Enable libFLAC to write to new file on changing metadata

Previously, altering metadata could only be done rewriting the
file (or with a tempfile with the assumption the tempfile would
replace the existing file). However, there are good reasons to
write a new file instead. One API call is added for that, and
one is changed to enable this.

include/FLAC++/metadata.h

@@ -1177,6 +1177,7 @@ namespace FLAC {
 			bool check_if_tempfile_needed(bool use_padding);                ///< See FLAC__metadata_chain_check_if_tempfile_needed().
 
 			bool write(bool use_padding = true, bool preserve_file_stats = false); ///< See FLAC__metadata_chain_write().
+			bool write(const char *filename, bool use_padding = false); ///< See FLAC__metadata_chain_write_new_file().
 			bool write(bool use_padding, ::FLAC__IOHandle handle, ::FLAC__IOCallbacks callbacks); ///< See FLAC__metadata_chain_write_with_callbacks().
 			bool write(bool use_padding, ::FLAC__IOHandle handle, ::FLAC__IOCallbacks callbacks, ::FLAC__IOHandle temp_handle, ::FLAC__IOCallbacks temp_callbacks); ///< See FLAC__metadata_chain_write_with_callbacks_and_tempfile().
 

include/FLAC/metadata.h

@@ -788,9 +788,6 @@ typedef enum {
 	/**< FLAC__metadata_chain_write_with_callbacks() was called when the
 	 *   chain write requires a tempfile; use
 	 *   FLAC__metadata_chain_write_with_callbacks_and_tempfile() instead.
-	 *   Or, FLAC__metadata_chain_write_with_callbacks_and_tempfile() was
-	 *   called when the chain write does not require a tempfile; use
-	 *   FLAC__metadata_chain_write_with_callbacks() instead.
 	 *   Always check FLAC__metadata_chain_check_if_tempfile_needed()
 	 *   before writing via callbacks. */
 
@@ -927,11 +924,11 @@ FLAC_API FLAC__bool FLAC__metadata_chain_read_ogg_with_callbacks(FLAC__Metadata_
  *  edited metadata back to the FLAC file does not require rewriting the
  *  entire file.  If rewriting is required, then a temporary workfile is
  *  required.  When writing metadata using callbacks, you must check
- *  this function to know whether to call
- *  FLAC__metadata_chain_write_with_callbacks() or
- *  FLAC__metadata_chain_write_with_callbacks_and_tempfile().  When
- *  writing with FLAC__metadata_chain_write(), the temporary file is
- *  handled internally.
+ *  this function to know whether
+ *  FLAC__metadata_chain_write_with_callbacks() can be used or
+ *  FLAC__metadata_chain_write_with_callbacks_and_tempfile() is
+ *  necessary.  When  writing with FLAC__metadata_chain_write(), the
+ *  temporary file is handled internally.
  *
  * \param chain    A pointer to an existing chain.
  * \param use_padding
@@ -994,6 +991,28 @@ FLAC_API FLAC__bool FLAC__metadata_chain_check_if_tempfile_needed(FLAC__Metadata
  */
 FLAC_API FLAC__bool FLAC__metadata_chain_write(FLAC__Metadata_Chain *chain, FLAC__bool use_padding, FLAC__bool preserve_file_stats);
 
