Plainbox RFC822 Specification

The syntax is only loosely inspired by the actual RFC 822 syntax. Since Plainbox is not processing email, the original specification is used only as an inspiration. One of the most important aspect of the syntax we’re using is relative familiarity for other users of the system and ease-of-use when using general, off-the-shelf text editors.

BNF

An approximated syntax can be summarized as the following BNF:

record-list: record-list '\n' record
             | record
record: entry-list '\n\n' entry
        | entry
entry: KEY ':' VALUE
KEY: ^[^:]+
VALUE: .+\n([ ].+)*

There are two quirks which not handled by this syntax (see below). Otherwise the syntax is very simple. It defines a list of records. Each record is a list of entries. Each entry is a key-value pair. Values can be multi-line, which allows for convenient expression of longer text fragments.

Quirk 1 – the magic dot

Due to the way the multi-line VALUE syntax is defined, it would be impossible (or possible but dependant only on whitespace, which is not friendly) to include two consecutive newlines. For that reason a line consisting of a single space, followed by a single dot is translated to an empty line.

The example below:

key:
 .
 more value

Is parsed as an ENTRY (in python syntax):

("key", "\nvalue")

Quirk 2 – the # comments

Since it’s a line-oriented format and people are used to being able to insert comments anywhere with the # comment notation, any line that _starts_ with a hash or pound character is discarded. This happens earlier than other parts of parsing so comments are invisible to the rest of the parser. They can be included anywhere, including in the middle of a multi-line value.

Example:

# this is a comment
key: value
 multi-line
# comment!
 and more
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