Switch user-supplied functions in C API to return int

examples/qpdfjob-c-save-attachment.c

@@ -12,11 +12,11 @@
 // something with QPDFJob. See qpdfjob-c-save-attachment.c for an
 // implementation that uses the C API.
 
-static void
+static int
 save_to_file(char const* data, size_t len, void* udata)
 {
     FILE* f = (FILE*)udata;
-    fwrite(data, 1, len, f);
+    return fwrite(data, 1, len, f) != len;
 }
 
 static FILE*

include/qpdf/qpdflogger-c.h

@@ -59,7 +59,8 @@ extern "C" {
         qpdf_log_dest_custom = 4,
     };
 
-    typedef void (*qpdf_log_fn_t)(char const* data, size_t len, void* udata);
+    /* Function should return 0 on success. */
+    typedef int (*qpdf_log_fn_t)(char const* data, size_t len, void* udata);
 
     QPDF_DLL
     void qpdflogger_set_info(

libqpdf/qpdflogger-c.cc

@@ -56,12 +56,7 @@ set_log_dest(
         method(l->discard());
         break;
     case qpdf_log_dest_custom:
-        method(std::make_shared<Pl_Function>(
-            identifier,
-            nullptr,
-            [fn, udata](unsigned char const* data, size_t len) {
-                fn(reinterpret_cast<char const*>(data), len, udata);
-            }));
+        method(std::make_shared<Pl_Function>(identifier, nullptr, fn, udata));
         break;
     }
 }

libtests/logger_c.c

@@ -8,11 +8,11 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-static void
+static int
 fn(char const* data, size_t len, void* udata)
 {
     FILE* f = (FILE*)udata;
-    fwrite(data, 1, len, f);
+    return fwrite(data, 1, len, f) != len;
 }
 
 static void