util: move HasPrefix() so it can be reused

Move the function `HasPrefix()` from `netaddress.cpp` to `util/string.h`
so it can be reused by `CNetAddr` methods (and possibly others).

src/netaddress.cpp

@@ -6,9 +6,10 @@
 
 #include "netaddress.h"
 #include "hash.h"
-#include "utilstrencodings.h"
-#include "util/asmap.h"
 #include "tinyformat.h"
+#include "util/asmap.h"
+#include "util/string.h"
+#include "utilstrencodings.h"
 
 #include <algorithm>
 #include <array>
@@ -50,13 +51,6 @@ void CNetAddr::SetIP(const CNetAddr& ipIn)
     m_addr = ipIn.m_addr;
 }
 
-template <typename T1, size_t PREFIX_LEN>
-inline bool HasPrefix(const T1& obj, const std::array<uint8_t, PREFIX_LEN>& prefix)
-{
-    return obj.size() >= PREFIX_LEN &&
-           std::equal(std::begin(prefix), std::end(prefix), std::begin(obj));
-}
-
 void CNetAddr::SetLegacyIPv6(Span<const uint8_t> ipv6)
 {
     assert(ipv6.size() == ADDR_IPV6_SIZE);

src/util/string.h

@@ -5,6 +5,10 @@
 #ifndef BITCOIN_UTIL_STRING_H
 #define BITCOIN_UTIL_STRING_H
 
+#include "attributes.h"
+
+#include <algorithm>
+#include <array>
 #include <cstring>
 #include <functional>
 #include <string>
@@ -41,4 +45,15 @@ inline bool ValidAsCString(const std::string& str) noexcept
     return str.size() == strlen(str.c_str());
 }
 
+/**
+ * Check whether a container begins with the given prefix.
+ */
+template <typename T1, size_t PREFIX_LEN>
+NODISCARD inline bool HasPrefix(const T1& obj,
+                                const std::array<uint8_t, PREFIX_LEN>& prefix)
+{
+    return obj.size() >= PREFIX_LEN &&
+           std::equal(std::begin(prefix), std::end(prefix), std::begin(obj));
+}
+
 #endif // BITCOIN_UTIL_STRENCODINGS_H