feat(profiling): Add optional pretty-printing for JSON output

Add --pretty flag to control JSON pretty-printing in the CLI converter.
By default, JSON output is compact for efficient processing. Use
--pretty for human-readable output with indentation.

Usage:
  # Compact JSON (default)
  ./gradlew convertJfr --args="--json input.jfr output.json"

  # Pretty-printed JSON
  ./gradlew convertJfr --args="--json --pretty input.jfr output.json"

The pretty-printer is a simple, dependency-free implementation that
adds newlines and 2-space indentation without external libraries.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jbachorik

dd-java-agent/agent-profiling/profiling-otel/doc/CLI.md

@@ -24,7 +24,8 @@ Convert to JSON for human inspection:
 
 ### Options
 
-- `--json` - Output JSON format instead of protobuf (useful for inspection)
+- `--json` - Output JSON format instead of protobuf (compact by default)
+- `--pretty` - Pretty-print JSON output with indentation (use with `--json`)
 - `--include-payload` - Include original JFR payload in output (increases size significantly)
 - `--help` - Show help message
 
@@ -41,11 +42,18 @@ Convert single JFR to protobuf:
 
 #### JSON Output for Inspection
 
-Output JSON format to examine the structure:
+Output compact JSON for processing:
 
 ```bash
 ./gradlew :dd-java-agent:agent-profiling:profiling-otel:convertJfr \
   --args="--json recording.jfr output.json"
+```
+
+Output pretty-printed JSON for human inspection:
+
+```bash
+./gradlew :dd-java-agent:agent-profiling:profiling-otel:convertJfr \
+  --args="--json --pretty recording.jfr output.json"
 
 # Inspect with jq
 cat output.json | jq '.dictionary.string_table | length'

dd-java-agent/agent-profiling/profiling-otel/src/main/java/com/datadog/profiling/otel/JfrToOtlpConverter.java

@@ -59,8 +59,10 @@ public final class JfrToOtlpConverter {
   public enum Kind {
     /** Protobuf binary format (default). */
     PROTO,
-    /** JSON text format. */
-    JSON
+    /** JSON text format (compact). */
+    JSON,
+    /** JSON text format with pretty-printing. */
+    JSON_PRETTY
   }
 
   private static final class PathEntry {
@@ -233,7 +235,9 @@ public byte[] convert(Kind kind) throws IOException {
 
       switch (kind) {
         case JSON:
-          return encodeProfilesDataAsJson();
+          return encodeProfilesDataAsJson(false);
+        case JSON_PRETTY:
+          return encodeProfilesDataAsJson(true);
         case PROTO:
         default:
           return encodeProfilesData();
@@ -762,7 +766,7 @@ private byte[] generateProfileId() {
 
   // JSON encoding methods
 
-  private byte[] encodeProfilesDataAsJson() {
+  private byte[] encodeProfilesDataAsJson(boolean prettyPrint) {
     JsonWriter json = new JsonWriter();
     json.beginObject();
 
@@ -776,7 +780,86 @@ private byte[] encodeProfilesDataAsJson() {
     encodeDictionaryJson(json);
 
     json.endObject();
-    return json.toByteArray();
+    byte[] compactJson = json.toByteArray();
+
+    // Pretty-print if requested
+    return prettyPrint ? prettyPrintJson(compactJson) : compactJson;
+  }
+
+  /**
+   * Pretty-prints compact JSON with indentation.
+   *
+   * <p>Simple pretty-printer that adds newlines and indentation without external dependencies.
+   */
+  private byte[] prettyPrintJson(byte[] compactJson) {
+    String compact = new String(compactJson, java.nio.charset.StandardCharsets.UTF_8);
+    StringBuilder pretty = new StringBuilder(compact.length() + compact.length() / 4);
+    int indent = 0;
+    boolean inString = false;
+    boolean escape = false;
+
+    for (int i = 0; i < compact.length(); i++) {
+      char c = compact.charAt(i);
+
+      if (escape) {
+        pretty.append(c);
+        escape = false;
+        continue;
+      }
+
+      if (c == '\\') {
+        pretty.append(c);
+        escape = true;
+        continue;
+      }
+
+      if (c == '"') {
+        pretty.append(c);
+        inString = !inString;
+        continue;
+      }
+
+      if (inString) {
+        pretty.append(c);
+        continue;
+      }
+
+      switch (c) {
