[GitHub] [trafficcontrol] ocket8888 commented on a change in pull request #4536: API Guidelines blueprint

GitBox Tue, 31 Mar 2020 12:23:39 -0700

ocket8888 commented on a change in pull request #4536: API Guidelines blueprint
URL: https://github.com/apache/trafficcontrol/pull/4536#discussion_r401157656

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File path: blueprints/api.guidelines.md
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+
+# API Guidelines
+
+## Problem Description
+The Traffic Ops API duplicates a lot of functionality, is at times
+self-inconsistent, and can be difficult to work with.
+
+## Proposed Changes
+Many manifestations of the above problems could be avoided entirely by adhering
+to a set of guidelines for how our API ought to behave. That would certainly
+make it more consistent, and would make the intended behavior much easier to
+discern. Herein lie a proposed set of API guidelines that have been discussed
+by the Traffic Ops working group over the past few months.
+
+These rules aren't meant to necessarily be ironclad, but there should be a very
+convincing argument accompanying endpoints that do not follow them.
+
+### Response Bodies
+All valid API responses will be in the form of some serialized object. The main
+data that represents the result of the client's request MUST appear in the
+`response` property of that object. If a warning, error message, success
+message, or informational message is to be issued by the server, then they MUST
+appear in the `alerts` property of the response. Some endpoints may return
+ancillary statistics such as the total number of objects when pagination
occurs,
+which should be placed in the `summary` property of the response.
+
+#### Response
+The `response` property of a serialized response object MUST only contain
object
+representations as requested by the client. In particular, it MUST NOT contain
+admonitions, success messages, informative messages, or statistic summaries
+beyond the scope requested by the client.
+
+Equally unacceptable API responses are shown below.
+
+```json
+{
+ "response": "Thing was successfully created."
+}
+```
+
+```json
+{
+ "response": {"foo": "bar"},
+ "someOtherField": {"someOtherObject"}
+}
+```
+
+When requests are serviced by Traffic Ops that pass data asking that the
+returned object list be filtered, the response property MUST be a filtered
array
+of those objects (assuming the request may be successfully serviced). This is
+true even if filtering is being done according to a uniquely identifying
+property - e.g. a numeric ID. The `response` field of an object returned in
+response to a request to create, update, or delete one or more resources may be
+either a single object representation or an array thereof according to the
+number of objects created, updated, or deleted. However, if a handler is
+*capable* of creating, updating, or deleting more than one object at a time,
the
+`response` field SHOULD consistently be represented as an array - even if its
+length would only be 1.
+
+The proper value of an empty collection is an empty collection. If a Foo can
+have zero or more Bars, then the representation of a Foo with no Bars MUST be
an
+empty array/list/set, and in particular MUST NOT be either missing from the
+representation or represented as the "Null" value of the representation format.
+That is, if Foos have no other property than their Bars, then a Foo with no
Bars
+may be represented in JSON encoding as `{"bars":[]}`, but not as
`{"bars":null}`
+or `{}`. Similarly, an empty string field is properly represented as an empty
+string - e.g. `{"bar":""}` not `{"bar":null}` or `{}` - and the "zero-value" of
+numbers is zero itself - e.g. `{"bar":0}` not `{"bar":null}` or `{}`. Note that
+"null" values *are allowed* when appropriate, but "null" values represent the
+*absence* of a value rather than the "zero-value" of a property. If a property
+is *missing* from an object representation it indicates the absence of that
+property, and because of that there must be a *very convincing* argument if and
+when that is the case.
+
+As a special case, endpoints that report statistics including minimums,
+maximums and arithmetic means of data sets MUST use the property names `min`,
+`max`, and `mean`, respectively, to express those concepts. These SHOULD be
+properties of `response` directly whenever that makes sense.
+
+#### Alerts
+Alerts should be presented as an array containing objects which each conform to
+the object definition laid out by
+[the ATC library's Alert
structure](https://godoc.org/github.com/apache/trafficcontrol/lib/go-tc#Alert).
+The allowable `level`s of an Alert are:
+
+- `error` - This level MUST be used to indicate conditions that caused a
request
+to fail. Because of this, this level MUST NOT appear in the `alerts` array of
+responses with any HTTP response code less than 400. Details of server workings
+and/or failing components MUST NOT be exposed in this message, which should
+otherwise be as descriptive as possible.
+- `info` - This level SHOULD be used to convey supplementary information to a
+user that is not directly the result of their request. This SHOULD NOT carry
+information indicating whether or not the request succeeded and why/why not, as
+that is best left to the `error` and `success` levels.
