net/http: document that ParseMultipartForm requires Content-Type: multipart/form-data as of Go 1.3

[gopherbot]

by dgrijalva@fitstar.com:

Prior to go1.3, calling ParseMultipartForm on a http.Request that did not have the
content type 'multipart/form-data' would silently just do the right thing.  As of 1.3,
an error is returned that looks like 'request Content-Type isn't multipart/form-data'. 
I couldn't find this behavior change anywhere in the release notes.

This different behavior seems logical, although less convenient for my use case.  What
strikes me as unusual is that it's not totally backwards compatible and there doesn't
seem to be mention of in the release notes.  Was this an intentional change or an
oversight?  Will it be changed back or should I work around it?

[bradfitz]

Comment 1:

This was a result of issue #6334 being fixed.
I was paranoid in the review (e.g. https://golang.org/cl/44040043#msg10) but
apparently not enough.
It probably should've been documented. I don't think changing it back at this point
makes sense, though.
I suppose we could amend the Go 1.3 release notes in Go 1.3.1 so at least people hitting
this (you're the first?) know what [not] to do.

Labels changed: added release-go1.3.1.

Status changed to Thinking.

[gopherbot]

Comment 2 by dgrijalva@fitstar.com:

I would likely not have run into this if I were building something new.  The
documentation doesn't say what will happen in this case, and one solution feels as good
as the other to me.  Code based on the old behavior will likely often be wrong.  It
would be nice if the documentation and/or release notes reflected the change.
Just for the sake of clarity: the code I'm working with assumed that an error meant the
whole request was bad (protocol/network error, etc) and bail out completely.  If there
was no error, it would check properties on the request to figure out what had actually
happened.

[rsc]

Comment 3:

Brad, can you take care of updating the release notes?

Owner changed to @bradfitz.

[adg]

Comment 4:

https://golang.org/cl/123860043

Owner changed to @adg.

Status changed to Started.

[gopherbot]

Comment 5:

CL https://golang.org/cl/123860043 mentions this issue.

[adg]

Comment 6:

This issue was closed by revision af403c0.

Status changed to Fixed.

[rsc]

Comment 7:

Doc-only change.
Approved for Go 1.3.1.

[gopherbot]

Comment 8 by dgrijalva@fitstar.com:

<3

[adg]

Comment 9:

This issue was closed by revision 1f7b50bf1050.

[adg]

Comment 10:

Applied to release-branch.go1.3.