+/** Write all metadata out to a new FLAC file.
+ *
+ *  This function works similar to FLAC__metadata_chain_write(), but is
+ *  useful if writing to a new file is desired. This is more efficient
+ *  than copying the file before changing it.
+ *
+ *  For this write function to be used, the chain must have been read with
+ *  FLAC__metadata_chain_read()/FLAC__metadata_chain_read_ogg(), not
+ *  FLAC__metadata_chain_read_with_callbacks()/FLAC__metadata_chain_read_ogg_with_callbacks().
+ *  See also FLAC__metadata_chain_write_with_callbacks_and_tempfile()
+ *
+ * \param chain               A pointer to an existing chain.
+ * \param use_padding         See FLAC__metadata_chain_write()
+ * \param filename            The filename of the new file.
+ * \assert
+ *    \code chain != NULL \endcode
+ * \retval FLAC__bool
+ *    \c true if the write succeeded, else \c false.  On failure,
+ *    check the status with FLAC__metadata_chain_status().
+ */
+FLAC_API FLAC__bool FLAC__metadata_chain_write_new_file(FLAC__Metadata_Chain *chain, const char *filename, FLAC__bool use_padding);
+
 /** Write all metadata out to a FLAC stream via callbacks.
  *
  *  (See FLAC__metadata_chain_write() for the details on how padding is
@@ -1035,7 +1054,8 @@ FLAC_API FLAC__bool FLAC__metadata_chain_write_with_callbacks(FLAC__Metadata_Cha
  *  FLAC file to edit, and a temporary handle to which the new FLAC
  *  file will be written.  It is the caller's job to move this temporary
  *  FLAC file on top of the original FLAC file to complete the metadata
- *  edit.
+ *  edit. This version of the write-with-callbacks function can also be
+ *  used if writing to a new file is desired anyway.
  *
  *  The \a handle must be open for reading and be seekable.  The
  *  equivalent minimum stdio fopen() file mode is \c "r" (or \c "rb"
@@ -1050,8 +1070,6 @@ FLAC_API FLAC__bool FLAC__metadata_chain_write_with_callbacks(FLAC__Metadata_Cha
  *  For this write function to be used, the chain must have been read with
  *  FLAC__metadata_chain_read_with_callbacks()/FLAC__metadata_chain_read_ogg_with_callbacks(),
  *  not FLAC__metadata_chain_read()/FLAC__metadata_chain_read_ogg().
- *  Also, FLAC__metadata_chain_check_if_tempfile_needed() must have returned
- *  \c true.
  *
  * \param chain        A pointer to an existing chain.
  * \param use_padding  See FLAC__metadata_chain_write()

src/libFLAC++/metadata.cpp

@@ -1619,6 +1619,12 @@ namespace FLAC {
 			return static_cast<bool>(::FLAC__metadata_chain_write(chain_, use_padding, preserve_file_stats));
 		}
 
+		bool Chain::write(const char* filename, bool use_padding)
+		{
+			FLAC__ASSERT(is_valid());
+			return static_cast<bool>(::FLAC__metadata_chain_write_new_file(chain_, filename, use_padding));
+		}
+
 		bool Chain::write(bool use_padding, ::FLAC__IOHandle handle, ::FLAC__IOCallbacks callbacks)
 		{
 			FLAC__ASSERT(is_valid());

src/libFLAC/metadata_iterators.c

@@ -1475,7 +1475,7 @@ static FLAC__bool chain_rewrite_metadata_in_place_(FLAC__Metadata_Chain *chain)
 	return ret;
 }
 
-static FLAC__bool chain_rewrite_file_(FLAC__Metadata_Chain *chain, const char *tempfile_path_prefix)
+static FLAC__bool chain_rewrite_file_(FLAC__Metadata_Chain *chain, const char *tempfile_path_prefix, const char *filename)
 {
 	FILE *f, *tempfile = NULL;
 	char *tempfilename;
@@ -1491,9 +1491,19 @@ static FLAC__bool chain_rewrite_file_(FLAC__Metadata_Chain *chain, const char *t
 		chain->status = FLAC__METADATA_CHAIN_STATUS_ERROR_OPENING_FILE;
 		return false;
 	}
-	if(!open_tempfile_(chain->filename, tempfile_path_prefix, &tempfile, &tempfilename, &status)) {
-		chain->status = get_equivalent_status_(status);
-		goto err;
+	if(filename == NULL) {
+		if(!open_tempfile_(chain->filename, tempfile_path_prefix, &tempfile, &tempfilename, &status)) {
+			chain->status = get_equivalent_status_(status);
+			goto err;
+		}
+	}
+	else {
+		if(0 == (tempfile = flac_fopen(filename, "wb"))) {
+			(void)fclose(f);
+			chain->status = FLAC__METADATA_CHAIN_STATUS_ERROR_OPENING_FILE;
+			return false;
+		}
+
 	}
 	if(!copy_n_bytes_from_file_(f, tempfile, chain->first_offset, &status)) {
 		chain->status = get_equivalent_status_(status);
@@ -1525,16 +1535,23 @@ static FLAC__bool chain_rewrite_file_(FLAC__Metadata_Chain *chain, const char *t
 
