From 3d3bc94e392b09e21520a059cb1f45bf237bae65 Mon Sep 17 00:00:00 2001
From: Martchus <martchus@gmx.net>
Date: Wed, 13 Feb 2019 20:19:46 +0100
Subject: [PATCH] Prevent warning "Cannot make an empty frame"

---
 exceptions.cpp     | 31 ++++++++++++++++++++++++++++++-
 exceptions.h       |  7 +++++++
 id3/id3v2frame.cpp | 37 ++++++++++++++++++++-----------------
 3 files changed, 57 insertions(+), 18 deletions(-)

diff --git a/exceptions.cpp b/exceptions.cpp
index 5492daf..06bc98c 100644
--- a/exceptions.cpp
+++ b/exceptions.cpp
@@ -35,7 +35,8 @@ const char *Failure::what() const USE_NOTHROW
 /*!
  * \class TagParser::NoDataFoundException
  * \brief The exception that is thrown when the data to be parsed holds no
- *        parsable information.
+ *        parsable information (e.g. relevant section in the file does not exist or
+ *        has size of zero).
  */
 
 /*!
@@ -88,6 +89,34 @@ const char *InvalidDataException::what() const USE_NOTHROW
     return "data to be parsed or to be made seems to be invalid";
 }
 
+/*!
+ * \class TagParser::NoDataException
+ * \brief The exception that is thrown when the value to be written is empty but that
+ *        is not allowed in that context (e.g. an empty ID3v2 frame is not allowed).
+ */
+
+/*!
+ * \brief Constructs a new exception.
+ */
+NoDataProvidedException::NoDataProvidedException() USE_NOTHROW
+{
+}
+
+/*!
+ * \brief Destroys the exception.
+ */
+NoDataProvidedException::~NoDataProvidedException() USE_NOTHROW
+{
+}
+
+/*!
+ * \brief Returns a C-style character string describing the cause of the exception.
+ */
+const char *NoDataProvidedException::what() const USE_NOTHROW
+{
+    return "can not write empty value";
+}
+
 /*!
  * \class TagParser::TruncatedDataException
  * \brief The exception that is thrown when the data to be parsed is truncated
diff --git a/exceptions.h b/exceptions.h
index f135a86..a23e003 100644
--- a/exceptions.h
+++ b/exceptions.h
@@ -29,6 +29,13 @@ public:
     virtual const char *what() const USE_NOTHROW;
 };
 
+class TAG_PARSER_EXPORT NoDataProvidedException : public Failure {
+public:
+    NoDataProvidedException() USE_NOTHROW;
+    virtual ~NoDataProvidedException() USE_NOTHROW;
+    virtual const char *what() const USE_NOTHROW;
+};
+
 class TAG_PARSER_EXPORT TruncatedDataException : public InvalidDataException {
 public:
     TruncatedDataException() USE_NOTHROW;
diff --git a/id3/id3v2frame.cpp b/id3/id3v2frame.cpp
index 44b1bc3..ad47ebf 100644
--- a/id3/id3v2frame.cpp
+++ b/id3/id3v2frame.cpp
@@ -430,23 +430,7 @@ Id3v2FrameMaker::Id3v2FrameMaker(Id3v2Frame &frame, byte version, Diagnostics &d
 {
     const string context("making " % m_frame.idToString() + " frame");
 
-    // get non-empty, assigned values
-    vector<const TagValue *> values;
-    values.reserve(1 + frame.additionalValues().size());
-    if (!frame.value().isEmpty()) {
-        values.emplace_back(&frame.value());
-    }
-    for (const auto &value : frame.additionalValues()) {
-        if (!value.isEmpty()) {
-            values.emplace_back(&value);
-        }
-    }
-
-    // validate assigned data
-    if (values.empty()) {
-        diag.emplace_back(DiagLevel::Critical, "Cannot make an empty frame.", context);
-        throw InvalidDataException();
-    }
+    // validate frame's configuration
     if (m_frame.isEncrypted()) {
         diag.emplace_back(DiagLevel::Critical, "Cannot make an encrypted frame (isn't supported by this tagging library).", context);
         throw InvalidDataException();
@@ -462,6 +446,25 @@ Id3v2FrameMaker::Id3v2FrameMaker(Id3v2Frame &frame, byte version, Diagnostics &d
         diag.emplace_back(DiagLevel::Warning,
             "The existing flag and group information is not supported by the version of ID3v2 and will be ignored/discarted.", context);
     }
+
+    // get non-empty, assigned values
+    vector<const TagValue *> values;
+    values.reserve(1 + frame.additionalValues().size());
+    if (!frame.value().isEmpty()) {
+        values.emplace_back(&frame.value());
+    }
+    for (const auto &value : frame.additionalValues()) {
+        if (!value.isEmpty()) {
+            values.emplace_back(&value);
+        }
+    }
+
+    // validate assigned values
+    if (values.empty()) {
+        throw NoDataProvidedException();
+        // note: This is not really an issue because in the case we're not provided with any value here just means that the field
+        //       is supposed to be removed. So don't add any diagnostic messages here.
+    }
     const bool isTextFrame = Id3v2FrameIds::isTextFrame(m_frameId);
     if (values.size() != 1) {
         if (!isTextFrame) {