fix: address PR review - rolling adler32, extract helpers, configurable max file size

- Fix rolling adler32: add missing -1 in s2 update formula (was producing
  wrong checksums, causing zero block matches)
- Fix file_send_sendfile signature to match typedef (add unused
  compression_level param)
- Extract receive_delta_file() from receive_incremental_check() to reduce
  nesting depth
- Extract send_file_incremental() helper in client_send.c
- Add delta_max_file_size to Config, serialized over wire
- Add --delta-max CLI flag
- Add test_large_file_delta (200KB) and extra delta_should_attempt cases
- Remove unused pos_in_block variable from delta_compute

src/shared/config.c

@@ -42,6 +42,7 @@ Config *config_create(char *version, char *send_directory,
   config->use_incremental = false;
   config->use_delta = false;
   config->delta_block_size = DELTA_BLOCK_SIZE_DEFAULT;
+  config->delta_max_file_size = DELTA_MAX_FILE_SIZE;
   config->use_tls = false;
   config->tls_cert = NULL;
   config->tls_key = NULL;
@@ -103,6 +104,7 @@ bool config_send(int file_descriptor, Config *config) {
   if (!send_int(file_descriptor, config->use_incremental)) return false;
   if (!send_int(file_descriptor, config->use_delta)) return false;
   if (!send_int(file_descriptor, (int)config->delta_block_size)) return false;
+  if (!send_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long))) return false;
   Status status;
   if (!receive_status(file_descriptor, &status)) return false;
   if (status != STATUS_OK) {
@@ -154,6 +156,7 @@ Config *config_receive(int file_descriptor) {
   config->use_delta = tmp;
   if (!receive_int(file_descriptor, &tmp)) goto error;
   config->delta_block_size = (uint32_t)tmp;
+  if (!receive_n_data(file_descriptor, &config->delta_max_file_size, sizeof(unsigned long long))) goto error;
   config->show_progress = false;
   config->dry_run = false;
   config->ssh_port = 22;

src/shared/config.h

@@ -36,6 +36,7 @@ typedef struct Config {
   bool use_incremental;
   bool use_delta;
   uint32_t delta_block_size;
+  unsigned long long delta_max_file_size;
   bool use_tls;
   char *tls_cert;
   char *tls_key;

src/shared/delta.c

@@ -128,6 +128,33 @@ void delta_signature_destroy(DeltaSignature *sig) {
   free(sig);
 }
 
+static bool ensure_capacity(DeltaInstruction **instrs, uint32_t *capacity,
+                             uint32_t count) {
+  if (count < *capacity) return true;
+  uint32_t new_cap = *capacity * 2;
+  DeltaInstruction *tmp = realloc(*instrs, new_cap * sizeof(DeltaInstruction));
+  if (!tmp) return false;
+  *instrs = tmp;
+  *capacity = new_cap;
+  return true;
+}
+
+static bool flush_literal(DeltaInstruction **instrs, uint32_t *capacity,
+                           uint32_t *count, const uint8_t *data,
+                           uint64_t start, uint64_t end) {
+  if (start >= end) return true;
+  uint32_t lit_len = (uint32_t)(end - start);
+  if (!ensure_capacity(instrs, capacity, *count)) return false;
+  uint8_t *lit_data = malloc(lit_len);
+  if (!lit_data) return false;
+  memcpy(lit_data, data + start, lit_len);
+  (*instrs)[*count].type = DELTA_INSTR_LITERAL;
+  (*instrs)[*count].literal.data = lit_data;
+  (*instrs)[*count].literal.length = lit_len;
+  (*count)++;
+  return true;
+}
+
 Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
                       const DeltaSignature *sig, uint32_t block_size) {
   if (!new_file_data || !sig || new_file_size == 0 || block_size == 0)
@@ -144,49 +171,67 @@ Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
   bool has_literal = false;
 
