fix: reject partial database pages as corruption

include/pager.h

@@ -11,7 +11,8 @@ typedef enum {
     PAGER_OK = 0,
     PAGER_INVALID_ARGUMENT,
     PAGER_IO_ERROR,
-    PAGER_OUT_OF_PAGES
+    PAGER_OUT_OF_PAGES,
+    PAGER_CORRUPT
 } PagerResult;
 
 typedef struct {

src/database.c

@@ -55,7 +55,7 @@ Table *table_open(const char *filename, SqliteResult *result)
     PagerResult pager_result;
     Pager *pager = pager_open(filename, &pager_result);
     if (pager == NULL) {
-        *result = SQLITE_IO_ERROR;
+        *result = pager_result == PAGER_CORRUPT ? SQLITE_CORRUPT : SQLITE_IO_ERROR;
         return NULL;
     }
 

src/pager.c

@@ -4,7 +4,7 @@
 
 static size_t page_count_for_length(size_t file_length)
 {
-    return (file_length + PAGE_SIZE - 1U) / PAGE_SIZE;
+    return file_length / PAGE_SIZE;
 }
 
 Pager *pager_open(const char *filename, PagerResult *result)
@@ -38,6 +38,12 @@ Pager *pager_open(const char *filename, PagerResult *result)
         return NULL;
     }
 
+    if ((size_t)length % PAGE_SIZE != 0U) {
+        fclose(file);
+        *result = PAGER_CORRUPT;
+        return NULL;
+    }
+
     Pager *pager = calloc(1, sizeof(*pager));
     if (pager == NULL) {
         fclose(file);
@@ -154,6 +160,8 @@ const char *pager_result_string(PagerResult result)
         return "I/O error";
     case PAGER_OUT_OF_PAGES:
         return "database exceeds maximum page count";
+    case PAGER_CORRUPT:
+        return "database file has a partial page";
     default:
         return "unknown error";
     }

tests/test_database.c

@@ -228,6 +228,21 @@ static void test_corrupt_node_count_is_rejected(void)
     remove(filename);
 }
 
+static void test_partial_page_database_is_reported_as_corrupt(void)
+{
+    const char *filename = "build/test_partial_page.db";
+    FILE *file = fopen(filename, "wb");
+    assert(file != NULL);
+    assert(fputc(0, file) != EOF);
+    assert(fclose(file) == 0);
+
+    SqliteResult result = SQLITE_OK;
+    Table *table = table_open(filename, &result);
+    assert(table == NULL);
+    assert(result == SQLITE_CORRUPT);
+    remove(filename);
+}
+
 static void test_corrupt_metadata_page_is_rejected(void)
 {
     const char *filename = "build/test_corrupt_metadata.db";
@@ -271,6 +286,7 @@ int main(void)
     test_validation();
     test_corrupt_node_count_is_rejected();
     test_corrupt_metadata_page_is_rejected();
+    test_partial_page_database_is_reported_as_corrupt();
     test_corrupt_child_reference_is_rejected();
     return 0;
 }

tests/test_pager.c

@@ -4,6 +4,33 @@
 #include <stdio.h>
 #include <string.h>
 
+static void write_file_of_size(const char *filename, size_t size)
+{
+    unsigned char bytes[PAGE_SIZE + 1U] = {0};
+    FILE *file = fopen(filename, "wb");
+    assert(file != NULL);
+    assert(size <= sizeof(bytes));
+    assert(fwrite(bytes, 1U, size, file) == size);
+    assert(fclose(file) == 0);
+}
+
+static void test_partial_page_files_are_rejected(void)
+{
+    const char *filename = "build/test_pager_partial.db";
+    const size_t invalid_sizes[] = {1U, PAGE_SIZE - 1U, PAGE_SIZE + 1U};
+
+    for (size_t i = 0; i < sizeof(invalid_sizes) / sizeof(invalid_sizes[0]); ++i) {
+        write_file_of_size(filename, invalid_sizes[i]);
+
+        PagerResult result = PAGER_OK;
+        Pager *pager = pager_open(filename, &result);
+        assert(pager == NULL);
+        assert(result == PAGER_CORRUPT);
+    }
+
+    remove(filename);
+}
+
 static void test_pager_round_trip(void)
 {
     const char *filename = "build/test_pager.db";
@@ -39,5 +66,6 @@ static void test_pager_round_trip(void)
 int main(void)
 {
     test_pager_round_trip();
+    test_partial_page_files_are_rejected();
     return 0;
 }