Request & Response

Overview

Alongside URL Structure, and other standards, the request and response standards help in part to enable and clarify our APIs as uniform interfaces.

// REQUEST
POST /articles HTTP/1.1
User-Agent: api-standards-v1
Content-Type: application/json
{
    "foo": "bar"
}
 
// RESPONSE
HTTP/1.1 200 OK
Content-Type: application/json
{
    "fooResult": "not-bar"
}

• All HTTP Requests and Responses to an API MUST support HTTP1.1. HTTP/1.0 is specifically unsupported given its age and limited protocol capability.

Using HTTP/1.0 as a request to any API may result in unintended side effects. For example, the API may send back an error if it is unsupported, or your response might be returned as HTTP/1.1.

NOTE: For the examples available in this documentation the HTTP protocol version will be intentionally left out.

HTTP Status Codes

General

RESTful services use HTTP status codes to specify the outcomes of HTTP method execution. HTTP protocol specifies the outcome of a request execution using an integer and a message. The number is known as the status code and the message as the reason phrase. The reason phrase is a human-readable message used to clarify the outcome of the response. HTTP protocol categorizes status codes in ranges.

• An API MUST return HTTP response codes in conformance with RFC-2616 and common usage in addition to these standards. When responding to API requests, the following status code ranges MUST be used.

"HTTP applications are not required to understand the meaning of all registered status codes, though such understanding is obviously desirable. However, applications **MUST** understand the class of any status code, as indicated by the first digit, and treat any unrecognized response as being equivalent to the x00 status code of that class, with the exception that an unrecognized response **MUST NOT** be cached" ([RFC 2616](https://www.ietf.org/rfc/rfc2616.txt)).

• Success MUST be reported with a status code in the 2xx range.
• Reason phrases MUST NOT be modified or customized. The default reason phrases deliver an industry-standard experience for API consumers. Use the response payload as necessary to communicate further reasoning.
• HTTP status codes in the 2xx range MUST be returned only if the complete code execution path is successful. There is no such thing as partial success.
  • Bulk synchronous request operations MUST return a 200` status code with a response body indicating failures as part of the payload for each processed entity.
• Failures MUST be reported in the 4xx or 5xx range. This is true for both system errors and application errors.
• All status codes used in the 4xx or 5xx range MUST return standardized error responses as outlined under Errors.
• A server returning a status code in the 2xx range MUST NOT return any error models defined in Errors, or any HTTP status code, as part of the response body.
• For client errors in the 4xx code range, the response message SHOULD provide enough information for the client to be able to determine what caused the error and how to fix it.
• For errors in the 4xx/5xx code range, the response MUST contain an error message following Errors. The message SHOULD limit the amount of information to avoid exposing internal service implementation details to clients. This is true for both external-facing and internal APIs. Service developers should use logging and tracking utilities to provide additional information.
• By default, 3xx status codes SHOULD NOT be used during API development. Exceptional usage use cases might be considered and require additional design discussion.

Supported Status Codes

• All REST APIs MUST use only the following status codes. APIs MUST NOT return a status code that is not defined here to express contractual or defined output of the endpoint. API Consumers may receive other status codes not presented because other infrastructure and proxies live in between the API and the consumer or other operational and platform constraints may return certain status codes.
• APIs may not use all status codes defined, or only require a subset for their operations.
• When an API must respond to a request that has potentially multiple valid status code responses, the API SHOULD respond with the “more-specific” status code. The “more-specific” status code is generally the highest number in the associated range.

200 OK

Description: Generic successful execution. Default successful response code to read requests.

Example Usage: Any type of request, unless more specific code fits better.

201 Created

Description: Used as a response to POST method execution to indicate the successful creation of a resource. If the resource was already created (by a previous execution of the same method, for example), then the server should return the status code 200 OK.

Example Usage: Used as response code to POST requests and indicates successful creation of the resource. This request is NOT IDEMPOTENT, meaning each request with the same body will create a new entity on the server (exception is when entity identifier specified by client-side, then a 409 response code should be used for subsequent requests).

202 Accepted

Description: Used for asynchronous method execution to specify the server has accepted the request and will execute it at a later time.

Example Usage: Used as a response request that initiates an asynchronous request.

204 No Content

Description: The server has successfully executed the method, but there is no entity-body to return.

Example Usage: Indicates where there is no payload returned as part of the response. Usually, PUT and DELETE requests don’t have the payload body returned.

