Re: [PATCH 4/8] http: read HTTP WWW-Authenticate response headers

> On 9/13/2022 3:25 PM, Matthew John Cheetham via GitGitGadget wrote:
> 
>> +	/**
>> +	 * A `strvec` of WWW-Authenticate header values. Each string
>> +	 * is the value of a WWW-Authenticate header in an HTTP response,
>> +	 * in the order they were received in the response.
>> +	 */
>> +	struct strvec wwwauth_headers;
> 
> I like this careful documentation.
> 
>> +	unsigned header_is_last_match:1;
> 
> But then this member is unclear how it is attached. It could use its
> own "for internal use" comment if we don't want to describe it in full
> detail here.

>> +static size_t fwrite_wwwauth(char *ptr, size_t eltsize, size_t nmemb, void *p)
>> +{
>> +	size_t size = eltsize * nmemb;
>> +	struct strvec *values = &http_auth.wwwauth_headers;
>> +	struct strbuf buf = STRBUF_INIT;
>> +	const char *val;
>> +	const char *z = NULL;
>> +
>> +	/*
>> +	 * Header lines may not come NULL-terminated from libcurl so we must
>> +	 * limit all scans to the maximum length of the header line, or leverage
>> +	 * strbufs for all operations.
>> +	 *
>> +	 * In addition, it is possible that header values can be split over
>> +	 * multiple lines as per RFC 2616 (even though this has since been
>> +	 * deprecated in RFC 7230). A continuation header field value is
>> +	 * identified as starting with a space or horizontal tab.
>> +	 *
>> +	 * The formal definition of a header field as given in RFC 2616 is:
>> +	 *
>> +	 *   message-header = field-name ":" [ field-value ]
>> +	 *   field-name     = token
>> +	 *   field-value    = *( field-content | LWS )
>> +	 *   field-content  = <the OCTETs making up the field-value
>> +	 *                    and consisting of either *TEXT or combinations
>> +	 *                    of token, separators, and quoted-string>
>> +	 */
>> +
>> +	strbuf_add(&buf, ptr, size);
>> +
>> +	/* Strip the CRLF that should be present at the end of each field */
> 
> Is it really a CRLF? Or just an LF?

>> +	strbuf_trim_trailing_newline(&buf);
> 
> Thankfully, this will trim an LF _or_ CR/LF pair, so either way would be fine.
> 
>> +	/* Start of a new WWW-Authenticate header */
>> +	if (skip_iprefix(buf.buf, "www-authenticate:", &val)) {
>> +		while (isspace(*val)) val++;
> 
> Break the "val++;" to its own line:
> 
> 		while (isspace(*val))
> 			val++;

> While we are here, do we need to be careful about the end of the string at
> this point? Is it possible that the server will send all spaces up until the
> maximum header size (as mentioned in the message)?
> 
>> +
>> +		strvec_push(values, val);
>> +		http_auth.header_is_last_match = 1;
>> +		goto exit;
>> +	}
>> +
>> +	/*
>> +	 * This line could be a continuation of the previously matched header
>> +	 * field. If this is the case then we should append this value to the
>> +	 * end of the previously consumed value.
>> +	 */
>> +	if (http_auth.header_is_last_match && isspace(*buf.buf)) {
>> +		const char **v = values->v + values->nr - 1;
> 
> I suppose we expect leading spaces as critical to this header, right?

>> +		char *append = xstrfmt("%s%.*s", *v, (int)(size - 1), ptr + 1);
> 
> We might have better luck using a strbuf, initializing it with the expected
> size and using strbuf_add() to append the strings. Maybe I'm just prematurely
> optimizing, though.

>> +
>> +		free((void*)*v);
>> +		*v = append;
>> +
>> +		goto exit;
>> +	}
>> +
>> +	/* This is the start of a new header we don't care about */
>> +	http_auth.header_is_last_match = 0;
>> +
>> +	/*
>> +	 * If this is a HTTP status line and not a header field, this signals
>> +	 * a different HTTP response. libcurl writes all the output of all
>> +	 * response headers of all responses, including redirects.
>> +	 * We only care about the last HTTP request response's headers so clear
>> +	 * the existing array.
>> +	 */
>> +	if (skip_iprefix(buf.buf, "http/", &z))
>> +		strvec_clear(values);
>> +
>> +exit:
>> +	strbuf_release(&buf);
>> +	return size;
>> +}
>> +
>>  size_t fwrite_null(char *ptr, size_t eltsize, size_t nmemb, void *strbuf)
>>  {
>>  	return nmemb;
>> @@ -1829,6 +1904,8 @@ static int http_request(const char *url,
>>  					 fwrite_buffer);
>>  	}
>>  
>> +	curl_easy_setopt(slot->curl, CURLOPT_HEADERFUNCTION, fwrite_wwwauth);
> 
> Nice integration point!
> 
> Thanks,
> -Stolee