Documented helper functions, added header table

docs/references/template-requirements.md

@@ -51,6 +51,50 @@
         -   Enable debugging symbols (if possible)
         -   Enable error output (if configurable)
 
+## Helper functions
+Ideally, your template should expose some helper functions, including
+but not limited to the following. Extra parameters can be added as 
+needed or wanted.
+
+
+| Function name      | Parameters            | Description |
+| ------------------ | --------------------- | ----------- |
+| error              | title: `string`, http_error_code: `int` | Returns a JSONAPI compliant error response with the given status code (default: 400). |
+| query              | query: `string`       | Executes the given SPARQL select/ask/construct query. [This function should automatically pass the correct headers](#passing-headers).  Also see `update`. |
+| session_id_header  | request: `object`     | Get the session id from the HTTP request headers. |
+| sparql_escape      | value: `any`          | Detects the value type and runs the appropiate [sparql escape function](#sparql_escape). |
+| update             | query: `string`       | Executes the given SPARQL update query. [This function should automatically pass the correct headers](#passing-headers). Also see `query`. |
+| uuid               | None                  | Generates an uuid. Meant for use in linked data (`mu:uuid`). | 
+
+*Note: camelcase is used in this documentation. However, when writing the helpers in the language of your choice, use the notation that is in line with the language in question.*
+
+### sparql_escape
+The following helper functions all have the same description/funcionality, but for different types. As such, the description column is omitted.
+
+**Description:** Converts the given object to a SPARQL-safe RDF object string with the right RDF-datatype.
+This functions should be used especially when inserting user-input to avoid SPARQL-injection.
+
+| Function name          | Parameters        |
+| ---------------------- | ----------------- |
+| sparql_escape_string   | value: `string`   |
+| sparql_escape_uri      | value: `url`      |
+| sparql_escape_decimal  | value: `decimal`  |
+| sparql_escape_int      | value: `int`      |
+| sparql_escape_float    | value: `float`    |
+| sparql_escape_date     | value: `date`     |
+| sparql_escape_datetime | value: `datetime` |
+| sparql_escape_bool     | value: `bool`     |
+
+### Passing headers
+The following headers should be passed when making queries:
+
+| Header name            | Type     | Description             |
+| ---------------------- | -------- | ----------------------- |
+| MU-SESSION-ID          |          |                         |
+| MU-CALL-ID             |          |                         |
+| MU-AUTH-ALLOWED-GROUPS |          | (bidirectional)         |
+| MU-AUTH-USED-GROUPS    |          |                         |
+
 
 ## Notes