bufref: buffer reference support

A struct bufref holds a buffer pointer, a data size and a destructor.
When freed or its contents are changed, the previous buffer is implicitly
released by the associated destructor. The data size, although not used
internally, allows binary data support.

A unit test checks its handling methods: test 1661

Closes #6654

1 files changed, 127 insertions, 0 deletions

diff --git a/lib/bufref.c b/lib/bufref.c
new file mode 100644
index 000000000..b84511e18
--- /dev/null
+++ b/lib/bufref.c
@@ -0,0 +1,127 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "curl_setup.h"
+#include "urldata.h"
+#include "bufref.h"
+
+#include "curl_memory.h"
+#include "memdebug.h"
+
+#define SIGNATURE 0x5c48e9b2    /* Random pattern. */
+
+/*
+ * Init a bufref struct.
+ */
+void Curl_bufref_init(struct bufref *br)
+{
+  DEBUGASSERT(br);
+  br->dtor = NULL;
+  br->ptr = NULL;
+  br->len = 0;
+
+#ifdef DEBUGBUILD
+  br->signature = SIGNATURE;
+#endif
+}
+
+/*
+ * Free the buffer and re-init the necessary fields. It doesn't touch the
+ * 'signature' field and thus this buffer reference can be reused.
+ */
+
+void Curl_bufref_free(struct bufref *br)
+{
+  DEBUGASSERT(br);
+  DEBUGASSERT(br->signature == SIGNATURE);
+  DEBUGASSERT(br->ptr || !br->len);
+
+  if(br->ptr && br->dtor)
+    br->dtor((void *) br->ptr);
+
+  br->dtor = NULL;
+  br->ptr = NULL;
+  br->len = 0;
+}
+
+/*
+ * Set the buffer reference to new values. The previously referenced buffer
+ * is released before assignment.
+ */
+void Curl_bufref_set(struct bufref *br, const void *ptr, size_t len,
+                     void (*dtor)(void *))
+{
+  DEBUGASSERT(ptr || !len);
+  DEBUGASSERT(len <= CURL_MAX_INPUT_LENGTH);
+
+  Curl_bufref_free(br);
+  br->ptr = (const unsigned char *) ptr;
+  br->len = len;
+  br->dtor = dtor;
+}
+
+/*
+ * Get a pointer to the referenced buffer.
+ */
+const unsigned char *Curl_bufref_ptr(const struct bufref *br)
+{
+  DEBUGASSERT(br);
+  DEBUGASSERT(br->signature == SIGNATURE);
+  DEBUGASSERT(br->ptr || !br->len);
+
+  return br->ptr;
+}
+
+/*
+ * Get the length of the referenced buffer data.
+ */
+size_t Curl_bufref_len(const struct bufref *br)
+{
+  DEBUGASSERT(br);
+  DEBUGASSERT(br->signature == SIGNATURE);
+  DEBUGASSERT(br->ptr || !br->len);
+
+  return br->len;
+}
+
+CURLcode Curl_bufref_memdup(struct bufref *br, const void *ptr, size_t len)
+{
+  unsigned char *cpy = NULL;
+
+  DEBUGASSERT(br);
+  DEBUGASSERT(br->signature == SIGNATURE);
+  DEBUGASSERT(br->ptr || !br->len);
+  DEBUGASSERT(ptr || !len);
+  DEBUGASSERT(len <= CURL_MAX_INPUT_LENGTH);
+
+  if(ptr) {
+    cpy = malloc(len + 1);
+    if(!cpy)
+      return CURLE_OUT_OF_MEMORY;
+    if(len)
+      memcpy(cpy, ptr, len);
+    cpy[len] = '\0';
+  }
+
+  Curl_bufref_set(br, cpy, len, curl_free);
+  return CURLE_OK;
+}