Fix path JSON: use snprintf length, not declared array size, for MMSI keys

Author: jvde-github

Source/Application/WebViewer.cpp

@@ -973,8 +973,8 @@ std::string WebViewer::buildMultiPathJSON(ReceiverTracker *s, const std::string
 			if (mmsi >= 1 && mmsi <= 999999999)
 			{
 				char keybuf[12];
-				snprintf(keybuf, sizeof(keybuf), "%d", mmsi);
-				w.key(keybuf).raw_val(s ? s->getPathJSON(mmsi) : std::string("{}"));
+				int n = snprintf(keybuf, sizeof(keybuf), "%d", mmsi);
+				w.key(keybuf, n).raw_val(s ? s->getPathJSON(mmsi) : std::string("{}"));
 			}
 		}
 		catch (const std::invalid_argument &)

Source/JSON/StringBuilder.h

@@ -721,6 +721,19 @@ namespace JSON
 			return *this;
 		}
 
+		// Explicit (ptr, len) overload for runtime-built keys (e.g. snprintf
+		// into a stack buffer). Avoids the KeyRef array ctor, which captures
+		// the declared array size N-1 — correct for literals, wrong for
+		// partially-filled buffers.
+		Writer &key(const char *s, size_t n)
+		{
+			reserve_more(n + 4);
+			put_sep_raw();
+			put_kvkey_raw(s, n);
+			need_sep = false;
+			return *this;
+		}
+
 		// Like val() but for already-serialised JSON fragments. Honors need_sep.
 		Writer &raw_val(const char *raw, size_t rawlen)
 		{

Source/Tracking/DB.cpp

@@ -376,8 +376,8 @@ std::string DB::getAllPathJSON()
 					break;
 
 				char keybuf[16];
-				snprintf(keybuf, sizeof(keybuf), "%u", ship.mmsi);
-				w.key(keybuf);
+				int n = snprintf(keybuf, sizeof(keybuf), "%u", ship.mmsi);
+				w.key(keybuf, n);
 				writeSinglePathJSONCompact(ptr, w);
 			}
 			ptr = ships[ptr].incoming.next;
@@ -482,8 +482,8 @@ std::string DB::getAllPathJSONSince(std::time_t since)
 			if (ship.mmsi != 0 && hasPathPointsSince(ptr, since))
 			{
 				char keybuf[16];
-				snprintf(keybuf, sizeof(keybuf), "%u", ship.mmsi);
-				w.key(keybuf);
+				int n = snprintf(keybuf, sizeof(keybuf), "%u", ship.mmsi);
+				w.key(keybuf, n);
 				writeSinglePathJSONCompactSince(ptr, since, w);
 			}
 			ptr = ships[ptr].incoming.next;