Base64: add isreadable and iswritable for Base64EncodePipe/Base64DecodePipe (#37520)

Author: johnnychen94

stdlib/Base64/src/decode.jl

@@ -43,6 +43,9 @@ struct Base64DecodePipe <: IO
     end
 end
 
+Base.isreadable(pipe::Base64DecodePipe) = !isempty(pipe.rest) || isreadable(pipe.io)
+Base.iswritable(::Base64DecodePipe) = false
+
 function Base.unsafe_read(pipe::Base64DecodePipe, ptr::Ptr{UInt8}, n::UInt)
     p = read_until_end(pipe, ptr, n)
     if p < ptr + n

stdlib/Base64/src/encode.jl

@@ -44,6 +44,9 @@ struct Base64EncodePipe <: IO
     end
 end
 
+Base.isreadable(::Base64EncodePipe) = false
+Base.iswritable(pipe::Base64EncodePipe) = iswritable(pipe.io)
+
 function Base.unsafe_write(pipe::Base64EncodePipe, ptr::Ptr{UInt8}, n::UInt)::Int
     buffer = pipe.buffer
     m = buffer.size

stdlib/Base64/test/runtests.jl

@@ -38,17 +38,31 @@ const longDecodedText = "name = \"Genie\"\nuuid = \"c43c736e-a2d1-11e8-161f-af95
     # Byte-by-byte encode and decode.
     buf = IOBuffer()
     pipe = Base64EncodePipe(buf)
+    @test !isreadable(pipe) && iswritable(pipe)
     for char in inputText
         write(pipe, UInt8(char))
     end
     close(pipe)
     pipe = Base64DecodePipe(IOBuffer(take!(buf)))
+    @test isreadable(ipipe) && !iswritable(ipipe)
     decoded = UInt8[]
     while !eof(pipe)
         push!(decoded, read(pipe, UInt8))
     end
     @test String(decoded) == inputText
 
+    buf = IOBuffer(write=false)
+    pipe = Base64EncodePipe(buf)
+    @test !isreadable(pipe) && !iswritable(pipe)
+    @test_throws ArgumentError write(pipe, "Hello!")
+    close(pipe)
+    buf = IOBuffer(read=false)
+    write(buf, "SGVsbG8h")
+    pipe = Base64DecodePipe(buf)
+    @test !isreadable(pipe) && !iswritable(pipe)
+    @test isempty(read(pipe))
+
+
     # Encode to string and decode
     @test String(base64decode(base64encode(inputText))) == inputText