Introduction to downloading HTML in Fortran

In this tutorial, we will explore how to download HTML content in Fortran. Fortran is a powerful programming language commonly used in scientific and engineering applications. Although it does not have built-in functions for handling network requests, we can still achieve downloading HTML by utilizing external libraries and system calls.

Prerequisites

To follow along with this tutorial, you need:

1. Basic knowledge of Fortran programming language.
2. Fortran compiler installed on your system (e.g., GNU Fortran, Intel Fortran).
3. Access to external libraries for making network requests (e.g., cURL library).

Steps

Step 1: Setting up Dependencies

Before we begin, make sure you have the necessary libraries installed on your system. In this tutorial, we will use the cURL library as an example.

To install cURL library on Ubuntu, run the following command in your terminal:

$ sudo apt-get install libcurl4-openssl-dev

Step 2: Writing the Code

Let's write a Fortran program that downloads HTML content from a given URL. Here is an example program:

program download_html
    use iso_c_binding

    implicit none
    
    interface
        function curl_easy_init() bind(c, name="curl_easy_init")
            type(c_ptr) :: curl_easy_init
        end function

        subroutine curl_easy_cleanup(curl) bind(c, name="curl_easy_cleanup")
            type(c_ptr), value :: curl
        end subroutine

        function curl_easy_setopt(curl, option, value) bind(c, name="curl_easy_setopt")
            type(c_ptr), value :: curl
            integer(c_int), value :: option
            integer(c_int), value :: value
            integer(c_int) :: curl_easy_setopt
        end function

        function curl_easy_perform(curl) bind(c, name="curl_easy_perform")
            type(c_ptr), value :: curl
            integer(c_int) :: curl_easy_perform
        end function
    end interface

    type(c_ptr) :: curl_handle
    integer(c_int) :: result, option

    character(len=256) :: url = "https://example.com"
    character(len=1024) :: error_buffer
    character(len=1024) :: response_buffer

    ! Initialize cURL
    curl_handle = curl_easy_init()

    ! Set the URL to download
    option = 10002  ! CURLOPT_URL
    result = curl_easy_setopt(curl_handle, option, loc(url))

    ! Set an error buffer for libcurl to use
    option = 10000  ! CURLOPT_ERRORBUFFER
    result = curl_easy_setopt(curl_handle, option, loc(error_buffer))

    ! Set the response buffer for libcurl to use
    option = 10001  ! CURLOPT_WRITEFUNCTION
    result = curl_easy_setopt(curl_handle, option, loc(write_callback))
    option = 10013  ! CURLOPT_WRITEDATA
    result = curl_easy_setopt(curl_handle, option, loc(response_buffer))

    ! Perform the download
    result = curl_easy_perform(curl_handle)

    ! Cleanup cURL handle
    call curl_easy_cleanup(curl_handle)

contains

    function write_callback(ptr, size, nmemb, stream) bind(c, name="write_callback")
        type(c_ptr), value :: ptr
        integer(c_size_t), value :: size, nmemb
        type(c_ptr), value :: stream
        integer(c_size_t) :: write_callback

        character(len=1, kind=c_char), pointer :: buffer
        character(len=size*nmemb, kind=c_char), target :: response_buffer

        buffer = transfer(ptr, buffer)
        response_buffer = transfer(stream, response_buffer)

        response_buffer(:size*nmemb) = buffer

        write_callback = size*nmemb
    end function

end program download_html

Step 3: Compiling and Running the Program

To compile the Fortran program, use the Fortran compiler with necessary flags and linking options. For example, using gfortran:

$ gfortran -o download_html download_html.f90 -lcurl

After successful compilation, you can run the program:

$ ./download_html

The program will download the HTML content from the specified URL and store it in the response_buffer variable.

Conclusion

In this tutorial, we have learned how to download HTML content in Fortran using external libraries like cURL. By leveraging the power of these libraries, we can extend Fortran's capabilities to perform network requests and handle web data. Remember to adapt the code to suit your specific needs and explore other libraries or methods available for downloading HTML in Fortran.

Happy coding!