types: ensure double serializatiion with decimal places

The `%g` printf format used for serializing double values into strings will not include any decimal place if the value happens to be integral, leading to an unwanted double to integer conversion when serializing and subsequently deserializing an integral double value as JSON. Solve this issue by checking the serialized string result for a decimal point or exponential notation and appending `.0` if neither is found. Ref: #173 Suggested-by: Felix Fietkau <[email protected]> Signed-off-by: Jo-Philipp Wich <[email protected]>
jow- · Oct 9, 2023 · 7c209d7 · 7c209d7
1 parent 9f9959c
commit 7c209d7
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diff --git a/tests/custom/99_bugs/43_types_json_double_format b/tests/custom/99_bugs/43_types_json_double_format
@@ -0,0 +1,24 @@
+When formatting integral double values as JSON, ensure that at least one
+decimal place is retained.
+
+-- Testcase --
+printf("%.J\n", [
+	1e100,
+	1.23,
+	4.00,
+	1.0/3*3,
+]);
+-- End --
+
+-- Args --
+-R
+-- End --
+
+-- Expect stdout --
+[
+	1e+100,
+	1.23,
+	4.0,
+	1.0
+]
+-- End --
diff --git a/types.c b/types.c
@@ -1561,6 +1561,21 @@ ucv_to_stringbuf_add_padding(uc_stringbuf_t *pb, char pad_char, size_t pad_size)
 	}
 }
 
+static void
+ucv_to_stringbuf_add_double(uc_stringbuf_t *pb, double val, bool json)
+{
+	int len = ucv_stringbuf_printf(pb, "%.14g", val);
+
+	if (!json)
+		return;
+
+	for (char *p = pb->buf + pb->bpos - len; len > 0; len--, p++)
+		if (*p == '.' || *p == 'e')
+			return;
+
+	ucv_stringbuf_append(pb, ".0");
+}
+
 void
 ucv_to_stringbuf_formatted(uc_vm_t *vm, uc_stringbuf_t *pb, uc_value_t *uv, size_t depth, char pad_char, size_t pad_size)
 {
@@ -1624,7 +1639,7 @@ ucv_to_stringbuf_formatted(uc_vm_t *vm, uc_stringbuf_t *pb, uc_value_t *uv, size
 		else if (d == -INFINITY)
 			ucv_stringbuf_append(pb, "-Infinity");
 		else
-			ucv_stringbuf_printf(pb, "%.14g", d);
+			ucv_to_stringbuf_add_double(pb, d, json);
 
 		break;