[Spice-devel] [PATCH 12/22] Add exception handling classes
Christophe de Dinechin
christophe at dinechin.org
Wed Feb 28 15:43:15 UTC 2018
From: Christophe de Dinechin <dinechin at redhat.com>
Throwing 'runtime_error' directly should be reserved for the support
library. Add an 'Error' class as a base class for all errors thrown
by the streaming agent, as well as subclasses used to discriminate
between categories of error.
The Error class offers:
- a 'format_message' member function that formats a message without
allocating memory, so that there is no risk of throwing another
exception at throw time.
- a 'syslog' member function that sends the formatted message to the syslog.
The derived classes are:
- IOError encapsulates typical I/O errors that report errors using
errno. The format_message in that case prints the original message,
along with the strerror message.
- The ReadError and WriteError are two classes derived from IOError,
with the sole purpose of making it possible to discriminate the
error type at catch time, e.g. to retry writes.
These classes are used in the subsequent patches
Signed-off-by: Christophe de Dinechin <dinechin at redhat.com>
---
include/spice-streaming-agent/Makefile.am | 2 +-
include/spice-streaming-agent/errors.hpp | 55 ++++++++++++++++++++++++++++++
src/Makefile.am | 1 +
src/errors.cpp | 56 +++++++++++++++++++++++++++++++
src/spice-streaming-agent.cpp | 5 +++
src/unittests/Makefile.am | 1 +
6 files changed, 119 insertions(+), 1 deletion(-)
create mode 100644 include/spice-streaming-agent/errors.hpp
create mode 100644 src/errors.cpp
diff --git a/include/spice-streaming-agent/Makefile.am b/include/spice-streaming-agent/Makefile.am
index 844f791..a223d43 100644
--- a/include/spice-streaming-agent/Makefile.am
+++ b/include/spice-streaming-agent/Makefile.am
@@ -3,5 +3,5 @@ public_includedir = $(includedir)/spice-streaming-agent
public_include_HEADERS = \
frame-capture.hpp \
plugin.hpp \
+ errors.hpp \
$(NULL)
-
diff --git a/include/spice-streaming-agent/errors.hpp b/include/spice-streaming-agent/errors.hpp
new file mode 100644
index 0000000..ca70d2e
--- /dev/null
+++ b/include/spice-streaming-agent/errors.hpp
@@ -0,0 +1,55 @@
+/* Errors that may be thrown by the agent
+ *
+ * \copyright
+ * Copyright 2018 Red Hat Inc. All rights reserved.
+ */
+#ifndef SPICE_STREAMING_AGENT_ERRORS_HPP
+#define SPICE_STREAMING_AGENT_ERRORS_HPP
+
+#include <exception>
+#include <stddef.h>
+
+namespace spice {
+namespace streaming_agent {
+
+class Error : public std::exception
+{
+public:
+ Error(const char *message): exception(), message(message) { }
+ Error(const Error &error): exception(error), message(error.message) {}
+ virtual const char *what() const noexcept override;
+ virtual int format_message(char *buffer, size_t size) const noexcept;
+ const Error &syslog() const noexcept;
+protected:
+ const char *message;
+};
+
+class IOError : public Error
+{
+public:
+ IOError(const char *msg, int saved_errno) : Error(msg), saved_errno(saved_errno) {}
+ int format_message(char *buffer, size_t size) const noexcept override;
+ int append_strerror(char *buffer, size_t size, int written) const noexcept;
+protected:
+ int saved_errno;
+};
+
+class WriteError : public IOError
+{
+public:
+ WriteError(const char *msg, const char *operation, int saved_errno)
+ : IOError(msg, saved_errno), operation(operation) {}
+ int format_message(char *buffer, size_t size) const noexcept override;
+protected:
+ const char *operation;
+};
+
+class ReadError : public IOError
+{
+public:
+ ReadError(const char *msg, int saved_errno): IOError(msg, saved_errno) {}
+};
+
+}} // namespace spice::streaming_agent
+
+#endif // SPICE_STREAMING_AGENT_ERRORS_HPP
diff --git a/src/Makefile.am b/src/Makefile.am
index 3717b5c..2507844 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -55,4 +55,5 @@ spice_streaming_agent_SOURCES = \
mjpeg-fallback.hpp \
jpeg.cpp \
jpeg.hpp \
+ errors.cpp \
$(NULL)
diff --git a/src/errors.cpp b/src/errors.cpp
new file mode 100644
index 0000000..01bb162
--- /dev/null
+++ b/src/errors.cpp
@@ -0,0 +1,56 @@
+/* Errors that may be thrown by the agent
+ *
+ * \copyright
+ * Copyright 2018 Red Hat Inc. All rights reserved.
+ */
+
+#include <spice-streaming-agent/errors.hpp>
+
+#include <stdio.h>
+#include <syslog.h>
+#include <string.h>
+
+namespace spice {
+namespace streaming_agent {
+
+const char *Error::what() const noexcept
+{
+ return message;
+}
+
+int Error::format_message(char *buffer, size_t size) const noexcept
+{
+ return snprintf(buffer, size, "%s", message);
+}
+
+const Error &Error::syslog() const noexcept
+{
+ char buffer[256];
+ format_message(buffer, sizeof(buffer));
+ ::syslog(LOG_ERR, "%s\n", buffer);
+ return *this;
+}
+
+int IOError::format_message(char *buffer, size_t size) const noexcept
+{
+ int written = snprintf(buffer, size, "%s", what());
+ return append_strerror(buffer, size, written);
+}
+
+int IOError::append_strerror(char *buffer, size_t size, int written) const noexcept
+{
+ // The conversion of written to size_t also deals with the case where written < 0
+ if (saved_errno && (size_t) written < size) {
+ written += snprintf(buffer + written, size - written, ": %s (errno %d)",
+ strerror(saved_errno), saved_errno);
+ }
+ return written;
+}
+
+int WriteError::format_message(char *buffer, size_t size) const noexcept
+{
+ int written = snprintf(buffer, size, "%s writing %s", what(), operation);
+ return append_strerror(buffer, size, written);
+}
+
+}} // namespace spice::streaming_agent
diff --git a/src/spice-streaming-agent.cpp b/src/spice-streaming-agent.cpp
index 8494a8b..23ee824 100644
--- a/src/spice-streaming-agent.cpp
+++ b/src/spice-streaming-agent.cpp
@@ -13,6 +13,7 @@
#include <spice-streaming-agent/frame-capture.hpp>
#include <spice-streaming-agent/plugin.hpp>
+#include <spice-streaming-agent/errors.hpp>
#include <stdio.h>
#include <stdlib.h>
@@ -597,6 +598,10 @@ int main(int argc, char* argv[])
try {
do_capture(stream, streamport, f_log);
}
+ catch (Error &err) {
+ err.syslog();
+ ret = EXIT_FAILURE;
+ }
catch (std::runtime_error &err) {
syslog(LOG_ERR, "%s\n", err.what());
ret = EXIT_FAILURE;
diff --git a/src/unittests/Makefile.am b/src/unittests/Makefile.am
index 0fc6d50..ce81b56 100644
--- a/src/unittests/Makefile.am
+++ b/src/unittests/Makefile.am
@@ -39,6 +39,7 @@ test_mjpeg_fallback_SOURCES = \
test-mjpeg-fallback.cpp \
../jpeg.cpp \
../mjpeg-fallback.cpp \
+ ../errors.cpp \
$(NULL)
test_mjpeg_fallback_LDADD = \
--
2.13.5 (Apple Git-94)
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