[SLES-2547] add metric namespace for DogStatsD (#920)

Follow up from DataDog/serverless-components#48

What does this PR do?
Add support for DD_STATSD_METRIC_NAMESPACE.

Motivation
This was brought up by a customer, they noticed issues migrating to
bottlecap. Our docs show we should support this, but we currently don't
have it implemented -
https://docs.datadoghq.com/serverless/guide/agent_configuration/#dogstatsd-custom-metrics.

Additional Notes
Requires changes in agent/extension. Will follow up with those PRs.

Describe how to test/QA your changes
Deployed changes to extension and tested with / without the custom
namespace env variable. Confirmed that metrics are getting the prefix
attached,
[metrics](https://ddserverless.datadoghq.com/metric/explorer?fromUser=false&graph_layout=stacked&start=1762783238873&end=1762784138873&paused=false#N4Ig7glgJg5gpgFxALlAGwIYE8D2BXJVEADxQEYAaELcqyKBAC1pEbghkcLIF8qo4AMwgA7CAgg4RKUAiwAHOChASAtnADOcAE4RNIKtrgBHPJoQaUAbVBGN8qVoD6gnNtUZCKiOq279VKY6epbINiAiGOrKQdpYZAYgUJ4YThr42gDGSsgg6gi6mZaBZnHKGABuMMiZeBoIOKoAdPJYTFJNcMRwtRIdmfgiCMAAVDwgfKCR0bmxWABMickIqel4WTl5iIXFIHPlVcgAVjiMIk3TmvIY2U219Y0tbYwdXT0EkucDeEOj4zwAXSornceEwoXCINUYIwMVK8QmFFAUJhcJ0CwmQJA9SwaByoGueIQCE2UBwMCcmXBGggmUSaFEcCcckUynSDKg9MZTnoTGUIjcHjQiKSEHsmCwzIUmwZIiUgJ4fGx8gZCAAwlJhDAUCIwWgeEA)

Author: jchrostek-dd

bottlecap/Cargo.lock

@@ -63,8 +63,8 @@ datadog-trace-utils = { git = "https://github.com/DataDog/libdatadog", rev = "ba
 datadog-trace-normalization = { git = "https://github.com/DataDog/libdatadog",  rev = "ba8955394cf35cf24a1a508fbe6264ad84702567" }
 datadog-trace-obfuscation = { git = "https://github.com/DataDog/libdatadog", rev = "ba8955394cf35cf24a1a508fbe6264ad84702567"  }
 datadog-trace-stats = { git = "https://github.com/DataDog/libdatadog", rev = "ba8955394cf35cf24a1a508fbe6264ad84702567"  }
-dogstatsd = { git = "https://github.com/DataDog/serverless-components", rev = "05b9dee1ac7c72d296ea12e85685c026cb6dbaaf", default-features = false }
-datadog-fips = { git = "https://github.com/DataDog/serverless-components", rev = "05b9dee1ac7c72d296ea12e85685c026cb6dbaaf", default-features = false }
+dogstatsd = { git = "https://github.com/DataDog/serverless-components", rev = "aa7961984f221ec3f1048ebf3379c4b94a33be0e", default-features = false }
+datadog-fips = { git = "https://github.com/DataDog/serverless-components", rev = "aa7961984f221ec3f1048ebf3379c4b94a33be0e", default-features = false }
 libddwaf = { version = "1.28.1", git = "https://github.com/DataDog/libddwaf-rust", rev = "d1534a158d976bd4f747bf9fcc58e0712d2d17fc", default-features = false, features = ["serde"] }
 
 [dev-dependencies]

bottlecap/Cargo.toml

@@ -1164,6 +1164,7 @@ async fn start_dogstatsd(
     let dogstatsd_config = DogStatsDConfig {
         host: EXTENSION_HOST.to_string(),
         port: DOGSTATSD_PORT,
+        metric_namespace: config.statsd_metric_namespace.clone(),
     };
     let cancel_token = tokio_util::sync::CancellationToken::new();
     let dogstatsd_agent = DogStatsD::new(

bottlecap/src/bin/bottlecap/main.rs

@@ -266,6 +266,11 @@ pub struct EnvConfig {
     #[serde(deserialize_with = "deserialize_option_lossless")]
     pub metrics_config_compression_level: Option<i32>,
 
+    /// @env `DD_STATSD_METRIC_NAMESPACE`
+    /// Prefix all `StatsD` metrics with a namespace.
+    #[serde(deserialize_with = "deserialize_optional_string")]
+    pub statsd_metric_namespace: Option<String>,
+
     // OTLP
     //
     // - APM / Traces
@@ -521,6 +526,10 @@ fn merge_config(config: &mut Config, env_config: &EnvConfig) {
     );
     merge_option_to_value!(config, env_config, metrics_config_compression_level);
 
