Add safe Util::dataToDecimal<T> and FileUtil::readDecimal to read…

… single decimals from files like `/proc/sys/net/ipv4/tcp_max_orphans` Implementation is value- and thread-safe, utilizing `std::strtoll`. Signed-off-by: Sven Göthel <[email protected]> Change-Id: Iad74f253bdac5636757b130b299b5deacda658db
CollaboraOnline · Nov 1, 2024 · 80c6478 · 80c6478
1 parent b5cd651
commit 80c6478
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diff --git a/common/FileUtil.hpp b/common/FileUtil.hpp
@@ -20,6 +20,7 @@
 #include <Poco/Path.h>
 
 #include "Log.hpp"
+#include "Util.hpp"
 
 namespace FileUtil
 {
@@ -183,6 +184,39 @@ namespace FileUtil
     /// Reads the whole file to memory. Only for small files.
     std::unique_ptr<std::vector<char>> readFile(const std::string& path, int maxSize = 256 * 1024);
 
+    /// Returns the decimal value of given file content being cached in the given data segment if parsed correctly by `std::strtoll`,
+    /// otherwise returns `defaultValue`.
+    template<typename T,
+             std::enable_if_t<  std::is_integral_v<T>, bool> = true>
+    T readDecimal(const std::string& path, char* data, const size_t dataLen, const T defaultValue)
+    {
+        if (dataLen <= 1) // no space for data + EOS
+            return defaultValue;
+        errno = 0;  // Flush previous error indicator. Reminder: errno is thread-local
+        const int fd = ::open(path.c_str(), O_RDONLY);
+        if (fd < 0)
+            return defaultValue;
+
+        ::memset(data, 0, dataLen);
+        size_t consumed = 0;
+        while ( dataLen-consumed-1 /* ex-EOS */ > 0 )
+        {
+            ssize_t n;
+            while ((n = ::read(fd, data+consumed, dataLen-consumed-1 /* ex-EOS */)) < 0 && errno == EINTR) {}
+            if (n < 0) // Error
+            {
+                consumed = 0;
+                break;
+            }
+            else if (n == 0) // EOF
+                break;
+            consumed += static_cast<size_t>(n);
+        }
+        ::close(fd);
+        return consumed > 0 ? Util::dataToDecimal(data, consumed+1 /* re-add EOS */, defaultValue) : defaultValue;
+    }
+
+
     /// File/Directory stat helper.
     class Stat
     {

diff --git a/common/Util.hpp b/common/Util.hpp
@@ -27,6 +27,7 @@
 #include <sstream>
 #include <string>
 #include <map>
+#include <type_traits>
 #include <utility>
 #include <inttypes.h>
 #include <cctype>
@@ -230,6 +231,25 @@ namespace Util
         return true;
     }
 
+    /// Returns the decimal value of given data segment if parsed correctly by `std::strtoll`,
+    /// otherwise returns `defaultValue`.
+    template<typename T,
+             std::enable_if_t<  std::is_integral_v<T>, bool> = true>
+    T dataToDecimal(const char* data, const size_t dataLen, const T defaultValue)
+    {
+        if( dataLen <= 1 ) // no space for data + EOS
+            return defaultValue;
+        char* endptr = const_cast<char*>(data) + dataLen;
+        errno = 0;  // Flush previous error indicator. Reminder: errno is thread-local
+        const long long num = std::strtoll(data, &endptr, 10);
+        if( 0 != errno || nullptr == endptr || endptr == data || // parsing error
+            ( std::is_unsigned_v<T> && num < 0 ) )               // unsigned target type
+        {
+            return defaultValue;
+        }
+        return static_cast<T>(num);
+    }
+
     /// Exception safe scope count/guard
     struct ReferenceHolder
     {