diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c6895a2a6..71a84d5c7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -44,6 +44,9 @@ jobs:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
       - uses: julia-actions/cache@v2
+      - name: Use Reseau Windows IOCP experiment
+        if: matrix.os == 'windows-latest'
+        run: julia --project=. --startup-file=no --history-file=no -e 'ENV["JULIA_PKG_PRECOMPILE_AUTO"]="0"; using Pkg; Pkg.add(PackageSpec(name="Reseau", url="https://github.com/JuliaServices/Reseau.jl", rev="d5350e16e770515c58cc21f317424584c2336e35")); Pkg.instantiate()'
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1
diff --git a/src/http_transport.jl b/src/http_transport.jl
index dd65039fd..26d58d1fb 100644
--- a/src/http_transport.jl
+++ b/src/http_transport.jl
@@ -1663,6 +1663,7 @@ function _roundtrip_incoming!(
                     )
                 catch err
                     writer_err[] = err isa Exception ? err : ProtocolError("request upload failed")
+                    _request_write_head_written(write_state) && return nothing
                     _request_write_allows_close(write_state) || return nothing
                     @try_ignore begin
                         _close_conn!(conn)
@@ -1686,7 +1687,9 @@ function _roundtrip_incoming!(
             if _request_write_done(write_state)
                 wait(writer_task::Task)
                 err = writer_err[]
-                err === nothing || throw(err::Exception)
+                if err !== nothing && !_request_write_head_written(write_state)
+                    throw(err::Exception)
+                end
             end
         else
             try
@@ -1713,6 +1716,10 @@ function _roundtrip_incoming!(
         end
         _set_conn_read_deadline!(conn, request_deadline)
         early_final = false
+        upload_err = has_request_body ? writer_err[] : nothing
+        if upload_err !== nothing && _request_upload_abort_error(upload_err::Exception)
+            early_final = true
+        end
         if _request_write_should_wait_for_continue(write_state) && _request_write_continue_state(write_state::_RequestWriteState) == _REQUEST_WRITE_CONTINUE_PENDING
             _request_write_mark_continue_suppressed!(write_state::_RequestWriteState)
             early_final = true
diff --git a/src/http_websockets.jl b/src/http_websockets.jl
index 1adeceef3..944dc87cc 100644
--- a/src/http_websockets.jl
+++ b/src/http_websockets.jl
@@ -11,7 +11,7 @@ with [`WebSocket`](@ref) values directly rather than the lower-level
 """
 module WebSockets
 
-import Base: close, iterate
+import Base: close, iterate, isready
 
 import ..Headers
 import ..HTTPError
@@ -516,6 +516,19 @@ function receive(ws::WebSocket)
     return take!(ws.readchannel)
 end
 
+"""
+    isready(ws) -> Bool
+
+Return `true` when at least one complete message is buffered and can be read with
+[`receive`](@ref) without blocking, and `false` otherwise. Useful for polling a
+WebSocket for incoming messages without committing to a blocking `receive`.
+
+A `false` result does not imply the connection is closed — more messages may
+still arrive. Conversely, messages buffered before the connection closed remain
+`isready` and are returned by `receive` before it throws.
+"""
+isready(ws::WebSocket)::Bool = isready(ws.readchannel)
+
 function Base.iterate(ws::WebSocket, st=nothing)
     # Note: do not early-return on isclosed(ws) here: messages may still be
     # buffered in ws.readchannel after the read task has set readclosed=true
diff --git a/test/http_client_tests.jl b/test/http_client_tests.jl
index b3b9b4d29..94040611c 100644
--- a/test/http_client_tests.jl
+++ b/test/http_client_tests.jl
@@ -339,6 +339,7 @@ end
             req1 = HT.read_request(HT._ConnReader(conn1))
             push!(seen_methods, req1.method)
             push!(seen_targets, req1.target)
+            _ = _read_all_body_bytes_client(req1.body)
             headers1 = HT.Headers()
             HT.setheader(headers1, "Location", "/final")
             HT.setheader(headers1, "Connection", "close")
diff --git a/test/http_parity_tests.jl b/test/http_parity_tests.jl
index 20c1c1706..b693dd90a 100644
--- a/test/http_parity_tests.jl
+++ b/test/http_parity_tests.jl
@@ -24,6 +24,14 @@ function _wait_task_parity!(task::Task; timeout_s::Float64 = 5.0)
     return nothing
 end
 
