add stream shutdown and support half-duplex operation

Fixes one of the issues mentioned in #24526

NEWS.md

@@ -55,6 +55,7 @@ New library features
 Standard library changes
 ------------------------
 
+* TCP socket objects now expose `shutdown` functionality and support half-open mode usage ([#TBD]).
 * `count` and `findall` now accept an `AbstractChar` argument to search for a character in a string ([#38675]).
 * `range` now supports the `range(start, stop)` and `range(start, stop, length)` methods ([#39228]).
 * `range` now supports `start` as an optional keyword argument ([#38041]).

base/coreio.jl

@@ -20,13 +20,14 @@ flush(::DevNull) = nothing
 wait_readnb(::DevNull) = wait()
 wait_close(::DevNull) = wait()
 eof(::DevNull) = true
+bytesavailable(io::DevNull) = 0
 
 let CoreIO = Union{Core.CoreSTDOUT, Core.CoreSTDERR}
     global write, unsafe_write
     write(io::CoreIO, x::UInt8) = Core.write(io, x)
     unsafe_write(io::CoreIO, x::Ptr{UInt8}, nb::UInt) = Core.unsafe_write(io, x, nb)
 end
-
+isopen
 stdin = devnull
 stdout = Core.stdout
 stderr = Core.stderr

base/exports.jl

@@ -795,6 +795,7 @@ export
 
 # I/O and events
     close,
+    shutdown,
     countlines,
     eachline,
     readeach,

base/io.jl

@@ -60,9 +60,36 @@ function isopen end
 Close an I/O stream. Performs a [`flush`](@ref) first.
 """
 function close end
+
+"""
+    shutdown(stream)
+
+Shutdown an I/O stream. Performs a [`flush`](@ref) first. Notify the other end that no
+more data can ever be written to the underlying file. This is not supported by all IO
+types.
+"""
+function shutdown end
+
+"""
+    flush(stream)
+
+Commit all currently buffered writes to the given stream.
+"""
 function flush end
-function wait_readnb end
-function wait_close end
+
+"""
+    bytesavailable(io)
+
+Return the number of bytes available for reading before a read from this stream or buffer will block.
+
+# Examples
+```jldoctest
+julia> io = IOBuffer("JuliaLang is a GitHub organization");
+
+julia> bytesavailable(io)
+34
+```
+"""
 function bytesavailable end
 
 """
@@ -81,7 +108,7 @@ function readavailable end
 """
     isreadable(io) -> Bool
 
-Return `true` if the specified IO object is readable (if that can be determined).
+Return `false` if the specified IO object is not readable.
 
 # Examples
 ```jldoctest
@@ -99,12 +126,12 @@ true
 julia> rm("myfile.txt")
 ```
 """
-function isreadable end
+isreadable(io::IO) = isopen(io)
 
 """
     iswritable(io) -> Bool
 
-Return `true` if the specified IO object is writable (if that can be determined).
+Return `false` if the specified IO object is not writable.
 
 # Examples
 ```jldoctest
@@ -122,10 +149,23 @@ false
 julia> rm("myfile.txt")
 ```
 """
-function iswritable end
-function copy end
+iswritable(io::IO) = isopen(io)
+
+"""
+    eof(stream) -> Bool
+
+Test whether an I/O stream is at end-of-file. If the stream is not yet exhausted, this
+function will block to wait for more data if necessary, and then return `false`. Therefore
+it is always safe to read one byte after seeing `eof` return `false`. `eof` will return
+`false` as long as buffered data is still available, even if the remote end of a connection
+is closed.
+"""
 function eof end
 
+function copy end
+function wait_readnb end
+function wait_close end
+
 """
     read(io::IO, T)
 
@@ -357,65 +397,37 @@ end
 function pipe_reader end
 function pipe_writer end
 
+for f in (:flush, :shutdown, :iswritable)
+    @eval $(f)(io::AbstractPipe) = $(f)(pipe_writer(io)::IO)
+end
 write(io::AbstractPipe, byte::UInt8) = write(pipe_writer(io)::IO, byte)
 write(to::IO, from::AbstractPipe) = write(to, pipe_reader(from))
 unsafe_write(io::AbstractPipe, p::Ptr{UInt8}, nb::UInt) = unsafe_write(pipe_writer(io)::IO, p, nb)::Union{Int,UInt}
 buffer_writes(io::AbstractPipe, args...) = buffer_writes(pipe_writer(io)::IO, args...)
-flush(io::AbstractPipe) = flush(pipe_writer(io)::IO)
 
