writing to a read-only IOStream should fail

[StefanKarpinski]

Likewise, reading from a write-only IOStream should probably fail too.

[staticfloat]

At the moment, I see the following behavior:

julia> a
2x2 Float64 Array:
 1.0  2.0
 3.0  4.0

julia> f = open("/tmp/jtest", "w")
IOStream(<file /tmp/jtest>)

julia> write(f,a)
0x0000000000000020

julia> position(f)
32

julia> seek(f,0)
true

julia> read(f,Array(Float64,2,2))
read: end of file
 in read at io.jl:241

So reading from a write-only stream seems to fail with an error, however writing to a read-only stream doesn't error out, it only returns zero:

julia> f = open("/tmp/jtest", "r")                                              
IOStream(<file /tmp/jtest>)

julia> read(f,Array(Float64,2,2))                                               
2x2 Float64 Array:
 1.0  2.0
 3.0  4.0

julia> seek(f,0)                                                                
true

julia> write(f,a)
0x0000000000000000

Should these two responses be matched? If so, what should the response be? This is typically the area where exceptions and such come into play in other languages, as it's pretty important to send IO errors and such back up to user flow control. However, you guys may have a different idea as to how this should be handled.

[vtjnash]

possibly similar to #1701 [closed]. what is the thoughts on the I/O system behavior here?

@loladiro this will possibly be relevant to us during libuv File API rewrite

[ViralBShah]

Seems like you can still write to a read-only IOStream as per the example above.