message-params: Add read/write functions for various simple data types

The following functions have been added:

pa_message_params_write_double() - writes a double to a pa_message_params structure
pa_message_params_write_int64() - writes an integer to a pa_message_params structure
pa_message_params_write_uint64() - writes an unsigned to a pa_message_params structure
pa_message_params_write_bool() - writes a boolean to a pa_message_params structure

pa_message_params_read_double() - read a double from a parameter list
pa_message_params_read_int64() - read an integer from a parameter list
pa_message_params_read_uint64() - read an unsigned from a parameter list
pa_message_params_read_bool() - read a boolean from a parameter list

The patch also improves the doxygen documentation im message-params.h

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/51>

src/pulse/message-params.h

@@ -26,28 +26,68 @@
 #include <pulse/version.h>
 
 /** \file
- * Utility functions for reading and writing message parameters */
+ * Utility functions for reading and writing message parameters.
+ * All read functions return a value from pa_message_params_error_code
+ * and the read value in result (or *result for string functions).
+ * The string read functions read_string() and read_raw() return a pointer
+ * to a sub-string within the parameter list in *result, therefore the
+ * string in *result must not be freed and is only valid within the
+ * message handler callback function. If the string is needed outside
+ * the callback, it must be copied using pa_xstrdup().
+ * When a read function is called, the state pointer is advanced to the
+ * next list element. The variable state points to should be initialized
+ * to NULL before the first call.\n
+ * Write functions operate on a pa_message_params structure which is a
+ * wrapper for pa_strbuf. A parameter list or sub-list is started by a
+ * call to begin_list() and ended by a call to end_list().
+ * A pa_message_params structure must be converted to a string using
+ * pa_message_params_to_string_free() before it can be passed to a
+ * message handler. */
 
 PA_C_DECL_BEGIN
 
 /** Structure which holds a parameter list. Wrapper for pa_strbuf  \since 15.0 */
 typedef struct pa_message_params pa_message_params;
 
+/** Read function return values  \since 15.0 */
+enum pa_message_params_error_code {
+    /** No value (empty element) found for numeric or boolean value */
+    PA_MESSAGE_PARAMS_IS_NULL = -2,
+    /** Error encountered while parsing a value */
+    PA_MESSAGE_PARAMS_PARSE_ERROR = -1,
+    /** End of parameter list reached */
+    PA_MESSAGE_PARAMS_LIST_END = 0,
+    /** Parsing successful */
+    PA_MESSAGE_PARAMS_OK = 1,
+};
+
 /** @{ \name Read functions */
 
-/** Read raw data from a parameter list. Used to split a message parameter
+/** Read a boolean from parameter list in c. \since 15.0 */
+int pa_message_params_read_bool(char *c, bool *result, void **state);
+
+/** Read a double from parameter list in c. \since 15.0 */
+int pa_message_params_read_double(char *c, double *result, void **state);
+
+/** Read an integer from parameter list in c. \since 15.0 */
+int pa_message_params_read_int64(char *c, int64_t *result, void **state);
+
+/** Read raw data from parameter list in c. Used to split a message parameter
  * string into list elements. The string returned in *result must not be freed.  \since 15.0 */
 int pa_message_params_read_raw(char *c, char **result, void **state);
 
-/** Read a string from a parameter list. Escaped curly braces and backslashes
+/** Read a string from a parameter list in c. Escaped curly braces and backslashes
  * will be unescaped. \since 15.0 */
 int pa_message_params_read_string(char *c, const char **result, void **state);
 
+/** Read an unsigned integer from parameter list in c. \since 15.0 */
+int pa_message_params_read_uint64(char *c, uint64_t *result, void **state);
+
 /** @} */
 
 /** @{ \name Write functions */
 
-/** Create a new pa_message_params structure  \since 15.0 */
+/** Create a new pa_message_params structure.  \since 15.0 */
 pa_message_params *pa_message_params_new(void);
 
 /** Free a pa_message_params structure.  \since 15.0 */
@@ -62,6 +102,17 @@ void pa_message_params_begin_list(pa_message_params *params);
 /** End a list by writing a closing brace.  \since 15.0 */
 void pa_message_params_end_list(pa_message_params *params);
 
+/** Append a boolean to parameter list. \since 15.0 */
+void pa_message_params_write_bool(pa_message_params *params, bool value);
+
+/** Append a double to parameter list. Precision gives the number of
+ * significant digits. The decimal separator will always be written as
+ * dot, regardless which locale is used. \since 15.0 */
+void pa_message_params_write_double(pa_message_params *params, double value, int precision);
+
+/** Append an integer to parameter list. \since 15.0 */
+void pa_message_params_write_int64(pa_message_params *params, int64_t value);
+
 /** Append string to parameter list. Curly braces and backslashes will be escaped.  \since 15.0 */
 void pa_message_params_write_string(pa_message_params *params, const char *value);
 
@@ -70,6 +121,9 @@ void pa_message_params_write_string(pa_message_params *params, const char *value
  * the string if add_braces is true.  \since 15.0 */
 void pa_message_params_write_raw(pa_message_params *params, const char *value, bool add_braces);
 
+/** Append an unsigned integer to parameter list. \since 15.0 */
+void pa_message_params_write_uint64(pa_message_params *params, uint64_t value);
+
 /** @} */
 
 PA_C_DECL_END