• Assignment 6 is due Wednesday night.
• Assignment 7, which requires that you build your very own HTTP proxy, goes out Wednesday and is due the Wednesday after we return from break.

• Introduce the struct hostent and the sockaddr hierarchy.
• Work through the implementations of two functions that we've been taking for granted since we dipped into the networking segment of the quarter: createServerSocket and createClientSocket.
• Work through one last networking example to illustrate a novel server-side architecture that's not at all far from how Facebook servers produce News Feeds, LinkedIn produces profiles, and Google produces search results.

• Assumes existence of standalone scrabble-word-finder.
• Code contributing to scrabble-word-finder, which has no idea it might contribute to a server, is right here.
  • Implemented using straightforward procedural recursion with pruning.
  • Hardly optimized to be fast—no caching, makes use of only the most obvious pruning strategies.

• Approach: allow URL to specify rack of letters.
• http://myth4.stanford.edu:13133/ieclxal should produce all words that can be formed from ieclxal.

{
  time: 0.223399,
  cached: false,
  possibilities: [
    'ace',
      // several words omitted
    'lex',
    'lexica',
    'lexical',
    'li',
    'lice',
    'lie',
    'lilac',
    'xi'
  ]
}

• Reimplementing is bad, and reinventing the wheel is wasteful and time consuming
• scrabble-word-finder, as an executable, already outputs the core of what we'd like to serve as plain text, as with:

myth4> ./scrabble-word-finder ieclxal
ace
lex
lexica
lexical
li
lice
lie
lilac
xi
myth4>

• Of course we can, else I wouldn't be asking.
• Leverage the implementation of subprocess from Assignment 3.

struct subprocess_t {
  pid_t pid;
  int supplyfd;
  int ingestfd;
};
subprocess_t subprocess(char *argv[], 
                        bool supplyChildInput, 
                        bool ingestChildOutput) throw (SubprocessException);

• Thread routine uses subprocess to marshal plain text output of scrabble-word-finder into JSON, and publishes that JSON as the payload of the HTTP response.
• Here's the core of the server-side computation:

static void publishScrabbleWords(int clientSocket) {
  sockbuf sb(clientSocket);
  iosockstream ss(&sb);
  string letters = getLetters(ss); // extracts tail of path from GET <path> <protocol>
  skipHeaders(ss); // skips everything else
  const char *command[] = {"./scrabble-word-finder", letters.c_str(), NULL};
  subprocess_t sp = subprocess(const_cast<char **>(command), false, true);
  vector<string> formableWords = pullFormableWords(sp.ingestfd);
  waitpid(sp.pid, NULL, 0);
  ostringstream payload;
  constructPayload(formableWords, payload); // posts JSON to payload
  sendResponse(ss, payload.str()); // publishes HTTP response to ss out of payload
}

• Helper functions, caching, and error checking are omitted from the above, but included as part of the full code base.