core: zstd: Implement dispatcher methods for zstd decompression

include/fluent-bit/flb_compression.h

@@ -26,6 +26,7 @@
 
 #define FLB_COMPRESSION_ALGORITHM_NONE                    0
 #define FLB_COMPRESSION_ALGORITHM_GZIP                    1
+#define FLB_COMPRESSION_ALGORITHM_ZSTD                    2
 
 #define FLB_DECOMPRESSOR_STATE_FAILED                    -1
 #define FLB_DECOMPRESSOR_STATE_EXPECTING_HEADER           0

include/fluent-bit/flb_zstd.h

@@ -22,8 +22,16 @@
 
 #include <fluent-bit/flb_info.h>
 #include <zstd.h>
+#include <zstd_errors.h>
+
+struct flb_decompression_context;
 
 size_t flb_zstd_compress(void *in_data, size_t in_len, void **out_data, size_t *out_len);
 size_t flb_zstd_uncompress(void *in_data, size_t in_len, void **out_data, size_t *out_len);
 
+int flb_zstd_decompressor_dispatch(struct flb_decompression_context *context,
+                                   void *output_buffer,
+                                   size_t *output_length);
+void *flb_zstd_decompression_context_create(void);
+void flb_zstd_decompression_context_destroy(void *context);
 #endif

src/flb_compression.c

@@ -21,6 +21,7 @@
 #include <fluent-bit/flb_mem.h>
 #include <fluent-bit/flb_log.h>
 #include <fluent-bit/flb_gzip.h>
+#include <fluent-bit/flb_zstd.h>
 #include <fluent-bit/flb_compression.h>
 
 static size_t flb_decompression_context_get_read_buffer_offset(
@@ -131,7 +132,12 @@ void flb_decompression_context_destroy(struct flb_decompression_context *context
         }
 
         if (context->inner_context != NULL) {
-            flb_gzip_decompression_context_destroy(context->inner_context);
+            if (context->algorithm == FLB_COMPRESSION_ALGORITHM_GZIP) {
+                flb_gzip_decompression_context_destroy(context->inner_context);
+            }
+            else if (context->algorithm == FLB_COMPRESSION_ALGORITHM_ZSTD) {
+                flb_zstd_decompression_context_destroy(context->inner_context);
+            }
 
             context->inner_context = NULL;
         }
@@ -178,6 +184,9 @@ struct flb_decompression_context *flb_decompression_context_create(int algorithm
     if (algorithm == FLB_COMPRESSION_ALGORITHM_GZIP) {
         context->inner_context = flb_gzip_decompression_context_create();
     }
+    else if (algorithm == FLB_COMPRESSION_ALGORITHM_ZSTD) {
+        context->inner_context = flb_zstd_decompression_context_create();
+    }
     else {
         flb_error("invalid compression algorithm : %d", algorithm);
 
@@ -197,9 +206,14 @@ struct flb_decompression_context *flb_decompression_context_create(int algorithm
     }
 
     context->input_buffer_size = input_buffer_size;
-    context->read_buffer = context->read_buffer;
+    context->read_buffer = context->input_buffer;
     context->algorithm = algorithm;
-    context->state = FLB_DECOMPRESSOR_STATE_EXPECTING_HEADER;
+    if (algorithm == FLB_COMPRESSION_ALGORITHM_GZIP) {
+        context->state = FLB_DECOMPRESSOR_STATE_EXPECTING_HEADER;
+    }
+    else if (algorithm == FLB_COMPRESSION_ALGORITHM_ZSTD) {
+        context->state = FLB_DECOMPRESSOR_STATE_EXPECTING_BODY;
+    }
 
     return context;
 }
@@ -215,6 +229,12 @@ int flb_decompress(struct flb_decompression_context *context,
                                                   output_length);
 