+for f in (
+        # peek/mark interface
+        :mark, :unmark, :reset, :ismarked,
+        # Simple reader functions
+        :read, :readavailable, :bytesavailable, :reseteof, :isreadable)
+    @eval $(f)(io::AbstractPipe) = $(f)(pipe_reader(io)::IO)
+end
 read(io::AbstractPipe, byte::Type{UInt8}) = read(pipe_reader(io)::IO, byte)::UInt8
 unsafe_read(io::AbstractPipe, p::Ptr{UInt8}, nb::UInt) = unsafe_read(pipe_reader(io)::IO, p, nb)
-read(io::AbstractPipe) = read(pipe_reader(io)::IO)
 readuntil(io::AbstractPipe, arg::UInt8; kw...) = readuntil(pipe_reader(io)::IO, arg; kw...)
 readuntil(io::AbstractPipe, arg::AbstractChar; kw...) = readuntil(pipe_reader(io)::IO, arg; kw...)
 readuntil(io::AbstractPipe, arg::AbstractString; kw...) = readuntil(pipe_reader(io)::IO, arg; kw...)
 readuntil(io::AbstractPipe, arg::AbstractVector; kw...) = readuntil(pipe_reader(io)::IO, arg; kw...)
 readuntil_vector!(io::AbstractPipe, target::AbstractVector, keep::Bool, out) = readuntil_vector!(pipe_reader(io)::IO, target, keep, out)
 readbytes!(io::AbstractPipe, target::AbstractVector{UInt8}, n=length(target)) = readbytes!(pipe_reader(io)::IO, target, n)
-
-for f in (
-        # peek/mark interface
-        :mark, :unmark, :reset, :ismarked,
-        # Simple reader functions
-        :readavailable, :isreadable)
-    @eval $(f)(io::AbstractPipe) = $(f)(pipe_reader(io)::IO)
-end
 peek(io::AbstractPipe, ::Type{T}) where {T} = peek(pipe_reader(io)::IO, T)::T
+wait_readnb(io::AbstractPipe, nb::Int) = wait_readnb(pipe_reader(io)::IO, nb)
+eof(io::AbstractPipe) = eof(pipe_reader(io)::IO)::Bool
 
-iswritable(io::AbstractPipe) = iswritable(pipe_writer(io)::IO)
 isopen(io::AbstractPipe) = isopen(pipe_writer(io)::IO) || isopen(pipe_reader(io)::IO)
 close(io::AbstractPipe) = (close(pipe_writer(io)::IO); close(pipe_reader(io)::IO))
-wait_readnb(io::AbstractPipe, nb::Int) = wait_readnb(pipe_reader(io)::IO, nb)
 wait_close(io::AbstractPipe) = (wait_close(pipe_writer(io)::IO); wait_close(pipe_reader(io)::IO))
 
-"""
-    bytesavailable(io)
-
-Return the number of bytes available for reading before a read from this stream or buffer will block.
-
-# Examples
-```jldoctest
-julia> io = IOBuffer("JuliaLang is a GitHub organization");
-
-julia> bytesavailable(io)
-34
-```
-"""
-bytesavailable(io::AbstractPipe) = bytesavailable(pipe_reader(io)::IO)
-bytesavailable(io::DevNull) = 0
-
-"""
-    eof(stream) -> Bool
-
-Test whether an I/O stream is at end-of-file. If the stream is not yet exhausted, this
-function will block to wait for more data if necessary, and then return `false`. Therefore
-it is always safe to read one byte after seeing `eof` return `false`. `eof` will return
-`false` as long as buffered data is still available, even if the remote end of a connection
-is closed.
-"""
-eof(io::AbstractPipe) = eof(pipe_reader(io)::IO)::Bool
-reseteof(io::AbstractPipe) = reseteof(pipe_reader(io)::IO)
-
 
 # Exception-safe wrappers (io = open(); try f(io) finally close(io))
 
@@ -1118,11 +1130,6 @@ ismarked(io::IO) = io.mark >= 0
 # Make sure all IO streams support flush, even if only as a no-op,
 # to make it easier to write generic I/O code.
 
-"""
-    flush(stream)
-
-Commit all currently buffered writes to the given stream.
-"""
 flush(io::IO) = nothing
 
 """

base/iobuffer.jl

@@ -334,6 +334,12 @@ end
 
 eof(io::GenericIOBuffer) = (io.ptr-1 == io.size)
 
+function shutdown(io::GenericIOBuffer)
+    io.writable = false
+    # OR throw(_UVError("shutdown", UV_ENOTSOCK))
+    nothing
+end
+
 @noinline function close(io::GenericIOBuffer{T}) where T
     io.readable = false
     io.writable = false

base/libuv.jl

@@ -107,6 +107,7 @@ end
 function uv_alloc_buf end
 function uv_readcb end
 function uv_writecb_task end
+function uv_shutdowncb_task end
 function uv_return_spawn end
 function uv_asynccb end
 function uv_timercb end

base/process.jl

@@ -274,6 +274,7 @@ function setup_stdio(stdio::Union{IOBuffer, BufferStream}, child_readable::Bool)
                 @warn "Process error" exception=(ex, catch_backtrace())
             finally
                 close(parent)
+                child_readable || shutdown(stdio)
             end
         end
     catch ex