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Validator.nu Web Service Interface: Difference between revisions

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<P>I am just writing this down so I don’t forget it. There are no
{{Obsolete|spec=https://github.com/validator/validator/wiki/Service-»-HTTP-interface}}
immediate implementation plans. There are no implementation promises,
Validator.nu can be called as a Web service. Input and output modes can be chosen completely orthogonally. Responses and requests can be optionally compressed (independently of each other).
either. There especially are no hosting promises at this time.
 
This is a inline-commentable wiki copy of [http://hsivonen.iki.fi/validator-ws-ideas/ the original article].</P>
(Please use the Web service API reasonably. See the [https://about.validator.nu/#tos Terms of Service].)
<H2 id='motivation'>Motivation</H2>
 
<P>First, I assume there is some level of interest in doing RELAX NG
==Input Modes==
/ Schematron validation and HTML5 conformance checking. Next, it
 
would be nice to enable applications that deal with documents to make
For most Web service use cases, you should probably POST the document as the HTTP entity body.
these checks automatically in addition to having the functionality
 
available for human operators as a Web app. For example, [http://golem.ph.utexas.edu/~distler/blog/archives/001054.html a content management system might check the input it is given].</P>
===Implemented===
<P>Java apps could just integrate a private copy of the Free Software
 
back end of the [http://hsivonen.iki.fi/validator/ validation]
* Document [[Validator.nu GET Input|URL as a GET parameter]]; the service retrieves the document by URL over HTTP or HTTPS.
/ [http://hsivonen.iki.fi/validator/html5/ conformance checking] service. However, non-Java apps would benefit from
* Document [[Validator.nu POST Body Input|POSTed as the HTTP entity body]]; parameters in query string as with GET.
having the validation / conformance checking service running out of
* Document [[Validator.nu Textarea Input|POSTed as a <code>textarea</code> value]].
process and having an interface for talking to the out-of-process
* Document [[Validator.nu Form Upload Input|POSTed as a form-based file upload]].
Java service. The service instance could be hosted publicly or as a
 
local copy. Even some Java developers would elect to use such a
===Not Implemented===
service instead of integrating the back end as part of their own app.</P>
 
<H2 id='input'>Input Modes</H2>
* Document in a <CODE>data:</CODE> URI as a GET parameter.
<P>The schemas are expected to be relatively static. Therefore, I
* <code>application/x-www-form-urlencoded</code>
think preloading them into the service or letting the service
 
retrieve them is sufficient. Identification by URI works in both
==Output Modes==
cases.</P>
 
<P>What needs different input modes is the document that is checked.</P>
When using Validator.nu as a Web service back end, the [[Validator.nu XML Output|XML]] and [[Validator.nu JSON Output|JSON]] output formats are recommended for forward compatibility. The available JSON tooling probably makes consuming JSON easier. The XML format contains XHTML elaborations that are not available in JSON. Both formats are streaming, but streaming XML parsers are more readily available. XML cannot represent some input strings faithfully.
<P>I think the following modes would make sense:</P>
 
<UL>
===Implemented===
<LI><P>Document URI as a GET parameter; the service retrieves the
 
document by URI (already implemented).</P>
* HTML with microformat-style <CODE>class</CODE> annotations (default output; should not be assumed to be forward-compatibly stable).
<LI><P>Document in a <CODE>data:</CODE> URI as a GET parameter.</P>
* XHTML with microformat-style <CODE>class</CODE> annotations (append <code>&out=xhtml</code> to URL; should not be assumed to be forward-compatibly stable).
<LI><P>Document POSTed as the HTTP entity body (the preferred Web
* [[Validator.nu XML Output|XML]] (append <code>&out=xml</code> to URL).
service mode).</P>
* [[Validator.nu JSON Output|JSON]] (append <code>&out=json</code> to URL).
<LI><P>Document POSTed as an <CODE>application/x-www-form-urlencoded</CODE>
* [[Validator.nu GNU Output|GNU error format]] (append <code>&out=gnu</code> to URL).
form field value.</P>
* Human-readably plain text (append <code>&out=text</code> to URL; should not be assumed to be forward-compatibly stable for machine parsing—use the GNU format for that).
<LI><P>Document POSTed as a <CODE>multipart/form-data</CODE> file
 
upload.</P>
===Not Implemented===
</UL>
 
<P>In the first three modes, additional parameters would be
* Relaxed-compatible (lacks a spec)
communicated in the URI query string. In the last two modes,
* Unicorn-compatible (hoping that Unicorn changes instead)
additional parameters would be communicated like corresponding from
* W3C Validator-compatible SOAP (legacy)
fields are communicated as <CODE>application/x-www-form-urlencoded</CODE>
* EARL (not implemented; domain modeling mismatch)
and <CODE>multipart/form-data</CODE>.</P>
 
