Refactor patty_kiss_tnc_recv()

Refactor patty_kiss_tnc_recv() to always read a fixed number of bytes
into a circular buffer

Other changes:

    * Avoid needing memmove() per packet processed

    * Allow processing packets larger than the internal read buffer

src/kiss.c

@@ -24,8 +24,13 @@ struct _patty_kiss_tnc {
          *frame;
 
     size_t bufsz,
-           buflen,
+           offset,
            dropped;
+
+    ssize_t readlen,
+            left;
+
+    int eof;
 };
 
 patty_kiss_tnc *patty_kiss_tnc_open_fd(int fd) {
@@ -41,8 +46,11 @@ patty_kiss_tnc *patty_kiss_tnc_open_fd(int fd) {
 
     tnc->fd      = fd;
     tnc->bufsz   = PATTY_KISS_BUFSZ;
-    tnc->buflen  = 0;
+    tnc->offset  = 0;
     tnc->dropped = 0;
+    tnc->readlen = 0;
+    tnc->left    = 0;
+    tnc->eof     = 0;
 
     return tnc;
 
@@ -84,36 +92,11 @@ void patty_kiss_tnc_close(patty_kiss_tnc *tnc) {
      free(tnc);
 }
 
-static ssize_t tnc_buffer(patty_kiss_tnc *tnc) {
-    ssize_t readlen;
-
-    if (tnc->buflen == tnc->bufsz) {
-        goto full;
-    }
-
-    if ((readlen = read(tnc->fd, tnc->buf, tnc->bufsz - tnc->buflen)) < 0) {
-        goto error_read;
-    }
-
-    tnc->buflen += readlen;
-
-    return readlen;
-
-full:
-    return 0;
-
-error_read:
-    return -1;
-}
-
-static void tnc_flush(patty_kiss_tnc *tnc, size_t len) {
-    memmove(tnc->buf, ((uint8_t *)tnc->buf) + len, tnc->buflen - len);
-
-    tnc->buflen -= len;
-}
-
 static void tnc_drop(patty_kiss_tnc *tnc) {
-    tnc->buflen = 0;
+    tnc->offset  = 0;
+    tnc->readlen = 0;
+    tnc->left    = 0;
+    tnc->eof     = 0;
     tnc->dropped++;
 }
 
@@ -125,17 +108,46 @@ ssize_t patty_kiss_tnc_recv(patty_kiss_tnc *tnc,
                             void *buf,
                             size_t len,
                             int *port) {
-    size_t i = 0,
-           b = 0;
+    size_t r = 0, /* Number of bytes read */
+           w = 0; /* Number of bytes written to buf */
 
     enum kiss_flags flags = KISS_NONE;
 
-    if (tnc_buffer(tnc) < 0) {
-        goto error_io;
+    if (tnc->eof) {
+        return 0;
     }
 
-    while (i < tnc->buflen && b < len) {
-        uint8_t c = ((uint8_t *)tnc->buf)[i++];
+    while (1) {
+        uint8_t c;
+
+        r++;
+
+        if (w == len) {
+            tnc_drop(tnc);
+
+            flags &= ~KISS_FRAME;
+                w  = 0;
+        }
+
+        if (tnc->offset == 0) {
+            if ((tnc->readlen = read(tnc->fd, tnc->buf, tnc->bufsz)) < 0) {
+                goto error_io;
+            } else if (tnc->readlen == 0) {
+                if (errno) {
+                    goto error_io;
+                }
+
+                goto done;
+            }
+
+            tnc->left = tnc->readlen;
+        }
+
+        c = ((uint8_t *)tnc->buf)[tnc->offset++];
+
+        if (tnc->offset == tnc->bufsz) {
+            tnc->offset = 0;
+        }
 
         if (!(flags & KISS_FRAME)) {
             if (c == PATTY_KISS_FEND) {
@@ -149,7 +161,7 @@ ssize_t patty_kiss_tnc_recv(patty_kiss_tnc *tnc,
             }
         } else {
             if (c == PATTY_KISS_FEND) {
-                if (b > 0) {
+                if (w > 0) {
                     flags &= ~KISS_FRAME;
 
                     goto done;
@@ -182,12 +194,12 @@ ssize_t patty_kiss_tnc_recv(patty_kiss_tnc *tnc,
         } else {
             switch (c) {
                 case PATTY_KISS_TFEND:
-                    ((uint8_t *)buf)[b++] = PATTY_KISS_FEND;
+                    ((uint8_t *)buf)[w++] = PATTY_KISS_FEND;
                     flags &= ~KISS_ESCAPE;
                     continue;
 
                 case PATTY_KISS_TFESC:
-                    ((uint8_t *)buf)[b++] = PATTY_KISS_FESC;
+                    ((uint8_t *)buf)[w++] = PATTY_KISS_FESC;
                     flags &= ~KISS_ESCAPE;
                     continue;
 
@@ -198,17 +210,23 @@ ssize_t patty_kiss_tnc_recv(patty_kiss_tnc *tnc,
             }
         }
 
-        ((uint8_t *)buf)[b++] = c;
+        ((uint8_t *)buf)[w++] = c;
     }
 
 done:
     if (flags & KISS_FRAME) {
         tnc_drop(tnc);
-    } else {
-        tnc_flush(tnc, i);
+
+        return 0;
     }
 
-    return (ssize_t)b;
+    tnc->left -= r;
+
+    if (tnc->readlen < tnc->bufsz && tnc->left == 0) {
+        tnc->eof = 1;
+    }
+
+    return (ssize_t)w;
 
 error_io:
     return -1;