+function _write_response_parity!(conn::NC.Conn, response::HT.Response)
+    io = IOBuffer()
+    HT.write_response!(io, response)
+    write(conn, take!(io))
+    HTTP.@try_ignore closewrite(conn)
+    return nothing
+end
+
 @testset "HTTP parity framing guards" begin
     raw_204 = "HTTP/1.1 204 No Content\r\nContent-Length: 10\r\n\r\nignored"
     response_204 = HT._read_response(IOBuffer(codeunits(raw_204)))
@@ -58,15 +66,13 @@ end
         conn1 = NC.accept(listener)
         try
             req1 = HT.read_request(HT._ConnReader(conn1))
+            _ = _read_all_parity(req1.body)
             push!(seen_methods, req1.method)
             headers = HT.Headers()
             HT.setheader(headers, "Location", "/next")
             HT.setheader(headers, "Connection", "close")
             resp1 = HT.Response(307, HT.EmptyBody(); reason = "Temporary Redirect", headers = headers, content_length = 0, close = true, request = req1)
-            io1 = IOBuffer()
-            HT.write_response!(io1, resp1)
-            bytes1 = take!(io1)
-            write(conn1, bytes1)
+            _write_response_parity!(conn1, resp1)
         finally
             HTTP.@try_ignore NC.close(conn1)
         end
@@ -75,10 +81,7 @@ end
             req2 = HT.read_request(HT._ConnReader(conn2))
             push!(seen_methods, req2.method)
             resp2 = HT.Response(200, HT.BytesBody(UInt8[0x6f, 0x6b]); content_length = 2, request = req2)
-            io2 = IOBuffer()
-            HT.write_response!(io2, resp2)
-            bytes2 = take!(io2)
-            write(conn2, bytes2)
+            _write_response_parity!(conn2, resp2)
         finally
             HTTP.@try_ignore NC.close(conn2)
         end
@@ -111,9 +114,7 @@ end
             HT.setheader(headers, "Location", "/next")
             HT.setheader(headers, "Connection", "close")
             resp = HT.Response(307, HT.BytesBody(UInt8[0x72]); reason = "Temporary Redirect", headers = headers, content_length = 1, close = true, request = req)
-            io = IOBuffer()
-            HT.write_response!(io, resp)
-            write(conn, take!(io))
+            _write_response_parity!(conn, resp)
         finally
             HTTP.@try_ignore NC.close(conn)
         end
@@ -177,9 +178,7 @@ end
             HT.setheader(headers, "Location", "/next")
             HT.setheader(headers, "Connection", "close")
             resp1 = HT.Response(307, HT.EmptyBody(); reason = "Temporary Redirect", headers = headers, content_length = 0, close = true, request = req1)
-            io1 = IOBuffer()
-            HT.write_response!(io1, resp1)
-            write(conn1, take!(io1))
+            _write_response_parity!(conn1, resp1)
         finally
             HTTP.@try_ignore NC.close(conn1)
         end
@@ -189,9 +188,7 @@ end
             push!(seen_bodies, String(_read_all_parity(req2.body)))
             push!(seen_content_types, HT.header(req2.headers, "Content-Type"))
             resp2 = HT.Response(200, HT.BytesBody(UInt8[0x6f, 0x6b]); content_length = 2, request = req2)
-            io2 = IOBuffer()
-            HT.write_response!(io2, resp2)
-            write(conn2, take!(io2))
+            _write_response_parity!(conn2, resp2)
         finally
             HTTP.@try_ignore NC.close(conn2)
         end
@@ -222,9 +219,7 @@ end
             HT.setheader(headers, "Location", "/next")
             HT.setheader(headers, "Connection", "close")
             resp = HT.Response(307, HT.BytesBody(UInt8[0x72]); reason = "Temporary Redirect", headers = headers, content_length = 1, close = true, request = req)
-            io = IOBuffer()
-            HT.write_response!(io, resp)
-            write(conn, take!(io))
+            _write_response_parity!(conn, resp)
         finally
             HTTP.@try_ignore NC.close(conn)
         end
diff --git a/test/http_websocket_integration_tests.jl b/test/http_websocket_integration_tests.jl
index a895bd032..d85323ba0 100644
--- a/test/http_websocket_integration_tests.jl
+++ b/test/http_websocket_integration_tests.jl
@@ -213,3 +213,23 @@ end
     stream = HT.Stream(bad)
     @test_throws W.WebSocketError W.upgrade(ws -> nothing, stream)
 end
+
+@testset "HTTP.WebSockets.isready reports buffered messages" begin
+    server = W.listen!("127.0.0.1", 0) do ws
+        msg = W.receive(ws)
+        W.send(ws, msg)
+    end
+    try
+        address = W.server_addr(server)
+        W.open("ws://$address/isready") do ws
+            @test !isready(ws)                                    # nothing buffered yet
+            W.send(ws, "ping")
+            @test timedwait(() -> isready(ws), 5.0) != :timed_out # echo arrives in the channel
+            @test isready(ws)                                     # a message is ready; receive won't block
+            @test W.receive(ws) == "ping"
+            @test !isready(ws)                                    # drained
+        end
+    finally
+        close(server)
+    end
+end