feat: Add DoIP discovery example with VIN selection callback to README

Author: Magolves

examples/doip_client/README.md

@@ -193,3 +193,54 @@ This codebase now includes a small DoIP transport abstraction, a split TCP/UDP i
 - Build Integration
   - CMake: when `BUILD_UDS_TP_DOIP=ON`, the DoIP target includes the new TCP/UDP transport sources.
   - Bazel: `src/BUILD` updated to include the new transport sources and headers.
+
+  ### Quick Start: Discovery + Selection
+
+  Minimal example of discovering DoIP responders and selecting one by VIN prefix:
+
+  ```c
+  #include <stdio.h>
+  #include <string.h>
+  #include <stdbool.h>
+  #include <stdint.h>
+  #include "tp/doip/doip_client.h"
+
+  static bool select_by_vin(const DoIPDiscoveryInfo *info, void *user) {
+      const char *needle = (const char *)user; // VIN prefix or full VIN
+      if (!needle || !*needle) return false;
+      if (info->vin[0] == '\0') return false;
+      return strncmp(info->vin, needle, strlen(needle)) == 0;
+  }
+
+  int main(int argc, char **argv) {
+      const char *vin_prefix = argc > 1 ? argv[1] : NULL;
+      bool loopback = argc > 2 ? (strcmp(argv[2], "loopback") == 0) : false;
+
+      DoIPClient_t tp;
+      memset(&tp, 0, sizeof(tp));
+
+      UDSDoIPSetSelectionCallback(&tp, select_by_vin, (void*)vin_prefix);
+
+      int count = UDSDoIPDiscoverVehicles(&tp, 2000, loopback);
+      printf("Discovered %d responders\n", count);
+      printf("Selected server: %s\n", tp.server_ip);
+      return 0;
+  }
+  ```
+
+  Build and run (ad hoc):
+
+  ```bash
+  gcc -DUDS_TP_DOIP -Isrc -I. -o build/doip_discovery_example \
+    src/tp/doip/doip_client.c src/tp/doip/doip_tp_udp.c src/tp/doip/doip_tp_tcp.c \
+    examples/doip_discovery_example/main.c
+
+  # Default multicast discovery (~2s), chooses first responder
+  ./build/doip_discovery_example
+
+  # Filter by VIN prefix
+  ./build/doip_discovery_example WBA
+
+  # Loopback discovery for local testing
+  ./build/doip_discovery_example "" loopback
+  ```

src/tp/doip/pr.md

@@ -0,0 +1,54 @@
+## Add DoIP (ISO 13400) Transport Layer Support
+
+This PR implements DoIP (Diagnostic over IP - ISO 13400) as a new transport layer for UDS, enabling diagnostic communication over TCP/IP networks.
+
+### Features
+
+- **DoIP Client Implementation** (`src/tp/doip/`)
+  - TCP-based diagnostic message transport (ISO 13400-2)
+  - Routing activation and alive check handling
+  - Proper DoIP message framing and state management
+  - Support for diagnostic message ACK/NACK
+  - Non-blocking I/O with configurable timeouts
+
+### Implementation Details
+
+- **Protocol Version**: DoIP v3 (ISO 13400:2019)
+- **Standard Port**: TCP 13400
+- **Addressing**: External test equipment range (0x0E00-0x0FFF)
+- **Message Types**: Routing activation, diagnostic messages, alive check
+
+### Testing
+
+- Compiles cleanly with `-Wall -Wpedantic -Wextra`
+- Integration test passes (`examples/doip_client/test.sh`)
+- Successfully exchanges RDBI/WDBI messages over DoIP
+
+### Code Quality
+
+- Consistent with iso14229 coding style
+- Comprehensive error handling and logging
+- Well-documented with inline comments and function documentation
+- No compiler warnings
+
+### Missing Features
+
+- UDP vehicle discovery
+- DoIP server implementation in `src/tp/doip/` (currently only in examples)
+- TLS support (port 3496)
+- Unit tests for DoIP module
+- Multi-client server support
+
+### Related Standards
+
+- ISO 13400-2:2019 - Road vehicles — Diagnostic communication over Internet Protocol (DoIP)
+- ISO 14229 - Unified Diagnostic Services (UDS)
+
+---
+
+**Testing Instructions:**
+
+```bash
+cd examples/doip_client
+make
+[test.sh](http://_vscodecontentref_/3)  # Automated integration test