+- `success` - This level MUST be used to convey success messages to the client.
+In general, it is expected that the message will be directly displayed to th
+user by the client, and therefore can be used to add human-friendly details
+about a request beyond the response payload. This level MUST NOT appear in the
+`alerts` array of responses with an HTTP response code that is not between 200
+and 399 (inclusive).
+- `warning` - This level is used to warn clients of potentially dangerous
+conditions when said conditions have not caused a request to fail. The best
+example of this is deprecation warnings, which should appear on all API routes
+that have been deprecated.
+
+#### Summary
+The `summary` object is used to provide summary statistics about object
+collections. In general the use of `summary` is left to be defined by API
+endpoints (subject to some restrictions). However, its use is not appropriate
in
+cases where the user is specifically requesting summary statistics, but should
+rather be used to provide supporting information - pre-calculated - about a set
+of objects or data that the client *has* requested.
+
+Endpoints MUST use the following, reserved properties of `summary` for their
+described purposes (when use of `summary` is appropriate) rather than defining
+new `summary` or `response` properties to suit the same purpose:
+
+- `count` - Count contains an unsigned integer that defines the total number of
+results that could possibly be returned given the non-pagination query
+parameters supplied by the client.
+
+### HTTP Request Methods
+[RFC 2616 Section 9](https://tools.ietf.org/html/rfc2616#section-9) defines the
+semantics of HTTP/1.1 request methods. Authors should conform to that set of
+standards whenever possible, but for convenience the methods recognized by
+Traffic Ops and their meanings in that context are herein defined.
+
+#### GET
+HTTP GET requests are issued by clients who want some data in response. In the
+context of Traffic Ops, this generally means a serialized representation of
some
+object. GET requests MUST NOT alter the state of the server. An example of an
+API endpoint created in API version 1 that violates this restriction is
+`cdns/name/{{name}}/dnsseckeys/delete`.
+
+This is the standard method to be used by all read-only operations, and as such
+handlers for this method should generally be accessible to users with the
+"read-only" Role.
+
+All endpoints dealing with the manipulation or fetching representations of
+"Traffic Control Objects" MUST support this method.
+
+#### POST
+POST requests ask the server to process some provided data. Most commonly, in
+Traffic Ops, this means creating an object based on the serialization of said
+object contained in the request body, but it can also be used virtually
whenever
+no other method is appropriate. When an object *is* created, the response body
+MUST contain a representation of the newly created object. POST requests do not
+need to be *idempotent*, unlike PUT requests.
+
+#### PUT
+PUT is used to replace existing data with new data that is provided in the
+request body.
+[RFC 2616 Section 9.1.2](https://tools.ietf.org/html/rfc2616#section-9.1.2)
+lists PUT as an "idempotent" request method, which means that subsequent
+identical requests should ensure the same state is maintained on the server.
+What this means is that a client that PUTs an object representation to Traffic
+Ops expects that if they then GET a representation of that object, do the same
+PUT again and GET another representation, the two retrieved representations
+should be identical. Effectively, the `lastUpdated` field that is common to
+objects in the Traffic Ops API violates this, but the other properties of
+objects - which can actually be defined - generally obey this restriction. In
+general, fulfilling this restriction means that handlers will need to require
+the entirety of an object be defined in the request body.
+
+When an object is modified, the response body MUST contain a representation of
+the object after modification.
+While RFC 2616 states that servers MAY create objects for the passed
+representations if they do not already exist, Traffic Ops API endpoint authors
+MUST instead use POST handlers for object creation.
+
+All endpoints that support the PUT request method MUST also support the
+If-Unmodified-Since HTTP header.
+
+#### PATCH
+At the time of this writing, no Traffic Ops API endpoints handle the PATCH
+request method. PATCH requests that the server's stored data be mutated in some
+way using data provided in the request body. Unlike PUT, PATCH is not
+*idempotent*, which essentially means that it can be used to change only part
of
+a stored object. When an object is modified, the response body MUST contain a
+representation of the object after modification, and that representation SHOULD
+fully describe the modified object, even the parts that were not modified.
+
+Handlers that implement PATCH in the Traffic Ops API MUST use conditional
+requests to ensure that race conditions are not a problem, specifically they
+MUST support using ETag and If-Match, and SHOULD also support
+If-Not-Modified-Since.
+
+Clients SHOULD use PATCH requests rather than PUT requests for modifying
+existing resources whenever it is supported.