   uint64_t i = 0;
+
+  uint32_t s1 = 1, s2 = 0;
+  bool rolling_valid = false;
+
   while (i < new_file_size) {
     uint32_t window_len = (uint32_t)((new_file_size - i < block_size)
                                          ? (new_file_size - i)
                                          : block_size);
-    uint32_t adler = delta_adler32(new_data + i, window_len);
-    uint32_t xxh = delta_xxhash32(new_data + i, window_len);
+    bool full_window = (window_len == block_size);
+
+    uint32_t adler;
+    if (rolling_valid && full_window) {
+      uint8_t old_byte = new_data[i - 1];
+      uint8_t new_byte = new_data[i + block_size - 1];
+      s1 = (s1 + DELTA_ADLER32_MODULUS - old_byte + new_byte) %
+           DELTA_ADLER32_MODULUS;
+      s2 = (s2 + DELTA_ADLER32_MODULUS -
+            (uint32_t)((uint64_t)block_size * old_byte % DELTA_ADLER32_MODULUS) +
+            s1 - 1) %
+           DELTA_ADLER32_MODULUS;
+      adler = (s2 << 16) | s1;
+    } else {
+      s1 = 1;
+      s2 = 0;
+      for (uint32_t k = 0; k < window_len; k++) {
+        s1 = (s1 + new_data[i + k]) % DELTA_ADLER32_MODULUS;
+        s2 = (s2 + s1) % DELTA_ADLER32_MODULUS;
+      }
+      adler = (s2 << 16) | s1;
+      rolling_valid = full_window;
+    }
 
     bool matched = false;
     for (uint32_t j = 0; j < sig->block_count; j++) {
-      if (adler == sig->blocks[j].adler32 && xxh == sig->blocks[j].xxhash) {
-        if (has_literal) {
-          uint32_t lit_len = (uint32_t)(i - literal_start);
-          if (count == capacity) {
-            capacity *= 2;
-            DeltaInstruction *tmp = realloc(instrs, capacity * sizeof(DeltaInstruction));
-            if (!tmp) { free(instrs); return NULL; }
-            instrs = tmp;
+      if (adler == sig->blocks[j].adler32 && full_window) {
+        uint32_t xxh = delta_xxhash32(new_data + i, window_len);
+        if (xxh == sig->blocks[j].xxhash) {
+          if (has_literal) {
+            if (!flush_literal(&instrs, &capacity, &count, new_data,
+                               literal_start, i)) {
+              free(instrs);
+              return NULL;
+            }
+            has_literal = false;
           }
-          uint8_t *lit_data = malloc(lit_len);
-          if (!lit_data) { free(instrs); return NULL; }
-          memcpy(lit_data, new_data + literal_start, lit_len);
-          instrs[count].type = DELTA_INSTR_LITERAL;
-          instrs[count].literal.data = lit_data;
-          instrs[count].literal.length = lit_len;
+
+          if (!ensure_capacity(&instrs, &capacity, count)) {
+            free(instrs);
+            return NULL;
+          }
+          instrs[count].type = DELTA_INSTR_BLOCK_MATCH;
+          instrs[count].match.block_index = j;
+          instrs[count].match.block_offset = 0;
+          instrs[count].match.length = window_len;
           count++;
-          has_literal = false;
-        }
 
-        if (count == capacity) {
-          capacity *= 2;
-          DeltaInstruction *tmp = realloc(instrs, capacity * sizeof(DeltaInstruction));
-          if (!tmp) { free(instrs); return NULL; }
-          instrs = tmp;
+          i += window_len;
+          rolling_valid = false;
+          matched = true;
+          break;
         }
-        instrs[count].type = DELTA_INSTR_BLOCK_MATCH;
-        instrs[count].match.block_index = j;
-        instrs[count].match.block_offset = 0;
-        instrs[count].match.length = window_len;
-        count++;
-
-        i += window_len;
-        matched = true;
-        break;
       }
     }
 
@@ -200,20 +245,11 @@ Delta *delta_compute(const void *new_file_data, uint64_t new_file_size,
   }
 
   if (has_literal) {
-    uint32_t lit_len = (uint32_t)(new_file_size - literal_start);
-    if (count == capacity) {
-      capacity *= 2;
-      DeltaInstruction *tmp = realloc(instrs, capacity * sizeof(DeltaInstruction));
-      if (!tmp) { free(instrs); return NULL; }
-      instrs = tmp;
+    if (!flush_literal(&instrs, &capacity, &count, new_data,
+                       literal_start, new_file_size)) {
+      free(instrs);
+      return NULL;
     }
-    uint8_t *lit_data = malloc(lit_len);
-    if (!lit_data) { free(instrs); return NULL; }
-    memcpy(lit_data, new_data + literal_start, lit_len);
-    instrs[count].type = DELTA_INSTR_LITERAL;
-    instrs[count].literal.data = lit_data;
-    instrs[count].literal.length = lit_len;
-    count++;
   }
 