400 Bad Request

Description: The request could not be understood by the server. Use this status code to specify:

• The data as part of the payload cannot be converted to the underlying data type.
• The data or parameters is not in the expected data format.
• The required field is not available.
• Simple data validation type of error.

Example Usage: Used to inform errors with accepting incoming requests that:

• Incorrectly formatted
• Does not correspond to the expected schema
• Has invalid values that do not correspond to defined data types of the field

401 Unauthorized

Description: The request requires valid authentication and none was provided or expired. Note the difference between this and 403 Forbidden.

403 Forbidden

Description: The client is not authorized to access the resource, although it may have valid credentials. The API could use this status code to handle business-level authorization failures. For example, the requestor does not have permission to request the organization’s information.

404 Not Found

Description: The server has not found anything matching the request URI. This either means that the URI is incorrect OR the resource is not available. For example, it may be that no data exists in the database at that key.

405 Method Not Allowed

Description: The server has not implemented the requested HTTP method. This is typically the default behavior for API frameworks.

406 Not Acceptable

Description: The server MUST return this status code when it cannot return the payload of the response using the media type requested by the client. For example, if the client sends an Accept: application/xml header and the API can only generate application/json, the server MUST return 406.

409 Conflict

Description: This response is sent when a request conflicts with the current state of the server.

Example Usage: Used to indicate conflicting situations:

• PUT with a payload that violates the uniqueness of the attribute that requires unique values. Example: “Unique name of the organization”
• POST of the entity with predefined “Id” attribute value which already exists in the system.

412 Precondition Failed

Description: The client has indicated preconditions in its headers which the server does not meet.

Example Usage: Used to indicate when conditional requests on methods not fulfilled with one of the preconditions:

• If-Unmodified-Since specified, modification date earlier than specified.
• If-Match specified, but its value on the server is different.
• If-None-Match specified, but the server has matching data.

415 Unsupported Media Type

Description: The server MUST return this status code when the media type of the request’s payload cannot be processed. For example, if the client sends a Content-Type: application/xml header, but the API can only accept application/json, the server MUST return a 415.

428 Precondition Required

Description: The origin server requires the request to be conditional. This response is intended to prevent the ‘lost update’ problem, where a client GETs a resource’s state, modifies it, and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.

Example Usage: Used to indicate when requests required to be conditional:

• If-Unmodified-Since is missing when expected.
• If-Match is missing when expected.
• If-None-Match is missing when expected.

429 Too Many Requests

Description: The server MUST return this status code if the rate limit for the user, the application, or the token has exceeded a predefined value. Defined in Additional HTTP Status Codes RFC 6585.

Retriable: Yes

500 Internal Server Errors

Description: This is either a system or application error and generally indicates that although the client appeared to provide a correct request, something unexpected has gone wrong on the server. A 500 the response indicates a server-side software defect or site outage.

• 500 MUST NOT be used for client validation or logic error handling.

Retriable: Yes

HTTP Headers

Standard Headers

The purpose of HTTP headers is to provide metadata information about the body or the sender of the message and provide instructions to help negotiate between client and server in a uniform, standardized, and isolated way.

• HTTP header names MUST NOT be case sensitive.
• HTTP headers SHOULD only be used for the purpose of handling cross-cutting concerns, such as security, traceability, monitoring, cachability, and state validation.
• Headers MUST NOT include API or domain-specific values data. For example, Location, Content-Type are headers that imply instructions between client and server but do not include domain-specific data in the header, that is content often communicated through the body of a request or a response.
• Service Consumers and Service Providers SHOULD NOT expect that a particular HTTP header is available. It is possible that an intermediary component in the call chain can drop an HTTP header. This is the reason business logic SHOULD NOT be based on HTTP headers.
• Service Consumers and Service Providers SHOULD NOT assume the value of a header has not been changed as part of HTTP message transmission.

**CLARIFICATION**: The following list of headers IS NOT meant as a complete list of headers that you as an API Consumer may send and/or receive. Rather it is intended as general guidelines of headers API Implementations are specifically meant to support for RESTful purposes.

Accept

Type: Request

Support: MUST

Description: This request header specifies the media types that the API client is capable of handling in the response.

• Systems issuing the HTTP request SHOULD send this header.
• Systems handling the request SHOULD NOT assume it is available.
• The header may OPTIONALLY be used to indicate a custom serialization model using the vnd specific format along with the Content-Type (See MIME Types below).
• The header MUST NOT indicate the version of the API contract and apply to content serialization formatting only.

