Responses always contain the same class.

[mmalenic]

JSON responses always contain the same class string, either only "body" or only "header". Requests that contain a body response label the header as "body" as well. For example, this test returns a "body" class for the first byte range, even though it represents a "header":

Ok(
    Response {
        format: Bam,
        urls: [
            Url {
                url: "http://127.0.0.1:8081/data/htsnexus_test_NA12878.bam",
                headers: Some(
                    Headers(
                        {
                            "Range": "bytes=0-4667",
                        },
                    ),
                ),
                class: Body,
            },
            Url {
                url: "http://127.0.0.1:8081/data/htsnexus_test_NA12878.bam",
                headers: Some(
                    Headers(
                        {
                            "Range": "bytes=256721-647345",
                        },
                    ),
                ),
                class: Body,
            },
            Url {
                url: "http://127.0.0.1:8081/data/htsnexus_test_NA12878.bam",
                headers: Some(
                    Headers(
                        {
                            "Range": "bytes=824361-842100",
                        },
                    ),
                ),
                class: Body,
            },
            Url {
                url: "http://127.0.0.1:8081/data/htsnexus_test_NA12878.bam",
                headers: Some(
                    Headers(
                        {
                            "Range": "bytes=977196-996014",
                        },
                    ),
                ),
                class: Body,
            },
            Url {
                url: "data:;base64,H4sIBAAAAAAA/wYAQkMCABsAAwAAAAAAAAAAAA==",
                headers: None,
                class: Body,
            },
        ],
    },
)

This does not line up with the example in the htsget protocol, which labels headers with the "header" class:

{
   "htsget" : {
      "format" : "BAM",
      "urls" : [
         {
            "url" : "data:application/vnd.ga4gh.bam;base64,QkFNAQ==",
            "class" : "header"
         },
         {
            "url" : "https://htsget.blocksrv.example/sample1234/header",
            "class" : "header"
         },
         {
            "url" : "https://htsget.blocksrv.example/sample1234/run1.bam",
            "headers" : {
               "Authorization" : "Bearer xxxx",
               "Range" : "bytes=65536-1003750"
             },
            "class" : "body"
         },
         {
            "url" : "https://htsget.blocksrv.example/sample1234/run1.bam",
            "headers" : {
               "Authorization" : "Bearer xxxx",
               "Range" : "bytes=2744831-9375732"
            },
            "class" : "body"
         }
      ]
   }
}

I'm not sure what the best class for ranges that contain both header and body bytes is. Maybe in this case it would be best to drop the class string, as it is optional anyway.