great need to have a "format" keyword that validates. The difficulty of going about with this before has been a couple things:
Reverse compatibility, some usage of "format" is intended to be annotation-only.
A validating "format" [potentially] rejects all types of values, instead of within a single type (like most keywords). This makes use with multi-type schemas (e.g. "type": ["integer", "string"]
) more difficult. This point motivated my earlier solution https://github.com/json-schema-org/json-schema-spec/issues/1391.
Even when unknown keywords are ignored, validation keywords typically cause errors when their value is outside the permitted values, so I'd expect an error. Similarly, a validating "format" is not too different from a $ref that has predefined names—you're referencing some external, arbitrary validator, and if you don't know what that is, that's an error.
@gregsdennis
Not all formats can be well-represented with regex, which is the only validation pattern provides. Further, not everyone agrees on the regexes to use for each format. IMO forcing people to use pattern doesn't fix anything and may actually make the problem worse.
Can you give some examples? And if a format wouldn't be well-represented with regex how would that format be validated by implementers?
A validating "format" rejects all types of values, instead of within a single type (like most keywords). - @awwright
Could you clarify this? Are you saying that a validating "email" format would reject a number? I can't find such a requirement. In fact the (optional) test suite verifies that format ignore value types to which the format doesn't apply.
Maybe I'm misunderstanding you.
Can you give some examples? - @SorinGFS
email
& uri
can't be completely represented by a regex. Some rather large regexes get close, but I haven't seen a perfect one.
And if a format wouldn't be well-represented with regex how would that format be validated by implementers? - @SorinGFS
These generally need parsers. The spec says that it's expected that an implementation will rely on established functionality to perform the validation.
@gregsdennis
These generally need parsers. The spec says that it's expected that an implementation will rely on established functionality to perform the validation.
Well, I think this is precisely the point where this concern goes into ambiguity: the same format: "uri"
could be interpreted differently from one implementer to another, and from user's perspective I think this shouldn't be acceptable. I think json-schema
should stick to things that are giving similar results in any context.
email & uri can't be completely represented by a regex. Some rather large regexes get close, but I haven't seen a perfect one.
As for the email
part using the pattern
is exactly the perfect solution, because the schema author has the authority to decide which pattern
is expected by own application.
Could you clarify this? Are you saying that a validating "email" format would reject a number? I can't find such a requirement. In fact the (optional) test suite verifies that format ignore value types to which the format doesn't apply.
So you're right, most of the formats won't reject e.g. numbers. There's still a related problem when if I have a schema like { "type": ["number", "string"] }
: Defining separate formats for the numbers and strings. Suppose I want to say numbers are unix timestamps, and strings are RFC3339 dates. While if/then (or oneOf) is a solution, selecting on "type" is supposed to have another solution: multiple keywords that don't cross "type" boundaries.
More specifically: if it's possible to break down a keyword into multiple parts, because someone might want one to reject and not the other, then separate keywords are justified. "type" is the most common instance of this.
making
format
to validate by default would be a massive breaking change
I think everyone has recognized this is a breaking change, but I'm glad this was brought up because we haven't stated explicitly the consequences of that fact. After the stable release, breaking changes won't be allowed, so if we want to make this change, it would have to be before the release.
format
keyword should stay as annotation and users should be encouraged to usepattern
In addition to Greg's response to this, there are other problems with relying on pattern
. Regular expressions can be hard to write and hard to read. That makes them error prone, hard to maintain, and impossible to produce useful error messaging for. Being able to use "format": "email"
rather than an incomprehensible pattern
is a better experience for schema authors as well as schema consumers... as long as there's a strict and enforced definition of how `"format": "email" should validate.
Being able to use "format": "email" rather than an incomprehensible
pattern
is a better experience for schema authors
I totally dissagree on this one, and I think others should express their opinion on this matter. As for me, I will always prefer pattern
as schema author because it gives me the oportunity to twick the pattern until I get the desired result, and from that on I will have the guarantee that I will get precisely what I intended in my app... while the format
keyword is fix! And despite the fact that format
is fix... the results across implementers would vary!
In fact, I think this should be a wider discussion, not about the format
keyword itself, but about up to where shoud go the json-schema
concern. IMHO json-shema
should respect a simple rule in this matter: no concern for matters that cannot produce similar results among implementers under any circumstances! All those concerns should go to application level where the schema author has the ability to require exactly what he needs in his application. The results of the implementers for the same schema must be identical by design, meaning that json-schema
should only provide capabilities that cannot be interpreted differently.
@jdesrosiers
I think validating uri
doesn't even belong to format
. In general format
validation is required on user inputs, and I think nobody expects to validate uri
s in a frontend. That would be terribly wrong! They may expect to validate a uri
just for being a string instead of a number, but actual validation of the string provided in frontend would be made in backend under application's control.
And if we think about validating $ref
s keyword definition that part also doesn't require validation because the actual place where the validation occures is where accessing $ref
in a schema would succed or not.
@jdesrosiers
similarly, if we talk about date
formats IMO date
values should always travel the network as number. Probably that's why json
doesn't have a type: date
or variations. Data interchange with date
as number will always guarantee the precision, then is up to applications how they choose to display or collect date
values.
@jdesrosiers
I totally understand the need for some sort of specifications about how imputs should look like in a frontend. But I think format
validation is not the answer. There is a missing piece of puzzle there: inputType
. Having inputType
schema authors may provide a hint about the expected type of input, but this wouldn't have any validation role, the validation would be made by other keywords provided in the schema location.
@SorinGFS I think we're talking about two different things. If I understand you correctly, you understand format
to be a kind of semantic identifier. "format": "date"
would indicate that the value represents a date. One schema might represent a date as a string and another might represent a date as a number, but they're both semantically a date. Given that interpretation, your arguments makes perfect sense.
But, that's not the way format
is defined in the spec. Every format has a very specific expectations defined by a standard. For example, "date" is defined as a string that conforms to RFC 3339, section 5.6. If you use "format": "date"
where you expect a timestamp, you're using format
in a way that isn't correct according to the spec. All the defined formats are the same. They aren't open-ended. They all have very specific definitions that aren't open to interpretation by schema authors.
But, that's not the way
format
is defined in the spec.
I didn't say that using format: date
would be wrong acording to the spec. I say that the very existence of format: date
(and date-time, and time, and duration) in the spec which are strings interpreted as date
values is wrong! Wrong acording to the logic! Here json-schema
leaves the precision area by introducing an element of ambiguity, offering the user the possibility to transport date
in the form of a string while the data type for date
is number! Data interchange for date
values should only be made as number, and how that date
value transported as number is displayed should be completely another concern.
data type for
date
is number
This is an incorrect assumption. Different systems handle dates differently. Some (like many spreadsheets) internally represent dates as numbers.
.Net uses the DateTime
struct, an object with multiple fields. When serializing a DateTime
to JSON, .Net chose to represent the date as an ISO 8601 string.
Data interchange for date values should only be made as number, and how that date value transported as number is displayed should be completely another concern.
This is a valid opinion, but it is not an industry standard or best practice.
JSON Schema (long ago) made a decision that the ideal way to represent dates in JSON should be strings per RFC 3339. My guess is that, at the time, JSON Schema was published under IETF, and they wanted to use an IETF standard for date representation. Since then, the majority of the internet (based on my experience, which is admittedly .Net heavy) seems to have decided they like ISO 8601 better. (Happy to be proven wrong.) So if anything, we should be changing format: date
to check for ISO 8601 dates.
But that's not what this discussion is about.
We're not discussing any format specifically. We're discussing whether the format
keyword in general should validate. I'm marking any of your comments that do not address this specifically as off-topic.
In the future, please keep discussions on topic. If you have something new to discuss, please open a new discussion. If it's related, add a link.
@jdesrosiers @gregsdennis
IMHO, as a rule of tomb, wherever json-schema requires an external library to function is a clear indication that it has exceeded its competence area. Json-schema must work using the basic capabilities of a language, with zero dependencies. Which is not the case with format: date,date-time,time,duration
, which needs an external library to work.
JSON Schema (long ago) made a decision that the ideal way to represent dates in JSON should be strings per RFC 3339. My guess is that, at the time, JSON Schema was published under IETF, and they wanted to use an IETF standard for date representation. Since then, the majority of the internet (based on my experience, which is admittedly .Net heavy) seems to have decided they like ISO 8601 better. (Happy to be proven wrong.) So if anything, we should be changing
format: date
to check for ISO 8601 dates.
that is another indication that json-schema
exceeded its competence area by entering in a land of 'choices and preferences' against precision! 😄 Since json-schema
as you said 'long ago' choosed to use RFC 3389 things are changed: that was just a 'proposed standard' and... now is updated with 9557
We're not discussing any format specifically. We're discussing whether the format keyword in general should validate. I'm marking any of your comments that do not address this specifically as off-topic.
No, I don't think this is off-topic, because it matters which formats are in discussion to be validated by default. If you ask me this whole discussion should be ... off-topic, since is a wrong thing to do in my opinion.
@gregsdennis
This is an incorrect assumption. Different systems handle dates differently. Some (like many spreadsheets) internally represent dates as numbers. .Net uses the DateTime struct, an object with multiple fields. When serializing a DateTime to JSON, .Net chose to represent the date as an ISO 8601 string.
I'm not talking about ancient languages. Even your .Net struct example object has all inner properties as number, and then comes the concern of conversion to string (which again, is a separate concern even in your example). In database you are probably (you should be) storing the dateTime
as a 64bit number.
Just to have my personal opinion documented here (which I've shared elsewhere although probably piecemeal):
So I'd be -1 personally for my vote, and would instead recommend inventing new keywords which can be richer (and express more nuance in how they allow for different "levels" of compliance).