         }
+        else if (context->algorithm == FLB_COMPRESSION_ALGORITHM_ZSTD) {
+            return flb_zstd_decompressor_dispatch(context,
+                                                  output_buffer,
+                                                  output_length);
+
+        }
     }
 
     return FLB_DECOMPRESSOR_FAILURE;

src/flb_gzip.c

@@ -690,9 +690,11 @@ static int flb_gzip_decompressor_process_header(
 
     /* Minimal length: header + crc32 */
     if (context->input_buffer_length < FLB_GZIP_HEADER_SIZE) {
-        flb_error("[gzip] unexpected content length");
-
-        return FLB_DECOMPRESSOR_FAILURE;
+        /*
+         * This is not a fatal error; it's the expected condition when waiting
+         * for more data. Return INSUFFICIENT_DATA without logging an error.
+         */
+        return FLB_DECOMPRESSOR_INSUFFICIENT_DATA;
     }
 
     memcpy(&inner_context->gzip_header,

src/flb_zstd.c

@@ -24,6 +24,9 @@
 #include <fluent-bit/flb_compression.h>
 #include <fluent-bit/flb_zstd.h>
 
+struct flb_zstd_decompression_context {
+    ZSTD_DCtx *dctx;
+};
 
 #define FLB_ZSTD_DEFAULT_CHUNK 64 * 1024  /* 64 KB buffer */
 
@@ -162,3 +165,102 @@ size_t flb_zstd_uncompress(void *in_data, size_t in_len, void **out_data, size_t
     return 0;
 }
 
+int flb_zstd_decompressor_dispatch(struct flb_decompression_context *context,
+                                   void *output_buffer,
+                                   size_t *output_length)
+{
+    struct flb_zstd_decompression_context *zstd_ctx;
+    size_t compressed_frame_size;
+    size_t decompressed_size;
+    size_t original_output_length;
+    size_t error_code;
+
+    if (context == NULL || context->inner_context == NULL || output_length == NULL) {
+        return FLB_DECOMPRESSOR_FAILURE;
+    }
+
+    zstd_ctx = (struct flb_zstd_decompression_context *) context->inner_context;
+    original_output_length = *output_length;
+    *output_length = 0;
+
+    if (context->input_buffer_length == 0) {
+        return FLB_DECOMPRESSOR_SUCCESS;
+    }
+
+    compressed_frame_size = ZSTD_findFrameCompressedSize(context->read_buffer,
+                                                         context->input_buffer_length);
+
+    error_code = ZSTD_getErrorCode(compressed_frame_size);
+
+    /*
+     * Distinguish between recoverable and fatal errors.
+     * If we get srcSize_wrong, it just means we need more data to find the
+     * end of the frame. This is expected in a streaming scenario.
+     */
+    if (error_code == ZSTD_error_srcSize_wrong) {
+        /* Not an error, just need more data. Return success with 0 bytes produced. */
+        return FLB_DECOMPRESSOR_SUCCESS;
+    }
+
+    /* Check for any other, truly fatal error from finding the frame. */
+    if (ZSTD_isError(compressed_frame_size)) {
+        flb_error("[zstd] frame is corrupted: %s",
+                  ZSTD_getErrorName(compressed_frame_size));
+        context->state = FLB_DECOMPRESSOR_STATE_FAILED;
+        return FLB_DECOMPRESSOR_FAILURE;
+    }
+
+    /* We have a full frame. Decompress it in one shot using the robust API. */
+    decompressed_size = ZSTD_decompressDCtx(zstd_ctx->dctx,
+                                            output_buffer,
+                                            original_output_length,
+                                            context->read_buffer,
+                                            compressed_frame_size);
+
+    if (ZSTD_isError(decompressed_size)) {
+        flb_error("[zstd] decompression failed: %s",
+                  ZSTD_getErrorName(decompressed_size));
+        context->state = FLB_DECOMPRESSOR_STATE_FAILED;
+        return FLB_DECOMPRESSOR_FAILURE;
+    }
+
+    /* Success. Update our pointers and report the decompressed size. */
+    context->read_buffer         += compressed_frame_size;
+    context->input_buffer_length -= compressed_frame_size;
+    *output_length = decompressed_size;
+
+    return FLB_DECOMPRESSOR_SUCCESS;
+}
+
+void *flb_zstd_decompression_context_create(void)
+{
+    struct flb_zstd_decompression_context *context;
+
+    context = flb_calloc(1, sizeof(struct flb_zstd_decompression_context));
+
+    if (context == NULL) {
+        flb_errno();
+        return NULL;
+    }
+
+    context->dctx = ZSTD_createDCtx();
+    if (context->dctx == NULL) {
+        flb_error("[zstd] could not create decompression context");
+        flb_free(context);
+        return NULL;
+    }
+
+    return (void *) context;
+}
+
+void flb_zstd_decompression_context_destroy(void *context)
+{
+    struct flb_zstd_decompression_context *zstd_ctx = context;
+
+    if (zstd_ctx != NULL) {
+        if (zstd_ctx->dctx != NULL) {
+            ZSTD_freeDCtx(zstd_ctx->dctx);
+        }
+        flb_free(zstd_ctx);
+    }
+}

