5. Extracting a single file from a SQLar archive

5.1. Extracting a file in C

5.1.1. sqlar_extract_file

The function sqlar_extract_file is used to extract a file from a sqlar archive.

static int sqlar_extract_file(const char *sqlar,
                              const char *name,
                              const char *out);

static int sqlar_extract_file(const char *sqlar,
                              const char *name,
                              const char *out)
{
    FILE *fp;
    char *output;
    unsigned long int out_size;
    int rc;
    sqlite3 *db;
    sqlite3_stmt *stmt;
    int imode;
    int sz;
    const char *data;
    int data_sz;

    rc = sqlite3_open(sqlar, &db);
    if(rc) return rc;

    rc = sqlite3_exec(db,
                      "CREATE TABLE IF NOT EXISTS sqlar(\n"
                      "  name TEXT PRIMARY KEY,\n"
                      "  mode INT,\n"
                      "  mtime INT,\n"
                      "  sz INT,\n"
                      "  data BLOB\n"
                      ");", 0, 0, 0);


    sqlite3_prepare(db,
                    "SELECT name, mode, mtime, sz, data FROM sqlar"
                    " WHERE name is ?1",
                    -1,
                    &stmt,
                    NULL);

    sqlite3_bind_text(stmt, 1, name, -1, SQLITE_STATIC);

    rc = sqlite3_step(stmt);

    if(rc != SQLITE_ROW) {
        fprintf(stderr, "Could find file %s\n", name);
        sqlite3_finalize(stmt);
        sqlite3_close(db);
        return rc;
    }

    imode = sqlite3_column_int(stmt,1);
    sz = sqlite3_column_int(stmt,3);
    data = sqlite3_column_blob(stmt,4);
    data_sz = sqlite3_column_bytes(stmt,4);

    fp = fopen(out, "wb");
    if(fp == NULL) {
        fprintf(stderr, "Could not open output file %s for writing\n", out);
        return SQLITE_CANTOPEN;
    }

    if(sz == data_sz) {
        fwrite(data, 1, data_sz, fp);
    } else {
        output = sqlite3_malloc(sz+1);
        out_size = sz;

        rc = uncompress((Bytef*)output,
                        &out_size,
                        (const Bytef*)data,
                        data_sz);
        if(rc != Z_OK) {
            fprintf(stderr, "Error: could not uncompress data\n");
            return SQLITE_ERROR;
        }
        fwrite(output, out_size, 1, fp);
        sqlite3_free(output);
    }
    fclose(fp);
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    rc = chmod(out, imode&0777);
    return SQLITE_OK;
}

5.2. Extracting a file in Scheme

{"sqlar:extract-file", pp_extract_file, 3, 3, {STR,STR,STR}},

static cell pp_extract_file(cell x)
{
    const char *db;
    const char *file;
    const char *name;
    int rc;
    cell cstr;

    cstr = car(x);
    db = string(car(x));
    x = cdr(x);
    file = string(car(x));
    x = cdr(x);
    name = string(car(x));
    rc = sqlar_extract_file(db, file, name);

    if(rc != SQLITE_OK) {
        error("Could not extract file from sqlar archive", cstr);
    }
    return UNSPECIFIC;
}

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