ESQL: Fix IpPrefix function not handling correctly ByteRefs (elastic#…

…109205)

- Fix IpPrefix function not using ByteRef offset on calculations, leading to wrong bytes being written to the prefix.
- Fixed the CSVTest case, which was also wrong, leading to a "_wrong * wrong = correct_" situation.
-  ~~Added` a BytesRef randomizer and applied it to the IpPrefixTests suppliers~~
    - ~~This highlighted another bug, which was fixed too~~
    - (Moved to elastic#109207)

Fixes elastic#109198

docs/changelog/109205.yaml

@@ -0,0 +1,6 @@
+pr: 109205
+summary: "ESQL: Fix `IpPrefix` function not handling correctly `ByteRefs`"
+area: ES|QL
+type: bug
+issues:
+ - 109198

muted-tests.yml

@@ -49,9 +49,6 @@ tests:
 - class: "org.elasticsearch.upgrades.SearchStatesIT"
   issue: "https://github.com/elastic/elasticsearch/issues/109190"
   method: "testBWCSearchStates"
-- class: "org.elasticsearch.xpack.esql.CsvTests"
-  issue: "https://github.com/elastic/elasticsearch/issues/109198"
-  method: "test {ip.IpPrefixLengthFromColumn}"
 - class: "org.elasticsearch.xpack.test.rest.XPackRestIT"
   issue: "https://github.com/elastic/elasticsearch/issues/109200"
   method: "test {p0=esql/70_locale/Date format with Italian locale}"

x-pack/plugin/esql/qa/testFixtures/src/main/resources/ip.csv-spec

@@ -531,7 +531,7 @@ required_capability: fn_ip_prefix
 from hosts
 | where host == "alpha"
 | sort card
-| eval prefix = ip_prefix(ip0, 24, 128)
+| eval prefix = ip_prefix(ip0, 24, 120)
 | keep card, ip0, prefix;
 
 card:keyword | ip0:ip    | prefix:ip

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/ip/IpPrefix.java

@@ -136,7 +136,14 @@ static BytesRef process(
             throw new IllegalArgumentException("Prefix length v6 must be in range [0, 128], found " + prefixLengthV6);
         }
 
-        boolean isIpv4 = Arrays.compareUnsigned(ip.bytes, 0, IPV4_PREFIX.length, IPV4_PREFIX, 0, IPV4_PREFIX.length) == 0;
+        boolean isIpv4 = Arrays.compareUnsigned(
+            ip.bytes,
+            ip.offset,
+            ip.offset + IPV4_PREFIX.length,
+            IPV4_PREFIX,
+            0,
+            IPV4_PREFIX.length
+        ) == 0;
 
         if (isIpv4) {
             makePrefix(ip, scratch, 12 + prefixLengthV4 / 8, prefixLengthV4 % 8);
@@ -154,7 +161,7 @@ private static void makePrefix(BytesRef ip, BytesRef scratch, int fullBytes, int
         // Copy the last byte ignoring the trailing bits
         if (remainingBits > 0) {
             byte lastByteMask = (byte) (0xFF << (8 - remainingBits));
-            scratch.bytes[fullBytes] = (byte) (ip.bytes[fullBytes] & lastByteMask);
+            scratch.bytes[fullBytes] = (byte) (ip.bytes[ip.offset + fullBytes] & lastByteMask);
         }
 
         // Copy the last empty bytes