Test code illustrating various troubleshooting and workarounds for https://github.com/racket/web-server
The code was tested with the following software versions:
- racket 8.0 CS
- curl 7.68.0
- timeout, from GNU coreutils 8.30
The programs in from-tcp/ demonstrate handling dropped (half-closed or half-open) TCP connections in racket. Limitations of racket's web-server requires these to be built from TCP.
| Name | Description |
|---|---|
| evtserve1.rkt | |
| evtserve1-handle-half-closed.rkt | Demonstrate handling tcp half-closed connections. |
| evtserve1-handle-half-closed-half-open.sh | Demonstrate handling half-closed and half-open connections (Linux only) |
| evtserve1-handle-half-closed-half-open.rkt | (driven by evtserve1-handle-half-closed-half-open.sh) |
Handling half-open TCP connections is implemented with the help of LD_PRELOAD and libkeepalive. On Ubuntu, install libkeepalive with:
sudo apt-get install libkeepalive0
The following examples in racket-web-server/ were created in the process of troubleshooting to rule out the possibility of using racket-web-server for our application. They demonstrate various behaviors, some sparsely documented elsewhere.
| Name | Description |
|---|---|
| serve1a.rkt | Show how server responds to a dropped TCP connection when serving a long response. |
| serve1b.rkt | Show how server responds to a dropped TCP connection when serving a slow (as opposed to long) response. |
| serve1c.rkt | Show how serve1b.rkt can be worked around by writing whitespace to the output channel in order to cause racket computation to actually get killed during a slow response. |
| serve4.rkt | An experiment to see if the serve/servelet #:servlet-responder parameter can improve error logging. |
| serve6.rkt | Builds upon serve1c.rkt workaround, allowing the dispatch path to be controlled. |
| serve6b.rkt | Builds upon serve6.rkt, logging both requests and responses as JSON, as best we can within the framework. |
| serve6c.rkt | Builds upon serve6b.rkt, adding use of the loosely coupled routine keepalive-and-timeout-via-thread. |
| serve7.rkt | Can the enable-break API somehow resurrect the ability to catch the dropped connection event? |
| serve8.rkt | The response logging mechanism of serve6b.rkt, ala carte. |
Each example shows in a comment at its end a way of exercising the example using curl and timeout.
A few other incomplete examples are provided in the directory incomplete/