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|
The `json()` function parses the given string value as JSON.
Throws an exception if the given input value is not a string.
Throws an exception if the given input string cannot be parsed as JSON.
Returns the resulting value.
-- Testcase --
{%
print(join("\n", [
json("null"),
json("true"),
json("false"),
json("123"),
json("456.7890000"),
json("-1.4E10"),
json("1e309"),
json('"A string \u2600"'),
json("[ 1, 2, 3 ]"),
json('{ "test": [ 1, 2, 3 ] }'),
// surrounding white space is ignored
json(' [ 1, 2, 3 ] ')
]), "\n");
%}
-- End --
-- Expect stdout --
null
true
false
123
456.789
-1.4e+10
Infinity
A string ☀
[ 1, 2, 3 ]
{ "test": [ 1, 2, 3 ] }
[ 1, 2, 3 ]
-- End --
Passing a non-string value throws an exception.
-- Testcase --
{%
json(true);
%}
-- End --
-- Expect stderr --
Type error: Passed value is neither a string nor an object
In line 2, byte 11:
` json(true);`
Near here ---^
-- End --
Unparseable JSON throws exceptions.
-- Testcase --
{%
json('[ "incomplete", "array" ');
%}
-- End --
-- Expect stderr --
Syntax error: Failed to parse JSON string: unexpected end of data
In line 2, byte 33:
` json('[ "incomplete", "array" ');`
Near here -------------------------^
-- End --
-- Testcase --
{%
json('invalid syntax');
%}
-- End --
-- Expect stderr --
Syntax error: Failed to parse JSON string: unexpected character
In line 2, byte 23:
` json('invalid syntax');`
Near here ---------------^
-- End --
-- Testcase --
{%
json('[] trailing garbage');
%}
-- End --
-- Expect stderr --
Syntax error: Trailing garbage after JSON data
In line 2, byte 28:
` json('[] trailing garbage');`
Near here --------------------^
-- End --
Additionally, `json()` accepts objects implementing a read method as input.
During JSON parsing, the read method is repeatedly invoked with a buffer size
hint as sole argument. The return value of the read method is converted to a
string if needed and passed on to the JSON parser. A `null` or an empty string
return value is treated as EOF, ending the parse process.
-- Testcase --
{%
let fs = require("fs");
// parse JSON from open file handle
printf("%.J\n",
json(fs.open("files/test.json"))
);
%}
-- End --
-- Expect stdout --
{
"hello": "world"
}
-- End --
-- File test.json --
{"hello":"world"}
-- End --
The `json()` function is able to parse JSON from any object providing a `read()`
method that incrementally yields JSON source data.
-- Testcase --
{%
let parts = [
'{"some"',
':',
'"object"',
', ',
'"etc."',
':',
!0, // this is stringified to "true"
'}'
];
let producer = {
read: function(size) {
return shift(parts);
}
};
// parse JSON from producer object
printf("%.J\n",
json(producer)
);
%}
-- End --
-- Expect stdout --
{
"some": "object",
"etc.": true
}
-- End --
Passing objects or resources not providing a `read()` method yields an exception.
-- Testcase --
{%
json({});
%}
-- End --
-- Expect stderr --
Type error: Input object does not implement read() method
In line 2, byte 9:
` json({});`
Near here -^
-- End --
Exceptions triggered by the `read()` method are properly forwarded.
-- Testcase --
{%
json({
read: function() {
die("Exception in read()");
}
});
%}
-- End --
-- Expect stderr --
Exception in read()
In [anonymous function](), line 4, byte 29:
called from function json ([C])
called from anonymous function ([stdin]:6:3)
` die("Exception in read()");`
Near here ---------------------------^
-- End --
EOF stops parsing and does not lead to further `read()` invocations.
-- Testcase --
{%
let parts = [
'["some",',
'"JSON array",',
'true,false,1,2,3',
']',
'', // empty string treated as EOF
'{"some":', // this is not reached in the first pass
'"object"}',
null, // null treated as EOF
'"test ', // this is not reached in the second pass
'value"'
];
let producer = { read: () => shift(parts) };
printf("%.J\n", [
json(producer),
json(producer),
json(producer)
]);
%}
-- End --
-- Expect stdout --
[
[
"some",
"JSON array",
true,
false,
1,
2,
3
],
{
"some": "object"
},
"test value"
]
-- End --
|
