make stream types a subtype of TranscodingStream

Author: bicycle1885

src/compression.jl

@@ -25,7 +25,7 @@ function ZstdCompression(;level::Integer=DEFAULT_COMPRESSION_LEVEL)
     return ZstdCompression(CStream(), level)
 end
 
-const ZstdCompressionStream{S} = TranscodingStream{ZstdCompression,S}
+const ZstdCompressionStream{S} = TranscodingStream{ZstdCompression,S} where S<:IO
 
 """
     ZstdCompressionStream(stream::IO; kwargs...)

src/decompression.jl

@@ -14,7 +14,7 @@ function ZstdDecompression()
     return ZstdDecompression(DStream())
 end
 
-const ZstdDecompressionStream{S} = TranscodingStream{ZstdDecompression,S}
+const ZstdDecompressionStream{S} = TranscodingStream{ZstdDecompression,S} where S<:IO
 
 """
     ZstdDecompressionStream(stream::IO)

test/runtests.jl

@@ -7,6 +7,9 @@ import TranscodingStreams
     @test read(ZstdDecompressionStream(IOBuffer(data))) == b"foo"
     @test read(ZstdDecompressionStream(IOBuffer(vcat(data, data)))) == b"foofoo"
 
+    @test ZstdCompressionStream <: TranscodingStreams.TranscodingStream
+    @test ZstdDecompressionStream <: TranscodingStreams.TranscodingStream
+
     TranscodingStreams.test_roundtrip_read(ZstdCompressionStream, ZstdDecompressionStream)
     TranscodingStreams.test_roundtrip_write(ZstdCompressionStream, ZstdDecompressionStream)
     TranscodingStreams.test_roundtrip_lines(ZstdCompressionStream, ZstdDecompressionStream)