net: wget - real HTTP over the link port via the gateway

Grow the link-port demo from echo to actual network access. The Game Boy
still only does SLIP framing + display; the host gateway does DNS/TCP/HTTP.

- c/netlib.h: SLIP framing factored out (header-only, per-program copy).
  necho.c now uses it too.
- c/wget.c: `wget URL` frames the URL, then prints the reply body. The
  gateway streams the body back as typed frames: 'D'<chunk> ... 'E'.
- tools/gateway.py: add --mode http (urlopen the frame as a URL, cap the
  body, chunk it) alongside --mode echo; --cmd runs any gbos command.

Verified: `wget example.com` streams back the full Example Domain HTML onto
the terminal; `wget sl0p.foo` fetches the real page. A Game Boy on the web,
over the link cable.

1 files changed, 18 insertions, 0 deletions

diff --git a/c/wget.c b/c/wget.c
new file mode 100644
index 0000000..013b326
--- /dev/null
+++ b/c/wget.c
@@ -0,0 +1,18 @@
+#include "netlib.h"
+/* wget URL : send the URL to the host gateway over SLIP, print the reply body.
+   The gateway does the real DNS/TCP/HTTP and streams the body back as frames:
+   each reply frame is 'D'<chunk>, ending with a single 'E' frame. */
+void main(void) {
+    char *argv[4];
+    unsigned char argc = argv_parse(argv, 4);
+    char buf[220];
+    unsigned char len, i;
+    if (argc < 1) { puts("usage: wget URL"); nl(); return; }
+    slip_send(argv[0], strlen(argv[0]));
+    for (;;) {
+        len = slip_recv(buf, 219);
+        if (len >= 1 && buf[0] == 'E') break;      /* end of stream */
+        for (i = 1; i < len; i++) putc(buf[i]);    /* skip the 'D' type byte */
+    }
+    nl();
+}