Example(s):

// CORRECT
Accept: application/json
Accept: text/html, application/xhtml+xml

Content-Type

Type: Request/Response

Support: MUST

Description: This request/response header indicates the media type of the request or response body.

• API client MUST include with the request if the request contains a body, e.g. it is a POST, PUT, or PATCH request.
• API developer MUST include it with a response if a response body is included (not used with 204 responses).
• If the content is a text-based type, such as JSON, the Content-Type MAY include a character-set parameter. The character-set MUST be UTF-8 if provided.

Refer further to MIME-Types below for additional details and supported types.

Example(s):

// CORRECT
Content-Type: application/json
Content-Type: application/json; charset=UTF-8

Location

Type: Response

Support: MUST

Description: This response-header field is used to redirect the recipient to a location other than the Request-URI for completion of the request or identification of a new resource.

• Usage of the Location header is MUST only be used with response codes 201 or 3xx.
• Relative URLs MUST be made relative to the URL host.

Example(s):

// CORRECT
Location: /users/profiles/1
Location: https://api.spscommerce.com/users/profiles/1
 
// INCORRECT
Location: /profiles/1 // missing "users" root resource, after host

User-Agent

Type: Request

Support: MUST

Description: The User-Agent header helps API implementations to identify certain groups of consumers of their API.

• User-Agent MUST be provided for all API requests for identification purposes. Requests without a valid User-Agent MUST return a 403 response status code.
• User-Agent SHOULD contain product information, product version, and other comments as necessary to identify an API Consumer. Provided product versions should indicate major version numbers only in accordance with User-Agent Client Hints. Common syntax:

User-Agent: <product>/<product-major-version> <comment>
User-Agent: my-calling-service/2

It would be appropriate to supply a general `403` at the platform or central ingress if no `User-Agent` header is provided.

Example(s):

// CORRECT
User-Agent: Mozilla/5.0 (platform; rv:geckoversion) Gecko/geckotrail Firefox/firefoxversion

Authorization

Type: Request

Support: MUST

Description: More information at Authentication.

Example(s):

// CORRECT
Authorization: Bearer <token>
 
// INCORRECT
Authorization: <token>
Authorization: bearer <token>
Authorization: Basic <token>

Content-Language

Type: Both

Support: OPTIONAL

Description: This request/response header is used to specify the language of the content.

• This header MUST be optional, and the default locale MUST be en-US when none is provided.
• API clients SHOULD identify the language of the data using the Content-Language header.
• APIs SHOULD provide this header in the response.

Example(s):

// CORRECT
Content-Language: en-US
Content-Language: en-US, de-DE, en-CA

ETag

Type: Response

Support: OPTIONAL

Description: The ETag response-header field provides the current value of the entity tag for the requested variant. Used with If-Match, If-None-Match and If-Range to implement optimistic concurrency control. Refer to GET request below.

• ETag SHOULD be returned for GET requests where the individual resource has a specific version.

Example(s):

// CORRECT
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4"

If-Match/If-None-Match

Type: Request

Support: OPTIONAL

Description: Used in association to the response value within an ETag header. It can be a CSV list containing multiple values if needed.

• Values of the header SHOULD always be derived from the value returned from a response with an ETag header.

Example(s):

// CORRECT
If-Match: "33a64df551425fcc55e4d42a148795d9f25f89d4"

Cache-Control

Type: Response

Support: OPTIONAL

Description: Responses MUST return no-store header value when sensitive data is present.

Example(s):

// CORRECT
Cache-Control: max-age=<seconds>
Cache-Control: max-stale[=<seconds>]
Cache-Control: min-fresh=<seconds>
Cache-Control: no-cache
Cache-Control: no-store
Cache-Control: no-transform
Cache-Control: only-if-cached

Access-Control-*

Type: Response

Support: OPTIONAL

Description: The headers for Access-Control are intended for usage with CORS-enablement.

• Access-Control-Allow-Origin SHOULD NOT specify a wildcard (“*”) for any API used by internal or external consumers.
• Access-Control-Allow-Methods MUST NOT use a wildcard (“*”).
• Access-Control-Allow-Headers MUST NOT use a wildcard (“*”) and MUST only be used to specify custom headers or headers used outside of the CORS-safelisted request headers.
• Access-Control-Expose-Headers MUST NOT use a wildcard(“*”) and MUST only be used to specify custom headers or headers used outside of the CORS-safelisted response headers.
• Access-Control-Allow-Credentials MUST NOT be set to true if Access-Control-Allow-Origin is wildcarded (“*”).
• Access-Control-Max-Age SHOULD NOT exceed 7200 seconds (2 hours) due to browser caps and limitations.

