fix cancelling upload requests

Cancelling an upload (PUT) request using the mechanism introduced in JuliaLang#256 was not effective. The upload task was not interrupted, which still blocked and the call to `request` did not return.
With this change, cancelling also closes the `input` stream of the request to unblock the upload task.

Also changed the `interrupted` variable to be an `Atomic{Bool}`. Ref discussion [here](JuliaLang#256 (comment)).

src/Downloads.jl

@@ -396,7 +396,7 @@ function request(
 
                 # do the request
                 add_handle(downloader.multi, easy)
-                interrupted = false
+                interrupted = Threads.Atomic{Bool}(false)
                 if interrupt !== nothing
                     interrupt_task = @async begin
                         # wait for the interrupt event
@@ -405,7 +405,8 @@ function request(
                         remove_handle(downloader.multi, easy)
                         close(easy.output)
                         close(easy.progress)
-                        interrupted = true
+                        interrupted[] = true
+                        close(input)
                     end
                 else
                     interrupt_task = nothing
@@ -425,7 +426,7 @@ function request(
                         end
                     end
                 finally
-                    if !interrupted
+                    if !(interrupted[])
                         if interrupt_task !== nothing
                             # trigger interrupt
                             notify(interrupt)

test/runtests.jl

@@ -478,6 +478,16 @@ include("setup.jl")
             timedwait(()->istaskdone(download_task), 5.0)
             @test istaskdone(download_task)
             @test download_task.result isa RequestError
+
+            url = "$server/put"
+            input=`sh -c 'sleep 15; echo "hello"'`
+            download_task = @async request(url; interrupt=interrupt, input=input)
+            sleep(0.1)
+            @test !istaskdone(download_task)
+            notify(interrupt)
+            timedwait(()->istaskdone(download_task), 5.0)
+            @test istaskdone(download_task)
+            @test download_task.result isa RequestError
         end
 
         @testset "progress" begin