import os
import SimpleHTTPServer
from SimpleHTTPServer import SimpleHTTPRequestHandler

class RangeHTTPRequestHandler(SimpleHTTPRequestHandler):
    """RangeHTTPRequestHandler is a SimpleHTTPRequestHandler
    with HTTP 'Range' support"""

    def send_head(self):
        """Common code for GET and HEAD commands.
        Return value is either a file object or None
        """

        path = self.translate_path(self.path)
        ctype = self.guess_type(path)

        # Handling file location
        ## If directory, let SimpleHTTPRequestHandler handle the request
        if os.path.isdir(path):
            return SimpleHTTPRequestHandler.send_head(self)

        ## Handle file not found
        if not os.path.exists(path):
            return self.send_error(404, self.responses.get(404)[0])

        ## Handle file request
        f = open(path, 'rb')
        fs = os.fstat(f.fileno())
        size = fs[6]

        # Parse range header
        # Range headers look like 'bytes=500-1000'
        start, end = 0, size-1
        if 'Range' in self.headers:
            start, end = self.headers.get('Range').strip().strip('bytes=').split('-')
        if start == "":
            ## If no start, then the request is for last N bytes
            ## e.g. bytes=-500
            try:
                end = int(end)
            except ValueError as e:
                self.send_error(400, 'invalid range')
            start = size-end
        else:
            try:
                start = int(start)
            except ValueError as e:
                self.send_error(400, 'invalid range')
            if start >= size:
                # If requested start is greater than filesize
                self.send_error(416, self.responses.get(416)[0])
            if end == "":
                ## If only start is provided then serve till end
                end = size-1
            else:
                try:
                    end = int(end)
                except ValueError as e:
                    self.send_error(400, 'invalid range')

        ## Correct the values of start and end
        start = max(start, 0)
        end = min(end, size-1)
        self.range = (start, end)
        ## Setup headers and response
        l = end-start+1
        if 'Range' in self.headers:
            self.send_response(206)
        else:
            self.send_response(200)
        self.send_header('Content-type', ctype)
        self.send_header('Accept-Ranges', 'bytes')
        self.send_header('Content-Range',
                         'bytes %s-%s/%s' % (start, end, size))
        self.send_header('Content-Length', str(l))
        self.send_header('Last-Modified', self.date_time_string(fs.st_mtime))
        self.end_headers()

        return f

    def copyfile(self, infile, outfile):
        """Copies data between two file objects
        If the current request is a 'Range' request then only the requested
        bytes are copied.
        Otherwise, the entire file is copied using SimpleHTTPServer.copyfile
        """
        if not 'Range' in self.headers:
            SimpleHTTPRequestHandler.copyfile(self, infile, outfile)
            return

        start, end = self.range
        infile.seek(start)
        bufsize=64*1024 ## 64KB
        while True:
            buf = infile.read(bufsize)
            if not buf:
                break
            outfile.write(buf)

if __name__ == '__main__':
    SimpleHTTPServer.test(HandlerClass=RangeHTTPRequestHandler)