Require explicit locales and charsets in tracer code

.agents/skills/perf-review/references/guide.md

@@ -128,7 +128,18 @@ every call. Fix: `static final Pattern`.
 
 **`String.format` / format-string parsing.** Re-parses and allocates per call. Fix: direct
 concatenation, or pre-compute the result. Also watch for locale-dependent formatting crossing the
-wire — a correctness issue on top of the perf one.
+wire - a correctness issue on top of the perf one.
+
+**Explicit locales and charsets.**
+
+- Overloads that use an implicit locale or charset are forbidden.
+- Use:
+  - `Strings.format(...)` for machine-readable formatting where `internal-api` is available.
+  - `Locale.ROOT` for case conversion and direct JDK formatting.
+  - The protocol's charset, usually `StandardCharsets.UTF_8`, for byte conversions.
+  - An explicit JVM default or a narrowly scoped `@SuppressForbidden`, with a comment explaining
+    why the default is intentional.
+- `Strings.format(...)` retains `String.format`'s parsing and allocation costs.
 
 **`Config.get()` per call.** Walks a config-resolution chain; not a free read. Fix: hoist to a
 `static final` field at class initialization. This is the single most recurring DBM finding —

components/environment/src/main/java/datadog/environment/JavaVirtualMachine.java

@@ -122,7 +122,7 @@ public static boolean isZulu8() {
   }
 
   public static boolean isGraalVM() {
-    return runtime.vendorVersion.toLowerCase().contains("graalvm");
+    return runtime.vendorVersion.toLowerCase(Locale.ROOT).contains("graalvm");
   }
 
   public static String getLangVersion() {

components/environment/src/main/java/datadog/environment/OperatingSystem.java

@@ -6,9 +6,11 @@
 import static java.util.Locale.ROOT;
 
 import java.io.BufferedReader;
-import java.io.FileReader;
+import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -88,7 +90,10 @@ public static boolean isMusl() {
   }
 
   private static boolean isMuslProcSelfMaps() throws IOException {
-    try (BufferedReader reader = new BufferedReader(new FileReader("/proc/self/maps"))) {
+    try (BufferedReader reader =
+        new BufferedReader(
+            new InputStreamReader(
+                new FileInputStream("/proc/self/maps"), StandardCharsets.ISO_8859_1))) {
       String line;
       while ((line = reader.readLine()) != null) {
         if (line.contains("-musl-")) {

components/json/src/main/java/datadog/json/JsonReader.java

@@ -6,6 +6,7 @@
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 /**
@@ -490,22 +491,33 @@ private String readLiteral(int length) throws IOException {
   private IOException unexpectedSyntaxError(String expected, String found) {
     return new IOException(
         String.format(
+            Locale.ROOT,
             "Syntax error at line %d, position %d: expected %s but found '%s'",
-            this.lineNumber, this.linePosition, expected, found));
+            this.lineNumber,
+            this.linePosition,
+            expected,
+            found));
   }
 
   private IOException unexpectedSyntaxError(String expected, char found) {
     return new IOException(
         String.format(
+            Locale.ROOT,
             "Syntax error at line %d, position %d: expected %s but found '%s'",
-            this.lineNumber, this.linePosition, expected, found));
+            this.lineNumber,
+            this.linePosition,
+            expected,
+            found));
   }
 
   private IOException syntaxError(String message) {
     return new IOException(
         String.format(
+            Locale.ROOT,
             "Syntax error at line %d, position %d: %s",
-            this.lineNumber, this.linePosition, message));
+            this.lineNumber,
+            this.linePosition,
+            message));
   }
 
   @Override

dd-java-agent/agent-aiguard/src/main/java/com/datadog/aiguard/AIGuardInternal.java

@@ -35,6 +35,7 @@
 import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.bootstrap.instrumentation.api.ClientIpAddressData;
 import datadog.trace.bootstrap.instrumentation.api.Tags;
+import datadog.trace.util.Strings;
 import java.io.IOException;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Type;
@@ -108,7 +109,7 @@ public static void install() {
     }
     String endpoint = config.getAiGuardEndpoint();
     if (isBlank(endpoint)) {
-      endpoint = String.format("https://app.%s/api/v2/ai-guard", config.getSite());
+      endpoint = Strings.format("https://app.%s/api/v2/ai-guard", config.getSite());
     }
     final Map<String, String> headers =
         mapOf(

dd-java-agent/agent-bootstrap/src/jmh/java/datadog/trace/bootstrap/instrumentation/buffer/InjectingPipeOutputStreamBenchmark.java

@@ -6,6 +6,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
@@ -51,14 +52,18 @@ public class InjectingPipeOutputStreamBenchmark {
   public void withPipe() throws Exception {
     try (final PrintWriter out =
         new PrintWriter(
-            new InjectingPipeOutputStream(new ByteArrayOutputStream(), marker, content))) {
+            new OutputStreamWriter(
+                new InjectingPipeOutputStream(new ByteArrayOutputStream(), marker, content),
+                StandardCharsets.UTF_8))) {
       htmlContent.forEach(out::println);
     }
   }
 
