Fix WebSocket concurrents send

src/WebSockets.jl

@@ -182,22 +182,24 @@ end
 
 # writing a single frame
 function writeframe(io::IO, x::Frame)
-    n = write(io.io, hton(uint16(x.flags)))
+    buff = IOBuffer()
+    n = write(buff, hton(uint16(x.flags)))
     if x.extendedlen !== nothing
-        n += write(io.io, hton(x.extendedlen))
+        n += write(buff, hton(x.extendedlen))
     end
     if x.mask != EMPTY_MASK
-        n += write(io.io, UInt32(x.mask))
+        n += write(buff, UInt32(x.mask))
     end
     pl = x.payload
     # manually unroll a few known type cases to help the compiler
     if pl isa Vector{UInt8}
-        n += write(io.io, pl)
-    elseif pl isa Base.CodeUnits{UInt8, String}
-        n += write(io.io, pl)
+        n += write(buff, pl)
+    elseif pl isa Base.CodeUnits{UInt8,String}
+        n += write(buff, pl)
     else
-        n += write(io.io, pl)
+        n += write(buff, pl)
     end
+    write(io.io, take!(buff))
     return n
 end
 

test/runtests.jl

@@ -31,6 +31,7 @@ isok(r) = r.status == 200
         "mwe.jl",
         "httpversion.jl",
         "websockets/autobahn.jl",
+        "websockets/multiple_writers.jl",
     ]
     # ARGS can be most easily passed like this:
     # import Pkg; Pkg.test("HTTP"; test_args=`ascii.jl parser.jl`)

test/websockets/multiple_writers.jl

@@ -0,0 +1,43 @@
+using Test
+using HTTP.WebSockets
+
+function write_message(ws, msg)
+    send(ws, msg)
+end
+
+function client_twin(ws)
+    for count in 1:10
+        @async write_message(ws, count)
+    end
+end
+
+function serve(ch)
+    WebSockets.listen!("127.0.0.1", 8081) do ws
+        client_twin(ws)
+        response = receive(ws)
+        put!(ch, response)
+    end
+end
+
+ch = Channel(1)
+srvtask = @async serve(ch)
+
+WebSockets.open("ws://127.0.0.1:8081") do ws
+    try
+        while true
+            s = receive(ws)
+            if s == "10"
+                send(ws, "ok")
+            end
+        end
+    catch e
+        if e.message.status !== 1000
+            @error "Ws client: $e"
+            !ws.writeclosed && send(ws, "error")
+        end
+    end
+end;
+
+@testset "WebSocket multiple writes" begin
+    @test take!(ch) == "ok"
+end