+
+#### DELETE
+DELETE destroys an object stored on the server. Typically the request will
+contain identifying information for the object(s) to be destroyed either in the
+request URI or in the request's body. Traffic Ops API endpoint authors MUST use
+this request method whenever an object identified by the request URI is being
+destroyed. When such deletion successfully occurs, the response body MUST
+contain a representation of the destroyed object.
+
+### HTTP Response Codes
+Proper use of HTTP response codes can significantly improve user interfaces
+built on top of the API. What follows is a (non-exhaustive) set of response
+codes and their appropriate use in the context of Traffic Ops. For more
complete
+information, refer to
+[the Mozilla Developer Network's HTTP Response Code
list](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status).
+
+#### 200 OK
+This indicates the request succeeded, with no additional semantics. This MUST
be
+the exact response status code of successful GET requests. This is also the
+default "success" response code for any other request.
+
+#### 201 Created
+This indicates that a resource was successfully created on the server. This
MUST
+be the response status code of POST requests that create a new object or
objects
+on the server, and in that case the response SHOULD also include a Location
+header that provides a URI where a representation of the newly created object
+may be requested.
+
+#### 202 Accepted
+`202 Accepted` MUST be used when the server is performing some task
+asynchronously (e.g. refreshing DNSSEC keys) but the status of that task
+cannot be ascertained at the current time. Ideally in this case, when the task
+completes - either successfully or by failing - the Traffic Ops changelog will
+be updated to indicate that status, along with information to uniquely identify
+the task (e.g. username and date/time when the task started).
+
+Endpoints that create asynchronous jobs SHOULD provide a URI to which the
+client may send GET requests to obtain a representation of the job's current
+state in the Location HTTP header. They MAY also provide an `info`-level
+Alert that provides the same or similar information in a more human-friendly
+manner.
+
+The responses to such GET requests are subject to the same restrictions as any
+other API endpoint, but have the added restriction that the `response` objects
+sent MUST have the `status` property, which is a string limited to one of the
+following values and having the associated semantics:
+
+- PENDING - This means the job has been started but is not yet completed.
+- SUCCEEDED - This means that the asynchronous job has completed and
encountered
+no errors.
+- FAILED - The task encountered errors and was unable to continue, and thus has
+been terminated.
+
+Note that the response code of the response carrying this information MUST NOT
+depend on the value of `status`. In particular, a response that successfully
+reports the status of a FAILED asynchronous task is still successfully
servicing
+a client's GET request, and therefore MUST have the `200 OK` response status
+code. However, a response encoding a FAILED `status` MUST be accompanied by one
+or more `error`-level Alerts that explain (to the greatest degree of detail
+allowable securely) why the job failed.
+
+These responses MUST also include the `startTime` and `endTime` properties
which
+indicate, respectively, the time at which the asynchronous job started and the
+time at which it concluded. A job that has not started MUST have a Null-valued
+`startTime` and likewise a job that has yet to conclude MUST have a Null-value
+`endTime`.
+
+#### 400 Bad Request
+In general this is used when there's something syntactically wrong with the
+client's request. For example, Traffic Ops MUST respond with this code when the
+request body was improperly encoded. In most cases, this is also the proper
+response code when the client submits data that is not semantically correct.
For
+example, dates/times represented as timestamp strings in an unsupported format
should trigger this response code.
+
+This is also the default "client failure" response code for any other request.
+
+The response body MUST include an entry in the `alerts` array that describes to
+the client what was wrong with the request.
+
+#### 401 Unauthorized
+This MUST be the response code when a client without valid authorization
+information in the HTTP headers requests a resource which cannot be accessed
+without first authorizing. Which should be everything except `/ping` and
+endpoints that provide authorization.
+
+#### 403 Forbidden
+This MUST be used whenever the client is logged-in, but still does not have
+access to the resource they are requesting. It MUST also be used when they have
+some access to the resource, but not with the specific request method they
used.
+This can pertain to restricted access on the basis of Role, User Permissions,
as
+well as Tenancy.
+
+The response body MUST NOT disclose any information regarding why the user was
+denied access.
+
+#### 404 Not Found
+This MUST be the returned status code when the client requests a path that does
+not exist on the server.
+
+#### 409 Conflict
+This SHOULD be used when the request cannot be completed because the current
+state of the server is fundamentally incompatible with the request. For
example,
+creating a new user with an email that is already in use should result in this
+response.
