And to come full circle, this poorly declared method, with hidden internal
implementation details, is exactly the cause of OP’s initial problem. Not
expecting that the Body passed in, and retrieved later could be used as a Body
of a new request - why wouldn’t he think that ?
> On Feb 7, 2019, at 2:55 PM, robert engels <reng...@ix.netcom.com> wrote:
>
> I see the documented use of the types in NewRequest - you are correct - I was
> wrong.
>
> But, it could of easily also declared that if the provided Reader is also a
> Lener, it uses it to determine the content length. Why have this behavior for
> Closer and not for Lener? Then you don’t need the type switch. You say, well
> the copy...
>
> The current code with the copy is broken - the caller could continue to
> modify the contents of the bytes.Buffer and things would not work as expected
> since the backing array of the slice is shared - so how is the copy helping ?
> The length will remain the same, but the data represented could be corrupted.
>
> The correct solution is to declare that NewRequest takes an interface
> Content, that has both Reader and ContentLength methods, where
> ContentLength() can return -1 if the content length is indeterminate. Then
> declare simple facades for Content from bytes.Buffer, a string, etc. And also
> declare that continued use of the Content after NewRequest is undefined. And
> if you wanted to retain the simplicity, just declare it uses ContentLength
> like it uses Closer.
>
> I am all for the simplicity of Go, but “solutions" like NewRequest are not
> the way modern software should be developed. Casting an interface to a
> concrete type is a sign of code that needs design work. Having to read the
> doc in addition to the method signature is also a sign the interface needs
> work (primarily since changes to the doc can/will/might change behavior but
> it avoids compile time type checking = brittle code with obscure bugs).
>
>
>> On Feb 7, 2019, at 1:56 PM, Dan Kortschak <d...@kortschak.io> wrote:
>>
>> I didn't mention the word internal, nor did I imply it; with
>> documentation stating that it would be used, it is clearly *not*
>> internal.
>>
>> If you look at the code in question, you can see a probable reason why
>> a Lener interface is not used; for each of the blessed types, a
>> concrete copy of the pointed-to-value is made to allow GetBody to
>> return it. This cannot be done with an interface value without the use
>> of reflect.
>>
>> Please show me a Len method in the standard library that does not
>> return the number of available-to-access elements in a collection.
>>
>>
>> On Thu, 2019-02-07 at 13:27 -0600, robert engels wrote:
>>> 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 <bserdar@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....@gma
>>>>>>>>>>>>> il.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!
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>> You received this message because you are
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>>>>>>>>>>>>> to
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>>>>>>>>>>>>> from
>>>>>>>>>>>>> it, send an email to golang-nuts...@googlegroups.
>>>>>>>>>>>>> com.
>>>>>>>>>>>>> For more options, visit https://groups.google.com
>>>>>>>>>>>>> /d/o
>>>>>>>>>>>>> ptou
>>>>>>>>>>>>> t.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
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>>>>>>>>>>>>> t.
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