protobuf.ebnf

Protobuf's language EBNF grammar by Alek Strom obtained from:
http://groups.google.com/group/protobuf/browse_thread/thread/1cccfc624cd612da

proto  ::= ( message | extend | enum | import | package | option | ";" )*

import ::= "import" strLit ";"

package ::= "package" ident ";"

option ::= "option" optionBody ";"

optionBody ::= ident ( "." ident )* "=" constant

message ::= "message" ident messageBody

extend ::= "extend" userType messageBody

enum ::= "enum" ident "{" ( option | enumField | ";" )* "}"

enumField ::= ident "=" intLit ";"

service ::= "service" ident "{" ( option | rpc | ";" )* "}"

rpc ::= "rpc" ident "(" userType ")" "returns" "(" userType ")" ";"

messageBody ::= "{" ( field | enum | message | extend | extensions |
group | option | ":" )* "}"

group ::= modifier "group" camelIdent "=" intLit messageBody

# tag number must be 2^28-1 or lower
field ::= modifier type ident "=" intLit ( "[" fieldOption ( ","
fieldOption )* "]" )? ";"

fieldOption ::= optionBody | "default" "=" constant

extensions ::= "extensions" intLit "to" ( intLit | "max" ) ";"

modifier ::= "required" | "optional" | "repeated"

type ::= "double" | "float" | "int32" | "int64" | "uint32" | "uint64"
       | "sint32" | "sint64" | "fixed32" | "fixed64" | "sfixed32" |
"sfixed64"
       | "bool" | "string" | "bytes" | userType

# leading dot for identifiers means they're fully qualified
userType ::= ( "."? ident )+

constant ::= ident | intLit | floatLit | strLit | boolLit

ident ::= /[A-Za-z_][\w_]*/

# according to parser.cc, group names must start with a capital letter as a
# hack for backwards-compatibility
camelIdent ::= /[A-Z][\w_]*/

intLit ::= decInt | hexInt | octInt

decInt ::= /\d+/

hexInt ::= /0[xX]([A-Fa-f0-9])+/

octInt ::= /0[0-7]+/

floatLit ::= /\d+(\.\d+)?([Ee][\+-]?\d+)?/ # allow_f_after_float_ is
disabled by default in tokenizer.cc

boolLit ::= "true" | "false"

strLit ::= quote ( hexEscape | octEscape | charEscape | /[^\0\n]/ )*
quote

quote ::= /["']/

hexEscape ::= /\\[Xx][A-Fa-f0-9]{1,2}/

octEscape ::= /\\0?[0-7]{1,3}/

charEscape ::= /\\[abfnrtv\\\?'"]/