Flush buffer to avoid deleting data when seeking NoopStream

src/noop.jl

@@ -64,18 +64,30 @@ function Base.position(stream::NoopStream)
 end
 
 function Base.seek(stream::NoopStream, pos::Integer)
+    mode = stream.state.mode
+    if mode === :write
+        flushbuffer(stream)
+    end
     seek(stream.stream, pos)
     initbuffer!(stream.buffer1)
     return stream
 end
 
 function Base.seekstart(stream::NoopStream)
+    mode = stream.state.mode
+    if mode === :write
+        flushbuffer(stream)
+    end
     seekstart(stream.stream)
     initbuffer!(stream.buffer1)
     return stream
 end
 
 function Base.seekend(stream::NoopStream)
+    mode = stream.state.mode
+    if mode === :write
+        flushbuffer(stream)
+    end
     seekend(stream.stream)
     initbuffer!(stream.buffer1)
     return stream

test/codecnoop.jl

@@ -335,19 +335,29 @@
         end
     end
 
-    @testset "seekstart doesn't delete data" begin
+    @testset "seek doesn't delete data" begin
         sink = IOBuffer()
         stream = NoopStream(sink, bufsize=16)
         write(stream, "x")
-        # seekstart must not delete user data even if it errors.
-        try
-            seekstart(stream)
-        catch e
-            e isa ArgumentError || rethrow()
-        end
-        write(stream, TranscodingStreams.TOKEN_END)
+        seekstart(stream)
         flush(stream)
-        @test_broken take!(sink) == b"x"
+        @test take!(sink) == b"x"
         close(stream)
+
+        op_expected = [
+            (seekstart, b"dbc"),
+            (seekend, b"abcd"),
+            (Base.Fix2(seek, 1), b"adc"),
+        ]
+        @testset "$op" for (op, expected) in op_expected
+            sink = IOBuffer()
+            stream = NoopStream(sink, bufsize=16)
+            write(stream, "abc")
+            @test op(stream) === stream
+            write(stream, "d")
+            flush(stream)
+            @test take!(sink) == expected
+            close(stream)
+        end
     end
 end

test/codecquadruple.jl

@@ -124,15 +124,22 @@ end
     end
 
     @testset "seekstart doesn't delete data" begin
-        sink = IOBuffer()
-        stream = TranscodingStream(QuadrupleCodec(), sink, bufsize=16)
-        write(stream, "x")
-        # seekstart must not delete user data even if it errors.
-        @test_throws ArgumentError seekstart(stream)
-        write(stream, TranscodingStreams.TOKEN_END)
-        flush(stream)
-        @test take!(sink) == b"xxxx"
-        close(stream)
+        for n in 0:3
+            sink = IOBuffer()
+            # wrap stream in NoopStream n times.
+            stream = foldl(
+                (s,_) -> NoopStream(s),
+                1:n;
+                init=TranscodingStream(QuadrupleCodec(), sink, bufsize=16)
+            )
+            write(stream, "x")
+            # seekstart must not delete user data even if it errors.
+            @test_throws ArgumentError seekstart(stream)
+            write(stream, TranscodingStreams.TOKEN_END)
+            flush(stream)
+            @test take!(sink) == b"xxxx"
+            close(stream)
+        end
     end
 
     @testset "eof is true after write" begin