 	/* move the tempfile on top of the original */
 	(void)fclose(f);
-	if(!transport_tempfile_(chain->filename, &tempfile, &tempfilename, &status)) {
-		chain->status = get_equivalent_status_(status);
-		return false;
+	if(filename == NULL) {
+		if(!transport_tempfile_(chain->filename, &tempfile, &tempfilename, &status)) {
+			chain->status = get_equivalent_status_(status);
+			return false;
+		}
 	}
+	else
+		(void)fclose(tempfile);
 
 	return true;
 
 err:
 	(void)fclose(f);
-	cleanup_tempfile_(&tempfile, &tempfilename);
+	if(filename == NULL)
+		cleanup_tempfile_(&tempfile, &tempfilename);
+	else
+		(void)fclose(tempfile);
 	return false;
 }
 
@@ -1820,7 +1837,7 @@ FLAC_API FLAC__bool FLAC__metadata_chain_write(FLAC__Metadata_Chain *chain, FLAC
 			return false;
 	}
 	else {
-		if(!chain_rewrite_file_(chain, tempfile_path_prefix))
+		if(!chain_rewrite_file_(chain, tempfile_path_prefix, NULL))
 			return false;
 
 		/* recompute lengths and offsets */
@@ -1839,6 +1856,48 @@ FLAC_API FLAC__bool FLAC__metadata_chain_write(FLAC__Metadata_Chain *chain, FLAC
 	return true;
 }
 
+FLAC_API FLAC__bool FLAC__metadata_chain_write_new_file(FLAC__Metadata_Chain *chain, const char *filename, FLAC__bool use_padding)
+{
+	FLAC__off_t current_length;
+
+	FLAC__ASSERT(0 != chain);
+
+	if (chain->is_ogg) { /* cannot write back to Ogg FLAC yet */
+		chain->status = FLAC__METADATA_CHAIN_STATUS_INTERNAL_ERROR;
+		return false;
+	}
+
+	if (0 == chain->filename) {
+		chain->status = FLAC__METADATA_CHAIN_STATUS_READ_WRITE_MISMATCH;
+		return false;
+	}
+
+	if (0 == filename) {
+		chain->status = FLAC__METADATA_CHAIN_STATUS_ILLEGAL_INPUT;
+		return false;
+	}
+
+	current_length = chain_prepare_for_write_(chain, use_padding);
+
+	/* a return value of 0 means there was an error; chain->status is already set */
+	if (0 == current_length)
+		return false;
+
+	if(!chain_rewrite_file_(chain, NULL, filename))
+		return false;
+
+	/* recompute lengths and offsets */
+	{
+		const FLAC__Metadata_Node *node;
+		chain->initial_length = current_length;
+		chain->last_offset = chain->first_offset;
+		for(node = chain->head; node; node = node->next)
+			chain->last_offset += (FLAC__STREAM_METADATA_HEADER_LENGTH + node->data->length);
+	}
+
+	return true;
+}
+
 FLAC_API FLAC__bool FLAC__metadata_chain_write_with_callbacks(FLAC__Metadata_Chain *chain, FLAC__bool use_padding, FLAC__IOHandle handle, FLAC__IOCallbacks callbacks)
 {
 	FLAC__off_t current_length;
@@ -1901,19 +1960,12 @@ FLAC_API FLAC__bool FLAC__metadata_chain_write_with_callbacks_and_tempfile(FLAC_
 		return false;
 	}
 
-	if (!FLAC__metadata_chain_check_if_tempfile_needed(chain, use_padding)) {
-		chain->status = FLAC__METADATA_CHAIN_STATUS_WRONG_WRITE_CALL;
-		return false;
-	}
-
 	current_length = chain_prepare_for_write_(chain, use_padding);
 
 	/* a return value of 0 means there was an error; chain->status is already set */
 	if (0 == current_length)
 		return false;
 
-	FLAC__ASSERT(current_length != chain->initial_length);
-
 	/* rewind */
 	if(0 != callbacks.seek(handle, 0, SEEK_SET)) {
 		chain->status = FLAC__METADATA_CHAIN_STATUS_SEEK_ERROR;