Developing Go implementation of JSONpath
This is a Go implementation of lexing and parsing of JSONpath, with a conventional split between lexical analysis (tokenising) and parsing (building from the token stream an abstract representation of a path sequence, with nested expression trees). That representation is converted into orders for a small abstract machine that evaluates a path expression given a root JSON value, yielding a collection of JSON values selected by the path expression.
It is currently in development and subject to change, but ready for friendly users.
The path image is from Joey Genovese on Unsplash.
Paths have the following grammar:
path ::= "$" step*
step ::= "." member | ".." member | "[" subscript "]" | ".." "[" subscript "]"
member ::= "*" | identifier | expr | signed-integer
subscript ::= subscript-expression | union-element ("," union-element)
subscript-expression ::= "*" | expr | filter
union-element ::= array-index | string-literal | array-slice
array-index ::= signed-integer
array-slice ::= start? ":" end? (":" stride?)?
start ::= signed-integer | expr
end ::= signed-integer | expr
stride ::= signed-integer | expr
expr ::= "(" script-expression ")"
filter ::= "?(" script-expression ")"
step ::= ... "[" subscript "]" ... | ".." "[" subscript "]"
subscript ::= subscript-expression | union-element ("," union-element)
subscript-expression ::= "*" | expr | filter
union-element ::= array-index | string-literal | array-slice
array-index ::= signed-integer
array-slice ::= start? ":" end? (":" step?)?
member ::= "*" | identifier | expr | signed-integer
expr ::= "(" script-expression ")"
signed-integer ::= "-"? integer
integer ::= [0-9]+
Script expressions (filters and calculations) share the same syntax:
script-expression ::= e // both filters and values share the same syntax
e ::= primary | e binary-op e | unary-op e
binary-op ::= "+" | "-" | "*" | "/" | "%" | "<" | ">" |
">=" | "<=" | "==" | "!=" | "~" | "in" | "nin" | "&&" | "||"
unary-op ::= "-" | "!"
unary ::= ("-" | "!")+ primary
primary ::= primary1 ("(" e-list? ")" | "[" e "]" | "." identifier)*
e-list ::= e ("," e)*
primary1 ::= identifier | integer | real | string |
"/" re "/" | "@" | "$" | "(" e ")" | "[" e-list? "]"
re ::= <regular expression of some style, with \/ escaping the delimiting "/">
real ::= integer "." integer? ("e" [+-]? integer)?
The semantics and built-in functions are generally those of https://danielaparker.github.io/JsonCons.Net/articles/JsonPath/Specification.html — a rare example of specifying JSONPath systematically instead of providing a few examples — although this grammar is more restrictive (eg, as regards the content of a union expression). Some of its extensions (eg, the parent operator) are also not provided.