Switch out Cloudflare zlib for libdeflate.

libdeflate is significantly faster than vanilla zlib, zlib-ng, and Cloudflare zlib. It is also MIT-licensed (so no licensing concerns). In addition, it simplifies a lot of the native code (something that's been tricky to get right).

While we're at it, I have also taken the time to fine-time compression in Velocity in general. Thanks to this work, native compression only requires one JNI call, an improvement from the more than 2 (sometimes up to 5) that were possible before. This optimization also extends to the existing Java compressors, though they require potentially two JNI calls.

native/src/main/c/jni_zlib_inflate.c

@@ -2,50 +2,21 @@
 #include <jni.h>
 #include <stdbool.h>
 #include <stdlib.h>
-#include <zlib.h>
+#include <libdeflate.h>
 #include "jni_util.h"
-#include "jni_zlib_common.h"
-
-static jfieldID finishedID;
-static jfieldID consumedID;
-
-JNIEXPORT void JNICALL
-Java_com_velocitypowered_natives_compression_NativeZlibInflate_initIDs(JNIEnv *env, jclass cls)
-{
-    finishedID = (*env)->GetFieldID(env, cls, "finished", "Z");
-    consumedID = (*env)->GetFieldID(env, cls, "consumed", "I");
-}
 
 JNIEXPORT jlong JNICALL
 Java_com_velocitypowered_natives_compression_NativeZlibInflate_init(JNIEnv *env,
     jobject obj)
 {
-    z_stream* stream = calloc(1, sizeof(z_stream));
-
-    if (stream == 0) {
+    struct libdeflate_decompressor *decompress = libdeflate_alloc_decompressor();
+    if (decompress == NULL) {
         // Out of memory!
-        throwException(env, "java/lang/OutOfMemoryError", "zlib allocate stream");
+        throwException(env, "java/lang/OutOfMemoryError", "libdeflate allocate decompressor");
         return 0;
     }
 
-    int ret = inflateInit(stream);
-    if (ret == Z_OK) {
-        return (jlong) stream;
-    } else {
-        const char *zlib_msg = stream->msg;
-        free(stream);
-        switch (ret) {
-            case Z_MEM_ERROR:
-                throwException(env, "java/lang/OutOfMemoryError", "zlib init");
-                return 0;
-            case Z_STREAM_ERROR:
-                throwException(env, "java/lang/IllegalArgumentException", "stream clobbered?");
-                return 0;
-            default:
-                throwException(env, "java/util/zip/DataFormatException", zlib_msg);
-                return 0;
-        }
-    }
+    return (jlong) decompress;
 }
 
 JNIEXPORT void JNICALL
@@ -53,51 +24,34 @@ Java_com_velocitypowered_natives_compression_NativeZlibInflate_free(JNIEnv *env,
     jobject obj,
     jlong ctx)
 {
-    z_stream* stream = (z_stream*) ctx;
-    check_zlib_free(env, stream, false);
+    libdeflate_free_decompressor((struct libdeflate_decompressor *) ctx);
 }
 
-JNIEXPORT int JNICALL
+JNIEXPORT jboolean JNICALL
 Java_com_velocitypowered_natives_compression_NativeZlibInflate_process(JNIEnv *env,
     jobject obj,
     jlong ctx,
     jlong sourceAddress,
     jint sourceLength,
     jlong destinationAddress,
-    jint destinationLength)
+    jint destinationLength,
+    jlong maximumSize)
 {
-    z_stream* stream = (z_stream*) ctx;
-    stream->next_in = (Bytef *) sourceAddress;
-    stream->next_out = (Bytef *) destinationAddress;
-    stream->avail_in = sourceLength;
-    stream->avail_out = destinationLength;
+    struct libdeflate_decompressor *decompress = (struct libdeflate_decompressor *) ctx;
+    enum libdeflate_result result = libdeflate_zlib_decompress(decompress, (void *) sourceAddress,
+        sourceLength, (void *) destinationAddress, destinationLength, NULL);
 
-    int res = inflate(stream, Z_PARTIAL_FLUSH);
-    switch (res) {
-        case Z_STREAM_END:
-            // The stream has ended
-            (*env)->SetBooleanField(env, obj, finishedID, JNI_TRUE);
-            // fall-through
-        case Z_OK:
-            // Not yet completed, but progress has been made. Tell Java how many bytes we've processed.
-            (*env)->SetIntField(env, obj, consumedID, sourceLength - stream->avail_in);
-            return destinationLength - stream->avail_out;
-        case Z_BUF_ERROR:
-            // This is not fatal. Just say we need more data. Usually this applies to the next_out buffer,
-            // which NativeVelocityCompressor will notice and will expand the buffer.
-            return 0;
-        default:
-            throwException(env, "java/util/zip/DataFormatException", stream->msg);
-            return 0;
+    switch (result) {
+        case LIBDEFLATE_SUCCESS:
+            // We are happy
+            return JNI_TRUE;
+        case LIBDEFLATE_BAD_DATA:
+            throwException(env, "java/util/zip/DataFormatException", "inflate data is bad");
+            return JNI_FALSE;
+        case LIBDEFLATE_SHORT_OUTPUT:
+        case LIBDEFLATE_INSUFFICIENT_SPACE:
+            // These cases are the same for us. We expect the full uncompressed size to be known.
+            throwException(env, "java/util/zip/DataFormatException", "uncompressed size is inaccurate");
+            return JNI_FALSE;
     }
-}
-
-JNIEXPORT void JNICALL
-Java_com_velocitypowered_natives_compression_NativeZlibInflate_reset(JNIEnv *env,
-    jobject obj,
-    jlong ctx)
-{
-    z_stream* stream = (z_stream*) ctx;
-    int ret = inflateReset(stream);
-    assert(ret == Z_OK);
 }