Description:
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SOAPClient compression seems broken. I see two problems.

First, the code places the Accept-Encoding and Content-Encoding HTTP headers before the POST /path HTTP/1.1 line, which is invalid HTTP. This causes 400 errors.

I fixed this by moving the logic for this section further down in the function. See this patch for more details:

http://www.trachtenberg.com/patches/soap_compression_patch.txt 

It works for me, but I did not verify this is a perfect fix.

Second, it seems impossible (or just not as documented) to trigger compression of out-going requests. I don't understand how "level" can evaluate to > 0 given the SOAP_COMPRESSION_* constants.

Do you need to also pass a gzip compression level (0-9) as part of the compression bit field? This is not part of the online documentation, which says you can do this:

$client = new SoapClient("some.wsdl",
  array('compression' => SOAP_COMPRESSION_ACCEPT | SOAP_COMPRESSION_GZIP));

This evaluates to 0x20. Inside php_http.c in the make_http_soap_request function, it then does:

if (zend_hash_find(Z_OBJPROP_P(this_ptr), "compression", sizeof("compression"), (void **)&tmp) == SUCCESS && Z_TYPE_PP(tmp) == IS_LONG) {
	int level = Z_LVAL_PP(tmp) & 0x0f;

  ...

  if (level > 0) {

0x20 & 0x0f evaluates to 0, so you never execute the last branch, and no compression is used.

Furthermore, since level seems to be passed into the compression functions as the gzip level, I don't know how that relates to the bit field.

I tries to verify this using the unit tests, but there are none for SOAPClient and compression.