tests/internal/zstd.c

@@ -3,6 +3,7 @@
 #include <fluent-bit/flb_info.h>
 #include <fluent-bit/flb_mem.h>
 #include <fluent-bit/flb_zstd.h>
+#include <fluent-bit/flb_compression.h>
 #include "flb_tests_internal.h"
 
 /* try a small string */
@@ -163,12 +164,167 @@ static void test_decompress_unknown_size()
     flb_free(decompressed_data);
 }
 
+static void append_to_context(struct flb_decompression_context *ctx, const void *data, size_t size)
+{
+    uint8_t *append_ptr;
+    size_t available_space;
+
+    available_space = flb_decompression_context_get_available_space(ctx);
+
+    if (size > available_space) {
+        size_t required_size = ctx->input_buffer_length + size;
+        flb_decompression_context_resize_buffer(ctx, required_size);
+    }
+
+    /* Get pointer to the write location */
+    append_ptr = flb_decompression_context_get_append_buffer(ctx);
+    TEST_CHECK(append_ptr != NULL);
+
+    /* Copy the data */
+    memcpy(append_ptr, data, size);
+
+    ctx->input_buffer_length += size;
+}
+
+static void *compress_with_checksum(const void *original_data, size_t original_len,
+                                    size_t *compressed_len)
+{
+    ZSTD_CCtx* cctx;
+    void *compressed_buffer;
+    size_t bound;
+    size_t ret;
+
+    /* Create a compression context */
+    cctx = ZSTD_createCCtx();
+    TEST_CHECK(cctx != NULL);
+
+    /*
+     * THIS IS THE KEY: Explicitly enable content checksums in the frame.
+     */
+    ret = ZSTD_CCtx_setParameter(cctx, ZSTD_c_checksumFlag, 1);
+    TEST_CHECK(!ZSTD_isError(ret));
+
+    /* Compress the data */
+    bound = ZSTD_compressBound(original_len);
+    compressed_buffer = flb_malloc(bound);
+    TEST_CHECK(compressed_buffer != NULL);
+
+    *compressed_len = ZSTD_compress2(cctx,
+                                     compressed_buffer, bound,
+                                     original_data, original_len);
+
+    TEST_CHECK(!ZSTD_isError(*compressed_len));
+
+    ZSTD_freeCCtx(cctx);
+
+    return compressed_buffer;
+}
+
+void test_zstd_streaming_decompress_multi_chunk(void)
+{
+    struct flb_decompression_context *ctx;
+    char   *output_buf;
+    size_t output_len;
+    size_t total_written = 0;
+    int    ret;
+    size_t chunk1_size = 0;
+    size_t chunk2_size = 0;
+    size_t chunk3_size = 0;
+    char  *original_text = "zstd streaming is a feature that must be tested with multiple, uneven chunks!";
+    size_t original_len;
+    void  *compressed_buf = NULL;
+    size_t compressed_len = 0;
+
+    original_len = strlen(original_text);
+    compressed_buf = compress_with_checksum(original_text, original_len, &compressed_len);
+    TEST_CHECK(compressed_buf != NULL);
+
+    ctx = flb_decompression_context_create(FLB_COMPRESSION_ALGORITHM_ZSTD, compressed_len);
+    TEST_CHECK(ctx != NULL);
+    output_buf = flb_malloc(original_len + 1);
+
+    chunk1_size = compressed_len / 3;
+    chunk2_size = compressed_len / 2;
+    chunk3_size = compressed_len - chunk1_size - chunk2_size;
+
+    append_to_context(ctx, compressed_buf, chunk1_size);
+    output_len = original_len;
