Add hexdump.h with iostream manipulators to dump a byte range as hex

or to produce readable text from a mix of printing and nonprinting ASCII
characters.

(cherry picked from commit 01a59bab1a4b7c4645271a21cfaadc3735b6029c)

indra/llcommon/hexdump.h

@@ -0,0 +1,106 @@
+/**
+ * @file   hexdump.h
+ * @author Nat Goodspeed
+ * @date   2023-10-03
+ * @brief  iostream manipulators to stream hex, or string with nonprinting chars
+ * 
+ * $LicenseInfo:firstyear=2023&license=viewerlgpl$
+ * Copyright (c) 2023, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_HEXDUMP_H)
+#define LL_HEXDUMP_H
+
+#include <cctype>
+#include <iomanip>
+#include <iostream>
+#include <string_view>
+
+namespace LL
+{
+
+// Format a given byte string as 2-digit hex values, no separators
+// Usage: std::cout << hexdump(somestring) << ...
+class hexdump
+{
+public:
+    hexdump(const std::string_view& data):
+        hexdump(data.data(), data.length())
+    {}
+
+    hexdump(const char* data, size_t len):
+        hexdump(reinterpret_cast<const unsigned char*>(data), len)
+    {}
+
+    hexdump(const std::vector<unsigned char>& data):
+        hexdump(data.data(), data.size())
+    {}
+
+    hexdump(const unsigned char* data, size_t len):
+        mData(data, data + len)
+    {}
+
+    friend std::ostream& operator<<(std::ostream& out, const hexdump& self)
+    {
+        auto oldfmt{ out.flags() };
+        auto oldfill{ out.fill() };
+        out.setf(std::ios_base::hex, std::ios_base::basefield);
+        out.fill('0');
+        for (auto c : self.mData)
+        {
+            out << std::setw(2) << unsigned(c);
+        }
+        out.setf(oldfmt, std::ios_base::basefield);
+        out.fill(oldfill);
+        return out;
+    }
+
+private:
+    std::vector<unsigned char> mData;
+};
+
+// Format a given byte string as a mix of printable characters and, for each
+// non-printable character, "\xnn"
+// Usage: std::cout << hexmix(somestring) << ...
+class hexmix
+{
+public:
+    hexmix(const std::string_view& data):
+        mData(data)
+    {}
+
+    hexmix(const char* data, size_t len):
+        mData(data, len)
+    {}
+
+    friend std::ostream& operator<<(std::ostream& out, const hexmix& self)
+    {
+        auto oldfmt{ out.flags() };
+        auto oldfill{ out.fill() };
+        out.setf(std::ios_base::hex, std::ios_base::basefield);
+        out.fill('0');
+        for (auto c : self.mData)
+        {
+            // std::isprint() must be passed an unsigned char!
+            if (std::isprint(static_cast<unsigned char>(c)))
+            {
+                out << c;
+            }
+            else
+            {
+                out << "\\x" << std::setw(2) << unsigned(c);
+            }
+        }
+        out.setf(oldfmt, std::ios_base::basefield);
+        out.fill(oldfill);
+        return out;
+    }
+
+private:
+    std::string mData;
+};
+
+} // namespace LL
+
+#endif /* ! defined(LL_HEXDUMP_H) */