<P>I don’t particularly like the last two modes, but they are
==Compression==
needed to address feature requests and for parity with other
 
services. Also, unlike the first three modes, the last two modes need
Validator.nu supports compression in order to save bandwidth.
companion UI changes, which is not nice. As a further complication,
 
the last two don’t come naturally with a <CODE>Content-Type</CODE>
===Request Compression===
for dispatching to an HTML5 parser or to an XML parser.</P>
 
<P>All these input modes would share the same “service endpoint
Validator.nu supports HTTP request compression. To use it, compress the request entity body using gzip and specify <code>Content-Encoding: gzip</code> as a ''request'' header.
URI” (and the same servlet class). The different cases can be
 
distinguished from the HTTP method and in the POST cases from the
===Response Compression===
<CODE>Content-Type</CODE> request header.</P>
 
<H2 id='output'>Output Modes</H2>
Validator.nu supports HTTP response compression. Please use it. Response compression is orthogonal to the input methods and output formats.
<P>A Web service probably calls for an XML output format for maximal
 
tool chain integration even though the current HTML output format
The standard HTTP gzip mechanism is used. To indicated that you prepared to handle gzipped responses, include the <code>Accept-Encoding: gzip</code> request header. When the header is present, Validator.nu will gzip compress the response. You should also be prepared to receive an uncompressed, though, since in the future it may make sense to turn off compression under heavy CPU load.
makes sense for browsers and can carry all the necessary data.</P>
 
<P>I think the following modes would make sense:</P>
==Sample Code==
<UL>
 
<LI><P>HTML with microformat-style <CODE>class</CODE> annotations
There a [https://about.validator.nu/html5check.py sample Python program] that shows how to deal with compression and redirects. (It may not be exemplary Python, though.)
(already implemented except the annotation granularity could be
 
better).</P>
==CORS Example==
<LI><P>XHTML with microformat-style <CODE>class</CODE> annotations.</P>
 
<LI><P>A custom XML format that it super-simple and use element
You can also hit the API using [https://developer.mozilla.org/en-US/docs/HTTP_access_control CORS] over AJAX. [https://gist.github.com/gists/3902535 Basic example using jQuery].
names for easier processing with tools that are biased towards
 
keying on element name rather than on attribute value.</P>
==Sample Messages==
</UL>
 
<P>For the HTML and XHTML output formats, there could be an option
There are [http://hsivonen.com/test/moz/messages-types/ documents for provoking different message types].
for suppressing the input form. The output default should be HTML for
 
