usr: httpd - the Game Boy serves its filesystem over HTTP

    /# httpd &
    host$ curl http://10.0.0.2/        -> a listing of the cart RAM
    host$ curl http://10.0.0.2/readme  -> the file, from battery-backed SRAM

GET only. "/" serves /index.html if present, else a generated listing; any
directory lists with every entry linked, so you can click around a 1997
handheld's disk from a browser. Content type from the extension. No
Content-Length: HTTP/1.0 + Connection: close delimits the body by closing,
which suits a stack with one in-flight segment.

All output goes through one 200-byte buffer, so each net_send is a full
segment instead of one tiny segment per string.

It drains the whole request, not just the request line. That is not
politeness: leaving the rest unread means those segments are never
acknowledged, so the client retransmits headers for a minute, never sends
its FIN, and its dead connection keeps arriving at port 80 long after we
re-listen. One curl with 1.4 KB of headers stalled every following request
for 30-120s.

It deliberately does NOT read the keyboard either. Backgrounded - the useful
way to run it - every key it polled would be a key stolen from the shell's
prompt. It is a daemon: kill(1) stops it, and the kernel reclaims its socket.

Verified with curl: index, byte-exact file bodies, nested paths, directory
listings, 404, 501, a 1.4 KB request spanning segments, browser user-agents,
three parallel clients (0.1/1.1/2.1s), the shell staying usable alongside it,
and six kill/restart cycles - more than there are sockets.

1 files changed, 9 insertions, 1 deletions

diff --git a/README.md b/README.md
index 95bc362..920ed1f 100644
--- a/README.md
+++ b/README.md
@@ -26,6 +26,10 @@ into the on-screen console. Regenerate it anytime with `tools/gbdemo` (below).*
   `nc` (netcat: `nc HOST PORT` interactively, or `nc -s HOST PORT < file` to
   pipe a request in and print the reply), `chat`, and a colorized **IRC
   client** (`irc HOST [NICK]`, `/join` and friends, SELECT for the keyboard).
+- **It serves, too**: the kernel does passive opens (`listen`/`accept`), and
+  `httpd` puts the cart's filesystem on the web — `httpd &`, then point a
+  browser at the Game Boy: files are served from battery-backed RAM and
+  directories come back as clickable listings.
 - **A network to plug into**: `tools/gbhub` is a virtual switch + DHCP server +
   NAT gateway — spawn a fleet of Game Boys that ping *each other* and reach
   the real internet; `tools/gbjoin` attaches an interactive GB to it, and
@@ -33,7 +37,7 @@ into the on-screen console. Regenerate it anytime with `tools/gbdemo` (below).*
 - **40×18 color terminal** on the LCD (4×8 font, two chars per tile, ANSI-ish
   colors) + an **on-screen keyboard** on the window layer (SELECT toggles it).
 - **Persistent filesystem** on battery-backed cart RAM: inodes, nested
-  directories, per-process cwd — survives power-off.
+  directories, per-process cwd — survives power-off (files up to 3 KiB).
 - **A C toolchain**: userland is plain C compiled with SDCC (`sm83`); ~35
   tools ship in `usr/` (`cat`, `wc`, `head`, `grep`, `cp`, `more`, `ls`,
   `uptime`, …). Adding a program is one `.c` file + a table entry.
@@ -51,6 +55,10 @@ make                                   # -> gbos.gb  (needs RGBDS + SDCC)
 sudo tools/gbhub --daemon              # virtual net + DHCP + NAT (needs root)
 tools/gbjoin                           # a windowed GB joins 10.0.0.0/24
 tools/gbtype 'ping 10.0.0.3'           # or type into it from the host
+
+# serve the Game Boy's filesystem to your browser:
+tools/gbtype 'httpd &'                 # then open http://10.0.0.2/
+curl http://10.0.0.2/readme            # files straight out of cart RAM
 ```
 
 On the Game Boy: **SELECT** toggles the on-screen keyboard, d-pad + **A**