SERVER-34313 Use hex-encoded string for resume token

1 files changed, 23 insertions, 0 deletions

diff --git a/src/mongo/util/hex.h b/src/mongo/util/hex.h
index 802d6b13737..382eb0bd86c 100644
--- a/src/mongo/util/hex.h
+++ b/src/mongo/util/hex.h
@@ -29,6 +29,8 @@
 
 #pragma once
 
+#include <algorithm>
+#include <cctype>
 #include <string>
 
 #include "mongo/base/string_data.h"
@@ -53,6 +55,27 @@ inline char fromHex(StringData c) {
     return (char)((fromHex(c[0]) << 4) | fromHex(c[1]));
 }
 
+/**
+ * Decodes 'hexString' into raw bytes, appended to the out parameter 'buf'. Callers must first
+ * ensure that 'hexString' is a valid hex encoding.
+ */
+inline void fromHexString(StringData hexString, BufBuilder* buf) {
+    invariant(hexString.size() % 2 == 0);
+    // Combine every pair of two characters into one byte.
+    for (std::size_t i = 0; i < hexString.size(); i += 2) {
+        buf->appendChar(fromHex(StringData(&hexString.rawData()[i], 2)));
+    }
+}
+
+/**
+ * Returns true if 'hexString' is a valid hexadecimal encoding.
+ */
+inline bool isValidHex(StringData hexString) {
+    // There must be an even number of characters, since each pair encodes a single byte.
+    return hexString.size() % 2 == 0 &&
+        std::all_of(hexString.begin(), hexString.end(), [](char c) { return std::isxdigit(c); });
+}
+
 inline std::string toHex(const void* inRaw, int len) {
     static const char hexchars[] = "0123456789ABCDEF";