the browser-targeted input formats. However, the custom XML format
{|
might be a reasonable default when the input document was POSTed as
|-
the entity body.</P>
! No message
<H3 id='xml'>The XML Output Format (Draft)</H3>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fno-message.html HTML]
<P>The elements in this XML vocabulary are in the namespace
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fno-message.html&out=xhtml XHTML]
“<CODE>http://hsivonen.iki.fi/validator/messages/</CODE>”. The
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fno-message.html&out=xml XML]
attributes in this XML vocabulary are not in a namespace. The
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fno-message.html&out=json JSON]
attribute values defined for this XML vocabulary must not have
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fno-message.html&out=gnu GNU]
preceding or trailing white space.</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fno-message.html&out=text Text]
<P>Note: The format has been designed to support streaming generation
|-
and consumption.</P>
! Info
<H4 id='structure'>Structure and Semantics</H4>
| [https://validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Finfo.svg HTML]
<P>The format consists of an XML 1.0 document that has the element
| [https://validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Finfo.svg&out=xhtml XHTML]
<CODE>messages</CODE> as the root element.  
| [https://validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Finfo.svg&out=xml XML]
</P>
| [https://validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Finfo.svg&out=json JSON]
<P>The root element may zero or more child elements named <CODE>info</CODE>,
| [https://validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Finfo.svg&out=gnu GNU]
<CODE>warning</CODE> and <CODE>error</CODE>. The element <CODE>info</CODE>
| [https://validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Finfo.svg&out=text Text]
means an informational message. The element <CODE>warning</CODE>
|-
signifies a potential problem that does not cause the
! Warning
validation/checking to fail. The element <CODE>error</CODE> signifies
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fwarning.html HTML]
a problem that causes the validation/checking to fail. The character
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fwarning.html&out=xhtml XHTML]
data content of these three elements may contain a human-readable
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fwarning.html&out=xml XML]
message. (Entity-escaped HTML is <EM>not</EM> allowed. :-)</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fwarning.html&out=json JSON]
<P>The elements <CODE>info</CODE>, <CODE>warning</CODE> and <CODE>error</CODE>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fwarning.html&out=gnu GNU]
have three optional attributes for indicating the context of the
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fwarning.html&out=text Text]
message: <CODE>uri</CODE>, <CODE>line</CODE> and <CODE>column</CODE>.
|-
The <CODE>column</CODE> attribute must not be present unless the <CODE>line</CODE>
! Error (precise location)
attribute is present as well.  
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fprecise-error.html HTML]
</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fprecise-error.html&out=xhtml XHTML]
<P>The <CODE>uri</CODE> attribute, if present, must containt the URI
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fprecise-error.html&out=xml XML]
(not IRI) of the HTTP resource with which the message is associated
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fprecise-error.html&out=json JSON]
or the literal string “<CODE>data:…</CODE>” (the last character
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fprecise-error.html&out=gnu GNU]
is U+2026) to signify that the message is associated with a data URI
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Fprecise-error.html&out=text Text]
resource but the exact URI has been omitted. (If a client application
|-
wishes to show IRIs to human users, it is up to the client
! Error (range location)
application to convert the URI into an IRI.)</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Frange-error.html HTML]
<P>The <CODE>line</CODE> attribute, if present, must contain a string
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Frange-error.html&out=xhtml XHTML]
consisting of characters in the range U+0030 DIGIT ZERO to U+0039
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Frange-error.html&out=xml XML]
DIGIT NINE which when interpreted as a base-ten integer is a positive
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Frange-error.html&out=json JSON]
integer (not zero). This number means the approximate source text
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Frange-error.html&out=gnu GNU]
line number associated with the message. The first line is 1.</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Frange-error.html&out=text Text]
<P>The <CODE>column</CODE> attribute, if present, must contain a
|-
string consisting of characters in the range U+0030 DIGIT ZERO to
! Fatal
U+0039 DIGIT NINE which when interpreted as a base-ten integer is a
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Ffatal.xhtml HTML]
positive integer (not zero). This number means the approximate source
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Ffatal.xhtml&out=xhtml XHTML]
column number associated with the message on the line indicated by
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Ffatal.xhtml&out=xml XML]
the <CODE>line</CODE> attribute. The first character on a line is in
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Ffatal.xhtml&out=json JSON]
column 1.</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Ffatal.xhtml&out=gnu GNU]
<P>The source lines and columns are approximate. For example, if a
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2Ffatal.xhtml&out=text Text]
message is related to an attribute, the line and column may point to
|-
the first character if the start tag, the character after the start
! IO
tag or to the attribute inside the tag depending on implementation.
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2F404.html HTML]
If a message is related to character data, the line and column may be
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2F404.html&out=xhtml XHTML]
inaccurate within a run of text e.g. due to buffering. Furthermore,
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2F404.html&out=xml XML]
implementation may count column numbers in terms of UTF-16 code units
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2F404.html&out=json JSON]
instead of characters.</P>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2F404.html&out=gnu GNU]
<P>The <CODE>error</CODE> element may have an attribute called <CODE>type</CODE>
| [https://html5.validator.nu/?doc=http%3A%2F%2Fhsivonen.com%2Ftest%2Fmoz%2Fmessages-types%2F404.html&out=text Text]
for indicating that an error is not a general error. Permissible
|}
values for the <CODE>type</CODE> attribute are: <CODE>fatal</CODE>
 