Example(s):

// CORRECT
Access-Control-Allow-Origin: https://cdn.domain.com/
Access-Control-Allow-Methods: GET,POST,PUT,PATCH,DELETE,HEAD,OPTIONS
 
// INCORRECT
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: *

**KEEP AN EYE ON IT**: The [Idempotency-Key Request header](https://tools.ietf.org/id/draft-idempotency-header-01.html) is in an experimental state but getting lots of attention as a pattern of making fault-tolerant resilient requests for traditionally non-idempotent methods like `POST`.

Custom Headers

• Custom Headers MAY be used and created as necessary.
• Custom Headers MUST only be used if not in conflict by a similar name or similar function to the standard headers or other widely used custom headers.
• Custom Headers MUST abide by the same rules and guidelines as standard headers.
• Custom Header names MUST NOT be longer than 50 characters.
• Custom Header names MUST only contain alpha, numeric, and dash characters: [a-zA-Z0-9-]
• Custom Headers MUST start with the prefix Sps- (Note: do not prefix with X-).
• Custom Headers SHOULD NOT include sensitive data that applies to customers/employees or is subject to legal, regulatory, contractual, and business requirements.

// CORRECT
Sps-Claims: { "Custom": "Value" }
Sps-User: 123456789012345678901234567890
Sps-Meta-Information: YourInformation/Goes/Here
 
// INCORRECT
X-Sps-User: 123456789012345678901234567890

The usage of non-standard headers is not considered custom headers. For example, your API may consume or interact with other infrastructure outside of the contract specification for your service, such as `X-Forwarded-Host` or `X-Request-ID`, these are appropriate to continue using, but would not expect to identify them in your Open API spec for example. As such these types of headers not relevant to REST are intentionally left out of this documentation.

Sps-Cors-Error

Type: Response

Support: OPTIONAL

Description: A CORS error from an invalid request will return a non-200 status code, but it can be difficult for an API consumer to understand the reason that their request was unsuccessful. A custom header provides more detailed information to the consumer on why their CORS preflight OPTIONS request was rejected.

• The header MUST be added when a CORS OPTIONS request is rejected.
• A response with this header SHOULD indicate a status code of 403 - Forbidden.
• The header MUST contain one of the following values:
  • bad origin - Indicates to the consumer that the provided request header Origin did not match the approved list of source hostnames.
  • bad method - Indicates to the consumer that the provided request header Access-Control-Request-Method contained request methods that are not allowed.
  • bad header - Indicates to the consumer that the provided request header Access-Control-Request-Headers contained request header names that are not allowed.

Example(s):

// CORRECT
Sps-Cors-Error: bad origin

Sps-Execution-Context

Type: Both

Support: OPTIONAL

Description: The Execution Context header provides a standard method of indicating the dataflow context that a request should be processed with. This is used to differentiate or test changes in customer configuration of non-production data. This isolates the version of the configuration state used in a request and allows identifying transactions that should leverage a specific tagged or aliased configuration set.

• A request without the presence of this header MUST indicate that the execution context is under the production dataflow and customer configuration, if applicable to this API.
• The header value contains any dynamic string value representing a named configuration or tagged dataflow preset.
  • preprod - Well-known value used to represent non-production customer configuration and can be supported as a static mode in some legacy services without full dynamic support. Usage of dynamically named configuration sets is preferred.
  • prod - Well-known value used to represent production customer configuration and can be supported as a static mode in some legacy services without full dynamic support. Usage of dynamically named configuration sets is preferred. When no request or response header is provided for Sps-Execution-Context this is interpreted as the default value.
• An invalid or unsupported header value provided MUST result in a 400 - Bad Request following standard error format.
• The header value MUST be at minimum 1 character in length and MUST NOT exceed a maximum length of 100 characters.
• The header value SHOULD contain human-readable tag for the context.
• The header SHOULD be propagated to any outgoing requests to retain the context for downstream usage.
• The header MUST be supplied in the response for every request containing the header, and match the original requested value.
• The header SHOULD be supplied in the response for every request in general, if applicable to the API, even if just defaulting to prod.

