UDP-receiver - improve high-scale performance by skipping usage of de…

…coder when nop encoding is defined (open-telemetry#28901)

**Description:** Enhancement - In udp receiver (stanza operator), change
handleMessage not to call decode method in case nop encoding is defined,
as it's unnecessary.
This improves performance in high scale scenarios by reducing memory
allocations.

**Link to tracking Issue:** <28899

**Testing:** Ran existing unitests.
Ran ran stress tests (sending 250k udp packets per second) - memory
allocation reduced by 10-20%.

**Documentation:** None

.chloggen/pkg-stanza-input-udp-dont-call-decode-on-nop.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: pkg/stanza
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Improve performance by not calling decode when nop encoding is defined
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [28899]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

pkg/stanza/operator/input/udp/udp.go

@@ -314,10 +314,14 @@ func truncateMaxLog(data []byte) (token []byte) {
 }
 
 func (u *Input) handleMessage(ctx context.Context, remoteAddr net.Addr, dec *decode.Decoder, log []byte) {
-	decoded, err := dec.Decode(log)
-	if err != nil {
-		u.Errorw("Failed to decode data", zap.Error(err))
-		return
+	decoded := log
+	if u.encoding != encoding.Nop {
+		var err error
+		decoded, err = dec.Decode(log)
+		if err != nil {
+			u.Errorw("Failed to decode data", zap.Error(err))
+			return
+		}
 	}
 
 	entry, err := u.NewEntry(string(decoded))