Mastering Curl and HTTR in R: A Step-by-Step Guide for File Uploads and Authentication

Understanding the Basics of Curl and HTTR in R

As a technical blogger, it’s essential to understand the basics of curl and httr in R before diving into more advanced topics. In this article, we’ll cover the fundamental concepts of these two packages and provide detailed examples to help you write effective code.

What is Curl?

Curl (short for “curl URL”) is a command-line tool used to transfer data with URLs. It can be used to send HTTP requests, upload files, and more. In R, we use the curl package to perform similar tasks.

The main functions in the curl package are:

curl_url: Sends an HTTP request
upload_file: Uploads a file

What is HTTR?

HTTR (short for “Hyper-Text Transfer Protocol”) is another popular package in R used for sending HTTP requests. It provides a more extensive set of features compared to curl, including support for JSON data and automatic headers.

The main functions in the httr package are:

POST: Sends an HTTP POST request
upload_file: Uploads a file
add_headers: Adds custom headers to the request

Authenticating with Basic Authentication in R

When sending requests, we often need to authenticate using basic authentication. This involves providing a username and password in the request header.

Here’s an example of how to authenticate using basic authentication:

# Install and load necessary libraries
install.packages("httr")
library(httr)

# Define the URL and credentials
url <- "http://example.com"
username <- "abc"
password <- "xyz"

# Authenticate with basic authentication
auth <- authenticate(user = username, password = password, type = "basic")

# Print the authenticated object
print(auth)

Uploading Files with Curl and HTTR

Uploading files can be achieved using both curl and httr. Here’s an example of how to use curl:

# Install and load necessary libraries
install.packages("curl")
library(curl)

# Define the URL, file path, and credentials
url <- "http://example.com/upload"
filepath <- "/path/to/your/file.txt"

# Authenticate with basic authentication
auth <- authenticate(user = username, password = password, type = "basic")

# Upload the file using curl
options(readbin = TRUE)
post_file <- post_file(url, auth, upload.file = filepath)

# Print the uploaded object
print(post_file)

And here’s an example of how to use httr:

# Install and load necessary libraries
install.packages("httr")
library(httr)

# Define the URL, file path, and credentials
url <- "http://example.com/upload"
filepath <- "/path/to/your/file.txt"

# Authenticate with basic authentication
auth <- authenticate(user = username, password = password, type = "basic")

# Upload the file using httr
post_file <- POST(url) %>%
  add_headers("Content-Type" = "multipart/form-data") %>%
  upload_file(filepath)

# Print the uploaded object
print(post_file)

Writing Curl POST in R: Uploading an Image to a Website

In your question, you provided a successful curl command that uploads an image file named plot.png:

curl --location --request POST 'http://xxxxx?laboratoryResultVisibleId=LR-116807&amp;assayAttribute=Trace&amp;onBehalfOf=minnie' \
--header 'Authorization: Basic U1JWR0JMLUdEQklPTDpQZjgyNTE5Mw==' \
--form 'imageFile=@/C:/Users/minnie/Downloads/plot.png'

Here’s how you can replicate this using R and httr:

# Install and load necessary libraries
install.packages("httr")
library(httr)

# Define the URL, credentials, and file path
url <- "http://xxxxx"
username <- "minnie"
password <- "abc"
filepath <- "/C:/Users/minnie/Downloads/plot.png"

# Authenticate with basic authentication
auth <- authenticate(user = username, password = password, type = "basic")

# Upload the image using httr
post_file <- POST(
  url = url,
  auth = auth,
  body = list(
    laboratoryResultVisibleId = 'LR-116807',
    assayAttribute = 'Trace',
    file = upload_file(filepath), 
    userid = username
  ),
  add_headers("Content-Type" = "multipart/form-data")
)

# Print the uploaded object
print(post_file)

Troubleshooting: No File Found

The issue you encountered is likely due to the fact that the file argument in the POST request was not correctly specified. When using httr, we need to explicitly specify the file type and name.

To fix this, make sure to use the correct file path and type:

post_file <- POST(
  url = url,
  auth = auth,
  body = list(
    laboratoryResultVisibleId = 'LR-116807',
    assayAttribute = 'Trace',
    file = httr::upload_file(filepath, filename = "plot.png", content_type = "image/png")
  ),
  add_headers("Content-Type" = "multipart/form-data")
)

Conclusion

Uploading files to a website using curl and httr in R can be achieved by following the steps outlined above. Make sure to authenticate with basic authentication, specify the correct file path and type, and use the correct request headers.

By understanding the basics of curl and httr, you’ll be able to tackle more complex tasks, such as sending JSON data and handling errors. Remember to always check the documentation for each library to ensure you’re using the most up-to-date features and best practices.

Last modified on 2023-12-03