Example(s):

// CORRECT
Sps-Execution-Context: prod
Sps-Execution-Context: preprod
Sps-Execution-Context: customer-testing
Sps-Execution-Context: example-customer-configuration

// INCORRECT
Sps-Execution-Context:                  // values must be at least a character long.
Sps-Execution-Context: 1                // valid, but SHOULD be human-readable.

MIME Types

Standard MIME Types

MIME (or Media) types indicate the nature and format of a request or response body when supplied as a Content-Type header in an HTTP request.

• MIME types MUST be supplied in the Content-Type header for any request or response that includes a body.
• MIME types SHOULD be provided by API consumers as an Accept header to indicate formats supported by the client when content negotiation is required.
  • application/json SHOULD be the default return MIME type when an Accept header includes application/json and other possible types for content negotiation.
• Resource endpoints MUST support application/json as the content type for both request/response bodies (refer to “Standard Headers”).
  • API endpoints that are responsible for returning data in different formats MUST support other content types depending on the requirements, in addition to application/json.
• MIME types provided MUST follow customization standards or be a common MIME type indicated in the IANA Media Types.
• Requests made with unsupported Content-Types (and MIME types) MUST result in a standard error response with a 415 status code following the standard error response format.
• Request and Response media type formats MUST NOT be implied using extensions on resources (i.e. .json or .xml). Instead, use the standard resource path with the appropriate Content-Type header.

// JSON SCENARIO                            // JSON media type MUST always be supported
// REQUEST
POST /articles                              // creating an article
Accept: application/json                    // this client making the request can only accept content back as JSON
Content-Type: application/json              // the serialization type of the request body
{
    "name": "New Article",
    "content": "The Best article because..."
}
 
// RESPONSE
201 OK
Content-Type: application/json              // the serialization type of the response body (negotiated based on common Accept header list).
Location: /articles/3
{
    "id": 3
}
 
// XML SCENARIO                             // other media types can be supported if needed, such as XML
// REQUEST
POST /articles                              // creating an article
Accept: application/xml                     // this client making the request can only accept content back as JSON or XML
Content-Type: application/json              // the serialization type of the request body can be different than the response, but likely rare.
{                                           // if the content-type provided for the request is not known or supported then this should result in a 415 status code.
    "name": "New Article",
    "content": "The Best article because..."
}
 
// RESPONSE
201 OK
Content-Type: application/xml       // the serialization type of the response body (negotiated based on common Accept header list, defaults to JSON if available).
Location: /articles/3
<response>
    <id>3</id>
</response>

Custom MIME Types

• Custom MIME types MUST only be used to define the formatting or schema for the version of data that it is associated with. It is not a mechanism for versioning the contract of the Request, Response, URL, Headers, Query Parameters, etc.
  • Custom MIME types MUST use the following format: application/vnd.sps-*+(json|xml) (i.e. application/vnd.sps-model+json), where * can be adjusted accordingly.
  • Custom MIME types SHOULD be limited in their usage as it provides an extra layer of complexity beyond the default application/json media type.
  • Documentation of your API MUST be clearly updated to indicate the purpose and usage of different MIME types on an endpoint.
  • Version information can be included in custom MIME types following the wildcard (i.e. application/vnd.sps-model.v1+json). The version number must follow the v indicator.

// INCORRECT
Content-Type: application/whatever                  // "whatever" does not follow the custom MIME type rules.
Content-Type: sps/vnd.whatever+json                 // Custom content type MUST be specified as an "application" type of content.
Content-Type: application/vnd.whatever              // MUST include "sps" as vendor prefix name, along with the format type of xml or json.
 
// CORRECT
Content-Type: application/vnd.sps-model+json        // Custom type indicates request or response has a body with model information specified in JSON format.
Content-Type: application/vnd.sps-model+xml         // Custom type indicates request or response has a body with model information specified in XML format.
Content-Type: application/vnd.sps-model.v1+json     // Version can be included in the custom Content Type if needed.
Content-Type: application/json                      // Default standard for all APIs to use.

