结构化 SipParser 实装 + RFC 4475 合规驱动测试（叠加 PR #3）

sip-codec/src/main/java/com/sip/codec/SipCodecException.java

@@ -1,22 +1,68 @@
 package com.sip.codec;
 
+import java.util.Objects;
+
 /**
  * Thrown when wire-format bytes cannot be parsed into a valid SIP message,
  * or when a message cannot be serialized.
  *
- * <p>The codec aims to be tolerant of common deviations described in
- * RFC 5118 / RFC 4475, but malformed input that prevents safe interpretation
- * must surface as an exception.</p>
+ * <p>Each exception carries a {@linkplain #category() stable category} that
+ * groups failure modes (e.g. {@code malformed-start-line},
+ * {@code malformed-header}, {@code unknown-version}). The category is the
+ * same vocabulary that fixture {@code .expect.properties} files declare,
+ * so the compliance harness can assert end-to-end behaviour without coupling
+ * to free-form messages.</p>
+ *
+ * <p>The {@linkplain #offset() byte offset} points to the location in the
+ * input that triggered the failure (or {@code -1} when no specific offset
+ * applies, e.g. for trailing-data failures).</p>
  */
 public class SipCodecException extends RuntimeException {
 
     private static final long serialVersionUID = 1L;
 
-    public SipCodecException(String message) {
-        super(message);
+    /** Stable, lower-kebab-case taxonomy. Extend as new failure modes appear. */
+    public static final class Category {
+        public static final String MALFORMED_START_LINE  = "malformed-start-line";
+        public static final String MALFORMED_HEADER      = "malformed-header";
+        public static final String UNKNOWN_VERSION       = "unknown-version";
+        public static final String BAD_CONTENT_LENGTH    = "bad-content-length";
+        public static final String TRUNCATED             = "truncated";
+        public static final String UNSUPPORTED_URI_SCHEME = "unsupported-uri-scheme";
+        public static final String ENCODE_FAILURE        = "encode-failure";
+
+        private Category() { }
+    }
+
+    private final String category;
+    private final int offset;
+
+    public SipCodecException(String category, int offset, String message) {
+        super(formatMessage(category, offset, message));
+        this.category = Objects.requireNonNull(category, "category");
+        this.offset = offset;
+    }
+
+    public SipCodecException(String category, int offset, String message, Throwable cause) {
+        super(formatMessage(category, offset, message), cause);
+        this.category = Objects.requireNonNull(category, "category");
+        this.offset = offset;
+    }
+
+    /** Stable taxonomy bucket; see {@link Category} for known values. */
+    public String category() {
+        return category;
+    }
+
+    /** Byte offset of the failure within the input, or {@code -1} if unknown. */
+    public int offset() {
+        return offset;
     }
 
-    public SipCodecException(String message, Throwable cause) {
-        super(message, cause);
+    private static String formatMessage(String category, int offset, String message) {
+        if (offset < 0) {
+            return "[" + category + "] " + message;
+        }
+        return "[" + category + " @ byte " + offset + "] " + message;
     }
 }