+
+Additionally, this MAY be used instead of `404 Not Found` when the client is
+requesting a link between an object identified by the request URI and some
+other object (e.g. when assigning a server to a Delivery Service) when the
other
+object does not exist. If the request URI identifies an object that does not
+exist, the response MUST use `404 Not Found` instead.
+
+This is also the proper response status code when the conditions of a request
+cannot be met, e.g. when a client submits a PATCH request for a resource with
an
+If-Match header that does not match the stored object's ETag.
+
+The request body MUST indicate what the conflict is that prevented the request
+from being fulfilled via one or more `error`-level alerts.
+
+#### 500 Internal Server Error
+When the Traffic Ops server encounters some error - through no fault of the
+client or their request - that renders it incapable of servicing the client's
+request, it MUST return this status code if no other code is more appropriate.
+The response body in this case SHOULD indicate that an error occurred, but
+MUST NOT divulge details about what data was being processed, what (if any)
+other components are not functioning properly, or what process failed.
Generally
+it is advisable that the resultant \code{alerts} array entry just say "Internal
+Server Error" and nothing else.
+
+#### 501 Not Implemented}
+This is the response code used when the client requests an API version not
+implemented by the server. It SHOULD NOT be used in any other case.
+
+#### 502 Bad Gateway
+This code indicates that some other service on which the endpoint's processes
+depend has given back improper data or an error response. It MAY be used (with
+caution) by plugin developers, but SHOULD NOT be used by authors of proper API
+endpoints, as that divulges information about failing connected systems and
+potentially gives an attacker information about Traffic Control's weak points.
+API endpoint authors should instead use `500 Internal Server Error`.
+
+#### 504 Gateway Timeout
+This code indicates that a connection timeout occurred when attempting to
+contact some other service on which the endpoint's processes depend. It MAY be
+used (with caution) by plugin developers, but SHOULD NOT be used by authors of
+proper API endpoints, as that divulges information about failing connected
+systems and potentially gives an attacker information about Traffic Control's
+weak points. API endpoint authors should instead use `500 Internal Server
+Error`.
+
+### Documentation
+All endpoints must be properly documented. For guidelines for writing API
+documentation, refer to
+[that section of the official ATC
documentation](https://traffic-control-cdn.readthedocs.io/en/latest/development/documentation_guidelines.html#documenting-api-routes).
+
+### Passing Request Data
+Request data may be passed in the request body or as a
+`application/x-www-form-urlencoded`-encoded query string in the request URI, or
+as a part of the request path. Request data MUST NOT be passed through a
portion
+of the request path unless it uniquely identifies a resource with which the
+client may interact. For example, `/foos/{{ID}}}` is an acceptable path for
+dealing with the particular "Foo" object that has some identifier `ID`, but
+`logs/{{Number of Days}}/days` is unacceptable because reasonable default
+behavior can be provided if no number of days is given in the query string
+parameters, and that doesn't help uniquely identify a resource. Request path
+parameters should use double "curly-braces" (<kbd>{</kbd> and <kbd>}</kbd>) to
+call out variable components of the request path in documentation and
+references. Request path parameters MUST NOT be used for data that is optional
+to the request (somewhat obviously). Note that all endpoints dealing with the
+manipulation of "Traffic Control Objects" MUST support the GET HTTP request
+method.
+
+When accepting data in the request body of requests, the endpoint MUST properly
+document the object representations (properties and their types) it accepts and
+MUST reject semantically invalid data with a `400 Bad Request`.
+
+The decision to pass data in the request body or query string is mainly up to
+the author, but some helpful tips:
+
+- GET and DELETE requests do not typically provide request bodies.
+- Query parameters should nearly always be optional. If data is required by an
+endpoint, consider requiring it in the request body. If the data identifies a
+resource, it ought to be a path parameter.
+- Request body data often represents objects that are being created or updated.
+If an object is being created or updated, it ought to be defined in the request
+body, and if any additional data is (possibly optionally) required then it
ought
+to be passed in the query string to separate it from the object definition.
+- The following query parameters are reserved for special use by Traffic Ops
+endpoint handlers, and may not be used for any purpose other than their
+prescribed functions.
+
+ - `limit`
+ - `newerThan`
+ - `offset`
+ - `olderThan`
+ - `orderby`

Review comment:
nope. Our current API uses "orderby," unfortunately. Changing that would be
a breaking change unless they both worked - and I don't think anyone wants to
bother with that. I know I don't. So we'll save consistent casing for v3 (or
even v4 maybe, at this point).

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[GitHub] [trafficcontrol] ocket8888 commented on a change in pull request #4536: API Guidelines blueprint

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