// STANDARD JSON SCENARIO                   // JSON media type MUST always be supported
// REQUEST
POST /articles                              // creating an article
...
Content-Type: application/json              // the serialization type of the request body
{
    "name": "New Article",
    "content": "The Best article because..."
}
 
// RESPONSE
201 OK
Content-Type: application/json              // the serialization type of the response body (negotiated based on common Accept header list).
Location: /articles/3
{
    "id": 3
}
 
// ALTERNATIVE CUSTOM MIME TYPE             // a custom MIME type is used to indicate another JSON schema for creating articles // REQUEST
POST /articles                              // creating an article
Accept: application/json
Content-Type: application/vnd.sps-article-import.v1+json    // custom content-type indicates a standards method for importing articles from another source location
{                                                           // in this example that might be a third party provider or another system.
    "system": "third-party",
    "url": "https://example.com/old-system/article/10
}
 
// RESPONSE
201 OK
Content-Type: application/json              // the serialization type of the response body is unchanged, as it returns regular JSON still.
Location: /articles/3
{
    "id": 3
}

HTTP Methods

Overview

• Operations MUST use only the HTTP methods as outlined.
• Custom HTTP Methods MUST NOT be used.
• Operations MUST respect the identified idempotency and body for each method.
• Operations SHOULD use consistent schema’s across different HTTP Methods when specifying the same addressable resource.

**Idempotency**: An idempotent method means that the result of a successfully performed request is independent of the number of times it is executed.

HTTP Method to Status Code Mapping

For each HTTP method with only the status codes specified below, API developers SHOULD use only status codes marked as “X” in this table. Status codes not present in the table maybe be used across any HTTP Method under the correct behaviors identified for that status code above.

GET

The purpose of the GET method is to retrieve a resource.

• HTTP GET Method MUST NOT accept a request body.
• HTTP GET Method MUST return a response body.
  • The response body SHOULD NOT produce a complex response that requires unreasonable hierarchy traversal. Beyond three levels of an object reference becomes unwieldy and SHOULD be avoided for API designs in favor of additional resources.
• HTTP GET Method MUST NOT modify the state of the API resources as it is for retrieval purposes only.
• HTTP GET Method MUST be idempotent.
• HTTP GET Method MUST return a 404 status code when a resource is not present by a specified identifier unless there is intent to expose a soft-delete status.
• HTTP GET Method may return ETag Header and support conditional headers such as If-None-Match for targeted caching of resources based on state.
• HTTP GET Method returning a collection:
  • MUST return a 200 status code when returning the results of an empty collection (not a 404 or 204).
  • MUST return a complex object following the collection standards, and not an array as the root body object.

// REQUEST
GET /articles/2
 
// RESPONSE
200 OK
Content-Type: application/json
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4"
{
    "id": 2,
    "name": "Article 2",
    "content": "My nice content for the article"
}

Consider the size of your `GET` request parameters. Without the ability to include parameters in a request body, the size of your query parameters may become unwieldy and highly inconvenient. In certain situations, it may be appropriate to use a `POST` Method to pass along request parameters as the body. Also, refer to size considerations on the URL as a whole in [URL Structure](/sps-api-standards/standards/url-structure.html). 

POST

The primary purpose of POST is to create a resource. It may also be used for non-RESTful actions when no other HTTP Method makes sense (see Actions in URL Structure).

• HTTP POST Method that results in the successful creation of the resource:
  • MUST indicate so with a 201 status code.
  • MUST return a reference to the resource created either as a link or a resource identifier in the response body or Location header or both.
  • may OPTIONALLY return the newly created entity as a whole reference if it is different or resolved in comparison to the request body, understanding that it may not contain an ETag or appropriate cache-control headers the same as a GET request.
• HTTP POST Method MUST return a 200 status code when successful with non-RESTful-based actions (see Actions in URL Structure).
• HTTP POST Method response body, if returned, MUST NOT be a primitive, but rather a complex object with the identifier or other response information.
• HTTP POST Method MUST indicate asynchronous acceptance of the request that is without resolution as a 202 status code.
• HTTP POST Method MUST return a 404 if other addressable resources in the URL do not exist as parents to the existing collection.
• HTTP POST Method SHOULD return a 409 when a resource cannot be created because it would result in an invalid state for a parent resource or be in violation of any constraints, including any database or persistent storage constraints.

// REQUEST
POST /articles
Content-Type: application/json
{
    "name": "New Article",
    "content": "The Best article because..."
}
 
// RESPONSE
201 OK
Content-Type: application/json
Location: /articles/3
{
    "id": 3
}

PUT

The primary purpose of PUT is to replace or update an entity as a whole.

