parsing response end with extended SMTP (ESMTP)

To use an example response from google when sent "EHLO":

250-mx.google.com at your service, [66.501.941.15]
250-SIZE 35651584
250-8BITMIME
250-AUTH LOGIN PLAIN
250-ENHANCEDSTATUSCODES
250 PIPELINING

Hex:

32 35 30 2D 6D 78 2E 67 6F 6F 67 6C 65 2E 63 6F 6D 20 61 74 20 79 6F 75 72 20 73 65 72 76 69 63 65 2C 20 5B 39 32 2E 34 32 31 2E 35 36 35 2E 34 32 5D 0D 0A 32 35 30 2D 53 49 5A 45 20 33 35 36 35 31 35 38 34 0D 0A 32 35 30 2D 38 42 49 54 4D 49 4D 45 0D 0A 32 35 30 2D 41 55 5开发者_运维知识库4 48 20 4C 4F 47 49 4E 20 50 4C 41 49 4E 0D 0A 32 35 30 2D 45 4E 48 41 4E 43 45 44 53 54 41 54 55 53 43 4F 44 45 53 0D 0A 32 35 30 20 50 49 50 45 4C 49 4E 49 4E 47 0D 0A

Since the SMTP spec states that a line must end with a CR LF (0D 0A), we can parse on those two bytes to find lines, but how do we determine the end of the response?

Over satellite, responses can be broken into pieces with a significant delay between. This means a response could end after a CR LF and not be complete ie:

250-mx.google.com at your service, [66.501.941.15]
250-SIZE 35651584
250-8BITMIME

Any logic that looks for a trailing CR LF would then assume the response is complete. IN this case I am using CryptLib to perform the SLL tunnel, but I can create the port with my own code and pass it to the library if there is some way to get an "end of response".

The response ends on the line where there is no hyphen between the 250 and the name.

So, if the 4th character of the line is a space, that will be the last line of the response.

From section 4.2.1 of RFC 2821:

The format for multiline replies requires that every line, except the last, begin with the reply code, followed immediately by a hyphen, "-" (also known as minus), followed by text. The last line will begin with the reply code, followed immediately by < SP >, optionally some text, and < CRLF >.

This is a multiline reply in the SMTP protocol (described in RFC 821 Appendix E)

You'll notice that the first line is formatted with

CODE-FirstLine
CODE-SecondLine

However the last line is formatted like so:

CODE LastLine

Each line is delimited by a CRLF like you explained, but you know you're on the last line of a multiline reply when the code and text are not delimited by a - (minus)