NSJSONSerialization - Unable to convert data to string

Question

I'm having a problem with NSJSONSerialization reading JSON from the Met Office Datapoint API.

I get the following error

Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (Unable to convert data to string around character 58208.

I have checked and think this is the offending line according to the character position

{"id":"353556","latitude":"57.1893","longitude":"-5.0929","name":"Sóil Chaorainn"}

The JSON itself appears to be valid according to a couple of Validators I tried, and I would expect it too be from a large organisation such as Met Office.

Shouldn't NSJSONSerialization work fine with characters such as 'ó'?

If not how do I go about changing the encoding type to deal with this?

Many Thanks in Advance

Try a different JSON package -- one that accepts an NSString -- so you can be sure about the conversion. — Hot Licks
– Hot Licks, Commented Jan 23, 2013 at 18:24

Eric Genet · Accepted Answer · 2013-01-23 20:41:22Z

21

The Met Office Datapoint sends back data in ISO-8859-1 which isn't one of the supported data format for NSJSONSerialization.

To make it work create a string from the URL content at first with NSISOLatin1StringEncoding and then create the NSData you want to use in the NSJSONSerialization with a NSUTF8 encoding.

The following works to create the corresponding json object

NSError *error;
NSString *string = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://datapoint.metoffice.gov.uk/public/data/val/wxfcs/all/json/sitelist?key=<YOUR_API_KEY"] encoding:NSISOLatin1StringEncoding error:&error];

NSData *metOfficeData = [string dataUsingEncoding:NSUTF8StringEncoding];

id jsonObject = [NSJSONSerialization JSONObjectWithData:metOfficeData options:kNilOptions error:&error];

if (error) {
    //Error handling
} else {
    //use your json object
    NSDictionary *locations = [jsonObject objectForKey:@"Locations"];
    NSArray *location = [locations objectForKey:@"Location"];
    NSLog(@"Received %d locations from the DataPoint", [location count]);
}

edited Jan 23, 2013 at 20:41

answered Jan 23, 2013 at 18:31

Eric Genet

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5 Comments

Matt Price Over a year ago

I'm using the following NSData* data = [NSData dataWithContentsOfURL: kMetOfficeAllSites]; From the following URL datapoint.metoffice.gov.uk/public/data/val/wxfcs/all/json/… API> Then NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

Eric Genet Over a year ago

Just made it work. In fact the encoding from the dataPoint is ISO-8859-1 (NSISOLatin1). you just need to get it in a String and create a UTF-8 NSData from it. I'm updating my answer above with it.

Matt Price Over a year ago

Many Thanks Eric for the solution. I guess this will be the best way to handle all JSON from Datapoint as its all likely to be ISO-8859-1. Can I ask how you found the encoding type?

Eric Genet Over a year ago

You're welcome, it's not that elegant but it works. To find the encoding I used curl http://...... -o outputfile on the command line and then looked at the encoding of the file. There's nothing on the HTTP header of the datapoint (which for me is a bug)

Matt Price Over a year ago

Yeah, I might try contact them and ask about the encoding of the JSON and their HTTP header. But I don't have a great deal of knowledge in this area. Once again many thanks.

Terence Yan · Accepted Answer · 2013-01-23 17:47:23Z

4

What is encoding for the JSON? JSON is supposed to UTF-8 but I have seen lousy APIs where they use ISO-8859-1. NSJSONSerialization only works UTF-8, UTF-16LE, UTF-16BE, UTF-32LE, UTF-32BE.

answered Jan 23, 2013 at 17:47

Terence Yan

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1 Comment

Matt Price Over a year ago

I'm not sure the best way to check the encoding, but i loaded the JSON feed in chrome and under Tools / Encoding it said Western(ISO-8859-1) so looks like i'm out of luck, can you re-encode?

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