libusb: cmake: Proper dependency on Iconv (#405)

- explicitly add Iconv as a dependent library;
- check if iconv requires pointer-to-const as input (introduce ICONV_CONST check);
- NetBSD CI (has external Iconv library implementation that uses all of the above);

.builds/netbsd.yml

@@ -0,0 +1,18 @@
+image: netbsd/latest
+packages:
+- cmake
+- pkgconf
+- libusb1
+- libiconv
+sources:
+- https://github.com/libusb/hidapi
+tasks:
+- setup: |
+    cd hidapi
+    mkdir -p build install
+    cmake -B build -S . -DCMAKE_INSTALL_PREFIX=install
+- build: |
+    cd hidapi/build
+    make
+    make install
+    make clean

libusb/CMakeLists.txt

@@ -19,6 +19,29 @@ endif()
 find_package(Threads REQUIRED)
 target_link_libraries(hidapi_libusb PRIVATE Threads::Threads)
 
+if(HIDAPI_NO_ICONV)
+    target_compile_definitions(hidapi_libusb PRIVATE NO_ICONV)
+else()
+    if(NOT ANDROID AND NOT CMAKE_VERSION VERSION_LESS 3.11)
+        find_package(Iconv REQUIRED)
+        include(CheckCSourceCompiles)
+        target_link_libraries(hidapi_libusb PRIVATE Iconv::Iconv)
+        set(CMAKE_REQUIRED_LIBRARIES "Iconv::Iconv")
+        # check for error: "conflicting types for 'iconv'"
+        check_c_source_compiles("#include<iconv.h>
+            extern size_t iconv (iconv_t cd, const char **inbuf, size_t *inbytesleft, char **outbuf, size_t *outbytesleft);
+            int main() {}"
+        HIDAPI_ICONV_CONST)
+        if(HIDAPI_ICONV_CONST)
+            target_compile_definitions(hidapi_libusb PRIVATE "ICONV_CONST=const")
+        endif()
+    endif()
+    # otherwise there is 3 options:
+    # 1) On Android Iconv is disabled on the code level anyway, so no issue;
+    # 2) iconv is provided by Standard C library and the build will be just fine;
+    # 4) The _user_ has to provide additiona compilation options for this project/target.
+endif()
+
 set_target_properties(hidapi_libusb
     PROPERTIES
         EXPORT_NAME "libusb"

libusb/hid.c

@@ -44,6 +44,9 @@
 #include <libusb.h>
 #if !defined(__ANDROID__) && !defined(NO_ICONV)
 #include <iconv.h>
+#ifndef ICONV_CONST
+#define ICONV_CONST
+#endif
 #endif
 
 #include "hidapi_libusb.h"
@@ -405,7 +408,7 @@ static wchar_t *get_usb_string(libusb_device_handle *dev, uint8_t idx)
 	size_t inbytes;
 	size_t outbytes;
 	size_t res;
-	char *inptr;
+	ICONV_CONST char *inptr;
 	char *outptr;
 #endif
 
@@ -421,7 +424,7 @@ static wchar_t *get_usb_string(libusb_device_handle *dev, uint8_t idx)
 			lang,
 			(unsigned char*)buf,
 			sizeof(buf));
-	if (len < 0)
+	if (len < 2) /* we always skip first 2 bytes */
 		return NULL;
 
 #if defined(__ANDROID__) || defined(NO_ICONV)

src/CMakeLists.txt

@@ -92,6 +92,7 @@ set(EXPORT_COMPONENTS)
 set(HIDAPI_NEED_EXPORT_THREADS FALSE)
 set(HIDAPI_NEED_EXPORT_LIBUSB FALSE)
 set(HIDAPI_NEED_EXPORT_LIBUDEV FALSE)
+set(HIDAPI_NEED_EXPORT_ICONV FALSE)
 
 if(WIN32)
     add_subdirectory("${PROJECT_ROOT}/windows" windows)
@@ -128,6 +129,9 @@ else()
         target_include_directories(hidapi_include INTERFACE
             "$<BUILD_INTERFACE:${PROJECT_ROOT}/libusb>"
         )
+        if(NOT DEFINED HIDAPI_NO_ICONV)
+            set(HIDAPI_NO_ICONV OFF)
+        endif()
         add_subdirectory("${PROJECT_ROOT}/libusb" libusb)
         list(APPEND EXPORT_COMPONENTS libusb)
         if(NOT EXPORT_ALIAS)
@@ -138,6 +142,9 @@ else()
             if(NOT TARGET usb-1.0)
                 set(HIDAPI_NEED_EXPORT_LIBUSB TRUE)
             endif()
+            if(NOT HIDAPI_NO_ICONV AND NOT ANDROID AND NOT CMAKE_VERSION VERSION_LESS 3.11)
+                set(HIDAPI_NEED_EXPORT_ICONV TRUE)
+            endif()
         endif()
     elseif(NOT TARGET hidapi_hidraw)
         message(FATAL_ERROR "Select at least one option to build: HIDAPI_WITH_LIBUSB or HIDAPI_WITH_HIDRAW")

src/cmake/hidapi-config.cmake.in

@@ -11,6 +11,7 @@ set(hidapi_FOUND FALSE)
 set(HIDAPI_NEED_EXPORT_THREADS @HIDAPI_NEED_EXPORT_THREADS@)
 set(HIDAPI_NEED_EXPORT_LIBUSB @HIDAPI_NEED_EXPORT_LIBUSB@)
 set(HIDAPI_NEED_EXPORT_LIBUDEV @HIDAPI_NEED_EXPORT_LIBUDEV@)
+set(HIDAPI_NEED_EXPORT_ICONV @HIDAPI_NEED_EXPORT_ICONV@)
 
 if(HIDAPI_NEED_EXPORT_THREADS)
   if(CMAKE_VERSION VERSION_LESS 3.4.3)
@@ -32,6 +33,14 @@ if(HIDAPI_NEED_EXPORT_LIBUSB OR HIDAPI_NEED_EXPORT_LIBUDEV)
   endif()
 endif()
 
+if(HIDAPI_NEED_EXPORT_ICONV)
+  if(CMAKE_VERSION VERSION_LESS 3.11)
+    message(WARNING "HIDAPI requires CMake target Iconv::Iconv, make sure to provide it")
+  else()
+    find_package(Iconv REQUIRED)
+  endif()
+endif()
+
 include("${CMAKE_CURRENT_LIST_DIR}/libhidapi.cmake")
 
 set(hidapi_FOUND TRUE)