Publish a Data Stream via a Web Service

Uses the package plumber to publish a data stream as a web service.

Usage

publish_DSD_via_WebService(
  dsd,
  port,
  task_file = NULL,
  serializer = "csv",
  serve = TRUE,
  background = TRUE,
  debug = FALSE
)

Arguments

dsd

A character string that creates a DSD.

port

port used to serve the DSD.

task_file

name of the plumber task script file.

serializer

method used to serialize the data. By default, csv (comma-separated values) is used. Other methods are json and rds (see plumber::serializer_csv).

serve

if TRUE, then a task file is written and a server started, otherwise, only a plumber task file is written.

background

logical; start a background process?

debug

if TRUE, then the service is started locally and a web client is started to explore the interface.

Value

a processx::process object created with callr::r_bg() which runs the plumber server in the background. The process can be stopped with rp$kill() or by killing the process using the operating system with the appropriate PID. rp$get_result() can be used to check for errors in the server process (e.g., when it terminates unexpectedly).

Details

The function writes a plumber task script file and starts the web server to serve the content of the stream using the endpoints

• http://localhost:port/get_points?n=100 and

• http://localhost:port/info.

APIs generated using plumber can be easily deployed. See: Hosting. By setting a task_file and serve = FALSE a plumber task script file is generated for deployment.

A convenient reader for stream data over web services is available as DSD_ReadWebService.

See also

Other WebService: DSC_WebService(), DSD_ReadWebService(), publish_DSC_via_WebService()

Other dsd: DSD_ReadSocket(), DSD_ReadWebService(), publish_DSD_via_Socket()

Examples

if (has_localhost_server(port = 8000)) {
  # find a free port
  port <- httpuv::randomPort()
  port

  # create a background DSD process sending data to the port
  rp1 <- publish_DSD_via_WebService("DSD_Gaussians(k = 3, d = 3)", port = port)
  rp1

  # connect to the port and read manually. See DSD_ReadWebService for
  # a more convenient way to connect to the WebService in R.
  library("httr")

  # we use RETRY to give the server time to spin up
  resp <- RETRY("GET", paste0("http://localhost:", port, "/info"))
  d <- content(resp, show_col_types = FALSE)
  d

  # example: Get 100 points and plot them
  resp <- GET(paste0("http://localhost:", port, "/get_points?n=100"))
  d <- content(resp, show_col_types = FALSE)
  head(d)

  dsd <- DSD_Memory(d)
  dsd
  plot(dsd, n = -1)

  # end the DSD process. Note: that closing the connection above
  # may already kill the process.
  rp1$kill()
  rp1

  # Publish using json

  rp2 <- publish_DSD_via_WebService("DSD_Gaussians(k = 3, d = 3)",
             port = port, serializer = "json")
  rp2

  # connect to the port and read
  # we use RETRY to give the server time to spin up
  resp <- RETRY("GET", paste0("http://localhost:", port, "/info"))
  content(resp, as = "text")

  resp <- GET(paste0("http://localhost:", port, "/get_points?n=5"))
  content(resp, as = "text")

  # cleanup
  rp2$kill()
  rp2

  # Debug the interface (run the service and start a web interface)
  if (interactive())
    publish_DSD_via_WebService("DSD_Gaussians(k = 3, d = 3)", port = port,
           debug = TRUE)
} else {
  message("localhost not available, example skipped.")
}

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