Merge pull request #4641 from telefonicaid/hardening/large-float-numbers

FIX improve double2string function to cope with very large float numbers

CHANGES_NEXT_RELEASE

@@ -1,3 +1,4 @@
+- Fix: rendering of large float numbers (according IEEE754 standard) (#4642)
 - Fix: improve attribute and metadata invalid format dates for DateTime types in logs (#4616)
 - Hardening: upgrade microhttpd dependency from 0.9.76 to 1.0.1
 - Hardening: upgrade libmosquitto dependency from 2.0.15 to 2.0.20

src/lib/common/string.cpp

@@ -22,6 +22,7 @@
 *
 * Author: Ken Zangelin
 */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string>
@@ -964,11 +965,17 @@ std::string double2string(double f)
   long long  intPart   = (long long) f;
   double     diff      = f - intPart;
   bool       isInteger = false;
+  bool       large     = false;
 
   // abs value for 'diff'
   diff = (diff < 0)? -diff : diff;
 
-  if (diff > 0.9999999998)
+  if (diff > 1)
+  {
+    // this is an overflow situation, pe. f = 1.79e308
+    large = true;
+  }
+  else if (diff > 0.9999999998)
   {
     intPart += 1;
     isInteger = true;
@@ -984,7 +991,14 @@ std::string double2string(double f)
   }
   else
   {
-    snprintf(buf, bufSize, "%.9f", f);
+    if (large)
+    {
+      snprintf(buf, bufSize, "%.17g", f);
+    }
+    else
+    {
+      snprintf(buf, bufSize, "%.9f", f);
+    }
 
     // Clear out any unwanted trailing zeroes
     char* last = &buf[strlen(buf) - 1];

test/functionalTest/cases/4642_large_float_numbers/large_float_numbers.test

@@ -0,0 +1,131 @@
+# Copyright 2025 Telefonica Investigacion y Desarrollo, S.A.U
+#
+# This file is part of Orion Context Broker.
+#
+# Orion Context Broker is free software: you can redistribute it and/or
+# modify it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# Orion Context Broker is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero
+# General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with Orion Context Broker. If not, see http://www.gnu.org/licenses/.
+#
+# For those usages not covered by this license please contact with
+# iot_support at tid dot es
+
+# VALGRIND_READY - to mark the test ready for valgrindTestSuite.sh
+
+--NAME--
+Large float numbers in attributes
+
+--SHELL-INIT--
+dbInit CB
+brokerStart CB
+
+--SHELL--
+
+# We are using the the limits included in the IEEE754 standard. However, note that
+# min non zero cases are rounded to 0 due to how double2string() function is implemented
+# (ten digits precision). We could remove that rounding, but consequences may not be
+# backward compatible (eg. places where we have now 1.7 could become in 1.666666666666666666669)
+#
+# 01. Create entity with large float number
+# 02. Retrieve entity with large float numbers
+#
+
+echo "01. Create entity with large float number"
+echo "========================================="
+payload='{
+  "id": "E",
+  "type": "T",
+  "A": {
+    "value": 1.79e308,
+    "type": "Number"
+  },
+  "maxPositive": {
+    "value": 1.7976931348623157e308,
+    "type": "Number"
+  },
+  "minNonZeroPositive": {
+    "value": 4.9406564584124654e-324,
+    "type": "Number"
+  },
+  "maxNegative": {
+    "value": -1.7976931348623157e308,
+    "type": "Number"
+  },
+  "minNonZeroNegative": {
+    "value": -4.9406564584124654e-324,
+    "type": "Number"
+  }
+}'
+orionCurl --url '/v2/entities' --payload "$payload"
+echo
+echo
+
+
+echo "02. Retrieve entity with large float numbers"
+echo "============================================"
+orionCurl --url '/v2/entities/E'
+echo
+echo
+
+
+--REGEXPECT--
+01. Create entity with large float number
+=========================================
+HTTP/1.1 201 Created
+Date: REGEX(.*)
+Fiware-Correlator: REGEX([0-9a-f\-]{36})
+Location: /v2/entities/E?type=T
+Content-Length: 0
+
+
+
+02. Retrieve entity with large float numbers
+============================================
+HTTP/1.1 200 OK
+Date: REGEX(.*)
+Fiware-Correlator: REGEX([0-9a-f\-]{36})
+Content-Type: application/json
+Content-Length: 358
+
+{
+    "A": {
+        "metadata": {},
+        "type": "Number",
+        "value": 1.79e+308
+    },
+    "id": "E",
+    "maxNegative": {
+        "metadata": {},
+        "type": "Number",
+        "value": -1.7976931348623157e+308
+    },
+    "maxPositive": {
+        "metadata": {},
+        "type": "Number",
+        "value": 1.7976931348623157e+308
+    },
+    "minNonZeroNegative": {
+        "metadata": {},
+        "type": "Number",
+        "value": 0
+    },
+    "minNonZeroPositive": {
+        "metadata": {},
+        "type": "Number",
+        "value": 0
+    },
+    "type": "T"
+}
+
+
+--TEARDOWN--
+brokerStop CB
+dbDrop CB