   @Benchmark
   public void withoutPipe() throws Exception {
-    try (final PrintWriter out = new PrintWriter(new ByteArrayOutputStream())) {
+    try (final PrintWriter out =
+        new PrintWriter(
+            new OutputStreamWriter(new ByteArrayOutputStream(), StandardCharsets.UTF_8))) {
       htmlContent.forEach(out::println);
     }
   }

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/benchmark/StaticEventLogger.java

@@ -4,9 +4,10 @@
 import java.io.BufferedReader;
 import java.io.BufferedWriter;
 import java.io.File;
-import java.io.FileWriter;
+import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
 import java.nio.charset.StandardCharsets;
 import java.util.Objects;
 import org.slf4j.Logger;
@@ -30,7 +31,10 @@ public class StaticEventLogger {
       String fileName = dir + "startup_" + System.currentTimeMillis() + ".csv";
 
       try {
-        writer = new BufferedWriter(new FileWriter(fileName), 32768);
+        writer =
+            new BufferedWriter(
+                new OutputStreamWriter(new FileOutputStream(fileName), StandardCharsets.UTF_8),
+                32768);
         writer.write("Event,State,Timestamp");
         writer.newLine();
       } catch (IOException e) {

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/AppVeyorInfo.java

@@ -65,7 +65,7 @@ private static String getCommitMessage(String messageSubject, String messageBody
     if (messageBody == null) {
       return messageSubject;
     }
-    return String.format("%s%n%s", messageSubject, messageBody);
+    return Strings.format("%s%n%s", messageSubject, messageBody);
   }
 
   @Override
@@ -126,13 +126,13 @@ private String buildGitCommit() {
 
   private String buildGitRepositoryUrl(final String repoProvider, final String repoName) {
     if ("github".equals(repoProvider) && (repoName != null && !repoName.isEmpty())) {
-      return String.format("https://github.com/%s.git", repoName);
+      return Strings.format("https://github.com/%s.git", repoName);
     }
     return null;
   }
 
   private String buildPipelineUrl(final String repoName, final String buildId) {
-    return String.format("https://ci.appveyor.com/project/%s/builds/%s", repoName, buildId);
+    return Strings.format("https://ci.appveyor.com/project/%s/builds/%s", repoName, buildId);
   }
 
   private PersonInfo buildGitCommitAuthor() {

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/AzurePipelinesInfo.java

@@ -11,6 +11,7 @@
 import datadog.trace.api.git.GitInfo;
 import datadog.trace.api.git.PersonInfo;
 import datadog.trace.civisibility.ci.env.CiEnvironment;
+import datadog.trace.util.Strings;
 import javax.annotation.Nonnull;
 
 class AzurePipelinesInfo implements CIProviderInfo {
@@ -144,12 +145,12 @@ private String buildCiJobUrl(
       final String buildId,
       final String jobId,
       final String taskId) {
-    return String.format(
+    return Strings.format(
         "%s%s/_build/results?buildId=%s&view=logs&j=%s&t=%s", uri, project, buildId, jobId, taskId);
   }
 
   private String buildCiPipelineUrl(final String uri, final String project, final String buildId) {
-    return String.format("%s%s/_build/results?buildId=%s", uri, project, buildId);
+    return Strings.format("%s%s/_build/results?buildId=%s", uri, project, buildId);
   }
 
   private PersonInfo buildGitCommitAuthor() {

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/BitBucketInfo.java

@@ -85,7 +85,7 @@ public PullRequestInfo buildPullRequestInfo() {
   }
 
   private String buildPipelineUrl(final String repo, final String number) {
-    return String.format(
+    return Strings.format(
         "https://bitbucket.org/%s/addon/pipelines/home#!/results/%s", repo, number);
   }
 

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/BuddyInfo.java

@@ -9,6 +9,7 @@
 import datadog.trace.api.git.GitInfo;
 import datadog.trace.api.git.PersonInfo;
 import datadog.trace.civisibility.ci.env.CiEnvironment;
+import datadog.trace.util.Strings;
 import javax.annotation.Nonnull;
 
 class BuddyInfo implements CIProviderInfo {
@@ -80,7 +81,7 @@ private String getPipelineId(String pipelineNumber) {
     if (pipelineNumber == null) {
       return pipelineId;
     }
-    return String.format("%s/%s", pipelineId, pipelineNumber);
+    return Strings.format("%s/%s", pipelineId, pipelineNumber);
   }
 
   private PersonInfo buildGitCommiter() {

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/BuildkiteInfo.java

@@ -11,6 +11,7 @@
 import datadog.trace.api.git.GitInfo;
 import datadog.trace.api.git.PersonInfo;
 import datadog.trace.civisibility.ci.env.CiEnvironment;
+import datadog.trace.util.Strings;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
@@ -73,7 +74,7 @@ public CIInfo buildCIInfo() {
         .ciPipelineNumber(environment.get(BUILDKITE_PIPELINE_NUMBER))
         .ciPipelineUrl(ciPipelineUrl)
         .ciJobId(environment.get(BUILDKITE_JOB_ID))
-        .ciJobUrl(String.format("%s#%s", ciPipelineUrl, environment.get(BUILDKITE_JOB_ID)))
+        .ciJobUrl(Strings.format("%s#%s", ciPipelineUrl, environment.get(BUILDKITE_JOB_ID)))
         .ciWorkspace(expandTilde(environment.get(BUILDKITE_WORKSPACE_PATH)))
         .ciNodeName(environment.get(BUILDKITE_AGENT_ID))
         .ciNodeLabels(buildCiNodeLabels())

