I am not following. You stated that the usage of Len was internal and a type
switch on known concrete types, so how is related to how the OP was attempting
to have things work?
There is no “generally accepted use of Len()”, otherwise it would not need to
perform a type switch on known concrete types - it would cast to an interface
declaring Len(), and use the interface, and then it would work with any type.
> On Feb 7, 2019, at 1:07 PM, Dan Kortschak <d...@kortschak.io> wrote:
>
> Yeah, I'm not agreeing with you.
>
> On Thu, 2019-02-07 at 07:07 -0600, Robert Engels wrote:
>> You are agreeing with me. A type switch on concrete types (that you
>> control) is far different than using an available Len() method and
>> assuming the same semantics.
>>
>>>
>>> On Feb 7, 2019, at 1:05 AM, Dan Kortschak <d...@kortschak.io> wrote:
>>>
>>> Addressing the first sentence, it was a direct answer to a comment
>>> you
>>> made:
>>>
>>>>
>>>> But is it really? If you read the description for Len() on
>>>> bytes.Buffer it is the length of unread portion. But that doesn’t
>>>> mean the buffer isn’t just a portion of the entire body - it can
>>>> be a
>>>> chunk which is continually reloaded.
>>> As far as the claim that there is a need to have a Len method in
>>> io.Reader, have a look at the code in question. It type asserts on
>>> three concrete types that are known to the function, all three have
>>> a
>>> Len method and this is used to obtain the known length. All other
>>> io.Readers are considered to have an unknown length.
>>>
>>> Whether it's wrong to use Len depends on whether there is a
>>> generally
>>> accepted and consistent set of semantics to Len() int. There is.
>>> This
>>> is strengthened if the use of an existing Len method is noted in
>>> the
>>> docs.
>>>
>>>>
>>>> On Wed, 2019-02-06 at 15:50 -0600, robert engels wrote:
>>>> I am not sure what that has to do with the discussion. My point
>>>> was
>>>> that for it to be applicable here, it needs to be defined as part
>>>> of
>>>> io.Reader, since that is what Body is declared as. It is not, so
>>>> using in the manner outlined is not correct IMO.
>>>>
>>>>>
>>>>>
>>>>> On Feb 6, 2019, at 3:37 PM, Dan Kortschak <d...@kortschak.io>
>>>>> wrote:
>>>>>
>>>>> The generalised semantics of Len are that it returns the number
>>>>> of
>>>>> available elements in the collection, being a cognate of the
>>>>> len
>>>>> built-
>>>>> in. This means that as you consume elements from a buffer, the
>>>>> Len
>>>>> value reduces. This is directly equivalent to
>>>>>
>>>>> for len(buf) != 0 {
>>>>> println(buf[0])
>>>>> buf = buf[1:]
>>>>> }
>>>>>
>>>>>>
>>>>>> On Wed, 2019-02-06 at 08:56 -0600, Robert Engels wrote:
>>>>>>
>>>>>> But is it really? If you read the description for Len() on
>>>>>> bytes.Buffer it is the length of unread portion. But that
>>>>>> doesn’t
>>>>>> mean the buffer isn’t just a portion of the entire body - it
>>>>>> can
>>>>>> be a
>>>>>> chunk which is continually reloaded.
>>>>>>
>>>>>> This is the danger in using private APIs publically based
>>>>>> upon
>>>>>> the
>>>>>> existence of a method - it leads to very brittle code - and
>>>>>> there
>>>>>> are
>>>>>> almost certainly better ways to design it to avoid these
>>>>>> issues.
>>>>>> If
>>>>>> the core api is not expressive enough then it will be more
>>>>>> difficult.
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Feb 6, 2019, at 8:30 AM, Burak Serdar <bser...@ieee.org>
>>>>>>> wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Wed, Feb 6, 2019 at 5:15 AM Robert Engels <rengels@ix.
>>>>>>>> netc
>>>>>>>> om.c
>>>>>>>> om> wrote:
>>>>>>>>
>>>>>>>> I see now, but if that can be the case, shouldn’t the
>>>>>>>> Body be
>>>>>>>> documented that the Reader may be a ReaderWithLen, and
>>>>>>>> the
>>>>>>>> consumer is free to type check/cast? If not, you are
>>>>>>>> using
>>>>>>>> internal details that you should not be.
>>>>>>> Yes, the documentation should say if the reader has a Len()
>>>>>>> method
>>>>>>> it
>>>>>>> would be used to set the ContentLength. Len is no longer an
>>>>>>> internal
>>>>>>> detail then.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> This is a problem with Go in general. Because the
>>>>>>>> returned
>>>>>>>> object
>>>>>>>> “implements” some interface because it happens to have
>>>>>>>> the
>>>>>>>> required method, doesn’t mean it was designed to be used
>>>>>>>> that
>>>>>>>> way, or that it has the required semantics - unless
>>>>>>>> documented to
>>>>>>>> have them.
>>>>>>> I agree with you there. Len() is straight forward, but in
>>>>>>> general
>>>>>>> just
>>>>>>> because a function is named something doesn't mean it'll do
>>>>>>> the
>>>>>>> same
>>>>>>> thing for all implementations. On the other end of the
>>>>>>> spectrum
>>>>>>> is
>>>>>>> Java-like interfaces where you want explicit inheritance of
>>>>>>> a
>>>>>>> specific
>>>>>>> interface. I don't know if there's anything in between, but
>>>>>>> I
>>>>>>> like
>>>>>>> Go's approach much better.
