Add runtime enumeration of supported schemas.

Fix src/ls.cxx to only print unique schemas.
Refactor src/ls.cxx to use src/input/InputPlugin functionality.

Add dynamic enumeration support to curl plugin.

src/input/plugins/AlsaInputPlugin.cxx

@@ -486,4 +486,5 @@ const struct InputPlugin input_plugin_alsa = {
 	alsa_input_init,
 	nullptr,
 	alsa_input_open,
+	nullptr
 };

src/input/plugins/CdioParanoiaInputPlugin.cxx

@@ -357,4 +357,5 @@ const InputPlugin input_plugin_cdio_paranoia = {
 	input_cdio_init,
 	nullptr,
 	input_cdio_open,
+	nullptr
 };

src/input/plugins/CurlInputPlugin.cxx

@@ -471,16 +471,25 @@ input_curl_open(const char *url, Mutex &mutex)
 	return CurlInputStream::Open(url, {}, mutex);
 }
 
-static constexpr const char *curl_prefixes[] = {
-	"http://",
-	"https://",
-	nullptr
-};
+static std::set<std::string>
+input_curl_protocols() {
+	std::set<std::string> protocols;
+	auto version_info = curl_version_info(CURLVERSION_FIRST);
+	for (auto proto_ptr = version_info->protocols; *proto_ptr != nullptr; proto_ptr++) {
+		if (protocol_is_whitelisted(*proto_ptr)) {
+			std::string schema(*proto_ptr);
+			schema.append("://");
+			protocols.emplace(schema);
+		}
+	}
+	return protocols;
+}
 
 const struct InputPlugin input_plugin_curl = {
 	"curl",
-	curl_prefixes,
+	nullptr,
 	input_curl_init,
 	input_curl_finish,
 	input_curl_open,
+	input_curl_protocols
 };

src/input/plugins/FfmpegInputPlugin.cxx

@@ -25,8 +25,13 @@
 #include "lib/ffmpeg/Init.hxx"
 #include "lib/ffmpeg/Error.hxx"
 #include "../InputStream.hxx"
-#include "../InputPlugin.hxx"
 #include "PluginUnavailable.hxx"
+#include "util/StringAPI.hxx"
+#include "../InputPlugin.hxx"
+#include <iostream>
+#include <exception>
+#include <typeinfo>
+#include <stdexcept>
 
 class FfmpegInputStream final : public InputStream {
 	Ffmpeg::IOContext io;
@@ -71,6 +76,22 @@ input_ffmpeg_init(EventLoop &, const ConfigBlock &)
 		throw PluginUnavailable("No protocol");
 }
 
+static std::set<std::string>
+input_ffmpeg_protocols() {
+	void *opaque = nullptr;
+	const char* protocol;
+	std::set<std::string> protocols;
+	while ((protocol = avio_enum_protocols(&opaque, 0))) {
+		if (protocol_is_whitelisted(protocol)) {
+			std::string schema(protocol);
+			schema.append("://");
+			protocols.emplace(schema);
+		}
+	}
+	
+	return protocols;
+}
+
 static InputStreamPtr
 input_ffmpeg_open(const char *uri,
 		  Mutex &mutex)
@@ -111,20 +132,11 @@ FfmpegInputStream::Seek(offset_type new_offset)
 	offset = result;
 }
 
-static constexpr const char *ffmpeg_prefixes[] = {
-	"gopher://",
-	"rtp://",
-	"rtsp://",
-	"rtmp://",
-	"rtmpt://",
-	"rtmps://",
-	nullptr
-};
-
 const InputPlugin input_plugin_ffmpeg = {
 	"ffmpeg",
-	ffmpeg_prefixes,
+	nullptr,
 	input_ffmpeg_init,
 	nullptr,
 	input_ffmpeg_open,
+	input_ffmpeg_protocols
 };

src/input/plugins/MmsInputPlugin.cxx

@@ -110,4 +110,5 @@ const InputPlugin input_plugin_mms = {
 	nullptr,
 	nullptr,
 	input_mms_open,
+	nullptr
 };

src/input/plugins/NfsInputPlugin.cxx

@@ -232,4 +232,5 @@ const InputPlugin input_plugin_nfs = {
 	input_nfs_init,
 	input_nfs_finish,
 	input_nfs_open,
+	nullptr
 };

src/input/plugins/QobuzInputPlugin.cxx

@@ -219,5 +219,6 @@ const InputPlugin qobuz_input_plugin = {
 	InitQobuzInput,
 	FinishQobuzInput,
 	OpenQobuzInput,
+	nullptr,
 	ScanQobuzTags,
 };

src/input/plugins/SmbclientInputPlugin.cxx

@@ -162,4 +162,5 @@ const InputPlugin input_plugin_smbclient = {
 	input_smbclient_init,
 	nullptr,
 	input_smbclient_open,
+	nullptr
 };

src/input/plugins/TidalInputPlugin.cxx

@@ -249,5 +249,6 @@ const InputPlugin tidal_input_plugin = {
 	InitTidalInput,
 	FinishTidalInput,
 	OpenTidalInput,
+	nullptr,
 	ScanTidalTags,
 };