[coap] fix copying option (#9894)

- remove typo that passed a uint64_t pointer to a function which need
  a sufficiently large buffer
- fix bug that coap copying uri path option or any other long option
  failed

3 files changed, 61 insertions, 5 deletions

diff --git a/src/core/coap/coap.cpp b/src/core/coap/coap.cpp
index 696d0fc83..6afd693a7 100644
--- a/src/core/coap/coap.cpp
+++ b/src/core/coap/coap.cpp
@@ -619,7 +619,6 @@ Error CoapBase::PrepareNextBlockRequest(Message::BlockType aType,
 {
     Error            error       = kErrorNone;
     bool             isOptionSet = false;
-    uint64_t         optionBuf   = 0;
     uint16_t         blockOption = 0;
     Option::Iterator iterator;
 
@@ -655,8 +654,9 @@ Error CoapBase::PrepareNextBlockRequest(Message::BlockType aType,
         }
 
         // Copy option
-        SuccessOrExit(error = iterator.ReadOptionValue(&optionBuf));
-        SuccessOrExit(error = aRequest.AppendOption(optionNumber, iterator.GetOption()->GetLength(), &optionBuf));
+        SuccessOrExit(error = aRequest.AppendOptionFromMessage(optionNumber, iterator.GetOption()->GetLength(),
+                                                               iterator.GetMessage(),
+                                                               iterator.GetOptionValueMessageOffset()));
     }
 
     if (!isOptionSet)
diff --git a/src/core/coap/coap_message.cpp b/src/core/coap/coap_message.cpp
index cbf544813..4998de7a6 100644
--- a/src/core/coap/coap_message.cpp
+++ b/src/core/coap/coap_message.cpp
@@ -146,8 +146,12 @@ uint8_t Message::WriteExtendedOptionField(uint16_t aValue, uint8_t *&aBuffer)
     return rval;
 }
 
-Error Message::AppendOption(uint16_t aNumber, uint16_t aLength, const void *aValue)
+Error Message::AppendOptionHeader(uint16_t aNumber, uint16_t aLength)
 {
+    /*
+     * Appends a CoAP Option header field (Option Delta/Length) per RFC 7252.
+     */
+
     Error    error = kErrorNone;
     uint16_t delta;
     uint8_t  header[kMaxOptionHeaderSize];
@@ -167,10 +171,33 @@ Error Message::AppendOption(uint16_t aNumber, uint16_t aLength, const void *aVal
     VerifyOrExit(static_cast<uint32_t>(GetLength()) + headerLength + aLength < kMaxHeaderLength, error = kErrorNoBufs);
 
     SuccessOrExit(error = AppendBytes(header, headerLength));
-    SuccessOrExit(error = AppendBytes(aValue, aLength));
 
     GetHelpData().mOptionLast = aNumber;
 
+exit:
+    return error;
+}
+
+Error Message::AppendOption(uint16_t aNumber, uint16_t aLength, const void *aValue)
+{
+    Error error = kErrorNone;
+
+    SuccessOrExit(error = AppendOptionHeader(aNumber, aLength));
+    SuccessOrExit(error = AppendBytes(aValue, aLength));
+
+    GetHelpData().mHeaderLength = GetLength();
+
+exit:
+    return error;
+}
+
+Error Message::AppendOptionFromMessage(uint16_t aNumber, uint16_t aLength, const Message &aMessage, uint16_t aOffset)
+{
+    Error error = kErrorNone;
+
+    SuccessOrExit(error = AppendOptionHeader(aNumber, aLength));
+    SuccessOrExit(error = AppendBytesFromMessage(aMessage, aOffset, aLength));
+
     GetHelpData().mHeaderLength = GetLength();
 
 exit:
diff --git a/src/core/coap/coap_message.hpp b/src/core/coap/coap_message.hpp
index 789c91939..62128b6a3 100644
--- a/src/core/coap/coap_message.hpp
+++ b/src/core/coap/coap_message.hpp
@@ -402,6 +402,23 @@ public:
     Error AppendOption(uint16_t aNumber, uint16_t aLength, const void *aValue);
 
     /**
+     * Appends a CoAP option reading Option value from another or potentially the same message.
+     *
+     * @param[in] aNumber   The CoAP Option number.
+     * @param[in] aLength   The CoAP Option length.
+     * @param[in] aMessage  The message to read the CoAP Option value from (it can be the same as the current message).
+     * @param[in] aOffset   The offset in @p aMessage to start reading the CoAP Option value from (@p aLength bytes are
+     *                      used as Option value).
+     *
+     * @retval kErrorNone         Successfully appended the option.
+     * @retval kErrorInvalidArgs  The option type is not equal or greater than the last option type.
+     * @retval kErrorNoBufs       The option length exceeds the buffer size.
+     * @retval kErrorParse        Not enough bytes in @p aMessage to read @p aLength bytes from @p aOffset.
+     *
+     */
+    Error AppendOptionFromMessage(uint16_t aNumber, uint16_t aLength, const Message &aMessage, uint16_t aOffset);
+
+    /**
      * Appends an unsigned integer CoAP option as specified in RFC-7252 section-3.2
      *
      * @param[in]  aNumber  The CoAP Option number.
@@ -966,6 +983,8 @@ private:
     }
 
     uint8_t WriteExtendedOptionField(uint16_t aValue, uint8_t *&aBuffer);
+
+    Error AppendOptionHeader(uint16_t aNumber, uint16_t aLength);
 };
 
 /**
@@ -1187,6 +1206,16 @@ public:
          */
         uint16_t GetPayloadMessageOffset(void) const { return mNextOptionOffset; }
 
+        /**
+         * Gets the offset of beginning of the CoAP Option Value.
+         *
+         * MUST be used during the iterator is in progress.
+         *
+         * @returns The offset of beginning of the CoAP Option Value
+         *
+         */
+        uint16_t GetOptionValueMessageOffset(void) const { return mNextOptionOffset - mOption.mLength; }
+
     private:
         // `mOption.mLength` value to indicate iterator is done.
         static constexpr uint16_t kIteratorDoneLength = 0xffff;