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Check whether input is valid JSON

Source: R/parse.R
json_validate.Rd

Parses x and reports whether it succeeded, without building an R result and without raising a condition. Use it to decide whether a response body is worth parsing; use json_parse() when a failure should be an error you can read.

Usage

json_validate(x)

Arguments

x

A single string of JSON text, or a raw vector of JSON bytes.

Value

A length-1 logical, never NA: TRUE when x is well-formed JSON by the reader's rules, FALSE otherwise. NA_character_ is FALSE rather than NA. A TRUE is not a promise that json_parse() will succeed – the two cases above are valid JSON that this package cannot turn into an R value.

Details

This answers "is this valid JSON", which is very nearly but not exactly "will json_parse() succeed". The two come apart on JSON that is valid and still cannot become an R value, of which there are two kinds:

  • a string or key R cannot hold: one containing an escaped NUL (\u0000), or one longer than .Machine$integer.max bytes. json_parse() raises zujson_parse_error.

  • nesting deeper than 1000 levels. RFC 8259 leaves any depth limit to the implementation, so such a document is still valid JSON. json_parse() raises zujson_depth_error, because its recursive tree builder has a C stack to protect; the reader underneath it is iterative and does not.

This function returns TRUE for both, and is right to: it is asked whether the bytes are JSON, not whether this package can materialise them. Code that must not fail should handle the condition from json_parse() rather than pre-screening with this.

Examples

json_validate('{"a": 1}')
#> [1] TRUE
json_validate('{"a": }')
#> [1] FALSE
json_validate(charToRaw("[]"))
#> [1] TRUE