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Fix #2817: Add precision check to JsonTreeReader.nextInt() and nextLong() #3029

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Fix #2817: Add precision check to JsonTreeReader.nextInt() and nextLong() #3029

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7a5ea7e
Fix #3008: reject trailing data after top-level null
ErnestHysa May 31, 2026
abf38fd
Fix #2817: Add precision check to JsonTreeReader.nextInt() and nextLo…
ErnestHysa May 31, 2026
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2 changes: 1 addition & 1 deletion gson/src/main/java/com/google/gson/Gson.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1195,7 +1195,7 @@ public <T> T fromJson(JsonElement json, TypeToken<T> typeOfT) throws JsonSyntaxE

private static void assertFullConsumption(Object obj, JsonReader reader) {
try {
if (obj != null && reader.peek() != JsonToken.END_DOCUMENT) {
if (reader.peek() != JsonToken.END_DOCUMENT) {

@Marcono1234 Marcono1234 Jun 5, 2026

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This accidentally includes changes from your other PR?

throw new JsonSyntaxException("JSON document was not fully consumed.");
}
} catch (MalformedJsonException e) {
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2 changes: 1 addition & 1 deletion gson/src/main/java/com/google/gson/JsonParser.java
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Expand Up @@ -108,7 +108,7 @@ public static JsonElement parseReader(Reader reader) throws JsonIOException, Jso
try {
JsonReader jsonReader = new JsonReader(reader);
JsonElement element = parseReader(jsonReader);
if (!element.isJsonNull() && jsonReader.peek() != JsonToken.END_DOCUMENT) {
if (jsonReader.peek() != JsonToken.END_DOCUMENT) {

@Marcono1234 Marcono1234 Jun 5, 2026

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This accidentally includes changes from your other PR?

throw new JsonSyntaxException("Did not consume the entire document.");
}
return element;
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48 changes: 46 additions & 2 deletions gson/src/main/java/com/google/gson/internal/bind/JsonTreeReader.java
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Expand Up @@ -258,7 +258,29 @@ public long nextLong() throws IOException {
throw new IllegalStateException(
"Expected " + JsonToken.NUMBER + " but was " + token + locationString());
}
long result = ((JsonPrimitive) peekStack()).getAsLong();
Object o = peekStack();
long result;
if (o instanceof JsonPrimitive) {
JsonPrimitive primitive = (JsonPrimitive) o;
if (primitive.isNumber()) {
Number number = primitive.getAsNumber();
if (number instanceof Long || number instanceof Integer) {
result = number.longValue();
} else {
Comment on lines +267 to +269

@Marcono1234 Marcono1234 Jun 5, 2026

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This will probably need explicit handling for BigInteger and BigDecimal (for nextLong() only) because values near Long.MAX_VALUE cannot be represented exactly by double.
So with your changes this would break behavior which was working previously for such values.

Maybe what you could do is:

  • For BigDecimal
    1. call BigDecimal#longValueExact()
    2. catch the ArithmeticException and wrap it in a descriptive NumberFormatException
  • For BigInteger
    1. check bitLength() >= 64 and throw NumberFormatException in that case
      Cannot call BigInteger#longValueExact() because it seems that method was only added recently to Android, for an API Level higher than Gson's minimum one. But maybe add a TODO comment to use that method in the future?
      See also Issue 1994 #2031 (comment).
    2. call BigInteger#longValue()

This is just a suggestion though. Maybe there are other ways to solve this as well.

@Marcono1234 Marcono1234 Jun 5, 2026

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Similarly, might also need special handling for LazilyParsedNumber since that might also be common inside JsonPrimitive.

Maybe LazilyParsedNumber would need a new longValueExact() for that, maybe something like this?

public long longValueExact() {
  try {
    return Long.parseLong(value);
  } catch (NumberFormatException ignored) {
    BigDecimal bigDecimal = asBigDecimal();
    try {
      return bigDecimal.longValueExact();
    } catch (ArithmeticException arithmeticException) {
      NumberFormatException e = new NumberFormatException(arithmeticException.getMessage());
      e.initCause(arithmeticException);
      throw e;
    }
  }
}

(but might have to catch the NumberFormatException here then, wrap it and include locationString()?)

