format: Add string to pa_format_info conversion function

This will help accept string formats from the command like (so we can
set formats using pactl).

src/pulse/format.c

@@ -41,20 +41,30 @@
 
 static int pa_format_info_prop_compatible(const char *one, const char *two);
 
-const char *pa_encoding_to_string(pa_encoding_t e) {
-    static const char* const table[]= {
+static const char* const _encoding_str_table[]= {
     [PA_ENCODING_PCM] = "pcm",
     [PA_ENCODING_AC3_IEC61937] = "ac3-iec61937",
     [PA_ENCODING_EAC3_IEC61937] = "eac3-iec61937",
     [PA_ENCODING_MPEG_IEC61937] = "mpeg-iec61937",
     [PA_ENCODING_DTS_IEC61937] = "dts-iec61937",
     [PA_ENCODING_ANY] = "any",
-    };
+};
 
+const char *pa_encoding_to_string(pa_encoding_t e) {
     if (e < 0 || e >= PA_ENCODING_MAX)
         return NULL;
 
-    return table[e];
+    return _encoding_str_table[e];
+}
+
+pa_encoding_t pa_encoding_from_string(const char *encoding) {
+    pa_encoding_t e;
+
+    for (e = PA_ENCODING_ANY; e < PA_ENCODING_MAX; e++)
+        if (pa_streq(_encoding_str_table[e], encoding))
+            return e;
+
+    return PA_ENCODING_INVALID;
 }
 
 pa_format_info* pa_format_info_new(void) {
@@ -125,6 +135,44 @@ char *pa_format_info_snprint(char *s, size_t l, const pa_format_info *f) {
     return s;
 }
 
+pa_format_info* pa_format_info_from_string(const char *str) {
+    pa_format_info *f = pa_format_info_new();
+    char *encoding = NULL, *properties = NULL;
+    size_t pos;
+
+    pos = strcspn(str, ",");
+
+    encoding = pa_xstrndup(str, pos);
+    f->encoding = pa_encoding_from_string(pa_strip(encoding));
+    if (f->encoding == PA_ENCODING_INVALID)
+        goto error;
+
+    if (pos != strlen(str)) {
+        pa_proplist *plist;
+
+        properties = pa_xstrdup(&str[pos+1]);
+        plist = pa_proplist_from_string(properties);
+
+        if (!plist)
+            goto error;
+
+        pa_proplist_free(f->plist);
+        f->plist = plist;
+    }
+
+out:
+    if (encoding)
+        pa_xfree(encoding);
+    if (properties)
+        pa_xfree(properties);
+    return f;
+
+error:
+    pa_format_info_free(f);
+    f = NULL;
+    goto out;
+}
+
 int pa_format_info_is_compatible(pa_format_info *first, pa_format_info *second) {
     const char *key;
     void *state = NULL;

src/pulse/format.h

@@ -62,6 +62,9 @@ typedef enum pa_encoding {
 /** Returns a printable string representing the given encoding type. \since 1.0 */
 const char *pa_encoding_to_string(pa_encoding_t e) PA_GCC_CONST;
 
+/** Converts a string of the form returned by \a pa_encoding_to_string() back to a \a pa_encoding_t. \since 1.0 */
+pa_encoding_t pa_encoding_from_string(const char *encoding);
+
 /**< Represents the format of data provided in a stream or processed by a sink. \since 1.0 */
 typedef struct pa_format_info {
     pa_encoding_t encoding;
@@ -105,6 +108,10 @@ int pa_format_info_is_compatible(pa_format_info *first, pa_format_info *second);
 /** Return a human-readable string representing the given format. \since 1.0 */
 char *pa_format_info_snprint(char *s, size_t l, const pa_format_info *f);
 
+/** Parse a human-readable string of the form generated by
+ * \a pa_format_info_snprint() into a pa_format_info structure. \since 1.0 */
+pa_format_info* pa_format_info_from_string(const char *str);
+
 /** Sets an integer property on the given format info */
 void pa_format_info_set_prop_int(pa_format_info *f, const char *key, int value);
 /** Sets a property with a list of integer values on the given format info */