+    ret = flb_decompress(ctx, output_buf, &output_len);
+    TEST_CHECK(ret == FLB_DECOMPRESSOR_SUCCESS);
+    total_written += output_len;
+
+    append_to_context(ctx, (char *)compressed_buf + chunk1_size, chunk2_size);
+    output_len = original_len - total_written;
+    ret = flb_decompress(ctx, output_buf + total_written, &output_len);
+    TEST_CHECK(ret == FLB_DECOMPRESSOR_SUCCESS);
+    total_written += output_len;
+
+    append_to_context(ctx, (char *)compressed_buf + chunk1_size + chunk2_size, chunk3_size);
+    output_len = original_len - total_written;
+    ret = flb_decompress(ctx, output_buf + total_written, &output_len);
+    TEST_CHECK(ret == FLB_DECOMPRESSOR_SUCCESS);
+    total_written += output_len;
+
+    TEST_CHECK(total_written == original_len);
+    TEST_CHECK(memcmp(original_text, output_buf, original_len) == 0);
+
+    flb_free(compressed_buf);
+    flb_free(output_buf);
+    flb_decompression_context_destroy(ctx);
+}
+
+/* In tests/internal/zstd.c */
+
+void test_zstd_streaming_decompress_corrupted_data(void)
+{
+    struct flb_decompression_context *ctx;
+    char   *output_buf;
+    size_t  output_len;
+    int     ret;
+    char   *original_text = "this test ensures corrupted data with a checksum fails";
+    size_t  original_len = strlen(original_text);
+    void   *compressed_buf = NULL;
+    size_t  compressed_len = 0;
+    char   *corrupted_input;
+
+    compressed_buf = compress_with_checksum(original_text, original_len, &compressed_len);
+    TEST_CHECK(compressed_buf != NULL);
+
+    ctx = flb_decompression_context_create(FLB_COMPRESSION_ALGORITHM_ZSTD, compressed_len);
+    TEST_CHECK(ctx != NULL);
+
+    /* Create a corrupted copy of the input */
+    corrupted_input = flb_malloc(compressed_len);
+    TEST_CHECK(corrupted_input != NULL);
+    memcpy(corrupted_input, compressed_buf, compressed_len);
+    /* Corrupt a byte in the middle */
+    corrupted_input[compressed_len / 2]++;
+
+    append_to_context(ctx, corrupted_input, compressed_len);
+
+    output_buf = flb_malloc(original_len + 1);
+    output_len = original_len;
+
+    ret = flb_decompress(ctx, output_buf, &output_len);
+
+    TEST_CHECK(ret == FLB_DECOMPRESSOR_FAILURE);
+    TEST_CHECK(ctx->state == FLB_DECOMPRESSOR_STATE_FAILED);
+
+    flb_free(compressed_buf);
+    flb_free(corrupted_input);
+    flb_free(output_buf);
+    flb_decompression_context_destroy(ctx);
+}
+
+
 TEST_LIST = {
     { "compress_small_string",          test_compress_small_string },
     { "decompress_small_string",        test_decompress_small_string },
     { "compress_empty_input",           test_compress_empty_input },
     { "decompress_invalid_data",        test_decompress_invalid_data },
     { "compress_decompress_large_data", test_compress_decompress_large_data },
     { "decompress_unknown_size",        test_decompress_unknown_size },
+    { "streaming_decompress_multi_chunk", test_zstd_streaming_decompress_multi_chunk },
+    { "streaming_decompress_corrupted_data", test_zstd_streaming_decompress_corrupted_data },
     { NULL, NULL }
 };