protocol/ArgParser: disallow negative seek times

Instead of stopping playback (due to seek time overflow), reject the seek command. Closes #240 Relative negative values (with "seekcur") are still allowed, and MPD will fix the resulting position if it turns out to be negative. But the "seek" and "seekid" commands use an unsigned time stamp which must not be negative.

protocol/ArgParser: disallow negative seek times
dadd3ca6 · Max Kellermann · 79535212 · dadd3ca6 · dadd3ca6
Commit dadd3ca6 authored Mar 04, 2018 by Max Kellermann
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NEWS NEWS +2 -0

ArgParser.cxx src/protocol/ArgParser.cxx +4 -0

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--- a/NEWS
+++ b/NEWS
 ver 0.20.19 (not yet released)
+* protocol
+  - validate absolute seek time, reject negative values
 * macOS: fix crash bug

 ver 0.20.18 (2018/02/24)

--- a/src/protocol/ArgParser.cxx
+++ b/src/protocol/ArgParser.cxx
@@ -164,6 +164,10 @@ SongTime
 ParseCommandArgSongTime(const char *s)
 {
 	auto value = ParseCommandArgFloat(s);
+	if (value < 0)
+		throw FormatProtocolError(ACK_ERROR_ARG,
+					  "Negative value not allowed: %s", s);
+
 	return SongTime::FromS(value);
 }