   Delta *delta = malloc(sizeof(Delta));
@@ -421,10 +457,10 @@ void delta_destroy(Delta *delta) {
   free(delta);
 }
 
-bool delta_should_attempt(uint64_t old_size, uint64_t new_size) {
+bool delta_should_attempt(uint64_t old_size, uint64_t new_size, uint64_t max_file_size) {
   if (old_size < DELTA_MIN_FILE_SIZE || new_size < DELTA_MIN_FILE_SIZE)
     return false;
-  if (old_size > DELTA_MAX_FILE_SIZE || new_size > DELTA_MAX_FILE_SIZE)
+  if (old_size > max_file_size || new_size > max_file_size)
     return false;
   double large = (old_size > new_size) ? (double)old_size : (double)new_size;
   double small = (old_size > new_size) ? (double)new_size : (double)old_size;

src/shared/delta.h

@@ -72,7 +72,7 @@ void *delta_apply(const void *old_data, uint64_t old_size, const Delta *delta,
                   uint32_t block_size);
 void delta_destroy(Delta *delta);
 
-bool delta_should_attempt(uint64_t old_size, uint64_t new_size);
+bool delta_should_attempt(uint64_t old_size, uint64_t new_size, uint64_t max_file_size);
 bool delta_is_worthwhile(const Delta *delta, uint64_t new_file_size);
 
 uint32_t delta_adler32(const void *data, uint32_t len);

src/shared/file.c

@@ -133,6 +133,150 @@ bool file_save_to_disk(const char *root_directory, File *file) {
   return ok;
 }
 
+static void *old_data_from_path(const char *full_path, unsigned long long old_size) {
+  void *data = malloc((size_t)old_size);
+  if (!data) return NULL;
+  FILE *fp = fopen(full_path, "rb");
+  if (!fp) { free(data); return NULL; }
+  size_t nread = fread(data, 1, (size_t)old_size, fp);
+  fclose(fp);
+  if (nread != (size_t)old_size) { free(data); return NULL; }
+  return data;
+}
+
+static File *receive_delta_file(int fd, Config *config, const char *check_path,
+                                 void *old_data, unsigned long long old_size) {
+  if (!old_data) return NULL;
+
+  DeltaSignature *sig = delta_signature_create(old_data, old_size,
+                                                config->delta_block_size);
+  if (!sig) { free(old_data); return NULL; }
+
+  Data *sig_data = delta_signature_serialize(sig);
+  if (!sig_data) { delta_signature_destroy(sig); free(old_data); return NULL; }
+
+  bool sig_sent = send_status(fd, STATUS_DELTA_SIGNATURE) &&
+                  send_data(fd, sig_data);
+  data_destroy(sig_data);
+
+  if (!sig_sent) { delta_signature_destroy(sig); free(old_data); return NULL; }
+
+  Status resp;
+  if (!receive_status(fd, &resp)) {
+    delta_signature_destroy(sig);
+    free(old_data);
+    return NULL;
+  }
+
+  if (resp == STATUS_DELTA_DATA) {
+    Data *delta_data = receive_data(fd);
+    if (!delta_data) {
+      delta_signature_destroy(sig);
+      free(old_data);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+
+    Data *raw_delta = delta_data;
+    if (config->use_compression) {
+      raw_delta = data_decompress(delta_data);
+      data_destroy(delta_data);
+      if (!raw_delta) {
+        free(old_data);
+        delta_signature_destroy(sig);
+        send_status(fd, STATUS_ERROR);
+        return NULL;
+      }
+    }
+
+    Delta *delta = delta_deserialize(raw_delta);
+    data_destroy(raw_delta);
+    if (!delta) {
+      free(old_data);
+      delta_signature_destroy(sig);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+
+    void *new_data = delta_apply(old_data, old_size, delta,
+                                  config->delta_block_size);
+    uint64_t new_size = delta->new_file_size;
+    delta_destroy(delta);
+
+    if (!new_data) {
+      free(old_data);
+      delta_signature_destroy(sig);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+
+    File *file = file_create(check_path);
+    if (!file) {
+      free(new_data);
+      free(old_data);
+      delta_signature_destroy(sig);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+
+    if (config->use_metadata) {
+      int meta_ok = 1;
+      file->metadata = metadata_receive(fd, &meta_ok);
+      if (!meta_ok) {
+        file_destroy(file);
+        free(new_data);
+        free(old_data);
+        delta_signature_destroy(sig);
+        send_status(fd, STATUS_ERROR);
+        return NULL;
+      }
+    }
+
+    data_destroy(file->data);
+    file->data = data_create(new_data, (size_t)new_size);
+
+    free(old_data);
+    delta_signature_destroy(sig);
+    return file;
+  }
+
+  if (resp == STATUS_NEXT) {
+    delta_signature_destroy(sig);
+    free(old_data);
+
+    File *file = file_create(check_path);
+    if (!file) { send_status(fd, STATUS_ERROR); return NULL; }
+
+    if (config->use_metadata) {
+      int meta_ok = 1;
+      file->metadata = metadata_receive(fd, &meta_ok);
+      if (!meta_ok) { file_destroy(file); send_status(fd, STATUS_ERROR); return NULL; }
+    }
+
+    Data *file_data = receive_data(fd);
+    if (file_data == NULL) {
+      file_destroy(file);
+      send_status(fd, STATUS_ERROR);
+      return NULL;
+    }
+
+    if (config->use_compression) {
+      Data *uncompressed = data_decompress(file_data);
+      data_destroy(file_data);
+      if (uncompressed == NULL) { file_destroy(file); send_status(fd, STATUS_ERROR); return NULL; }
+      file_data = uncompressed;
+    }
+
+    data_destroy(file->data);
+    file->data = file_data;
+    return file;
+  }
+
+  delta_signature_destroy(sig);
+  free(old_data);
+  return NULL;
+}
+
 File *receive_incremental_check(int fd, Config *config, bool *skipped) {
   *skipped = false;
   char *check_path = receive_str(fd);
@@ -165,182 +309,18 @@ File *receive_incremental_check(int fd, Config *config, bool *skipped) {
   }
 
