#ee-rest-headers

The ee-rest-headers package mainly consists of a parser which parses complex http headers based on the rest header DSL specified in the Joinbox RESTFul Styleguide.

The parser itself is implemented as a PEG. For more information see the Joinbox RESTFul Styleguide and PEG.js. Currently the parser seems to be a little slow.

##Middleware The package exposes a middleware to be used with ee-webservices. The middleware modifies the http request (@see: ee-webserver) by wrapping the getHeader(key, parsed) method. Parseable headers will be parsed and cached in a LRU cache.

##Parser The following headers are specified in the aforementioned styleguide.

###Select Models a projection on the fields of the queried resource. If all fields should be selected the wilcard must be set.

GET /user HTTP/1.1
Select: id, name, tenant.id, tenant.name, friend.name, friend.id

Selections support wildcards, marked by an asterisk.

GET /user HTTP/1.1
Select: id, name, friend.*

###Filter Filters allow to restrict queries on collections and consist of a list of comparisons. Since version 2.0 the filter rules support chaining via an or operator. Consider the following base case:

GET /user HTTP/1.1
Filter: id=in(3,4), friend.firstName like 'mich%25'

The comma , per default corresponds to an and operator. To do choices, use the pipe | operator:

GET /user HTTP/1.1
Filter: age > 100 | gender = 'f' , age = null

This represents a query which filters users older than 100 years or are women which didn't want you to tell about their age (the and operator has a higher precedence than the or operator). If your statement requires you to give the or constraints a higher precedence, you can group them together in parentheses:

GET /user HTTP/1.1
Filter: (age > 100  | gender = 'f' , age = null) , deleted != null

The grouping ensures that both, the old users as well as the conceited women are not deleted. Have a look at the Expressions below to see which comparators are supported. All values can be combined and nested.

###Order Allows sorting of the returned collections in ASC(ending) or DESC(ending) order.

GET /user HTTP/1.1
Order: name, friends.name DESC

##Nodes The parser generates AST nodes. These nodes can be traversed using the visitor pattern (with a double dispatch).

###Misc

Dates

The parser supports dates and datetimes (possible ambiguity with number!!)

Filter: created=2013-11-18 
Filter: created!=2013-11-18
Filter: created>=2013-11-18 20:00:02
Filter: created<=2013-11-18
Filter: created>2013-11-18
Filter: created<2013-11-18
Filter: created=in(2013,2014)
Filter: created=null

####Expressions The parser supports a minimal expression syntax for comparison. The parser does not do any type checking! Furthermore, future versions may have to care about the difference between an assignment and a comparison.

Filter: id=1
Filter: id!=1
Filter: id>=1
Filter: id<=1
Filter: id>1
Filter: id<1
Filter: id=in(1,2,3,4)
Filter: id=null

####Values The parser supports a variety of different value types:

1. integers
2. floats
3. function calls
4. booleans
5. arrays
6. variables (and nested variable accesses)

###Full Grammar Please find the full grammar in `lib/parser/_HeaderParser.pegjs'