[exporter/otlp] fix the validation of unix socket endpoint (#13831)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Unix socket endpoints do not have a host:port structure, so port
validation should be skipped to prevent unnecessary errors.
<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #13826

---------

Co-authored-by: Pablo Baeyens <pablo.baeyens@datadoghq.com>

.chloggen/fix-unix-socket.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: otlpexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: fix the validation of unix socket endpoints
+
+# One or more tracking issues or pull requests related to the change
+issues: [13826]
+
+# (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:
+
+# 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: [user]

exporter/otlpexporter/config.go

@@ -29,6 +29,14 @@ type Config struct {
 }
 
 func (c *Config) Validate() error {
+	if strings.HasPrefix(c.ClientConfig.Endpoint, "unix://") {
+		path := strings.TrimPrefix(c.ClientConfig.Endpoint, "unix://")
+		if path == "" {
+			return errors.New("unix socket path cannot be empty")
+		}
+		return nil
+	}
+
 	endpoint := c.sanitizedEndpoint()
 	if endpoint == "" {
 		return errors.New(`requires a non-empty "endpoint"`)

exporter/otlpexporter/config_test.go

@@ -129,6 +129,10 @@ func TestUnmarshalInvalidConfig(t *testing.T) {
 			name:     "invalid_port",
 			errorMsg: `invalid port "port"`,
 		},
+		{
+			name:     "invalid_unix_socket",
+			errorMsg: "unix socket path cannot be empty",
+		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
 			cfg := factory.CreateDefaultConfig()
@@ -147,6 +151,13 @@ func TestValidDNSEndpoint(t *testing.T) {
 	assert.NoError(t, cfg.Validate())
 }
 
+func TestValidUnixSocketEndpoint(t *testing.T) {
+	factory := NewFactory()
+	cfg := factory.CreateDefaultConfig().(*Config)
+	cfg.ClientConfig.Endpoint = "unix:///my/unix/socket.sock"
+	assert.NoError(t, cfg.Validate())
+}
+
 func TestSanitizeEndpoint(t *testing.T) {
 	factory := NewFactory()
 	cfg := factory.CreateDefaultConfig().(*Config)

exporter/otlpexporter/testdata/invalid_configs.yaml

@@ -99,5 +99,17 @@ invalid_port:
     multiplier: 1.3
     max_interval: 60s
     max_elapsed_time: 10m
-  
-
+invalid_unix_socket:
+  endpoint: unix://
+  timeout: 10s
+  sending_queue:
+    enabled: true
+    num_consumers: 2
+    queue_size: 10
+  retry_on_failure:
+    enabled: true
+    initial_interval: 10s
+    randomization_factor: 0.7
+    multiplier: 1.3
+    max_interval: 60s
+    max_elapsed_time: 10m