R: Create an HTTP/WebSocket server

startServer {httpuv} | R Documentation

## Create an HTTP/WebSocket server

### Description

Creates an HTTP/WebSocket server on the specified host and port.

### Usage

    startServer(host, port, app, quiet = FALSE)

    startPipeServer(name, mask, app, quiet = FALSE)

### Arguments

`host` | A string that is a valid IPv4 address that is owned by this server, or `"0.0.0.0"` to listen on all IP addresses.
`port` | A number or integer that indicates the server port that should be listened on. Note that on most Unix-like systems including Linux and Mac OS X, port numbers smaller than 1025 require root privileges.
`app` | A collection of functions that define your application. See Details.
`quiet` | If `TRUE`, suppress error messages from starting app.
`name` | A string that indicates the path for the domain socket (on Unix-like systems) or the name of the named pipe (on Windows).
`mask` | If non-`NULL` and non-negative, this numeric value is used to temporarily modify the process's umask while the domain socket is being created. To ensure that only root can access the domain socket, use `strtoi("777", 8)`; or to allow owner and group read/write access, use `strtoi("117", 8)`. If the value is `NULL` then the process's umask is left unchanged. (This parameter has no effect on Windows.)

### Details

`startServer` binds the specified port and listens for connections on an thread running in the background. This background thread handles the I/O, and when it receives a HTTP request, it will schedule a call to the user-defined R functions in `app` to handle the request. This scheduling is done with `later()`. When the R call stack is empty – in other words, when an interactive R session is sitting idle at the command prompt – R will automatically run the scheduled calls. However, if the call stack is not empty – if R is evaluating other R code – then the callbacks will not execute until either the call stack is empty, or the `run_now()` function is called. This function tells R to execute any callbacks that have been scheduled by `later()`. The `service()` function is essentially a wrapper for `run_now()`.

In older versions of httpuv (1.3.5 and below), it did not use a background thread for I/O, and when this function was called, it did not accept connections immediately. It was necessary to call `service` repeatedly in order to actually accept and handle connections.

If the port cannot be bound (most likely due to permissions or because it is already bound), an error is raised.

The application can also specify paths on the filesystem which will be served from the background thread, without invoking `$call()` or `$onHeaders()`. Files served this way will be only use a C++ code, which is faster than going through R, and will not be blocked when R code is executing. This can greatly improve performance when serving static assets.

The `app` parameter is where your application logic will be provided to the server. This can be a list, environment, or reference class that contains the following methods and fields:

`call(req)`

  Process the given HTTP request, and return an HTTP response. This method should be implemented in accordance with the Rook specification.

Note that httpuv augments `req` with an additional item, `req$HEADERS`, which is a named character vector of request headers.

`onHeaders(req)`

  Optional. Similar to `call`, but occurs when headers are received. Return `NULL` to continue normal processing of the request, or a Rook response to send that response, stop processing the request, and ask the client to close the connection. (This can be used to implement upload size limits, for example.)

`onWSOpen(ws)`

  Called back when a WebSocket connection is established. The given object can be used to be notified when a message is received from the client, to send messages to the client, etc. See `WebSocket`.

`staticPaths`

  A named list of paths that will be served without invoking `call()` or `onHeaders`. The name of each one is the URL path, and the value is either a string referring to a local path, or an object created by the `staticPath` function.

`staticPathOptions`

  A set of default options to use when serving static paths. If not set or `NULL`, then it will use the result from calling `staticPathOptions()` with no arguments.

The `startPipeServer` variant can be used instead of `startServer` to listen on a Unix domain socket or named pipe rather than a TCP socket (this is not common).

### Value

A handle for this server that can be passed to `stopServer` to shut the server down.

A `WebServer` or `PipeServer` object.

### See Also

`stopServer`, `runServer`, `listServers`, `stopAllServers`.

### Examples

    ## Not run:
    # A very basic application
    s <- startServer("0.0.0.0", 5000,
      list(
        call = function(req) {
          list(
            status = 200L,
            headers = list(
              'Content-Type' = 'text/html'
            ),
            body = "Hello world!"
          )
        }
      )
    )

    s$stop()

    # An application that serves static assets at the URL paths /assets and /lib
    s <- startServer("0.0.0.0", 5000,
      list(
        call = function(req) {
          list(
            status = 200L,
            headers = list(
              'Content-Type' = 'text/html'
            ),
            body = "Hello world!"
          )
        },
        staticPaths = list(
          "/assets" = "content/assets/",
          "/lib" = staticPath(
            "content/lib",
            indexhtml = FALSE
          ),
          # This subdirectory of /lib should always be handled by the R code path
          "/lib/dynamic" = excludeStaticPath()
        ),
        staticPathOptions = staticPathOptions(
          indexhtml = TRUE
        )
      )
    )

    s$stop()

    ## End(Not run)

[Package httpuv version 1.5.4 Index]