feat: improve error messaging

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ## [Unreleased](https://github.com/openfga/java-sdk/compare/v0.9.3...HEAD)
+- feat: Improve error messaging by parsing error details from response bodies (#258)
 
 ## v0.9.3
 

src/main/java/dev/openfga/sdk/errors/FgaApiValidationError.java

@@ -1,14 +1,122 @@
 package dev.openfga.sdk.errors;
 
+import com.fasterxml.jackson.databind.JsonNode;
 import java.net.http.HttpHeaders;
 
 public class FgaApiValidationError extends FgaError {
+
+    // String prefixes for parsing error messages
+    private static final String RELATION_PREFIX = "relation '";
+    private static final String TYPE_PREFIX = "type '";
+    private static final String CHECK_REQUEST_TUPLE_KEY_PREFIX = "CheckRequestTupleKey.";
+    private static final String TUPLE_KEY_PREFIX = "TupleKey.";
+    private static final String QUOTE_SUFFIX = "'";
+    private static final String NOT_FOUND_SUFFIX = "' not found";
+    private static final String MUST_NOT_BE_EMPTY = "must not be empty";
+
+    private String invalidField;
+    private String invalidValue;
+
     public FgaApiValidationError(
             String message, Throwable cause, int code, HttpHeaders responseHeaders, String responseBody) {
         super(message, cause, code, responseHeaders, responseBody);
+        parseValidationDetails(responseBody);
     }
 
     public FgaApiValidationError(String message, int code, HttpHeaders responseHeaders, String responseBody) {
         super(message, code, responseHeaders, responseBody);
+        parseValidationDetails(responseBody);
+    }
+
+    /**
+     * Try to extract specific validation details from the error message.
+     * <p>
+     * This parsing is best-effort and based on current OpenFGA API error message formats.
+     * If the message format changes or doesn't match expected patterns, fields will be null.
+     * The application should not rely on these fields for critical logic.
+     *
+     * @param responseBody The API error response body
+     */
+    private void parseValidationDetails(String responseBody) {
+        if (responseBody == null || responseBody.trim().isEmpty()) {
+            return;
+        }
+
+        try {
+            JsonNode root = getErrorMapper().readTree(responseBody);
+            String message = root.has("message") ? root.get("message").asText() : null;
+
+            if (message != null) {
+                // Parse patterns like: "relation 'document#invalid_relation' not found"
+                if (message.contains(RELATION_PREFIX) && message.contains(NOT_FOUND_SUFFIX)) {
+                    int start = message.indexOf(RELATION_PREFIX) + RELATION_PREFIX.length();
+                    int end = message.indexOf(QUOTE_SUFFIX, start);
+                    if (end > start) {
+                        this.invalidField = "relation";
+                        this.invalidValue = message.substring(start, end);
+                        addMetadata("invalid_field", invalidField);
+                        addMetadata("invalid_value", invalidValue);
+                    }
+                }
+                // Parse patterns like: "type 'invalid_type' not found"
+                else if (message.contains(TYPE_PREFIX) && message.contains(NOT_FOUND_SUFFIX)) {
+                    int start = message.indexOf(TYPE_PREFIX) + TYPE_PREFIX.length();
+                    int end = message.indexOf(QUOTE_SUFFIX, start);
+                    if (end > start) {
+                        this.invalidField = "type";
+                        this.invalidValue = message.substring(start, end);
+                        addMetadata("invalid_field", invalidField);
+                        addMetadata("invalid_value", invalidValue);
+                    }
+                }
+                // Parse patterns like: "invalid CheckRequestTupleKey.User: value does not match regex..."
+                else if (message.contains(CHECK_REQUEST_TUPLE_KEY_PREFIX)) {
+                    int start =
+                            message.indexOf(CHECK_REQUEST_TUPLE_KEY_PREFIX) + CHECK_REQUEST_TUPLE_KEY_PREFIX.length();
+                    int end = message.indexOf(":", start);
+                    if (end > start) {
+                        this.invalidField = message.substring(start, end);
+                        addMetadata("invalid_field", invalidField);
+                    }
+                }
+                // Parse patterns like: "invalid TupleKey.User: value does not match regex..."
+                else if (message.contains(TUPLE_KEY_PREFIX)) {
+                    int start = message.indexOf(TUPLE_KEY_PREFIX) + TUPLE_KEY_PREFIX.length();
+                    int end = message.indexOf(":", start);
+                    if (end > start) {
+                        this.invalidField = message.substring(start, end);
+                        addMetadata("invalid_field", invalidField);
+                    }
+                }
+                // Parse patterns like: "object must not be empty"
+                else if (message.contains(MUST_NOT_BE_EMPTY)) {
+                    String[] parts = message.trim().split("\\s+");
+                    if (parts.length > 0 && !parts[0].isEmpty()) {
+                        this.invalidField = parts[0];
+                        addMetadata("invalid_field", invalidField);
+                    }
+                }
+            }
+        } catch (Exception e) {
+            // Parsing is best-effort, ignore failures
+        }
+    }
+
+    /**
+     * Gets the field name that failed validation, if it could be parsed from the error message.
+     *
+     * @return The invalid field name (e.g., "relation", "type", "User"), or null if not parsed
+     */
+    public String getInvalidField() {
+        return invalidField;
+    }
+
+    /**
+     * Gets the invalid value that caused the validation error, if available.
+     *
+     * @return The invalid value, or null if not parsed from the error message
+     */
+    public String getInvalidValue() {
+        return invalidValue;
     }
 }