Url Parsing in Fortran

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

Our program will demonstrate how to parse URLs in Fortran. URLs provide a uniform way to locate resources.

program url_parsing
    use iso_fortran_env, only: error_unit
    implicit none
    
    character(len=:), allocatable :: url
    character(len=:), allocatable :: scheme, user_info, host, path, query, fragment
    integer :: port, status
    
    ! We'll parse this example URL, which includes a scheme, authentication info,
    ! host, port, path, query params, and query fragment.
    url = "postgres://user:pass@host.com:5432/path?k=v#f"
    
    ! Parse the URL
    call parse_url(url, scheme, user_info, host, port, path, query, fragment, status)
    
    if (status /= 0) then
        write(error_unit,*) "Error parsing URL"
        stop
    end if
    
    ! Accessing the scheme is straightforward
    print *, "Scheme: ", scheme
    
    ! Print user info (authentication)
    print *, "User info: ", user_info
    
    ! Print host and port
    print *, "Host: ", host
    print *, "Port: ", port
    
    ! Print path and fragment
    print *, "Path: ", path
    print *, "Fragment: ", fragment
    
    ! Print query string
    print *, "Query: ", query
    
contains

    subroutine parse_url(url, scheme, user_info, host, port, path, query, fragment, status)
        character(len=*), intent(in) :: url
        character(len=:), allocatable, intent(out) :: scheme, user_info, host, path, query, fragment
        integer, intent(out) :: port, status
        
        integer :: i, j
        
        ! This is a simplified URL parser and doesn't handle all cases
        
        i = index(url, "://")
        if (i > 0) then
            scheme = url(:i-1)
            j = i + 3
        else
            status = 1
            return
        end if
        
        i = index(url(j:), "@")
        if (i > 0) then
            user_info = url(j:j+i-2)
            j = j + i
        else
            user_info = ""
        end if
        
        i = index(url(j:), ":")
        if (i > 0) then
            host = url(j:j+i-2)
            read(url(j+i:), *, iostat=status) port
            if (status /= 0) return
            j = index(url(j+i:), "/") + j + i - 1
        else
            i = index(url(j:), "/")
            if (i > 0) then
                host = url(j:j+i-2)
                j = j + i - 1
            else
                host = url(j:)
                path = ""
                query = ""
                fragment = ""
                port = 80  ! Default HTTP port
                status = 0
                return
            end if
        end if
        
        i = index(url(j:), "?")
        if (i > 0) then
            path = url(j:j+i-2)
            j = j + i
            i = index(url(j:), "#")
            if (i > 0) then
                query = url(j:j+i-2)
                fragment = url(j+i:)
            else
                query = url(j:)
                fragment = ""
            end if
        else
            i = index(url(j:), "#")
            if (i > 0) then
                path = url(j:j+i-2)
                fragment = url(j+i:)
                query = ""
            else
                path = url(j:)
                query = ""
                fragment = ""
            end if
        end if
        
        status = 0
    end subroutine parse_url
    
end program url_parsing

This Fortran program demonstrates URL parsing. Here’s what it does:

We define a URL string that includes various components like scheme, authentication info, host, port, path, query params, and fragment.
We call a custom parse_url subroutine to break down the URL into its components.
The program then prints out each component of the URL.
The parse_url subroutine is a simplified URL parser. It uses string manipulation functions like index to find specific characters and split the URL into its parts.
Error handling is implemented using a status variable. If there’s an error during parsing, the program will print an error message and stop.

To run this program:

Save the code in a file, for example, url_parsing.f90.
Compile the program using a Fortran compiler. For example, with gfortran:
```
$ gfortran url_parsing.f90 -o url_parsing
```
Run the compiled program:
```
$ ./url_parsing
```

The output will show the different components of the parsed URL.

Note that this is a basic implementation and may not handle all possible URL formats or edge cases. For production use, consider using a well-tested URL parsing library if available for Fortran.

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Url Parsing in Fortran