Fix misleading comment on Base64 prefix case sensitivity

Tarek Mahmoud Sayed · Tarek Mahmoud Sayed · commit 66deb5e75c01 · 2026-05-12T15:07:35.000-07:00
The comment incorrectly stated the case-insensitive prefix check was
per the SEP. The spec defines lowercase '=?base64?' only; the SDK
intentionally matches case-insensitively for robustness against
non-conforming senders.
diff --git a/src/ModelContextProtocol.Core/Protocol/McpHeaderEncoder.cs b/src/ModelContextProtocol.Core/Protocol/McpHeaderEncoder.cs
@@ -119,7 +119,8 @@ public static class McpHeaderEncoder
             return headerValue;
         }
 
-        // Check for Base64 wrapper (case-insensitive prefix check per SEP)
+        // Check for Base64 wrapper. The spec defines the prefix as lowercase "=?base64?"
+        // but we match case-insensitively for robustness against non-conforming senders.
         if (headerValue.StartsWith(Base64Prefix, StringComparison.OrdinalIgnoreCase) &&
             headerValue.EndsWith(Base64Suffix, StringComparison.Ordinal))
         {

Original file line number	Diff line number	Diff line change
`@@ -119,7 +119,8 @@ public static class McpHeaderEncoder`
`119`	`119`	`return headerValue;`
`120`	`120`	`}`
`121`	`121`
`122`		`- // Check for Base64 wrapper (case-insensitive prefix check per SEP)`
	`122`	`+ // Check for Base64 wrapper. The spec defines the prefix as lowercase "=?base64?"`
	`123`	`+ // but we match case-insensitively for robustness against non-conforming senders.`
`123`	`124`	`if (headerValue.StartsWith(Base64Prefix, StringComparison.OrdinalIgnoreCase) &&`
`124`	`125`	`headerValue.EndsWith(Base64Suffix, StringComparison.Ordinal))`
`125`	`126`	`{`