make puzbus slightly more robust

1 files changed, 24 insertions, 9 deletions

diff --git a/proto/puzbusv1.c b/proto/puzbusv1.c
index d6cd597..3be4939 100644
--- a/proto/puzbusv1.c
+++ b/proto/puzbusv1.c
@@ -7,21 +7,32 @@
 
 #include "puzbusv1.h"
 
-bool pb_read(struct pb_msg* target, char* buf, size_t buf_sz) {
-	// remaining bytes to be read to target->data; this is the only variable that
-	// needs to persist between buffer blocks, and is therefore static
-	static size_t rdata = 0;
+/**
+ * \brief Remaining bytes to be read to target->data
+ *
+ * This is the only variable that needs to persist between buffer blocks. It is
+ * declared in the global scope to allow resetting using the \c pb_read_reset()
+ * function.
+ *
+ * \note \p rdata may be reset by calling \c pb_read_reset()
+ */
+static size_t rdata = 0;
 
+int pb_read(struct pb_msg* target, char* buf, size_t buf_sz) {
 	// a new reader is used per buffer block passed to this function
 	mpack_reader_t reader;
 	mpack_reader_init_data(&reader, buf, buf_sz);
 
 	// at start of message
 	if (rdata == 0) {
-		// NOTE: This approach will crash and burn when target->addr can be read
-		// and target->length is past the end of the current buffer block. This is
-		// a highly unlikely scenario, as pb_read is called for each chunk of a TCP
-		// frame, and frames (should) include only one puzzle bus message.
+		// NOTE: The entire start of a message needs to be readable from the buffer
+		// at this point. When target->addr can be read and target->length is past
+		// the end of the current buffer block, this function will crash and burn.
+		// This is a highly unlikely scenario, as pb_read is called for each chunk
+		// of a TCP frame, and frames (should) include only one puzzle bus message.
+		// The check here is kind of optional.
+		if (buf_sz < 4) return -1;
+
 		target->addr = mpack_expect_u16(&reader);
 		target->length = rdata = mpack_expect_bin(&reader);
 		target->data = (char*) malloc(target->length);
@@ -35,7 +46,11 @@ bool pb_read(struct pb_msg* target, char* buf, size_t buf_sz) {
 	rdata -= to_read;
 
 	// if rdata = 0, the message was completely read
-	return rdata == 0;
+	return rdata;
+}
+
+void pb_read_reset() {
+	rdata = 0;
 }
 
 bool pb_write(struct pb_msg* target, char** buf, size_t* buf_sz) {