Url Parsing in Co-array Fortran

Here’s the translation of the URL parsing example from Go to Co-array Fortran:

program url_parsing
  use iso_fortran_env
  use iso_c_binding
  implicit none

  character(len=:), allocatable :: url_string
  character(len=:), allocatable :: scheme, user_info, host, path, query, fragment
  integer :: port
  
  ! We'll parse this example URL, which includes a
  ! scheme, authentication info, host, port, path,
  ! query params, and query fragment.
  url_string = "postgres://user:pass@host.com:5432/path?k=v#f"

  ! Parse the URL and ensure there are no errors.
  call parse_url(url_string, scheme, user_info, host, port, path, query, fragment)

  ! Accessing the scheme is straightforward.
  print *, "Scheme: ", scheme

  ! user_info contains all authentication info
  print *, "User Info: ", user_info
  
  ! The host contains both the hostname and the port
  print *, "Host: ", host
  print *, "Port: ", port

  ! Here we extract the path and the fragment after the #
  print *, "Path: ", path
  print *, "Fragment: ", fragment

  ! To get query params in a string of k=v format,
  ! we can use the query string directly
  print *, "Query: ", query

  ! Note: Parsing query params into a map is not straightforward in Fortran
  ! and would require additional custom implementation

contains

  subroutine parse_url(url, scheme, user_info, host, port, path, query, fragment)
    character(len=*), intent(in) :: url
    character(len=:), allocatable, intent(out) :: scheme, user_info, host, path, query, fragment
    integer, intent(out) :: port

    integer :: i, j, k

    ! Extract scheme
    i = index(url, "://")
    if (i > 0) then
      scheme = url(:i-1)
    else
      scheme = ""
    end if

    ! Extract user info and host
    j = index(url, "@")
    if (j > 0) then
      user_info = url(i+3:j-1)
      k = index(url(j+1:), ":")
      if (k > 0) then
        host = url(j+1:j+k-1)
        read(url(j+k+1:), *) port
      else
        host = url(j+1:)
        port = -1
      end if
    else
      user_info = ""
      k = index(url(i+3:), ":")
      if (k > 0) then
        host = url(i+3:i+k+1)
        read(url(i+k+4:), *) port
      else
        host = url(i+3:)
        port = -1
      end if
    end if

    ! Extract path, query, and fragment
    i = index(url, "/", back=.true.)
    j = index(url, "?")
    k = index(url, "#")

    if (i > 0) then
      path = url(i:)
    else
      path = ""
    end if

    if (j > 0) then
      if (k > 0) then
        query = url(j+1:k-1)
        fragment = url(k+1:)
      else
        query = url(j+1:)
        fragment = ""
      end if
    else
      if (k > 0) then
        query = ""
        fragment = url(k+1:)
      else
        query = ""
        fragment = ""
      end if
    end if

  end subroutine parse_url

end program url_parsing

This Co-array Fortran program demonstrates URL parsing, similar to the original Go example. Here’s an explanation of the key differences and adaptations:

Fortran doesn’t have built-in URL parsing libraries like Go does, so we’ve implemented a basic URL parsing subroutine.
The parse_url subroutine extracts different components of the URL (scheme, user info, host, port, path, query, and fragment) using string manipulation functions.
Fortran doesn’t have a native map data structure, so parsing query parameters into a map is not included. The query string is simply extracted as a whole.
Error handling in Fortran is different from Go. This example doesn’t include explicit error handling for simplicity, but in a real-world application, you’d want to add appropriate error checks.
The program structure in Fortran is different. We define the main program and then include the parse_url subroutine within the contains section.
Fortran uses different I/O statements. We use print * for output instead of fmt.Println.

This Fortran code provides similar functionality to the Go example, parsing a URL and extracting its components. However, due to language differences, some aspects (like query parameter parsing into a map) are simplified or omitted.

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Url Parsing in Co-array Fortran