Tim Bray on the style chosen for writing the HTML5 and WebSockets standards

http://www.tbray.org/ongoing/When/201x/2010/02/15/HTML5

by bensummers • 16 years ago

39 7 16 years ago

axod• 16 years ago

>> So I went and read the Web Socket protocol and my reaction was more or less the opposite. I like the protocol and I gather it’s already been implemented and works. But I found the spec hard to read, amazingly long and complex for such an admirably simple protocol, and missing information that seemed important.

Completely agree. I found it very hard to get to the 'meat' of what the data format actually was. Look at the following.

Here's a sample from the spec:

   The server must run through the following steps to process the bytes
   sent by the client.  If at any point during these steps a read is
   attempted but fails because the Web Socket connection is closed, then
   abort.

   1.  _Frame_: Read a byte from the client.  Let /type/ be that byte.

   2.  If /type/ is not a 0x00 byte, then the server may disconnect from
       the client.

   3.  If the most significant bit of /type/ is not set, then run the
       following steps:

       1.  Let /raw data/ be an empty byte array.

       2.  _Data_: Read a byte, let /b/ be that byte.

       3.  If /b/ is not 0xFF, then append /b/ to /raw data/ and return
           to the previous step (labeled _data_).

       4.  Interpret /raw data/ as a UTF-8 string, and apply whatever
           server-specific processing is to occur for the resulting
           string (the message from the client).

       Otherwise, the most significant bit of /type/ is set.  Run the
       following steps.  This can never happen if /type/ is 0x00, and
       therefore these steps are not necessary if the server aborts when
       /type/ is not 0x00, as allowed above.

       5.   Let /length/ be zero.

       6.   _Length_: Read a byte, let /b/ be that byte.

       7.   Let /b_v/ be integer corresponding to the low 7 bits of /b/
            (the value you would get by _and_ing /b/ with 0x7F).

       8.   Multiply /length/ by 128, add /b_v/ to that result, and
            store the final result in /length/.

       9.   If the high-order bit of /b/ is set (i.e. if /b/ _and_ed
            with 0x80 returns 0x80), then return to the step above
            labeled _length_.

       10.  Read /length/ bytes.

       11.  Discard the read bytes.

   4.  Return to the step labeled _frame_.

I think you could better write this as:

  Data is either framed as a 0xff terminated UTF8 string
  (If the first byte of the frame has a 0 high bit), or as
  a length specified byte array if the first byte has a
  1 high bit. The length is specified using 7 bit variable
  length encoding, with the last byte having a 0 high bit.

  Example: 0x00 | 0x01 0x02 0x03 0x04 | 0xff
  UTF8 string (0x01,0x02,0x03,0x04)

  Example: 0x82 0x03 | 0x55 0xaa 0x55 ... 
  Data length = 0x103, data bytes follow.

pvg• 16 years ago

The style of the spec very elegantly combines the disadvantages of a declarative written description and pseudocode.

mhansen• 16 years ago

Goddamn do I hate specs that try and write code in English. Specifications are for WHAT I have to implement, not HOW.

For another offender, see ECMA-262, the Javascript specification.

mark_l_watson• 16 years ago

A good read, good points criticizing the spec. At first, I was dead set against HTML5 because I had been waiting for wide XHTML+RDFa adoption. That isn't going to happen now. Still, if HTML5 implementations are good and support web app portability between browsers, then I am happy enough with it. I also liked Bray's point on bring patent troll problems with video codecs more into the public view.

hypermatt• 16 years ago

Read Ian's response in the comments, its brilliant. I love when the author of the spec casually comments on some blog ;)

RyanMcGreal• 16 years ago

Also worth noting is Dorian Taylor's amusing troll.

doriantaylor• 16 years ago

I have more where that came from.

Tim Bray on the style chosen for writing the HTML5 and WebSockets standards

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