Merge pull request #165 from ladyada-eagleclaw/main

Fix bounded termination of checksum-delimited NMEA text

extras/tests/parse_str/parse_str.ino

@@ -0,0 +1,54 @@
+// Two-sentence regression test. Runs without a GPS receiver.
+
+#include <Adafruit_GPS.h>
+
+Adafruit_GPS GPS;
+bool testsPassed = false;
+
+void setup() {
+  Serial.begin(115200);
+  // Wait briefly for the Serial Monitor on native USB boards.
+  while (!Serial && millis() < 5000) {
+    delay(10);
+  }
+  delay(250);
+  Serial.println("Adafruit GPS text field bounds regression");
+
+  char valid[] =
+      "$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47";
+  Serial.println(valid);
+  if (!GPS.parse(valid)) {
+    Serial.println("FAIL: valid GGA sentence did not parse");
+    return;
+  }
+  Serial.println("PASS: valid GGA sentence parsed");
+
+  // Valid checksum, but the unknown identifier exceeds the 19-character
+  // destination. Before the fix, its terminator overwrites lastSource[0].
+  char invalid[] = "$GPXXXXXXXXXXXXXXXXXXXX*17";
+  Serial.println(invalid);
+  if (GPS.parse(invalid)) {
+    Serial.println("FAIL: unknown sentence was accepted");
+    return;
+  }
+  Serial.println("PASS: unknown sentence rejected");
+
+  // Rejection alone passed before the fix too. The last valid sentence's
+  // identity must also survive, proving that the rejected input stayed in bounds.
+  if (strcmp(GPS.lastSource, "GP") != 0 ||
+      strcmp(GPS.lastSentence, "GGA") != 0) {
+    Serial.println("FAIL: rejected sentence corrupted the previous result");
+    return;
+  }
+  Serial.println("PASS: previous result preserved");
+  testsPassed = true;
+}
+
+void loop() {
+  if (testsPassed) {
+    Serial.println("PASS: two-sentence regression");
+  } else {
+    Serial.println("FAIL: two-sentence regression");
+  }
+  delay(2000);
+}

src/NMEA_parse.cpp

@@ -760,7 +760,7 @@ char *Adafruit_GPS::parseStr(char *buff, char *p, int n) {
     if (e) {
       len = min(int(e - p), n - 1);
       strncpy(buff, p, len); // or up to the *
-      buff[e - p] = 0;
+      buff[len] = 0;
     } else {
       len = min((int)strlen(p), n - 1);
       strncpy(buff, p, len); // or to the end or max capacity