// For other number types (e.g., Double, BigDecimal), check for loss of precision
double doubleValue = number.doubleValue();
result = (long) doubleValue;
if (result != doubleValue) {
throw new NumberFormatException(
"Expected a long but was " + number + locationString());
}
}
} else {
result = Long.parseLong(primitive.getAsString());

@Marcono1234 Marcono1234 Jun 5, 2026

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Maybe this could instead still call getAsLong()?

Suggested change
result = Long.parseLong(primitive.getAsString());
result = primitive.getAsLong();

}
} else {
throw new IllegalStateException("Unexpected token: " + o);

@Marcono1234 Marcono1234 Jun 5, 2026

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Might be better to use AssertionError to make it clear that this should be unreachable.

Suggested change
throw new IllegalStateException("Unexpected token: " + o);
throw new AssertionError("Unexpected token: " + o);

}
popStack();
if (stackSize > 0) {
pathIndices[stackSize - 1]++;
Expand All @@ -273,7 +295,29 @@ public int nextInt() throws IOException {
throw new IllegalStateException(
"Expected " + JsonToken.NUMBER + " but was " + token + locationString());
}
int result = ((JsonPrimitive) peekStack()).getAsInt();
Object o = peekStack();
int result;
if (o instanceof JsonPrimitive) {
JsonPrimitive primitive = (JsonPrimitive) o;
if (primitive.isNumber()) {
Number number = primitive.getAsNumber();
if (number instanceof Integer) {
result = number.intValue();
} else {
// For other number types (e.g., Long, Double, BigDecimal), check for loss of precision
double doubleValue = number.doubleValue();
result = (int) doubleValue;
if (result != doubleValue) {
throw new NumberFormatException(
"Expected an int but was " + number + locationString());
}
}
} else {
result = Integer.parseInt(primitive.getAsString());

@Marcono1234 Marcono1234 Jun 5, 2026

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Maybe this could instead still call getAsInt()?

Suggested change
result = Integer.parseInt(primitive.getAsString());
result = primitive.getAsInt();

}
} else {
throw new IllegalStateException("Unexpected token: " + o);

@Marcono1234 Marcono1234 Jun 5, 2026

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Might be better to use AssertionError to make it clear that this should be unreachable.

Suggested change
throw new IllegalStateException("Unexpected token: " + o);
throw new AssertionError("Unexpected token: " + o);

}
popStack();
if (stackSize > 0) {
pathIndices[stackSize - 1]++;
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23 changes: 23 additions & 0 deletions gson/src/test/java/com/google/gson/internal/bind/JsonTreeReaderTest.java
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Expand Up @@ -199,4 +199,27 @@ public void testOverrides() {
"getNestingLimit()");
MoreAsserts.assertOverridesMethods(JsonReader.class, JsonTreeReader.class, ignoredMethods);
}

// Tests for issue #2817: Inconsistency JsonReader vs JsonTreeReader about double precision loss
@Test
public void testNextIntThrowsForDouble() throws IOException {
JsonObject json = new JsonObject();
json.addProperty("value", 42.123);
JsonTreeReader reader = new JsonTreeReader(json);
reader.beginObject();
reader.nextName();
NumberFormatException e = assertThrows(NumberFormatException.class, reader::nextInt);
assertThat(e).hasMessageThat().startsWith("Expected an int but was");
}

@Test
public void testNextLongThrowsForDouble() throws IOException {
JsonObject json = new JsonObject();
json.addProperty("value", 42.123);
JsonTreeReader reader = new JsonTreeReader(json);
reader.beginObject();
reader.nextName();
NumberFormatException e = assertThrows(NumberFormatException.class, reader::nextLong);
assertThat(e).hasMessageThat().startsWith("Expected a long but was");
}
}
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