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/CircleCIInfo.java

@@ -9,6 +9,7 @@
 import datadog.trace.api.git.CommitInfo;
 import datadog.trace.api.git.GitInfo;
 import datadog.trace.civisibility.ci.env.CiEnvironment;
+import datadog.trace.util.Strings;
 import javax.annotation.Nonnull;
 
 class CircleCIInfo implements CIProviderInfo {
@@ -71,7 +72,7 @@ private String buildPipelineUrl(final String pipelineId) {
       return null;
     }
 
-    return String.format("https://app.circleci.com/pipelines/workflows/%s", pipelineId);
+    return Strings.format("https://app.circleci.com/pipelines/workflows/%s", pipelineId);
   }
 
   @Override

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/GithubActionsInfo.java

@@ -204,25 +204,25 @@ private String buildGitRepositoryUrl(final String host, final String repo) {
       return null;
     }
 
-    return String.format("%s/%s.git", host, repo);
+    return Strings.format("%s/%s.git", host, repo);
   }
 
   private String buildPipelineUrl(
       final String host, final String repo, final String pipelineId, final String retry) {
     if (retry != null && !retry.isEmpty()) {
-      return String.format("%s/%s/actions/runs/%s/attempts/%s", host, repo, pipelineId, retry);
+      return Strings.format("%s/%s/actions/runs/%s/attempts/%s", host, repo, pipelineId, retry);
     } else {
-      return String.format("%s/%s/actions/runs/%s", host, repo, pipelineId);
+      return Strings.format("%s/%s/actions/runs/%s", host, repo, pipelineId);
     }
   }
 
   private String buildJobUrl(final String host, final String repo, final String commit) {
-    return String.format("%s/%s/commit/%s/checks", host, repo, commit);
+    return Strings.format("%s/%s/commit/%s/checks", host, repo, commit);
   }
 
   private String buildJobUrlWithNumericId(
       final String host, final String repo, final String pipelineId, final String jobId) {
-    return String.format("%s/%s/actions/runs/%s/job/%s", host, repo, pipelineId, jobId);
+    return Strings.format("%s/%s/actions/runs/%s/job/%s", host, repo, pipelineId, jobId);
   }
 
   /**

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/ci/TravisInfo.java

@@ -9,6 +9,7 @@
 import datadog.trace.api.git.GitInfo;
 import datadog.trace.api.git.PersonInfo;
 import datadog.trace.civisibility.ci.env.CiEnvironment;
+import datadog.trace.util.Strings;
 import javax.annotation.Nonnull;
 
 class TravisInfo implements CIProviderInfo {
@@ -100,7 +101,7 @@ private String buildGitRepositoryUrl() {
     if (repoSlug == null || repoSlug.isEmpty()) {
       return null;
     }
-    return String.format("https://github.com/%s.git", repoSlug);
+    return Strings.format("https://github.com/%s.git", repoSlug);
   }
 
   private String buildCiPipelineName() {

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/domain/buildsystem/ModuleSignalRouter.java

@@ -6,6 +6,7 @@
 import datadog.trace.civisibility.ipc.Signal;
 import datadog.trace.civisibility.ipc.SignalResponse;
 import datadog.trace.civisibility.ipc.SignalType;
+import datadog.trace.util.Strings;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Function;
@@ -41,7 +42,7 @@ public SignalResponse onModuleSignalReceived(ModuleSignal result) {
         moduleHandlersById.get(moduleId);
     if (handlersByType == null) {
       String message =
-          String.format(
+          Strings.format(
               "Could not find signal handlers for module ID %s, test execution result will be ignored: %s",
               moduleId, result);
       LOGGER.warn(message);

dd-java-agent/agent-ci-visibility/src/main/java/datadog/trace/civisibility/git/GitConfig.java

@@ -2,8 +2,10 @@
 
 import de.thetaphi.forbiddenapis.SuppressForbidden;
 import java.io.BufferedReader;
-import java.io.FileReader;
+import java.io.FileInputStream;
 import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -30,7 +32,9 @@ private void load(final String path) {
     //   url = https://some-host/user/repository.git
     // 	 fetch = +refs/heads/*:refs/remotes/origin/*
 
-    try (final BufferedReader br = new BufferedReader(new FileReader(path))) {
+    try (final BufferedReader br =
+        new BufferedReader(
+            new InputStreamReader(new FileInputStream(path), StandardCharsets.UTF_8))) {
       String line;
       String section = null;
       while ((line = br.readLine()) != null) {