From 730b94fa4afd0d0384569b9d3800b08a41f35dfe Mon Sep 17 00:00:00 2001
From: Enno Rehling <enno.rehling@gmail.com>
Date: Wed, 3 Oct 2018 20:29:45 +0200
Subject: [PATCH] reuse the internal buffer when we don't have to malloc.

---
 src/util/order_parser.c | 55 +++++++++++++++++++++++++++++------------
 1 file changed, 39 insertions(+), 16 deletions(-)

diff --git a/src/util/order_parser.c b/src/util/order_parser.c
index 55b03accd..21268f163 100644
--- a/src/util/order_parser.c
+++ b/src/util/order_parser.c
@@ -13,6 +13,7 @@ struct OrderParserStruct {
     void *m_userData;
     char *m_buffer;
     char *m_bufferPtr;
+    size_t m_bufferSize;
     const char *m_bufferEnd;
     OP_OrderHandler m_orderHandler;
     enum OP_Error m_errorCode;
@@ -35,6 +36,7 @@ static void buffer_free(OP_Parser parser)
 {
     /* TODO: recycle buffers, reduce mallocs. */
     free(parser->m_buffer);
+    parser->m_bufferSize = 0;
     parser->m_bufferEnd = parser->m_bufferPtr = parser->m_buffer = NULL;
 }
 
@@ -58,8 +60,28 @@ void OP_ParserFree(OP_Parser parser) {
 
 static enum OP_Error buffer_append(OP_Parser parser, const char *s, int len)
 {
+    size_t total = len + 1;
+    size_t remain = parser->m_bufferEnd - parser->m_bufferPtr;
+    total += remain;
+    if (remain > 0) {
+        /* there is remaining data in the buffer, should we move it to the front? */
+        if (total <= parser->m_bufferSize) {
+            /* reuse existing buffer */
+            memmove(parser->m_buffer, parser->m_bufferPtr, remain);
+            memcpy(parser->m_buffer + remain, s, len);
+            parser->m_buffer[total - 1] = '\0';
+            parser->m_bufferPtr = parser->m_buffer;
+            parser->m_bufferEnd = parser->m_bufferPtr + total - 1;
+            return OP_ERROR_NONE;
+        }
+    }
+    else if (parser->m_bufferPtr >= parser->m_bufferEnd) {
+        buffer_free(parser);
+    }
+
     if (parser->m_buffer == NULL) {
-        parser->m_buffer = malloc(len + 1);
+        parser->m_bufferSize = len + 1;
+        parser->m_buffer = malloc(parser->m_bufferSize);
         if (!parser->m_buffer) {
             return OP_ERROR_NO_MEMORY;
         }
@@ -69,21 +91,26 @@ static enum OP_Error buffer_append(OP_Parser parser, const char *s, int len)
         parser->m_bufferEnd = parser->m_buffer + len;
     }
     else {
-        size_t total = len;
         char * buffer;
-        total += (parser->m_bufferEnd - parser->m_bufferPtr);
         /* TODO: recycle buffers, reduce mallocs. */
-        buffer = malloc(total + 1);
-        memcpy(buffer, parser->m_bufferPtr, total - len);
-        memcpy(buffer + total - len, s, len);
-        buffer[total] = '\0';
-        free(parser->m_buffer);
-        parser->m_buffer = buffer;
-        if (!parser->m_buffer) {
-            return OP_ERROR_NO_MEMORY;
+        if (parser->m_bufferSize < total) {
+            parser->m_bufferSize = total;
+            buffer = malloc(parser->m_bufferSize);
+            if (!buffer) {
+                return OP_ERROR_NO_MEMORY;
+            }
+            memcpy(buffer, parser->m_bufferPtr, total - len - 1);
+            memcpy(buffer + total - len - 1, s, len);
+            free(parser->m_buffer);
+            parser->m_buffer = buffer;
         }
+        else {
+            memcpy(parser->m_buffer, parser->m_bufferPtr, total - len);
+            memcpy(parser->m_buffer + total - len, s, len);
+        }
+        parser->m_buffer[total - 1] = '\0';
         parser->m_bufferPtr = parser->m_buffer;
-        parser->m_bufferEnd = parser->m_buffer + total;
+        parser->m_bufferEnd = parser->m_buffer + total - 1;
     }
     return OP_ERROR_NONE;
 }
@@ -250,10 +277,6 @@ enum OP_Status OP_Parse(OP_Parser parser, const char *s, int len, int isFinal)
 {
     enum OP_Error code;
 
-    if (parser->m_bufferPtr >= parser->m_bufferEnd) {
-        buffer_free(parser);
-    }
-
     code = buffer_append(parser, s, len);
     if (code != OP_ERROR_NONE) {
         parser->m_errorCode = code;