config/Parser: add ParseSize()

Supports suffixes such as "kB" and "MB".

doc/user.rst

@@ -712,8 +712,9 @@ Do not change these unless you know what you are doing.
 
    * - Setting
      - Description
-   * - **audio_buffer_size KBYTES**
-     - Adjust the size of the internal audio buffer. Default is 4096 (4 MiB).
+   * - **audio_buffer_size SIZE**
+     - Adjust the size of the internal audio buffer. Default is
+       :samp:`4 MB` (4 MiB).
 
 Zeroconf
 ~~~~~~~~

src/Main.cxx

@@ -58,6 +58,7 @@
 #include "config/Defaults.hxx"
 #include "config/Option.hxx"
 #include "config/Domain.hxx"
+#include "config/Parser.hxx"
 #include "util/RuntimeError.hxx"
 #include "util/ScopeExit.hxx"
 
@@ -280,12 +281,10 @@ initialize_decoder_and_player(Instance &instance,
 	param = config.GetParam(ConfigOption::AUDIO_BUFFER_SIZE);
 	if (param != nullptr) {
 		buffer_size = param->With([](const char *s){
-			char *test;
-			long tmp = strtol(s, &test, 10);
-			if (*test != '\0' || tmp <= 0 || tmp == LONG_MAX)
+			size_t result = ParseSize(s, KILOBYTE);
+			if (result <= 0)
 				throw FormatRuntimeError("buffer size \"%s\" is not a "
 							 "positive integer", s);
-			size_t result = tmp * KILOBYTE;
 
 			if (result < MIN_BUFFER_SIZE) {
 				FormatWarning(config_domain, "buffer size %lu is too small, using %lu bytes instead",

src/config/Parser.cxx

@@ -19,6 +19,7 @@
 
 #include "Parser.hxx"
 #include "util/RuntimeError.hxx"
+#include "util/StringStrip.hxx"
 #include "util/StringUtil.hxx"
 
 bool
@@ -35,3 +36,69 @@ ParseBool(const char *value)
 
 	throw FormatRuntimeError("Not a valid boolean (\"yes\" or \"no\"): \"%s\"", value);
 }
+
+template<size_t OPERAND>
+static size_t
+Multiply(size_t value)
+{
+	static constexpr size_t MAX_INPUT = SIZE_MAX / OPERAND;
+	if (value > MAX_INPUT)
+		throw std::runtime_error("Value too large");
+
+	return value * OPERAND;
+}
+
+size_t
+ParseSize(const char *s, size_t default_factor)
+{
+	char *endptr;
+	size_t value = strtoul(s, &endptr, 10);
+	if (endptr == s)
+		throw std::runtime_error("Failed to parse integer");
+
+	static constexpr size_t KILO = 1024;
+	static constexpr size_t MEGA = 1024 * KILO;
+	static constexpr size_t GIGA = 1024 * MEGA;
+
+	s = StripLeft(endptr);
+
+	bool apply_factor = false;
+
+	switch (*s) {
+	case 'k':
+		value = Multiply<KILO>(value);
+		++s;
+		break;
+
+	case 'M':
+		value = Multiply<MEGA>(value);
+		++s;
+		break;
+
+	case 'G':
+		value = Multiply<GIGA>(value);
+		++s;
+		break;
+
+	case '\0':
+		apply_factor = true;
+		break;
+
+	default:
+		throw std::runtime_error("Unknown size suffix");
+	}
+
+	/* ignore 'B' for "byte" */
+	if (*s == 'B') {
+		apply_factor = false;
+		++s;
+	}
+
+	if (*s != '\0')
+		throw std::runtime_error("Unknown size suffix");
+
+	if (apply_factor)
+		value *= default_factor;
+
+	return value;
+}

src/config/Parser.hxx

@@ -20,10 +20,20 @@
 #ifndef MPD_CONFIG_PARSER_HXX
 #define MPD_CONFIG_PARSER_HXX
 
+#include <stddef.h>
+
 /**
  * Throws on error.
  */
 bool
 ParseBool(const char *value);
 
+/**
+ * Parse a string as a byte size.
+ *
+ * Throws on error.
+ */
+size_t
+ParseSize(const char *s, size_t default_factor=1);
+
 #endif