input/icy: support "charset" parameter in URI fragment

Closes https://github.com/MusicPlayerDaemon/MPD/issues/616

NEWS

@@ -5,6 +5,7 @@ ver 0.22 (not yet released)
 * tags
   - new tags "Grouping" (for ID3 "TIT1") and "Work"
 * input
+  - curl: support "charset" parameter in URI fragment
   - ffmpeg: allow partial reads
 * archive
   - iso9660: support seeking

doc/user.rst

@@ -985,6 +985,22 @@ is no way for :program:`MPD` to find out whether the DAC supports
 it. DSD to PCM conversion is the fallback if DSD cannot be used
 directly.
 
+ICY-MetaData
+------------
+
+Some MP3 streams send information about the current song with a
+protocol named `"ICY-MetaData"
+<http://www.smackfu.com/stuff/programming/shoutcast.html>`_.
+:program:`MPD` makes its ``StreamTitle`` value available as ``Title``
+tag.
+
+By default, :program:`MPD` assumes this tag is UTF-8-encoded.  To tell
+:program:`MPD` to assume a different character set, specify it in the
+``charset`` URL fragment parameter, e.g.::
+
+ mpc add 'http://radio.example.com/stream#charset=cp1251'
+
+
 Client Hacks
 ************
 

src/input/IcyInputStream.cxx

@@ -20,11 +20,27 @@
 #include "IcyInputStream.hxx"
 #include "IcyMetaDataParser.hxx"
 #include "tag/Tag.hxx"
+#include "util/UriExtract.hxx"
+#include "util/UriQueryParser.hxx"
+#include "util/StringView.hxx"
+
+#include <string>
 
 IcyInputStream::IcyInputStream(InputStreamPtr _input,
-			       std::shared_ptr<IcyMetaDataParser> _parser) noexcept
+			       std::shared_ptr<IcyMetaDataParser> _parser)
 	:ProxyInputStream(std::move(_input)), parser(std::move(_parser))
 {
+#ifdef HAVE_ICU_CONVERTER
+	const char *fragment = uri_get_fragment(GetURI());
+	if (fragment != nullptr) {
+		const auto charset = UriFindRawQueryParameter(fragment,
+							      "charset");
+		if (charset != nullptr) {
+			const std::string copy(charset.data, charset.size);
+			parser->SetCharset(copy.c_str());
+		}
+	}
+#endif
 }
 
 IcyInputStream::~IcyInputStream() noexcept = default;

src/input/IcyInputStream.hxx

@@ -52,9 +52,12 @@ public:
 	 * with our input; it needs to be shared because our input
 	 * needs to feed parameters (e.g. from the "icy-metaint"
 	 * header) into it
+	 *
+	 * Throws on error (e.g. if the charset converter specified by
+	 * the URI fragment fails to initialize).
 	 */
 	IcyInputStream(InputStreamPtr _input,
-		       std::shared_ptr<IcyMetaDataParser> _parser) noexcept;
+		       std::shared_ptr<IcyMetaDataParser> _parser);
 	virtual ~IcyInputStream() noexcept;
 
 	IcyInputStream(const IcyInputStream &) = delete;