Partial read from urls with READ/PART or READ/SEEK

Question

Partial read via HTTP Range header works fine for me:

rebol []
client: open tcp://www.apache.org/

client/awake: func [event /local port] [
    port: event/port
    switch event/type [
        lookup [open port]
        connect [
            write port rejoin [
                {GET / HTTP/1.1} crlf
                {User-Agent: curl/7.26.0} crlf
                {Host: www.apache.org} crlf
                {Accept: */*} crlf
                {Range: bytes=0-9} crlf
                crlf
            ]
        ]
        wrote [read port]
        read [
            probe to-string port/data
            probe length? port/data
            clear port/data
        ]        
    ]
    false
]

wait [client 3]
close client
print "Done"

I think I could use READ/PART to do the same thing:

length? read/part http://www.apache.org/ 10   ;40195
length? read http://www.apache.org/           ;40195

but it does't work, still get all the bytes. The same with READ/SEEK. Why was that? (By the way, it works in Rebol2.)

Graham Chiu · Accepted Answer · 2014-06-25T10:15:39.957

You can see from the source

https://github.com/rebol/rebol/blob/master/src/mezz/prot-http.r#L424

that the read actor does not have any refinements defined. This doesn't mean they can't be defined but at present no decision has been made on whether it should be done by using refinements, or by using a query dialect.

You can see by setting trace/net on, that it's faking it in Rebol2

>> trace/net on
>> read/part http://www.apache.org 10
URL Parse: none none www.apache.org none none none
Net-log: ["Opening" "tcp" "for" "HTTP"]
connecting to: www.apache.org
Net-log: {GET / HTTP/1.0
Accept: */*
Connection: close
User-Agent: REBOL View 2.7.8.3.1
Host: www.apache.org
}
Net-log: "HTTP/1.1 200 OK"
Net-log: ["low level read of " 2048 "bytes"]
Net-log: ["low level read of " 2048 "bytes"]
.. many lines removed
Net-log: ["low level read of " 2048 "bytes"]
Net-log: ["low level read of " 2048 "bytes"]
Net-log: ["low level read of " 2048 "bytes"]
== "<!DOCTYPE "

So in Rebol2, READ/PART just gets all the data and returns part of it? `trace` is cool! — Wayne Cui, Jun 25 '14 at 12:14

score 0 · Answer 2 · answered Jun 25 '14 at 06:27

0

It's a safe guess that it's simply not implemented in current version of HTTP scheme. There are other missing parts also like redirection, so I would assume it's not supported yet.

answered Jun 25 '14 at 06:27

rebolek

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Partial read from urls with READ/PART or READ/SEEK

2 Answers2