(signifies a well-formedness violation or another error after which
 
no more checking was performed), <CODE>io</CODE> (signifies an
 
input/output error),  <CODE>schema</CODE> (indicates that
[[Category:Validator.nu Documentation]]
initializing a schema-based validator failed) and <CODE>internal</CODE>
(indicates that the validator/checker found an error bug in itself,
ran out of memory, etc., but was still able to emit a message).</P>
<P>The validation/checking is considered to have failed if there is
one or more <CODE>error</CODE> element.</P>
<H4 id='processing'>Processing Model</H4>
<P>Clients that consume the message format are referred to as
processors. They must use a conforming XML 1.0 processor to parse the
format.</P>
<P>If the root element is not an element named <CODE>messages</CODE>,
the document is deemed to be in an unknown format and not processable
according to this processing model.</P>
<P>If a processor encounters an element that it doesn’t recognize,
it must process the content of the element as if the start tag and
the end tag of the element were not there. If the processor encounter
character data as a child of the root element (after applying the
rule stated in the previous sentence), it must act as if the
character data was not there. If a processor encounters an attribute
that it does not recognize, it must ignore the entire attribute. If a
processor encounters an attribute that it does recognize but the
value of the attribute is not permissible under the previous section,
the processor must ignore the entire attribute. If an <CODE>info</CODE>,
<CODE>warning</CODE> or <CODE>error</CODE> element does not have a
<CODE>line</CODE> attribute with a permissible value, a <CODE>column</CODE>
attribute on the element must be ignored if present.</P>
<P>Note: These rules make it possible to add markup for source code
dumps, document outlines and parse trees later without breaking
clients. Also, it make it possible to introduce e.g. XHTML markup in
the human-readable messages.</P>
<P>Processors must process elements in a way that is consistent with
the semantics of the elements.</P>
<P>The determine if the validation/checking succeeded, processors
must determine whether the root element has no <CODE>error</CODE>
element children. If there are no <CODE>error</CODE> children, the
validation/checking succeeded. Otherwise, it failed.</P>
<H2 id='prior'>Prior Art</H2>
<P>The W3C has defined two XML output formats for the W3C Validator:
[http://validator.w3.org/docs/api.html the SOAP format]
and [http://www.w3.org/QA/2006/obs_framework/response/ the Unicorn format]. I think there are two problems with these
formats: they are unnecessarily complex and they don’t support
streaming output. For example, they require a redundant declaration
of the number of errors before the errors themselves (which a client
could count on its own if it wants to know the number).</P>
<P>The W3C Validator also provides simple pass/fail information as
[http://validator.w3.org/docs/api.html#http_headers HTTP headers], which is nice if you only care about a boolean
pass/fail. However, this approach also has the problem the it
precludes streaming, because the validation process has to finish
before the HTTP headers can be written.</P>
<P>For these reasons, I am not particularly keen on reusing the
output formats of the W3C Validator unless it turns out that there
are significant [http://en.wikipedia.org/wiki/Network_effect network benefits] to be reaped from plugging into an existing network of
client software. It seems to me that there isn’t a significant
network of existing client software.</P>

Latest revision as of 04:36, 29 December 2016

This document is obsolete.

For the current specification, see: https://github.com/validator/validator/wiki/Service-»-HTTP-interface

Validator.nu can be called as a Web service. Input and output modes can be chosen completely orthogonally. Responses and requests can be optionally compressed (independently of each other).

(Please use the Web service API reasonably. See the Terms of Service.)

Input Modes

For most Web service use cases, you should probably POST the document as the HTTP entity body.

Implemented

Not Implemented

  • Document in a data: URI as a GET parameter.
  • application/x-www-form-urlencoded

Output Modes

When using Validator.nu as a Web service back end, the XML and JSON output formats are recommended for forward compatibility. The available JSON tooling probably makes consuming JSON easier. The XML format contains XHTML elaborations that are not available in JSON. Both formats are streaming, but streaming XML parsers are more readily available. XML cannot represent some input strings faithfully.

Implemented

  • HTML with microformat-style class annotations (default output; should not be assumed to be forward-compatibly stable).
  • XHTML with microformat-style class annotations (append &out=xhtml to URL; should not be assumed to be forward-compatibly stable).
  • XML (append &out=xml to URL).
  • JSON (append &out=json to URL).
  • GNU error format (append &out=gnu to URL).
  • Human-readably plain text (append &out=text to URL; should not be assumed to be forward-compatibly stable for machine parsing—use the GNU format for that).

Not Implemented

  • Relaxed-compatible (lacks a spec)
  • Unicorn-compatible (hoping that Unicorn changes instead)
  • W3C Validator-compatible SOAP (legacy)
  • EARL (not implemented; domain modeling mismatch)

Compression

Validator.nu supports compression in order to save bandwidth.

Request Compression

Validator.nu supports HTTP request compression. To use it, compress the request entity body using gzip and specify Content-Encoding: gzip as a request header.

Response Compression

Validator.nu supports HTTP response compression. Please use it. Response compression is orthogonal to the input methods and output formats.

The standard HTTP gzip mechanism is used. To indicated that you prepared to handle gzipped responses, include the Accept-Encoding: gzip request header. When the header is present, Validator.nu will gzip compress the response. You should also be prepared to receive an uncompressed, though, since in the future it may make sense to turn off compression under heavy CPU load.

Sample Code

There a sample Python program that shows how to deal with compression and redirects. (It may not be exemplary Python, though.)

CORS Example

You can also hit the API using CORS over AJAX. Basic example using jQuery.

Sample Messages

There are documents for provoking different message types.

No message HTML XHTML XML JSON GNU Text
Info HTML XHTML XML JSON GNU Text
Warning HTML XHTML XML JSON GNU Text
Error (precise location) HTML XHTML XML JSON GNU Text
Error (range location) HTML XHTML XML JSON GNU Text
Fatal HTML XHTML XML JSON GNU Text
IO HTML XHTML XML JSON GNU Text
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