1 files changed, 141 insertions, 0 deletions
diff --git a/slip.c b/slip.c
new file mode 100644
index 0000000..3b448f4
--- /dev/null
+++ b/slip.c
@@ -0,0 +1,141 @@
+/* SLIP send/recv code, from RFC 1055 */
+
+#include <stdio.h>      /* perror */
+
+#include "slip_internal.h"
+
+/* SLIP special character codes
+ */
+#define END             0300    /* indicates end of packet */
+#define ESC             0333    /* indicates byte stuffing */
+#define ESC_END         0334    /* ESC ESC_END means END data byte */
+#define ESC_ESC         0335    /* ESC ESC_ESC means ESC data byte */
+
+/* SLIP_SEND: sends a packet of length "len", starting at
+ * location "p".
+ */
+int hal_slip_send(const uint8_t * const ptr, const size_t len)
+{
+    int i;
+    uint8_t *p = (uint8_t *)ptr;
+
+#define check_send_char(c) if (hal_slip_send_char(c) == -1) return perror("write"), -1;
+
+    /* send an initial END character to flush out any data that may
+     * have accumulated in the receiver due to line noise
+     */
+    check_send_char(END);
+
+    /* for each byte in the packet, send the appropriate character
+     * sequence
+     */
+    for (i = 0; i < len; ++i) {
+        switch (*p) {
+            /* if it's the same code as an END character, we send a
+             * special two character code so as not to make the
+             * receiver think we sent an END
+             */
+        case END:
+            check_send_char(ESC);
+            check_send_char(ESC_END);
+            break;
+
+            /* if it's the same code as an ESC character,
+             * we send a special two character code so as not
+             * to make the receiver think we sent an ESC
+             */
+        case ESC:
+            check_send_char(ESC);
+            check_send_char(ESC_ESC);
+            break;
+
+            /* otherwise, we just send the character
+             */
+        default:
+            check_send_char(*p);
+        }
+
+        p++;
+    }
+
+    /* tell the receiver that we're done sending the packet
+     */
+    check_send_char(END);
+
+    return 0;
+#undef check_send_char
+}
+
+/* SLIP_RECV: receives a packet into the buffer located at "p".
+ *      If more than len bytes are received, the packet will
+ *      be truncated.
+ *      Returns the number of bytes stored in the buffer.
+ */
+int hal_slip_recv(uint8_t * const p, const size_t len)
+{
+    uint8_t c;
+    size_t received = 0;
+
+#define check_recv_char(c) if (hal_slip_recv_char(&c) == -1) return perror("read"), -1;
+
+    /* sit in a loop reading bytes until we put together
+     * a whole packet.
+     * Make sure not to copy them into the packet if we
+     * run out of room.
+     */
+    while (1) {
+        /* get a character to process
+         */
+        check_recv_char(c);
+
+        /* handle bytestuffing if necessary
+         */
+        switch (c) {
+
+            /* if it's an END character then we're done with
+             * the packet
+             */
+        case END:
+            /* a minor optimization: if there is no
+             * data in the packet, ignore it. This is
+             * meant to avoid bothering IP with all
+             * the empty packets generated by the
+             * duplicate END characters which are in
+             * turn sent to try to detect line noise.
+             */
+            if (received)
+                return received;
+            else
+                break;
+
+            /* if it's the same code as an ESC character, wait
+             * and get another character and then figure out
+             * what to store in the packet based on that.
+             */
+        case ESC:
+            check_recv_char(c);
+
+            /* if "c" is not one of these two, then we
+             * have a protocol violation.  The best bet
+             * seems to be to leave the byte alone and
+             * just stuff it into the packet
+             */
+            switch(c) {
+            case ESC_END:
+                c = END;
+                break;
+            case ESC_ESC:
+                c = ESC;
+                break;
+            }
+
+            /* here we fall into the default handler and let
+             * it store the character for us
+             */
+        default:
+            if (received < len)
+                p[received++] = c;
+        }
+    }
+#undef check_recv_char
+}