• HTTP PUT Method MUST replace an entity in its entirety, as it relates to the preceding collection specified in the URL.
• HTTP PUT Method MUST NOT be used to create a new entity on a collection unless the collection as a whole is being replaced with new child entities on it.
• HTTP PUT Method MUST be idempotent.
• HTTP PUT Method SHOULD return a 204 status code for any success responses (implying no response body is appropriate), other than asynchronous acceptance with a 202 status code.
• HTTP PUT Method SHOULD NOT return a response body that is an echo of the request body.
• HTTP PUT Method SHOULD return a 409 when a resource cannot be updated because it would result in an invalid state for the resource, or be in opposition to any constraints, including any database or persistent storage constraints.

// REQUEST
PUT /articles/3
Content-Type: application/json
{
    "id": 3,
    "name": "New Article",
    "content": "Updated content for the article..."
}
 
// RESPONSE
204 OK

• HTTP PUT Method SHOULD be used on a resource collection when you intend to replace the entire collection with a new one, such as a bulk update scenario.
• HTTP PUT Method SHOULD be used to create a new resource when all aspects of the creation, including its primary identifier, are known by the client, and a fully addressable URL can be referenced with it.

//// INCORRECT!!!
// REQUEST
PUT /articles
Content-Type: application/json                      // THE ID IS NOT KNOWN AT TIME OF CREATION
{                                                   // THE IDS IS RETURNED IN THE RESPONSE
    "name": "New Article",                          // SO CREATION INSTEAD SHOULD OCCUR AS A POST REQUEST
    "content": "The Best article because..."
}
 
// RESPONSE
201 OK
Content-Type: application/json
Location: /articles/3
{
    "id": 3
}
 
//// CORRECT
// REQUEST
PUT /books/ISBN-10-0199535566                       // CREATION VIA PUT REQUEST IS ALLOWED SINCE THE ISBN IS A WELL-KNOWN PRIMARY KEY
Content-Type: application/json                      // ITS MORE APPROPRIATE TO PROCESS THIS CREATE SIMILAR TO AN UPDATE OF THE WELL-KNOWN ITEM
{                                                   // THIS IS VERY COMMON WITH EXISTING WORLD UNIQUE IDENTIFIERS.
    "isbn": "ISBN-10-0199535566",
    "name": "My Book",
    "content": "The Best book because..."
}
 
// RESPONSE
201 OK

• HTTP PUT Method SHOULD use an ETag (Entity Tag) for state validation, if required, to ensure that the entity has not been modified since it was last retrieved by a client before replacing or updating it in its entirety.
  • ETags MUST always be retrieved from a server HTTP GET Request, provided in the ETag Response Header.
  • ETags MUST always be provided to the HTTP PUT Method via the If-Match Request Header.
  • ETags MUST be treated as opaque values.
  • State Validation failure in an HTTP PUT Method as a result of an invalid If-Match ETag value should result in a 412 status code (Precondition Failed).
  • HTTP PUT Method may not require the If-Match header for state validation, but if it does, and the header is not provided it should return a 428 status code (Precondition Required).

// REQUEST
PUT /articles/3
If-Match: "33a64df551425fcc55e4d42a148795d9f25f89d4"
Content-Type: application/json
{
    "id": 3,
    "name": "New Article",
    "content": "Updated content for the article..."
}
 
// RESPONSE
204 OK

**Consider**: Further information on resource versioning with `ETags` may be helpful, along with understanding the [differences between strong and weak ETags](https://developers.google.com/gdata/docs/2.0/reference#ResourceVersioning).

DELETE

The primary purpose of DELETE is to remove an addressable entity in its entirety.

• HTTP DELETE Method MUST NOT accept a request body.
• HTTP DELETE Method MUST return a status code of 204 when successfully responding with no response body.
• HTTP DELETE Method SHOULD be idempotent in repeated deletions when the state is effectively available to identify previous delete requests and may return status code 204 instead of 404 as long as the resource no longer exists with the desired state.
• HTTP DELETE Method SHOULD return a 409 when a resource cannot be deleted because that would result in an invalid state for that resource representation, including related children resources that may be required to be deleted first, where cascade deletion is not present.
• HTTP DELETE Method SHOULD take advantage of the same ETag state validation, if required, for DELETE requests as described under HTTP PUT Method.

// REQUEST
DELETE /articles/3
 
// RESPONSE
204 OK

The request body of a DELETE is not allowed. At times an individual may intend to perform a bulk DELETE action and want to provide a request body or need information about the response of a DELETE. You will find that in this case, a PATCH request against the collection is an appropriate alternative.

