It seems a bug of Yahoo Weather API that every time I send a request I get the same weather. What’s interesting design, there isn’t any timestamp field in the response to identify the time of the weather.
$ curl "http://weather.yahooapis.com/forecastjson?p=CHXX0099&u=c" -v
* About to connect() to weather.yahooapis.com port 80 (#0)
* Trying 180.233.115.34... connected
* Connected to weather.yahooapis.com (180.233.115.34) port 80 (#0)
> GET /forecastjson?p=CHXX0099&u=c HTTP/1.1
> User-Agent: curl/7.21.3 (i386-redhat-linux-gnu) libcurl/7.21.3 NSS/3.12.9.0 zlib/1.2.5 libidn/1.19 libssh2/1.2.7
> Host: weather.yahooapis.com
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Tue, 31 May 2011 12:58:10 GMT
< Cache-Control: private, max-age=1200
< Expires: Tue, 31 May 2011 13:18:10 GMT
< Connection: close
< Transfer-Encoding: chunked
< Content-Type: application/json;charset=UTF-8
<
* Closing connection #0
{"units":{"temperature":"C","speed":"km\/h","distance":"km","pressure":"mb"},"location":{"location_id":"CHXX0099","city":"Nanjing","state_abbreviation":"JI","country_abbreviation":"CH","elevation":3,"latitude":32,"longitude":118.80000000000000},"wind":{"speed":6.00000000000000,"direction":"N"},"atmosphere":{"humidity":"22","visibility":12.01000000000000,"pressure":1024.00000000000000,"rising":""},"url":"http:\/\/weather.yahoo.com\/forecast\/CHXX0099.html","logo":"http:\/\/l.yimg.com\/a\/i\/us\/nt\/ma\/ma_nws-we_1.gif","astronomy":{"sunrise":"06:22","sunset":"18:09"},"condition":{"text":"Sunny","code":"32","image":"http:\/\/l.yimg.com\/a\/i\/us\/we\/52\/32.gif","temperature":14.00000000000000},"forecast":[{"day":"Today","condition":"Mostly Clear","high_temperature":13.00000000000000,"low_temperature":3.00000000000000},{"day":"Tomorrow","condition":"Partly Cloudy","high_temperature":16.00000000000000,"low_temperature":5.00000000000000}]}
However, if I request the same interface via VPN, the data returned is just right.
$ curl "http://weather.yahooapis.com/forecastjson?p=CHXX0099&u=c" -v
* About to connect() to weather.yahooapis.com port 80 (#0)
* Trying 180.233.115.34... connected
* Connected to weather.yahooapis.com (180.233.115.34) port 80 (#0)
> GET /forecastjson?p=CHXX0099&u=c HTTP/1.1
> User-Agent: curl/7.21.3 (i386-redhat-linux-gnu) libcurl/7.21.3 NSS/3.12.9.0 zlib/1.2.5 libidn/1.19 libssh2/1.2.7
> Host: weather.yahooapis.com
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Tue, 31 May 2011 12:58:10 GMT
< Cache-Control: private, max-age=1200
< Expires: Tue, 31 May 2011 13:18:10 GMT
< Connection: close
< Transfer-Encoding: chunked
< Content-Type: application/json;charset=UTF-8
<
* Closing connection #0
{"units":{"temperature":"C","speed":"km\/h","distance":"km","pressure":"mb"},"location":{"location_id":"CHXX0099","city":"Nanjing","state_abbreviation":"JI","country_abbreviation":"CH","elevation":3,"latitude":32,"longitude":118.80000000000000},"wind":{"speed":6.00000000000000,"direction":"N"},"atmosphere":{"humidity":"22","visibility":12.01000000000000,"pressure":1024.00000000000000,"rising":""},"url":"http:\/\/weather.yahoo.com\/forecast\/CHXX0099.html","logo":"http:\/\/l.yimg.com\/a\/i\/us\/nt\/ma\/ma_nws-we_1.gif","astronomy":{"sunrise":"06:22","sunset":"18:09"},"condition":{"text":"Sunny","code":"32","image":"http:\/\/l.yimg.com\/a\/i\/us\/we\/52\/32.gif","temperature":14.00000000000000},"forecast":[{"day":"Today","condition":"Mostly Clear","high_temperature":13.00000000000000,"low_temperature":3.00000000000000},{"day":"Tomorrow","condition":"Partly Cloudy","high_temperature":16.00000000000000,"low_temperature":5.00000000000000}]}
Personally, I think this is something related by Varnish or Squid stuff. Are you also affected by this issue? Before I can find the official support link, what can I do to expire the server-side cache ?
In your question as posted, the two Curl examples look identical, but I imagine you are noticing that the data returned was different depending on your network path.
There is some level of caching on these JSON responses (30 minutes I believe), but there may be additional caching on your network.
One important issue is the weather forecast data on the backend is updated on intervals, because the forecast itself does not change that frequently.
In fact, the JSON weather interface you’re using is not officially supported, but I believe it’s just used by Yahoo itself on various pages.
Refer to the Yahoo! Weather page on YDN for the “official” supported interface. By itself this interface is not as useful because it’s only in XML format. Instead you could use the YQL console to pass in your location and receive back JSON formatted data.
For example, try this query: select * from weather.bylocation where location=”Nanjing, CN”. In the results, notice the
lastBuildDatavalue which is the last time the forecast was updated: