Write EC when writing data blocks.

include/aaruformat/context.h

@@ -374,6 +374,21 @@ typedef struct aaruformat_context
     uint64_t wii_cached_physical_group;   ///< Physical group number of cached block
     bool     wii_cache_valid;             ///< Whether the encrypted group cache is valid
     bool     wii_building_crypto_block;   ///< True while gathering sectors for re-encryption (suppresses recursion)
+
+    /* Erasure coding (write path) */
+    uint8_t   ec_algorithm;           ///< ErasureCodingAlgorithm (0=XOR, 1=RS-Vandermonde).
+    uint16_t  ec_K;                   ///< Data blocks per stripe.
+    uint16_t  ec_M;                   ///< Parity blocks per stripe.
+    uint32_t  ec_data_shard_size;     ///< Max on-disk block size for data blocks (fixed at creation).
+    void     *ec_rs_ctx;              ///< rs_context* (opaque RS codec), NULL if EC disabled.
+    uint8_t **ec_data_parity;         ///< Array of K * M parity buffers (interleaved stripe slots).
+    uint64_t *ec_data_block_offsets;  ///< Array of K * K file offsets for blocks in active stripes.
+    uint32_t *ec_data_block_sizes;    ///< Array of K * K actual on-disk sizes for blocks in active stripes.
+    uint64_t *ec_data_shard_crcs;     ///< Array of K * K CRC64 values for blocks in active stripes.
+    uint16_t *ec_data_stripe_counts;  ///< Array of K: blocks accumulated per stripe slot.
+    uint32_t  ec_total_data_blocks;   ///< Total data blocks written (counter for round-robin assignment).
+    UT_array *ec_data_stripes;        ///< Completed data stripe descriptors (serialized to ECMB).
+    bool      ec_enabled;             ///< True if erasure coding is active.
 } aaruformat_context;
 
 #ifndef AARUFORMAT_CONTEXT_DECLARED

include/aaruformat/decls.h

@@ -292,4 +292,7 @@ AARU_EXPORT int have_arm_crypto();
 AARU_EXPORT TARGET_WITH_SIMD uint64_t AARU_CALL aaruf_crc64_vmull(uint64_t previous_crc, const uint8_t *data, long len);
 #endif
 
+/* Erasure coding */
+AARU_EXPORT int32_t AARU_CALL aaruf_set_erasure_coding(void *context, uint8_t algorithm, uint16_t K, uint16_t M);
+
 #endif  // LIBAARUFORMAT_DECLS_H

include/erasure_internal.h

@@ -0,0 +1,52 @@
+/*
+ * This file is part of the Aaru Data Preservation Suite.
+ * Copyright (c) 2019-2026 Natalia Portillo.
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of the
+ * License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef LIBAARUFORMAT_ERASURE_INTERNAL_H
+#define LIBAARUFORMAT_ERASURE_INTERNAL_H
+
+#include "aaruformat/context.h"
+#include "aaruformat/structs/data.h"
+
+/**
+ * @brief Accumulate parity for a data block just written to disk.
+ *
+ * Called from aaruf_close_current_block() after writing header + payload.
+ */
+void ec_accumulate_data_block(aaruformat_context *ctx, const BlockHeader *block_header, const uint8_t *lzma_props,
+                              const uint8_t *payload, uint32_t payload_size, uint64_t file_offset);
+
+/**
+ * @brief Flush a completed data stripe slot: write parity blocks and record descriptor.
+ */
+void ec_flush_data_stripe(aaruformat_context *ctx, uint32_t slot);
+
+/**
+ * @brief Flush partial stripes, write ECMB and recovery footer.
+ *
+ * Called from aaruf_finalize_write() after index is written.
+ */
+void ec_finalize(aaruformat_context *ctx);
+
+/**
+ * @brief Free all erasure coding state.
+ *
+ * Called from aaruf_close().
+ */
+void ec_free(aaruformat_context *ctx);
+
+#endif /* LIBAARUFORMAT_ERASURE_INTERNAL_H */