+        case '{':
+        case '[':
+          pretty.append(c).append('\n');
+          indent++;
+          appendIndent(pretty, indent);
+          break;
+        case '}':
+        case ']':
+          pretty.append('\n');
+          indent--;
+          appendIndent(pretty, indent);
+          pretty.append(c);
+          break;
+        case ',':
+          pretty.append(c).append('\n');
+          appendIndent(pretty, indent);
+          break;
+        case ':':
+          pretty.append(c).append(' ');
+          break;
+        default:
+          if (!Character.isWhitespace(c)) {
+            pretty.append(c);
+          }
+          break;
+      }
+    }
+
+    return pretty.toString().getBytes(java.nio.charset.StandardCharsets.UTF_8);
+  }
+
+  private void appendIndent(StringBuilder sb, int indent) {
+    for (int i = 0; i < indent * 2; i++) {
+      sb.append(' ');
+    }
   }
 
   private void encodeResourceProfilesJson(JsonWriter json) {

dd-java-agent/agent-profiling/profiling-otel/src/main/java/com/datadog/profiling/otel/JfrToOtlpConverterCLI.java

@@ -15,9 +15,12 @@
  * # Convert single JFR file to protobuf (default)
  * java -cp ... com.datadog.profiling.otel.JfrToOtlpConverterCLI input.jfr output.pb
  *
- * # Convert to JSON format
+ * # Convert to JSON format (compact)
  * java -cp ... com.datadog.profiling.otel.JfrToOtlpConverterCLI --json input.jfr output.json
  *
+ * # Convert to pretty-printed JSON
+ * java -cp ... com.datadog.profiling.otel.JfrToOtlpConverterCLI --json --pretty input.jfr output.json
+ *
  * # Include original JFR payload
  * java -cp ... com.datadog.profiling.otel.JfrToOtlpConverterCLI --include-payload input.jfr output.pb
  *
@@ -45,6 +48,7 @@ public static void main(String[] args) {
   private void run(String[] args) throws IOException {
     JfrToOtlpConverter.Kind outputKind = JfrToOtlpConverter.Kind.PROTO;
     boolean includePayload = false;
+    boolean prettyPrint = false;
     int firstInputIndex = 0;
 
     // Parse flags
@@ -55,6 +59,10 @@ private void run(String[] args) throws IOException {
           outputKind = JfrToOtlpConverter.Kind.JSON;
           firstInputIndex++;
           break;
+        case "--pretty":
+          prettyPrint = true;
+          firstInputIndex++;
+          break;
         case "--include-payload":
           includePayload = true;
           firstInputIndex++;
@@ -67,6 +75,11 @@ private void run(String[] args) throws IOException {
       }
     }
 
+    // Apply pretty-printing to JSON output
+    if (prettyPrint && outputKind == JfrToOtlpConverter.Kind.JSON) {
+      outputKind = JfrToOtlpConverter.Kind.JSON_PRETTY;
+    }
+
     // Remaining args: input1.jfr [input2.jfr ...] output.pb/json
     if (args.length - firstInputIndex < 2) {
       throw new IllegalArgumentException(
@@ -140,6 +153,7 @@ private static void printUsage() {
     System.out.println();
     System.out.println("Options:");
     System.out.println("  --json              Output JSON format instead of protobuf");
+    System.out.println("  --pretty            Pretty-print JSON output (use with --json)");
     System.out.println(
         "  --include-payload   Include original JFR payload in output (increases size)");
     System.out.println("  --help              Show this help message");
@@ -148,9 +162,12 @@ private static void printUsage() {
     System.out.println("  # Convert to protobuf (default)");
     System.out.println("  JfrToOtlpConverterCLI recording.jfr output.pb");
     System.out.println();
-    System.out.println("  # Convert to JSON for inspection");
+    System.out.println("  # Convert to compact JSON");
     System.out.println("  JfrToOtlpConverterCLI --json recording.jfr output.json");
     System.out.println();
+    System.out.println("  # Convert to pretty-printed JSON");
+    System.out.println("  JfrToOtlpConverterCLI --json --pretty recording.jfr output.json");
+    System.out.println();
     System.out.println("  # Merge multiple recordings");
     System.out.println("  JfrToOtlpConverterCLI file1.jfr file2.jfr file3.jfr merged.pb");
     System.out.println();