Adding binary helper functions to ease crazy pointer arithmetic/copying when passing data back to erlang

c_src/bdberl_drv.c

@@ -12,6 +12,7 @@
 
 #include "hive_hash.h"
 #include "bdberl_drv.h"
+#include "bin_helper.h"
 
 /**
  * Function prototypes
@@ -199,11 +200,12 @@ static int bdberl_drv_control(ErlDrvData handle, unsigned int cmd,
         // Pack the status and dbref (or errno) into a binary and return it
         // Byte 0   : Status
         // Byte 1..4: dbref/errno
-        ErlDrvBinary* result = driver_alloc_binary(5);
-        result->orig_bytes[0] = status;
-        memcpy(result->orig_bytes+1, (char*)&dbref, sizeof(dbref));
-        *outbuf = (char*)result;
-        return result->orig_size;
+        BinHelper bh;
+        bin_helper_init(&bh, 5);
+        bin_helper_push_byte(&bh, status);
+        bin_helper_push_int32(&bh, dbref);
+        *outbuf = (char*)bh.bin;
+        return bh.bin->orig_size;
     }
     case CMD_CLOSE_DB:
     {
@@ -214,10 +216,11 @@ static int bdberl_drv_control(ErlDrvData handle, unsigned int cmd,
         int rc = close_database(dbref, d);
         
         // Setup to return the rc
-        ErlDrvBinary* result = driver_alloc_binary(4);
-        memcpy(result->orig_bytes, (char*)&rc, sizeof(rc));
-        *outbuf = (char*)result;
-        return result->orig_size;
+        BinHelper bh;
+        bin_helper_init(&bh, 4);
+        bin_helper_push_int32(&bh, rc);
+        *outbuf = (char*)bh.bin;
+        return bh.bin->orig_size;
     }
     }
     *outbuf = 0;

c_src/bin_helper.c

@@ -0,0 +1,48 @@
+/* -------------------------------------------------------------------
+ *
+ * bin_helper: ErlDrvBinary helper functions
+ * Copyright (c) 2008 The Hive.  All rights reserved.
+ *
+ * ------------------------------------------------------------------- */
+#include "bin_helper.h"
+
+#include <string.h>
+#include <stdlib.h>
+
+
+static void bin_helper_check_size(BinHelper* bh, int space_needed)
+{
+    if (bh->offset + space_needed > bh->bin->orig_size)
+    {
+        // Need to realloc space -- grow by 2 * space_needed
+        bh->bin = driver_realloc_binary(bh->bin, bh->bin->orig_size + (2 * space_needed));
+    }
+}
+
+void bin_helper_init(BinHelper* bh, unsigned int size)
+{
+    bh->bin = driver_alloc_binary(size);
+    bh->offset = 0;
+}
+
+void bin_helper_push_byte(BinHelper* bh, int value)
+{
+    bin_helper_check_size(bh, 1);
+    bh->bin->orig_bytes[bh->offset] = (char)value;
+    bh->offset++;
+}
+
+void bin_helper_push_int32(BinHelper* bh, int value)
+{
+    bin_helper_check_size(bh, 4);
+    memcpy(bh->bin->orig_bytes+(bh->offset), (char*)&value, 4);
+    bh->offset += 4;
+}
+
+void bin_helper_push_string(BinHelper* bh, const char* string)
+{
+    int sz = strlen(string);
+    bin_helper_check_size(bh, sz+1);
+    strncpy(bh->bin->orig_bytes+(bh->offset), string, sz+1);
+    bh->offset += sz + 1;
+}

c_src/bin_helper.h

@@ -0,0 +1,23 @@
+/* -------------------------------------------------------------------
+ *
+ * bin_helper: ErlDrvBinary helper functions
+ * Copyright (c) 2008 The Hive.  All rights reserved.
+ *
+ * ------------------------------------------------------------------- */
+#ifndef _BIN_HELPER
+#define _BIN_HELPER
+
+#include "erl_driver.h"
+
+typedef struct
+{
+    ErlDrvBinary* bin;
+    unsigned int offset;
+} BinHelper;
+
+void bin_helper_init(BinHelper* bh, unsigned int size);
+void bin_helper_push_byte(BinHelper* bh, int value);
+void bin_helper_push_int32(BinHelper* bh, int value);
+void bin_helper_push_string(BinHelper* bh, const char* string);
+
+#endif