Implementing Call Retries with httr::RETRY() Function in API Calls (R)

In recent years, the need to handle failed API calls has become increasingly important. This can happen due to various reasons such as network connectivity issues, server overload, or incorrect input parameters. One popular R package that helps in achieving this is httr. In this article, we will explore how to use httr::RETRY() function to implement call retries in API calls.

What is httr?

httr is a powerful and flexible HTTP client for R. It provides an easy-to-use interface for making HTTP requests and can be used to send GET, POST, PUT, and DELETE requests among other types of requests. One of the key features of httr is its ability to handle retries.

What is httr::RETRY()?

The RETRY() function in httr allows you to specify the number of attempts a request should be made before it times out. If the request fails, RETRY() will wait for the specified time and then make another attempt at making the request until it succeeds.

Implementing Call Retries with httr::RETRY() Function

In this section, we’ll explore how to use httr::RETRY() function in an API call. Let’s consider the example of a UN Comtrade data API.

library(httr)
library(jsonlite)

res <- RETRY(
  verb = "GET",
  url = "http://comtrade.un.org/",
  path = "api/get",
  encode = "json",
  times = 3,
  query = list(
    max = 50000,
    type = "C",
    freq = "A",
    px = "HS",
    ps = "now",
    r = 842,
    p = "124,484",
    rg = "all",
    cc = "TOTAL",
    fmt = "json"
  )
)

# alternativ: returns dataset as a `list`:
# parsed_content <- content(res, as = "parsed")    

# returns dataset as a `data.frame`:
json_content <- content(res, as = "text")
parsed_content <- parse_json(json_content, simplifyVector = TRUE)
parsed_content$validation
parsed_content$dataset

In this example, we are making a GET request to the UN Comtrade data API with certain query parameters. The RETRY() function is used to make three attempts at making the request before it times out.

Rewriting the get.Comtrade Function Using httr

The get.Comtrade function provided in the question is rewritten using httr as follows:

get.Comtrade <- function(verb = "GET",
                         url = "http://comtrade.un.org/",
                         path = "api/get",
                         encode = "json",
                         times = 3,
                         max = 50000,
                         type = "C",
                         freq = "A",
                         px = "HS",
                         ps = "now",
                         r,
                         p,
                         rg = "all",
                         cc = "TOTAL",
                         fmt = "json") {
  res <- httr::RETRY(
    verb = verb,
    url = url,
    path = path,
    encode = encode,
    times = times,
    query = list(
      max = max,
      type = type,
      freq = freq,
      px = px,
      ps = ps,
      r = r,
      p = p,
      rg = rg,
      cc = cc,
      fmt = fmt
    )
  )
  jsonlite::parse_json(content(res, as = "text"), simplifyVector = TRUE)
}

In this rewritten version of the get.Comtrade function, we are using httr::RETRY() to make attempts at making the request before it times out.

Example Usage

Let’s consider an example usage of the rewritten get.Comtrade function:

s1 <- get.Comtrade(r = "842", p = "124,484", times = 5)
print(s1)

In this example, we are making a GET request to the UN Comtrade data API with certain query parameters. The get.Comtrade function uses httr::RETRY() to make five attempts at making the request before it times out.

Conclusion

In this article, we explored how to use httr::RETRY() function to implement call retries in API calls using R. We also provided an example usage of the rewritten get.Comtrade function that uses httr. By using httr, developers can handle failed API calls and ensure that their applications remain stable and functional even in the presence of network connectivity issues or server overload.

References

[1] httr documentation, available at https://cran.r-project.org/package=httr
[2] jsonlite documentation, available at https://cran.r-project.org/package=jsonlite

Last modified on 2024-08-23