Headers default value and restrictions

[antoniyatrifonova]

According the specification:

1. What is the default value for the following headers?

• content-type
• correlation-id
• ditto-originator
• if-match
• if-none-match
• version

2. Are there any restrictions for the header values? For example: It is possible to set empty string for the correlation-id? What is the range of the timeout?

[thjaeckle]

Hi @antoniyatrifonova

1. The mentioned headers do not have static default values which could be specified, however:
   • if content-type is missing from the headers, application/json will be assumed for commands - for messages, application/octet-stream will be assumed
   • correlation-id will be generated (in UUID format) if none was provided
   • ditto-originator cannot be set by a device/application at all, but will always be set by the Ditto backend with the "authorization subject that caused an event"
   • if-match and if-none-match don't have defaults - if they are missing, no conditional request will be performed
   • version - as Ditto only supports version 2 currently, this will be 2 if omitted - I will fix the spec which says that this may be 1 or 2
2. Yes, some headers have restrictions - you can find the used validators here (as last argument of the header enum value): https://github.com/eclipse/ditto/blob/master/base/model/src/main/java/org/eclipse/ditto/base/model/headers/DittoHeaderDefinition.java
   • e.g. timeout header uses the HeaderValueValidators.getTimeoutValueValidator() which uses DittoDuration.parseDuration(): https://github.com/eclipse/ditto/blob/e30d9f93e820d6dcab143727590a44bec7f4f7f9/base/model/src/main/java/org/eclipse/ditto/base/model/common/DittoDuration.java#L61-L77 a "range" is however not enforced currently
   • the correlation-id header uses the HeaderValueValidators.getNonEmptyValidator() - so no, it may not be empty
   • etc.

[antoniyatrifonova]

Hi, @thjaeckle It is possible to provide this information in the documentation here - Doc ? Our implementation is based on this documentation. Thank you!

[thjaeckle]

I fear that is a bigger topic as not even all available headers are currently documented on that page. What kind of information do you need and what do you need that information for?