Fix and test infinity handling

Author: JonasKunz

x-pack/plugin/mapper-exponential-histogram/src/main/java/org/elasticsearch/xpack/exponentialhistogram/ExponentialHistogramFieldMapper.java

@@ -304,9 +304,7 @@ public void parse(DocumentParserContext context) throws IOException {
                         );
                     }
                 } else if (fieldName.equals(SUM_FIELD.getPreferredName())) {
-                    token = subParser.nextToken();
-                    ensureExpectedToken(XContentParser.Token.VALUE_NUMBER, token, subParser);
-                    sum = subParser.doubleValue();
+                    sum = parseDoubleAllowingInfinity(subParser);
                 } else if (fieldName.equals(ZERO_FIELD.getPreferredName())) {
                     zeroBucket = parseZeroBucket(subParser);
                 } else if (fieldName.equals(POSITIVE_FIELD.getPreferredName())) {
@@ -407,6 +405,24 @@ public void parse(DocumentParserContext context) throws IOException {
         context.path().remove();
     }
 
+    private double parseDoubleAllowingInfinity(XContentParser parser) throws IOException {
+        XContentParser.Token token = parser.nextToken();
+        boolean isValidNumber = token == XContentParser.Token.VALUE_NUMBER;
+        if (token == XContentParser.Token.VALUE_STRING) {
+            String text = parser.text();
+            if (text.equals("-Infinity") || text.equals("Infinity")) {
+                isValidNumber = true;
+            }
+        }
+        if (isValidNumber) {
+            return parser.doubleValue();
+        }
+        throw new DocumentParsingException(
+            parser.getTokenLocation(),
+            "error parsing field [" + fullPath() + "], expected a number but got " + token
+        );
+    }
+
     private static long getTotalValueCount(
         ParsedZeroBucket zeroBucket,
         List<IndexWithCount> positiveBuckets,

x-pack/plugin/mapper-exponential-histogram/src/test/java/org/elasticsearch/xpack/exponentialhistogram/ExponentialHistogramFieldMapperTests.java

@@ -129,7 +129,9 @@ private static Map<String, Object> createRandomHistogramValue(int maxBucketCount
                 Map.of("indices", negativeIndices, "counts", negativeCounts)
             )
         );
-        if (randomBoolean() && (positiveIndices.isEmpty() == false || negativeIndices.isEmpty() == false)) {
+        if ((positiveIndices.isEmpty() == false || negativeIndices.isEmpty() == false)) {
+            // we always add the sum field to avoid numeric problems with the estimation due to random buckets
+            // sum generation is tested in the yaml tests
             result.put("sum", randomDoubleBetween(-1000, 1000, true));
         }
         return result;

x-pack/plugin/mapper-exponential-histogram/src/yamlRestTest/resources/rest-api-spec/test/10_synthetic_source.yml

@@ -279,3 +279,55 @@ setup:
         negative:
           indices: [0, 1]
           counts: [1, 5]
+
+---
+"Positive infinity sum":
+  - do:
+      index:
+        index: test_exponential_histogram
+        id: "1"
+        refresh: true
+        body:
+          my_histo:
+            scale: 0
+            positive:
+              indices: [2000]
+              counts: [1]
+
+  - do:
+      get:
+        index: test_exponential_histogram
+        id: "1"
+  - match:
+      _source.my_histo:
+        scale: 0
+        sum: Infinity
+        positive:
+          indices: [2000]
+          counts: [1]
+
+---
+"negative infinity sum":
+  - do:
+      index:
+        index: test_exponential_histogram
+        id: "1"
+        refresh: true
+        body:
+          my_histo:
+            scale: 0
+            negative:
+              indices: [2000]
+              counts: [1]
+
+  - do:
+      get:
+        index: test_exponential_histogram
+        id: "1"
+  - match:
+      _source.my_histo:
+        scale: 0
+        sum: -Infinity
+        negative:
+          indices: [2000]
+          counts: [1]