$ show FreeTDS/freetds
FreeTDS is an open-source C library that implements the Tabular Data Stream (TDS) protocol, providing client connectivity to Sybase and Microsoft SQL Server databases. It exposes three API layers: DB-Library (compatible with Sybase/Microsoft's db-lib), CT-Library (Sybase's client library), and a full ODBC driver. The library also includes a connection pool server, server-side test infrastructure, and command-line tools such as `tsql`, `fisql`, `freebcp`, `bsqldb`, and `defncopy`. Core protocol handling lives in `src/tds/`, which manages login, authentication (NTLM, Kerberos, SSPI), encryption (TLS via OpenSSL or GnuTLS), packet framing, query submission, cursor management, and bulk copy. The architecture is layered and modular, with clean stream I/O, threading, and character conversion abstractions that make components independently reusable. The codebase is cross-platform (Unix, Windows, VMS) and supports TDS versions 4.2 through 8.0, adapting to server-specific behaviors. Despite its age and some legacy compatibility code, it remains actively maintained and widely used as a reliable database connectivity layer in production environments.
The LLM identified 6 files worth highlighting for reuse:
A generic doubly-linked list implemented as a header-only template using macros (DLIST_NODE, DLIST_FOREACH, etc.). Provides O(1) insert/remove and safe iteration with removal. The template pattern allows instantiation for any node type and is fully type-safe with no external dependencies. Ideal for any C project needing a linked list without pulling in a larger library.
Simple multiprecision arithmetic for fixed-size (up to 128-bit) integers. Implements addition, subtraction, multiplication, division, comparison, and right/left shifting on arrays of TDS_SMP_UNSIGNED limbs. Used internally for numeric/decimal conversion but is self-contained and portable. Can be extracted by any project needing basic large-number operations without a heavy dependency like GMP.
A high-performance UTF-8 decoder using Bjoern Hoehrmann's DFA algorithm. Processes one byte at a time, handling sequences of 1-4 bytes and all error conditions (overlong, invalid bytes, etc.) with minimal branching. The implementation is a single self-contained function with no external dependencies. Extractable into any C project requiring robust UTF-8 validation and decoding.
A header-only set of macros for reading and writing integers in big-endian (network order) and little-endian, with support for aligned and unaligned memory access. Covers sizes from 1 to 8 bytes. The macros use platform-specific builtins (e.g., bswap on GCC/Clang) for efficiency but fall back to portable shifts. Ideal for networking code, binary parsers, or any cross-platform data serialization.
An abstract stream I/O layer (TDSINSTREAM/TDSOUTSTREAM) with implementations for file, static buffer, dynamic buffer, and TDS socket. Supports layered character set conversion via iconv. The interface provides read/write/peek for input and write/flush for output, with a 'converter' stream that transparently transcodes data. The design is clean and database-agnostic, making it reusable in any C project needing pluggable I/O backends with optional encoding transformations.
A robust ODBC connection-string parser that handles quoted values (braces), case-insensitive keys, and two-pass expansion (DSN → server name → detailed parameters). Supports server discovery via SQL Browser. The implementation handles edge cases like escaped braces and multiple semicolons. Isolated from the rest of ODBC, this parser can be reused in any C application that needs to interpret ODBC-style or key-value configuration strings.