From 6937908478c7ffd19b255e0dc0d5c2e43fa0ec54 Mon Sep 17 00:00:00 2001
From: Peter Wu <peter@lekensteyn.nl>
Date: Thu, 8 May 2014 12:43:47 +0200
Subject: find-bytes: fix case where key_len > 0

---
 find-bytes.c | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/find-bytes.c b/find-bytes.c
index b81aebc..6e5af9c 100644
--- a/find-bytes.c
+++ b/find-bytes.c
@@ -52,36 +52,43 @@ void find_key(FILE *fp, char *key, size_t key_len) {
 		perror("malloc");
 		abort();
 	}
-	size_t fill_size = buf_size;
-	if (key_len > 1) fill_size -= key_len - 1;
+	size_t fill_size = buf_size - key_len + 1;
 	size_t position = 0;
 	size_t new_bytes;
 	int as_hex = !!getenv("HEX");
+	/*----------------+------------------------------*
+	 * prev data size |          new data            *
+	 *   key_len - 1  |     size is max fill_size    *
+	 *----------------+------------------------------*/
+	char *new_data_p = buf + key_len - 1;
+	/* initially, data is valid starting at the point where it gets filled */
+	char *buf_start = new_data_p;
 	do {
-		/*----------------+------------------------------*
-		 * prev data size |          new data            *
-		 *   key_len - 1  |     size is max fill_size    *
-		 *----------------+------------------------------*/
-		new_bytes = read(fd, buf + key_len - 1, fill_size);
-		/* initially, the beginning is uninitialized */
-		char *new_data_p = buf;
-		char *end_p = buf + new_bytes;
-		if (position) {
-			end_p += key_len;
-		} else {
-			new_data_p += key_len - 1;
+		new_bytes = read(fd, new_data_p, fill_size);
+		if ((ssize_t) new_bytes == -1) {
+			perror("read");
+			break;
 		}
-		char *next_p = new_data_p;
+
+		char *next_p = buf_start;
+		char *end_p = new_data_p + new_bytes;
 		while (next_p && end_p >= next_p + key_len) {
 			next_p = memmem(next_p, end_p - next_p, key, key_len);
 			if (next_p) {
-				size_t offset = (next_p - new_data_p) + position;
+				size_t offset = (next_p - buf_start) + position;
 				printf(as_hex ? "%zx\n" : "%zi\n", offset);
 				next_p += key_len;
 			}
 		}
-		/* copy trailing buffer chars to the beginning */
-		if (key_len > 1) memcpy(buf, buf + fill_size, key_len - 1);
+		/* copy trailing buffer chars to the beginning, just before new data */
+		if (key_len > 1) {
+			size_t keep_size = key_len - 1;
+			if (keep_size > new_bytes) {
+				keep_size = new_bytes;
+			}
+			buf_start = new_data_p - keep_size;
+			memmove(buf_start, end_p - keep_size, keep_size);
+		}
 		position += new_bytes;
 	} while (new_bytes == fill_size);
 	free(buf);
-- 
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