3bc97fd592
Right now, qmp-output-visitor happens to produce a QNull result if nothing is actually visited between the creation of the visitor and the request for the resulting QObject. A stronger protocol would require that a QMP output visit MUST visit something. But to still be able to produce a JSON 'null' output, we need a new visitor function that states our intentions. Yes, we could say that such a visit must go through visit_type_any(), but that feels clunky. So this patch introduces the new visit_type_null() interface and its no-op interface in the dealloc visitor, and stubs in the qmp visitors (the next patch will finish the implementation). For the visitors that will not implement the callback, document the situation. The code in qapi-visit-core unconditionally dereferences the callback pointer, so that a segfault will inform a developer if they need to implement the callback for their choice of visitor. Note that JSON has a primitive null type, with the single value null; likewise with the QNull type for QObject; but for QAPI, we just have the 'null' value without a null type. We may eventually want to add more support in QAPI for null (most likely, we'd use it via an alternate type that permits 'null' or an object); but we'll create that usage when we need it. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <1461879932-9020-15-git-send-email-eblake@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>
31 lines
788 B
C
31 lines
788 B
C
/*
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* String printing Visitor
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*
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* Copyright Red Hat, Inc. 2012
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#ifndef STRING_OUTPUT_VISITOR_H
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#define STRING_OUTPUT_VISITOR_H
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#include "qapi/visitor.h"
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typedef struct StringOutputVisitor StringOutputVisitor;
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/*
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* The string output visitor does not implement support for visiting
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* QAPI structs, alternates, null, or arbitrary QTypes.
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*/
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StringOutputVisitor *string_output_visitor_new(bool human);
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void string_output_visitor_cleanup(StringOutputVisitor *v);
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char *string_output_get_string(StringOutputVisitor *v);
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Visitor *string_output_get_visitor(StringOutputVisitor *v);
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#endif
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