   bool try_delta = config->use_delta && has_old_file &&
-                   delta_should_attempt(old_size, check_size);
+                   delta_should_attempt(old_size, check_size, config->delta_max_file_size);
 
   if (try_delta) {
-    void *old_data = malloc((size_t)old_size);
-    if (!old_data) {
-      try_delta = false;
-    } else {
-      FILE *fp = fopen(full_path, "rb");
-      if (!fp) {
-        free(old_data);
-        try_delta = false;
-      } else {
-        size_t nread = fread(old_data, 1, (size_t)old_size, fp);
-        fclose(fp);
-        if (nread != (size_t)old_size) {
-          free(old_data);
-          try_delta = false;
-        }
-      }
-    }
-
-    if (try_delta) {
-      DeltaSignature *sig = delta_signature_create(old_data, old_size,
-                                                    config->delta_block_size);
-      if (!sig) {
-        free(old_data);
-        try_delta = false;
-      } else {
-        Data *sig_data = delta_signature_serialize(sig);
-        if (!sig_data) {
-          delta_signature_destroy(sig);
-          free(old_data);
-          try_delta = false;
-        } else {
-          bool sig_sent = send_status(fd, STATUS_DELTA_SIGNATURE) &&
-                          send_data(fd, sig_data);
-          data_destroy(sig_data);
-
-          if (!sig_sent) {
-            delta_signature_destroy(sig);
-            free(old_data);
-            try_delta = false;
-          } else {
-            Status resp;
-            if (!receive_status(fd, &resp)) {
-              delta_signature_destroy(sig);
-              free(old_data);
-              free(full_path);
-              free(check_path);
-              return NULL;
-            }
-
-            if (resp == STATUS_DELTA_DATA) {
-              Data *delta_data = receive_data(fd);
-              if (!delta_data) {
-                delta_signature_destroy(sig);
-                free(old_data);
-                send_status(fd, STATUS_ERROR);
-                free(full_path);
-                free(check_path);
-                return NULL;
-              }
-
-              Data *raw_delta = delta_data;
-              if (config->use_compression) {
-                raw_delta = data_decompress(delta_data);
-                data_destroy(delta_data);
-                if (!raw_delta) {
-                  free(old_data);
-                  delta_signature_destroy(sig);
-                  send_status(fd, STATUS_ERROR);
-                  free(full_path);
-                  free(check_path);
-                  return NULL;
-                }
-              }
-
-              Delta *delta = delta_deserialize(raw_delta);
-              data_destroy(raw_delta);
-              if (!delta) {
-                free(old_data);
-                delta_signature_destroy(sig);
-                send_status(fd, STATUS_ERROR);
-                free(full_path);
-                free(check_path);
-                return NULL;
-              }
-
-              void *new_data = delta_apply(old_data, old_size, delta,
-                                            config->delta_block_size);
-              uint64_t new_size = delta->new_file_size;
-              delta_destroy(delta);
-
-              if (!new_data) {
-                free(old_data);
-                delta_signature_destroy(sig);
-                send_status(fd, STATUS_ERROR);
-                free(full_path);
-                free(check_path);
-                return NULL;
-              }
-
-              File *file = file_create(check_path);
-              free(check_path);
-              free(full_path);
-
-              if (!file) {
-                free(new_data);
