From 0ce5c0c206c20414692b7309488e8ea26264af30 Mon Sep 17 00:00:00 2001
From: Maurizio Porrato <maurizio.porrato@gmail.com>
Date: Fri, 14 Dec 2018 10:13:06 +0000
Subject: [PATCH] Use ring buffer for packet decoding in frame parser tool

---
 .gitignore           |  4 +++
 tools/frame-parser.c | 60 +++++++++++++++++++++++++++++++-------------
 2 files changed, 46 insertions(+), 18 deletions(-)
 create mode 100644 .gitignore

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..2fa30bd
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+*~
+*%
+*.swp
+*.py[co]
diff --git a/tools/frame-parser.c b/tools/frame-parser.c
index bf3aeb1..176150c 100644
--- a/tools/frame-parser.c
+++ b/tools/frame-parser.c
@@ -10,7 +10,6 @@ struct packet_s {
     char status;
     char options[4];
     char eol[2];
-    char eos;
 };
 
 enum unit_e {
@@ -91,26 +90,51 @@ int parse_packet(struct packet_s *packet) {
     return 0;
 }
 
-int read_packet(struct packet_s *packet) {
-    char *r;
+void log_packet(struct packet_s *packet) {
     int i;
-    int valid;
+    char *c = (char *)packet;
 
-    while (1) {
-        r = fgets((char *)packet, sizeof(*packet), stdin);
-        if (r == NULL)
+    for (i=0; i<sizeof(*packet); i++)
+        putc(c[i], stderr);
+}
+
+int read_packet(struct packet_s *packet) {
+    char ring[sizeof(*packet)];
+    char *p;
+    int ring_pos;
+    char c;
+    int ch;
+    int shift;
+
+    p = (char *)packet;
+    ring_pos = 0;
+    shift = sizeof(*packet);
+    for (;;) {
+        ch = getc(stdin);
+        if (ch == EOF)
             return 0;
-        // Sanity checks
-        // Packet must end with CR+LF
-        if (packet->eol[0] != '\r' || packet->eol[1] != '\n')
-            continue;
-        // All fields must be encoded as 0x3X
-        for (valid=1, i=0; i<sizeof(*packet)-4; i++)
-            if ((r[i] & 0xf0) != 0x30)
-                valid = 0;
-        // Should also check for valid BCD values for digits
-        if (valid)
-            return 1;
+        c = (char) ch;
+        ring[ring_pos] = c;
+        ring_pos = (ring_pos + 1) % sizeof(*packet);
+        if (((c & 0xf0) != 0x30) && (c != '\r') && (c != '\n')) {
+            shift = sizeof(*packet);
+        } else {
+            if ((c == '\r') && (shift != 2)) {
+                shift = sizeof(*packet);
+                continue;
+            }
+            if (c == '\n') {
+                if (shift == 1) {
+                    for (int i=0; i<sizeof(ring); i++)
+                        p[i] = ring[(ring_pos + i) % sizeof(*packet)];
+                    log_packet(packet);
+                    return 1;
+                }
+                shift = sizeof(*packet);
+                continue;
+            }
+            shift = (shift > 0) ? shift - 1 : 0;
+        }
     }
 }