// REQUEST
PATCH /articles
Content-Type: application/json 
{
    "op": "delete",   
    "ids": [1,2,3]
}
 
// RESPONSE
204 OK

PATCH

The primary purpose of PATCH is to update parts of an entity and not replace them entirely.

• HTTP PATCH Method MUST only update parts or certain fields of an entity in compliance with JSON Merge Patch semantics.
  • Fields that are not intended to be updated MUST not be provided in the request body.
  • Fields that are intended to be removed, MUST be set to NULL in the request body.
  • Arrays that are provided in a PATCH request MUST replace the entire array on the destination field.
• HTTP PATCH Method MUST NOT be used to create a new entity on a collection.
• HTTP PATCH Method SHOULD return a 204 status code for any success responses, other than asynchronous acceptance with a 202 status code.
• HTTP PATCH Method SHOULD NOT return a response body that is an echo of the request body if they are the same. It is acceptable to return a similar resolved entity as a convenience from calling the GET method.
• HTTP PATCH Method SHOULD return a 409 when a resource cannot be updated because it would result in an invalid, or be in opposition to any constraints, including any database or persistent storage constraints.
• HTTP PATCH Method SHOULD be used when updating attributes of a resource collection.
• HTTP PATCH Method SHOULD take advantage of the same ETag state validation, if required, for PATCH requests as described under HTTP PUT Method.

// REQUEST
// OTHER FIELDS ARE LEFT OUT OF THE REQUEST THAT WE DO NOT INTEND TO UPDATE
PATCH /articles/3
Content-Type: application/json
{
    "content": "Updated only this field...",    // THIS FIELD IS UPDATED WITH THE NEW CONTENT
    "notes": null,                              // THIS FIELD IS SET TO NULL, AND ANY CONTENT IN NOTES IS REMOVED.
    "categories": [ "pets", "flowers" ]         // THIS ARRAY IS REPLACED WITH THESE 2 ITEMS
}
 
// RESPONSE
204 OK

**Consider**: For updating multiple entities in bulk on a given resource refer to [bulk operations](/sps-api-standards/standards/bulk.html).

HEAD

The HTTP HEAD request is used to check the attributes (e.g. availability, size, last modification date) of a resource without downloading or deserializing all the content. For example, you may use a HEAD option to validate that a resource exists, by receiving a 200 status code, without having to stream the entire contents of the resource or article. If the resource did not exist a status code of 400 may be returned by example. Execution of an HTTP HEAD request may result in a workload being completed to determine the idempotent response status code effectively.

• HTTP HEAD Method MUST be idempotent.
• HTTP HEAD Method SHOULD return the same status code as a GET Method would return under the same addressable resource.
• HTTP HEAD Method SHOULD return a 200 even though there is no response body if that matches the typical status code returned by the GET Method request.
• HTTP HEAD Method MUST NOT contain a request or response body.
• HTTP HEAD Method MUST NOT be used to update the state of any resource or to retrieve the actual resource itself.
• HTTP HEAD Method MUST NOT be used with any sensitive data.
• HTTP HEAD Method responses MUST be cacheable.

// REQUEST
HEAD /articles/2
 
// RESPONSE
200 OK

OPTIONS

The OPTIONS method is used to describe communication options for the target resource.

• HTTP OPTIONS Method MUST be idempotent.
• HTTP OPTIONS Method MUST only provide information on how to interact with a resource.
• HTTP OPTIONS Method MUST NOT contain a request or response body.
• HTTP OPTIONS Method MUST NOT be used to update the state of any resource or to retrieve the actual resource itself.
• HTTP OPTIONS Method MUST NOT be used with any sensitive data.
• HTTP OPTIONS Method responses MUST NOT be intended to be cached.
• HTTP OPTIONS Method used for CORS integration MUST provide standard CORS headers for access control (Access-Control-Allow-*).
  • Rejected CORS requests should return a 403 status code, including the Sps-Cors-Error custom header indicating the reason for rejection.

// REQUEST
OPTIONS /articles/2
 
// RESPONSE
200 OK
Allow: GET,POST,PUT,PATCH,DELETE,HEAD,OPTIONS
Access-Control-Allow-Origin: https://api.spscommerce.com
Access-Control-Allow-Methods: GET,POST,PUT,PATCH,DELETE,HEAD,OPTIONS
Access-Control-Allow-Headers: Content-Type