From 30dcb1328bf9a5d538e8f87254930c3a76c0d2e3 Mon Sep 17 00:00:00 2001
From: "Sean C. Rhea" <sean.c.rhea@gmail.com>
Date: Sun, 1 Apr 2007 05:41:38 +0000
Subject: [PATCH] Hardware echo detection was being fooled because in the
 normal case, the result of a version request, triggered by writing 'V', is
 the string "VER...". Sometimes, this was preceeded by a zero byte, in which
 case hardware echo detection worked, but other times it wasn't, and we
 stripped the 'V' from "VER...", only to wait forever for one extra byte that
 wasn't coming.  The new approach is to read until we get the "\r\n", then
 search for "VER", then see if any other 'V's preceed it, in which case we
 assume we're dealing with hardware echo.

---
 src/lib/pt.c | 48 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 39 insertions(+), 9 deletions(-)

diff --git a/src/lib/pt.c b/src/lib/pt.c
index 6a3c58b9a..8ea5938ed 100644
--- a/src/lib/pt.c
+++ b/src/lib/pt.c
@@ -134,10 +134,9 @@ pt_read_version(struct pt_read_version_state *state, int fd, int *hwecho)
     }
 
     assert(state->state == 1);
-    while (state->i < 29) {
+    while (1) {
         if (pt_debug_level >= PT_DEBUG_MAX)
-            fprintf(stderr, "Need %d bytes.  Calling read on device.\n",
-                    29 - state->i);
+            fprintf(stderr, "Calling read on device.\n");
         n = read(fd, state->buf + state->i, sizeof(state->buf) - state->i);
         if (n <= 0) {
             if ((n < 0) && (errno == EAGAIN)) {
@@ -153,16 +152,47 @@ pt_read_version(struct pt_read_version_state *state, int fd, int *hwecho)
             fprintb(stderr, state->buf + state->i, n);
             fprintf(stderr, ".\n");
         }
-        if ((state->i == 0) && (state->buf[0] == 0x56)) {
+        state->i += n;
+        if ((state->i >= 2) 
+            && (state->buf[state->i - 2] == 0x0d)
+            && (state->buf[state->i - 1] == 0x0a)) { 
+            break;
+        }
+    }
+
+    /* 
+     * We expect the version string to be something like 
+     * "VER 02.21 PRO...", so if we see two V's, it's probably 
+     * because there's a hardware echo going on.
+     */
+
+    int start = -1;
+    for (int i = 0; i < state->i - 3; ++i) {
+        if (strncmp((char*) state->buf + i, "VER", 3) == 0) {
+            start = i;
+            break;
+        }
+    }
+
+    if (start < 0) {
+        // TODO: return something like PT_ERROR?
+        fprintf(stderr, "Unrecognized version string.\n");
+    }
+    else {
+        int count = 0;
+        for (int i = 0; i < start; ++i) {
+            if (state->buf[i] == 0x56)
+                ++count;
+        }
+        if (count > 0) {
             if (pt_debug_level >= PT_DEBUG_MAX)
                 fprintf(stderr, "Hardware echo detected.\n");
             *hwecho = 1;
-            for (int j = 0; j < n - 1; ++j)
-                state->buf[j] = state->buf[j+1];
-            state->i = n - 1;
         }
-        else {
-            state->i += n;
+        else { 
+            if (pt_debug_level >= PT_DEBUG_MAX)
+                fprintf(stderr, "No hardware echo detected.\n");
+            *hwecho = 0;
         }
     }