-                free(old_data);
-                delta_signature_destroy(sig);
-                send_status(fd, STATUS_ERROR);
-                return NULL;
-              }
-
-              if (config->use_metadata) {
-                int meta_ok = 1;
-                file->metadata = metadata_receive(fd, &meta_ok);
-                if (!meta_ok) {
-                  file_destroy(file);
-                  free(new_data);
-                  free(old_data);
-                  delta_signature_destroy(sig);
-                  send_status(fd, STATUS_ERROR);
-                  return NULL;
-                }
-              }
-
-              data_destroy(file->data);
-              file->data = data_create(new_data, (size_t)new_size);
-
-              free(old_data);
-              delta_signature_destroy(sig);
-              return file;
-            }
-
-            if (resp == STATUS_NEXT) {
-              delta_signature_destroy(sig);
-              free(old_data);
-
-              File *file = file_create(check_path);
-              free(check_path);
-              free(full_path);
-              if (!file) { send_status(fd, STATUS_ERROR); return NULL; }
-
-              if (config->use_metadata) {
-                int meta_ok = 1;
-                file->metadata = metadata_receive(fd, &meta_ok);
-                if (!meta_ok) { file_destroy(file); send_status(fd, STATUS_ERROR); return NULL; }
-              }
-
-              Data *file_data = receive_data(fd);
-              if (file_data == NULL) {
-                file_destroy(file);
-                send_status(fd, STATUS_ERROR);
-                return NULL;
-              }
-
-              if (config->use_compression) {
-                Data *uncompressed = data_decompress(file_data);
-                data_destroy(file_data);
-                if (uncompressed == NULL) { file_destroy(file); send_status(fd, STATUS_ERROR); return NULL; }
-                file_data = uncompressed;
-              }
-
-              data_destroy(file->data);
-              file->data = file_data;
-              return file;
-            }
-
-            delta_signature_destroy(sig);
-            free(old_data);
-            try_delta = false;
-          }
-        }
-      }
+    void *old_data = old_data_from_path(full_path, old_size);
+    File *delta_file = receive_delta_file(fd, config, check_path,
+                                           old_data, old_size);
+    if (delta_file) {
+      free(full_path);
+      free(check_path);
+      return delta_file;
     }
+    try_delta = false;
   }
 
   if (!try_delta) {
@@ -406,7 +386,8 @@ bool to_disk(const char *path, const void *data, unsigned long long data_size) {
   return true;
 }
 
-bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, bool send_path) {
+bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, int compression_level, bool send_path) {
+  (void)compression_level;
   if (send_path && !send_str(file_descriptor, file->path)) return false;
   if (use_metadata && !metadata_send(file_descriptor, file->metadata)) return false;
 

src/shared/file.h

@@ -25,7 +25,7 @@ void file_destroy(void *item);
 bool file_load_data(File *file);
 File *file_receive(Config *config, int file_descriptor);
 bool file_send_single_calls(File *file, int file_descriptor, bool use_metadata, int compression_level, bool send_path);
-bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, bool send_path);
+bool file_send_sendfile(File *file, int file_descriptor, bool use_metadata, int compression_level, bool send_path);
 size_t file_content_to_buffer(File *file);
 FileMetadata *file_metadata_create(struct stat *stats);
 void file_metadata_destroy(void *metadata);