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Feb 6, 2019, at 2:22 AM, Matteo Biagetti
>>>>>>>> <matteo.biagetti@
>>>>>>>> gmai
>>>>>>>> l.com> wrote:
>>>>>>>>
>>>>>>>> Make sense, thanks for explanation
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Il giorno mercoledì 6 febbraio 2019 07:28:54 UTC+1, Burak
>>>>>>>> Serdar
>>>>>>>> ha scritto:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Tue, Feb 5, 2019 at 8:13 PM robert engels <ren...@ix
>>>>>>>>> .net
>>>>>>>>> com.
>>>>>>>>> com> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> That’s what I was trying to point out. Your design is
>>>>>>>>>> not
>>>>>>>>>> correct. The Body is a Reader, not a Buffer - the
>>>>>>>>>> length
>>>>>>>>>> of
>>>>>>>>>> the request/body may be indeterminate - that is, a
>>>>>>>>>> stream.
>>>>>>>>>> Attempting to get the length of an underlying buffer
>>>>>>>>>> is
>>>>>>>>>> not
>>>>>>>>>> only probably not possible, but not correct in many
>>>>>>>>>> situations.
>>>>>>>>> The length of the body *may* be indeterminate, and if
>>>>>>>>> that's
>>>>>>>>> the case,
>>>>>>>>> the underlying Reader will not have a Len method. The
>>>>>>>>> design is
>>>>>>>>> to
>>>>>>>>> handle the case where the underlying Reader is a Buffer
>>>>>>>>> with a
>>>>>>>>> Len
>>>>>>>>> method. If the Reader has Len, then the NopCloser
>>>>>>>>> derived
>>>>>>>>> from
>>>>>>>>> that
>>>>>>>>> will also have a Len, and NewRequest can set the
>>>>>>>>> content
>>>>>>>>> length. If
>>>>>>>>> the Reader does not have Len, then the content length
>>>>>>>>> is
>>>>>>>>> unknown.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> There is a reason the Body is a ReaderCloser and not
>>>>>>>>>> a
>>>>>>>>>> buffer. It is part of the http specification.
>>>>>>>>>>
>>>>>>>>>> On Feb 5, 2019, at 9:00 PM, Burak Serdar <bse...@ieee
>>>>>>>>>> .org
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> On Tue, Feb 5, 2019 at 7:00 PM Robert Engels <ren...@
>>>>>>>>>> ix.n
>>>>>>>>>> etco
>>>>>>>>>> m.com> wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Shouldn’t you just be taking the content length from
>>>>>>>>>> the
>>>>>>>>>> header if forwarding the same body. There is no need
>>>>>>>>>> for
>>>>>>>>>> the
>>>>>>>>>> length of the body.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> True. What I was suggesting is a fix for the general
>>>>>>>>>> case.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Feb 5, 2019, at 6:53 PM, Burak Serdar <bse...@ieee
>>>>>>>>>> .org
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>> On Tue, Feb 5, 2019 at 5:18 PM Dan Kortschak <d...@ko
>>>>>>>>>> rtsc
>>>>>>>>>> hak.
>>>>>>>>>> io> wrote:
>>>>>>>>>>
>>>>>>>>>> Personally, I think this is a bug in the behaviour of
>>>>>>>>>> NewRequest. See h
>>>>>>>>>> ttps://github.com/golang/go/issues/18117 for some
>>>>>>>>>> additional
>>>>>>>>>> context.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Agreed. One solution could be to have:
>>>>>>>>>>
>>>>>>>>>> type HasLen interface {
>>>>>>>>>> int Len()
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> Then have NopCloser return a nopCloser with len if
>>>>>>>>>> the
>>>>>>>>>> underlying
>>>>>>>>>> implementation has len, with the obvious changes to
>>>>>>>>>> NewRequest.Ugly,
>>>>>>>>>> but can be done without API changes.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Tue, 2019-02-05 at 05:18 -0800, matteo....@gmail.c
>>>>>>>>>> om
>>>>>>>>>> wrote:
>>>>>>>>>> I've the following situation:
>>>>>>>>>> I proxy a request to another server and when I made a
>>>>>>>>>> POST
>>>>>>>>>> and create
>>>>>>>>>> a new
>>>>>>>>>> request, the contentLength is zero:
>>>>>>>>>>
>>>>>>>>>> req2, _ := http.NewRequest(req.Method, newApiUrl
>>>>>>>>>> ,
>>>>>>>>>> req.Body)
>>>>>>>>>> fmt.Println("New request from body:",
>>>>>>>>>> req2.ContentLength) //
>>>>>>>>>> print 0
>>>>>>>>>>
>>>>>>>>>> Checking in the source code of the NewRequest func
>>>>>>>>>> Body
>>>>>>>>>> don't
>>>>>>>>>> respect
>>>>>>>>>> some
>>>>>>>>>> interface and populate the ContentLength field.
>>>>>>>>>>
>>>>>>>>>> Could be a bug? Which could be a valid approach in
>>>>>>>>>> order
>>>>>>>>>> to
>>>>>>>>>> create a
>>>>>>>>>> new
>>>>>>>>>> request from an existing one and correct set the Body
>>>>>>>>>> length?
>>>>>>>>>>
>>>>>>>>>> A working example here:
>>>>>>>>>>
>>>>>>>>>> https://play.golang.org/p/SvCDLj0NrXb
>>>>>>>>>>
>>>>>>>>>> Thanks!
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
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>>>>>>>>>> For more options, visit https://groups.google.com/d/o
>>>>>>>>>> ptou
>>>>>>>>>> t.
>>>>>>>>>>
>>>>>>>>>>
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>>>>>>>>>> t.
>>>>>>>>>>
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