@Julian what would it take to get Bowtie to report on formats, maybe even just locally, so we can get some rough numbers?
It's a bit of work, since I'd have to go enable format validation in each implementation, but nothing too crazy? If it's really helpful I can try to get to it this week at some point.
There's still a related problem when if I have a schema like { "type": ["number", "string"] }: Defining separate formats for the numbers and strings. Suppose I want to say numbers are unix timestamps, and strings are RFC3339 dates. While if/then (or oneOf) is a solution, selecting on "type" is supposed to have another solution: multiple keywords that don't cross "type" boundaries. - @awwright
I see what you're getting at (I think, correct me if I'm wrong), but format
already doesn't support multiple values, e.g. format: ["timestamp", "datetime"]
, where timestamp
applies to numbers as you suggest. I like the idea, actually, but it's not something we currently do.
Users have to do something like this currently:
{
"type": ["number", "string"],
"allOf/anyOf/oneOf": [
{ "format": "timestamp" },
{ "format": "datetime" }
]
}
(You can use allOf
in this case because format
ignores instances that aren't the right type. You only have to use oneOf
/anyOf
if you have two formats that validate the same type; then they probably aren't both valid.)
Still, I'm not sure how this applies to whether we have format
validate by default or not. I think most users would expect both format
keywords to validate in this case.
... because someone might want one to reject and not the other
This also isn't really something that the spec currently or historically supports. It's been all-or-nothing: either format
validates or it doesn't. While an implementation technically has the right to allow its users to select which formats are validated and which aren't, that behavior isn't and hasn't been supported by the specification.
Supposing that a schema author did want only annotation behavior, yes, I agree with the rest of that statement: that they'd need to use different keywords. And in this case, I'd recommend using format
, which validates, and x-format
which doesn't.
Still, I'm not sure how this applies to whether we have format validate by default or not. I think most users would expect both format keywords to validate in this case.
To bring it back around, it's because the primary motivation for https://github.com/json-schema-org/json-schema-spec/issues/1391 was this issue, to introduce "format" keywords that are definitively validation keywords. Since validation keywords often apply only to a single type, typed keywords e.g. "stringFormat" would be a convenient way of adding format validation.
That makes sense. Thanks for the connection.
if you are going to make format to validate by default this option goes away
No, it doesn't. People can still use x-format (or any x- keyword) if they must have an annotation.
...or they can define their own metaschema, with the format-assertion vocabulary removed and format-annotation added. (Or, we can formally publish a metaschema variant with this change in it already. You may recall that we've previously discussed publishing a draft2020-12 metaschema with format-assertion enabled; and then with this change, for the next spec release we would have the hing only in reverse: the "main" schema has format-assertion turned on, and the "secondary" schema has it turned off).
or they can define their own metaschema, with the format-assertion vocabulary removed and format-annotation added
This isn't an option anymore. We're removing vocabularies. They're being extracted into the new Feature Life Cycle as a proposal. That means the specification can't rely on vocabs anymore.
There is no format-assertion or format-annotation vocab. There's only the format
keyword now.
A validating "format" [potentially] rejects all types of values, instead of within a single type (like most keywords). This makes use with multi-type schemas (e.g. "type": ["integer", "string"]) more difficult.
We could explicitly state in the spec that while a format may choose to only match strings, it MUST NOT reject other data types for which it is not possible to have valid data (that is: you can have a format that matches against both string and number values, but it cannot produce a "valid":false result for objects, arrays etc. Or to rephrase, a "valid":false result may only be produced for a particular data type so long as there is at least one instance of that type for which "valid":true would be produced).
This isn't an option anymore. We're removing vocabularies.
I did not have the impression that this had been decided yet.
There's a long and sticky history around
format
.format
has never required validation.format
validation has always been the decision of the implementation.The result of all of this is that implementation support for validation has been spotty at best. Despite the JSON Schema specs referencing very concretely defined formats (by referencing other specs), implementations that do support validation don't all support each format equally. This has been the primary driving force behind keeping
format
as an opt-in validation.With 2019-09, we decided that it was time to give the option of
format
validation to the schema author. They could enable validation by using a meta-schema which listed the Format Vocabulary with atrue
value, which meant, "format
validation is required to process this schema."In 2020-12, we further refined this by offering two separate vocabularies, one that treats the keyword as an annotation and one that treats it as an assertion. The argument was that the behavior of a keyword shouldn't change based on whether the vocabulary was required or not.
However, the fact remains that our users consistently report (via questions in Slack, GitHub, and StackOverflow) that they expect
format
to validate. (The most recent case I can think of was only last week, in .Net's effort to build a short-term solution for schema generation from types.)This consistency in user expectations leads me to believe that we should officially make
format
an assertion keyword and strictly enforce it by moving the appropriate tests into the required section of the Test Suite.(Personally, I'm not passing all of the optional
format
tests, so I'll have to do some work to get there or document why they're not supported.)