Implement isreadable and iswritable (#185)

Author: nhz2

ext/TestExt.jl

@@ -90,6 +90,7 @@ function TranscodingStreams.test_chunked_read(Encoder, Decoder)
             stream = TranscodingStream(Decoder(), buffer, stop_on_end=true)
             ok &= hash(read(stream)) == hash(chunk)
             ok &= eof(stream)
+            ok &= isreadable(stream)
             close(stream)
         end
         Test.@test ok

src/stream.jl

@@ -103,7 +103,7 @@ julia> using TranscodingStreams
 
 julia> file = open(joinpath(dirname(dirname(pathof(TranscodingStreams))), "README.md"));
 
-julia> stream = NoopStream(file);
+julia> stream = TranscodingStream(Noop(), file);
 
 julia> readline(file)
 "TranscodingStreams.jl"
@@ -182,6 +182,16 @@ function Base.isopen(stream::TranscodingStream)
     return stream.state.mode != :close && stream.state.mode != :panic
 end
 
+function Base.isreadable(stream::TranscodingStream)::Bool
+    mode = stream.state.mode
+    (mode === :idle || mode === :read || mode === :stop) && isreadable(stream.stream)
+end
+
+function Base.iswritable(stream::TranscodingStream)::Bool
+    mode = stream.state.mode
+    (mode === :idle || mode === :write) && iswritable(stream.stream)
+end
+
 function Base.close(stream::TranscodingStream)
     mode = stream.state.mode
     if mode != :panic

test/codecnoop.jl

@@ -240,18 +240,26 @@
     TranscodingStreams.test_roundtrip_write(NoopStream, NoopStream)
     TranscodingStreams.test_roundtrip_lines(NoopStream, NoopStream)
 
-    # switch write => read
-    stream = NoopStream(IOBuffer(b"foobar", read=true, write=true))
-    @test_throws ArgumentError begin
-        write(stream, b"xyz")
-        read(stream, 3)
+    @testset "switch write => read" begin
+        stream = NoopStream(IOBuffer(collect(b"foobar"), read=true, write=true))
+        @test isreadable(stream)
+        @test iswritable(stream)
+        @test_throws ArgumentError begin
+            write(stream, b"xyz")
+            read(stream, 3)
+        end
+        @test !isreadable(stream)
+        @test iswritable(stream)
     end
 
-    # switch read => write
-    stream = NoopStream(IOBuffer(b"foobar", read=true, write=true))
-    @test_throws ArgumentError begin
-        read(stream, 3)
-        write(stream, b"xyz")
+    @testset "switch read => write" begin
+        stream = NoopStream(IOBuffer(collect(b"foobar"), read=true, write=true))
+        @test_throws ArgumentError begin
+            read(stream, 3)
+            write(stream, b"xyz")
+        end
+        @test isreadable(stream)
+        @test !iswritable(stream)
     end
 
     stream = NoopStream(IOBuffer(""))