... locate the offsets/lengths of the substrings containing the headers.

That, and account for the fact that the substitution may change the length of a header, and thus the offsets to subsequent headers. It's often easiest to reverse() the list of header locations and work your way backwards.

Anno

In reply to Re^2: Creating MIME entities with CRLF line endings by Anno
in thread Creating MIME entities with CRLF line endings by sgifford

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