Examples of HTTP requests and responses for Salesforce SOAP and Metadata API calls.

CreateCustomField.xml

POST https://na15.salesforce.com/services/Soap/m/29.0/00Di0000000icUB HTTP/1.1
SOAPAction: create
Content-Type: text/xml; charset=utf-8
Host: na15.salesforce.com
Content-Length: 894
Expect: 100-continue

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:apex="http://soap.sforce.com/2006/08/apex" xmlns:cmd="http://soap.sforce.com/2006/04/metadata" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <soapenv:Header>
      <cmd:SessionHeader>
         <cmd:sessionId>00Di0000000icUB!ASAAQF0stgINehCxOnHPGuLI4TMVx.jP8rEkLY5axmf0XWLfj0WFsmXhfXoFFgJ2gw1b2DImwyzSFPgB2wuIwNtG94ytkpoh</cmd:sessionId>
      </cmd:SessionHeader>
   </soapenv:Header>
   <soapenv:Body>
      <create xmlns="http://soap.sforce.com/2006/04/metadata">
         <metadata xsi:type="CustomField">
            <fullName>MyCustomObject2__c.MyField__c</fullName>
            <label>MyField</label>
            <length>100</length>
            <type>Text</type>
         </metadata>
      </create>
   </soapenv:Body>
</soapenv:Envelope>

CreateCustomObject.xml

POST https://na15.salesforce.com/services/Soap/m/29.0/00Di0000000icUB HTTP/1.1
SOAPAction: create
Content-Type: text/xml; charset=utf-8
Host: na15.salesforce.com
Content-Length: 1057


<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:apex="http://soap.sforce.com/2006/08/apex" xmlns:cmd="http://soap.sforce.com/2006/04/metadata" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <soapenv:Header>
      <cmd:SessionHeader>
         <cmd:sessionId>00Di0000000icUB!ASAAQF0stgINehCxOnHPGuLI4TMVx.jP8rEkLY5axmf0XWLfj0WFsmXhfXoFFgJ2gw1b2DImwyzSFPgB2wuIwNtG94ytkpoh</cmd:sessionId>
      </cmd:SessionHeader>
   </soapenv:Header>
   <soapenv:Body>
      <create xmlns="http://soap.sforce.com/2006/04/metadata">
         <metadata xsi:type="CustomObject">
            <fullName>MyCustomObject2__c</fullName>
            <label>MyCustomObject2</label>
            <pluralLabel>MyCustomObject2</pluralLabel>
            <deploymentStatus>Deployed</deploymentStatus>
            <sharingModel>ReadWrite</sharingModel>
            <nameField>
               <label>ID</label>
               <type>AutoNumber</type>
            </nameField>
         </metadata>
      </create>
   </soapenv:Body>
</soapenv:Envelope>

CustomObjectResponse.xml

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns="http://soap.sforce.com/2006/04/metadata">
   <soapenv:Body>
      <createResponse>
         <result>
            <done>false</done>
            <id>04si0000000tpbwAAA</id>
            <state>InProgress</state>
         </result>
      </createResponse>
   </soapenv:Body>
</soapenv:Envelope>

EnterpriseLogin.xml

POST https://login.salesforce.com/services/Soap/c/29.0/0DFi00000008UYO HTTP/1.1
SOAPAction: login
Content-Type: text/xml; charset=utf-8
Host: login.salesforce.com
Content-Length: 307
Expect: 100-continue
Connection: Keep-Alive

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Body>
       <login xmlns="urn:enterprise.soap.sforce.com">
           <username>you@yourdomain.com</username>
           <password>password</password>
       </login>
   </soapenv:Body>
</soapenv:Envelope>

LoginResponse.xml

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns="urn:enterprise.soap.sforce.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <soapenv:Body>
      <loginResponse>
         <result>
            <metadataServerUrl>https://na15.salesforce.com/services/Soap/m/29.0/00Di0000000icUB</metadataServerUrl>
            <passwordExpired>false</passwordExpired>
            <sandbox>false</sandbox>
            <serverUrl>https://na15.salesforce.com/services/Soap/c/29.0/00Di0000000icUB/0DFi00000008UYO</serverUrl>
            <sessionId>00Di0000000icUB!ASAAQF0stgINehCxOnHPGuLI4TMVx.jP8rEkLY5axmf0XWLfj0WFsmXhfXoFFgJ2gw1b2DImwyzSFPgB2wuIwNtG94ytkpoh</sessionId>
            <userId>005i0000002MUqLAAW</userId>
            <userInfo>
               <accessibilityMode>false</accessibilityMode>
               <currencySymbol>$</currencySymbol>
               <orgAttachmentFileSizeLimit>5242880</orgAttachmentFileSizeLimit>
               <orgDefaultCurrencyIsoCode>USD</orgDefaultCurrencyIsoCode>
               <orgDisallowHtmlAttachments>false</orgDisallowHtmlAttachments>
               <orgHasPersonAccounts>false</orgHasPersonAccounts>
               <organizationId>00Di0000000icUBEAY</organizationId>
               <organizationMultiCurrency>false</organizationMultiCurrency>
               <organizationName>salesforce.com</organizationName>
               <profileId>00ei0000001CMKcAAO</profileId>
               <roleId xsi:nil="true" />
               <sessionSecondsValid>7200</sessionSecondsValid>
               <userDefaultCurrencyIsoCode xsi:nil="true" />
               <userEmail>you@yourdomain.com</userEmail>
               <userFullName>Wade Wegner</userFullName>
               <userId>005i0000002MUqLAAW</userId>
               <userLanguage>en_US</userLanguage>
               <userLocale>en_US</userLocale>
               <userName>you@yourdomain.com</userName>
               <userTimeZone>America/Los_Angeles</userTimeZone>
               <userType>Standard</userType>
               <userUiSkin>Theme3</userUiSkin>
            </userInfo>
         </result>
      </loginResponse>
   </soapenv:Body>
</soapenv:Envelope>

PartnerLogin.xml

POST https://login.salesforce.com/services/Soap/u/29.0/0DFi00000008UYO HTTP/1.1
SOAPAction: login
Content-Type: text/xml; charset=utf-8
Host: login.salesforce.com
Content-Length: 306
Expect: 100-continue

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Body>
       <login xmlns="urn:partner.soap.sforce.com">
           <username>you@yourdomain.com</username>
           <password>password</password>
       </login>
   </soapenv:Body>
</soapenv:Envelope>

@wadewegner Thank you so much for making this. It was made a long ago, but it helped me today. I would not have had figured this out on my own - Forming request xml for metadata API. I used it with createMetaData and updateMetaData.