Test export private keys in C.

Result : fails.
Reason : password callback is never called.

With default pinentry mode, the password is requested normally 
and the private key is exported. But this can't be done on a web server.

Enclosed in #ifdef DEVTIME.

GpgMECWorker.cpp

@@ -9,6 +9,37 @@
 
 #include "GpgMECWorker.h"
 
+#ifdef DEVTIME
+
+/**
+ * This callback is never called when exporting private keys.
+ * From gpgme-1.14.0/tests/run-support.h
+ */
+gpgme_error_t passphrase_cb(void *opaque, const char *uid_hint, const char *passphrase_info,
+                            int last_was_bad, int fd)
+{
+    int res;
+    char pass[] = "test_pwd\n";
+    int passlen = strlen(pass);
+    int off = 0;
+
+    (void) opaque;
+    (void) uid_hint;
+    (void) passphrase_info;
+    (void) last_was_bad;
+
+    do
+    {
+        res = gpgme_io_write(fd, &pass[off], passlen - off);
+        if (res > 0)
+            off += res;
+    }
+    while (res > 0 && off != passlen);
+
+    return off == passlen ? 0 : gpgme_error_from_errno(errno);
+}
+#endif
+
 GpgMECWorker::GpgMECWorker()
 {
     gpgme_error_t c_err = gpgme_new(&c_ctx);
@@ -37,3 +68,66 @@ bool GpgMECWorker::DeleteKey(const char * fpr, bool secret, GpgME::Error& e)
     }
     return true;
 }
+
+#ifdef DEVTIME
+
+/**
+ * Much code here is obtained from gpgme-1.14.0/tests/run-export.c
+ * @param fpr
+ * @param e
+ * @return 
+ */
+bool GpgMECWorker::ExportPrivateKey(const char* fpr, GpgME::Error& e)
+{
+    gpgme_key_t c_key;
+    gpgme_data_t out;
+    gpgme_set_armor(c_ctx, 1);
+
+    gpgme_error_t c_err = gpgme_get_key(c_ctx, fpr, &c_key, true);
+    if (c_key == NULL)
+    {
+        e = GpgME::Error::fromCode(c_err);
+        return false;
+    }
+
+    FILE * kFp = fopen("/tmp/data", "wb");
+    if (kFp == NULL)
+        return false;
+    c_err = gpgme_data_new_from_stream(&out, kFp);
+    if (c_err != 0)
+    {
+        fclose(kFp);
+        e = GpgME::Error::fromCode(c_err);
+        return false;
+    }
+
+    gpgme_key_t aKeys[2];
+    aKeys[0] = c_key;
+    aKeys[1] = NULL;
+
+    c_err = gpgme_set_pinentry_mode(c_ctx, GPGME_PINENTRY_MODE_LOOPBACK);
+    if (c_err != 0)
+    {
+        fclose(kFp);
+        e = GpgME::Error::fromCode(c_err);
+        return false;
+    }
+    gpgme_set_passphrase_cb(c_ctx, passphrase_cb, NULL);
+
+    gpgme_export_mode_t flags = GPGME_EXPORT_MODE_SECRET;
+    c_err = gpgme_op_export_keys(c_ctx, aKeys, flags, out);
+    if (c_err != 0)
+    {
+        fclose(kFp);
+        gpgme_data_release(out);
+        e = GpgME::Error::fromCode(c_err);
+        return false;
+    }
+    fflush(NULL);
+    fclose(kFp);
+
+    gpgme_data_release(out);
+
+    return true;
+}
+#endif

GpgMECWorker.h

@@ -31,6 +31,20 @@ public:
      */
     bool DeleteKey(const char * fpr, bool secret, GpgME::Error& e);
 
+#ifdef DEVTIME
+    /**
+     * Status : testing
+     * \n Result : fails to export a private key
+     * \n Reason : passphrase callback is never called
+     * \n With default pinentry mode, the password is requested normally 
+     * and the private key is exported. But this can't be done on a web server.
+     * @param fpr
+     * @param e
+     * @return 
+     */
+    bool ExportPrivateKey(const char* fpr, GpgME::Error& e);
+#endif
+
 private:
     gpgme_ctx_t c_ctx;
 };