Refuse a PDU whose optional parameters do not end on command_length (#87)

* Regression tests for a truncated TLV tail refused rather than accepted

* Refuse a PDU whose optional parameters do not end on command_length

* Assert the bare TLV header refusal against jsmpp instead of recording it as a defect

* Note the truncated TLV tail defect as fixed in the java-client findings

* Derive the padding position, share the bare TLV fixture and trim the decision record

* Regression tests for a PDU whose trailing C-Octet String a peer left out

* An absent trailing C-Octet String consumes no octet, so a bodyless PDU still parses

* Bound the TLV loop by the buffer it was given rather than a second spelling of its length

* Answer the stability review's questions in the record and pin the array contract

src/defs/types.ts

@@ -146,7 +146,6 @@ function wantUnsuccessSmes(value: ParamValue): Result<{ smes: UnsuccessSme[] }>
 }
 
 function readCstring(buffer: Buffer, offset: number): Result<{ bytesRead: number; value: string }> {
-	// An offset at the end exactly is an absent trailing field, which real peers do send.
 	if (outOfRange(buffer, offset, 0)) {
 		return {
 			err: new Error(
@@ -155,6 +154,9 @@ function readCstring(buffer: Buffer, offset: number): Result<{ bytesRead: number
 		};
 	}
 
+	// An offset at the end exactly is an absent trailing field, which real peers do send.
+	if (offset === buffer.length) return { bytesRead: 0, value: '' };
+
 	let length = 0;
 
 	while (buffer[offset + length]) {