+    if let Some(namespace) = &env_config.statsd_metric_namespace {
+        config.statsd_metric_namespace = super::validate_metric_namespace(namespace);
+    }
+
     // OTLP
     merge_option_to_value!(config, env_config, otlp_config_traces_enabled);
     merge_option_to_value!(
@@ -938,6 +947,7 @@ mod tests {
                 otlp_config_metrics_summaries_mode: Some("quantiles".to_string()),
                 otlp_config_traces_probabilistic_sampler_sampling_percentage: Some(50),
                 otlp_config_logs_enabled: true,
+                statsd_metric_namespace: None,
                 api_key_secret_arn: "arn:aws:secretsmanager:region:account:secret:datadog-api-key"
                     .to_string(),
                 kms_api_key: "test-kms-key".to_string(),

bottlecap/src/config/env.rs

@@ -298,6 +298,7 @@ pub struct Config {
 
     // Metrics
     pub metrics_config_compression_level: i32,
+    pub statsd_metric_namespace: Option<String>,
 
     // OTLP
     //
@@ -411,6 +412,7 @@ impl Default for Config {
 
             // Metrics
             metrics_config_compression_level: 3,
+            statsd_metric_namespace: None,
 
             // OTLP
             otlp_config_traces_enabled: true,
@@ -699,6 +701,39 @@ where
     }
 }
 
+fn validate_metric_namespace(namespace: &str) -> Option<String> {
+    let trimmed = namespace.trim();
+    if trimmed.is_empty() {
+        return None;
+    }
+
+    let mut chars = trimmed.chars();
+
+    if let Some(first_char) = chars.next() {
+        if !first_char.is_ascii_alphabetic() {
+            error!(
+                "DD_STATSD_METRIC_NAMESPACE must start with a letter, got: '{}'. Ignoring namespace.",
+                trimmed
+            );
+            return None;
+        }
+    } else {
+        return None;
+    }
+
+    if let Some(invalid_char) =
+        chars.find(|&ch| !ch.is_ascii_alphanumeric() && ch != '_' && ch != '.')
+    {
+        error!(
+            "DD_STATSD_METRIC_NAMESPACE contains invalid character '{}' in '{}'. Only ASCII alphanumerics, underscores, and periods are allowed. Ignoring namespace.",
+            invalid_char, trimmed
+        );
+        return None;
+    }
+
+    Some(trimmed.to_string())
+}
+
 pub fn deserialize_option_lossless<'de, D, T>(deserializer: D) -> Result<Option<T>, D::Error>
 where
     D: Deserializer<'de>,
@@ -1476,4 +1511,53 @@ pub mod tests {
         expected.insert("valid".to_string(), "tag".to_string());
         assert_eq!(result.tags, expected);
     }
+
+    #[test]
+    fn test_validate_metric_namespace_valid() {
+        assert_eq!(
+            validate_metric_namespace("myapp"),
+            Some("myapp".to_string())
+        );
+        assert_eq!(
+            validate_metric_namespace("my_app"),
+            Some("my_app".to_string())
+        );
+        assert_eq!(
+            validate_metric_namespace("my.app"),
+            Some("my.app".to_string())
+        );
+        assert_eq!(
+            validate_metric_namespace("MyApp123"),
+            Some("MyApp123".to_string())
+        );
+        assert_eq!(
+            validate_metric_namespace("  myapp  "),
+            Some("myapp".to_string())
+        );
+    }
+
+    #[test]
+    fn test_validate_metric_namespace_empty() {
+        assert_eq!(validate_metric_namespace(""), None);
+        assert_eq!(validate_metric_namespace("   "), None);
+        assert_eq!(validate_metric_namespace("\t\n"), None);
+    }
+
+    #[test]
+    fn test_validate_metric_namespace_invalid_first_char() {
+        assert_eq!(validate_metric_namespace("1myapp"), None);
+        assert_eq!(validate_metric_namespace("_myapp"), None);
+        assert_eq!(validate_metric_namespace(".myapp"), None);
+        assert_eq!(validate_metric_namespace("-myapp"), None);
+    }
+
+    #[test]
+    fn test_validate_metric_namespace_invalid_chars() {
+        assert_eq!(validate_metric_namespace("my-app"), None);
+        assert_eq!(validate_metric_namespace("my app"), None);
+        assert_eq!(validate_metric_namespace("my@app"), None);
+        assert_eq!(validate_metric_namespace("my#app"), None);
+        assert_eq!(validate_metric_namespace("my$app"), None);
+        assert_eq!(validate_metric_namespace("my!app"), None);
+    }
 }

bottlecap/src/config/mod.rs

@@ -993,6 +993,7 @@ api_security_sample_delay: 60 # Seconds
                 apm_filter_tags_reject: None,
                 apm_filter_tags_regex_require: None,
                 apm_filter_tags_regex_reject: None,
+                statsd_metric_namespace: None,
             };
 
             // Assert that