MIME Headers

The Traffic Server **MIME header functions ** enable you to retrieve and modify information about HTTP MIME fields.

An HTTP request or response consists of a header, body, and trailer. The HTTP header contains a request (or response) line and a MIME header. A MIME header is composed of zero or more MIME fields. A MIME field is composed of a field name, a colon, and zero or more field values (values in a field are separated by commas).

In the example below: Foo is the MIME field name, bar is the first MIME field value, and car is the second MIME field value.

Foo: bar, car

The following example is an augmented Backus-Naur Form (BNF) for the form of a MIME header - it specifies exactly what was described above. A header consists of zero or more fields that contain a name, separating colon, and zero or more values. A name or value is simply a string of tokens that is potentially zero length; a token is any character except certain control characters and separators (such as colons). For the purpose of retrieving a field, field names are not case-sensitive; therefore, the field names Foo, foo and fOO are all equivalent.

MIME-header = *MIME-field
MIME-field = field-name ":" #field-value
field-name = *token
field-value = *token

The MIME header data structure is a parsed version of a standard Internet MIME header. The MIME header data structure is similar to the URL data structure (see URLs). The actual data is stored in a marshal buffer; the MIME header functions operate on a marshal buffer and a location (TSMLoc) within the buffer.

After a call to TSMimeHdrFieldDestroy or TSMimeHdrFieldRemove is made, you must deallocate the TSMLoc handle with a call to TSHandleMLocRelease. You do not need to deallocate a NULL handles. For example: if you call TSMimeHdrFieldValueStringGet to get the value of the content type field and the field does not exist, then it returns TS_NULL_MLOC. In such a case, you wouldn’t need to deallocate the handle with a call to TSHandleMLocRelease.

The location (TSMLoc) in the MIME header functions can be either an HTTP header location or a MIME header location. If an HTTP header location is passed to these functions, then the system locates the MIME header associated with that HTTP header and executes the corresponding MIME header operations specified by the functions (see the example in the description of TSMimeHdrCopy()).

Note: MIME headers may contain more than one MIME field with the same name. Previous versions of Traffic Server joined multiple fields with the same name into one field with composite values, but this behavior came at a performance cost and caused compatability issues with older clients and servers. Hence, the current version of Traffic Server does not coalesce duplicate fields. Correctly-behaving plugins should check for the presence of duplicate fields and iterate over the duplicate fields by using TSMimeHdrFieldNextDup.

To facilitate fast comparisons and reduce storage size, Traffic Server defines several pre-allocated field names. These field names correspond to the field names in HTTP and NNTP headers.

const char* TS_MIME_FIELD_ACCEPT
"Accept"
int TS_MIME_LEN_ACCEPT
const char* TS_MIME_FIELD_ACCEPT_CHARSET
"Accept-Charset"
int TS_MIME_LEN_ACCEPT_CHARSET
const char* TS_MIME_FIELD_ACCEPT_ENCODING
"Accept-Encoding"
int TS_MIME_LEN_ACCEPT_ENCODING
const char* TS_MIME_FIELD_ACCEPT_LANGUAGE
"Accept-Language"
int TS_MIME_LEN_ACCEPT_LANGUAGE
const char* TS_MIME_FIELD_ACCEPT_RANGES
"Accept-Ranges"
int TS_MIME_LEN_ACCEPT_RANGES
const char* TS_MIME_FIELD_AGE
"Age"
int TS_MIME_LEN_AGE
const char* TS_MIME_FIELDALLOW
"Allow"
int TS_MIME_LEN_ALLOW
const char* TS_MIME_FIELDAPPROVED
"Approved"
int TS_MIME_LEN_APPROVED
const char* TS_MIME_FIELDAUTHORIZATION
"Authorization"
int TS_MIME_LEN_AUTHORIZATION
const char* TS_MIME_FIELDBYTES
"Bytes"
int TS_MIME_LEN_BYTES
const char* TS_MIME_FIELDCACHE_CONTROL
"Cache-Control"
int TS_MIME_LEN_CACHE_CONTROL
const char* TS_MIME_FIELDCLIENT_IP
"Client-ip"
int TS_MIME_LEN_CLIENT_IP
const char* TS_MIME_FIELDCONNECTION
"Connection"
int TS_MIME_LEN_CONNECTION
const char* TS_MIME_FIELDCONTENT_BASE
"Content-Base"
int TS_MIME_LEN_CONTENT_BASE
const char* TS_MIME_FIELDCONTENT_ENCODING
"Content-Encoding"
int TS_MIME_LEN_CONTENT_ENCODING
const char* TS_MIME_FIELDCONTENT_LANGUAGE
"Content-Language"
int TS_MIME_LEN_CONTENT_LANGUAGE
const char* TS_MIME_FIELDCONTENT_LENGTH
"Content-Length"
int TS_MIME_LEN_CONTENT_LENGTH
const char* TS_MIME_FIELDCONTENT_LOCATION
"Content-Location"
int TS_MIME_LEN_CONTENT_LOCATION
const char* TS_MIME_FIELDCONTENT_MD5
"Content-MD5"
int TS_MIME_LEN_CONTENT_MD5
const char* TS_MIME_FIELDCONTENT_RANGE
"Content-Range"
int TS_MIME_LEN_CONTENT_RANGE
const char* TS_MIME_FIELDCONTENT_TYPE
"Content-Type"
int TS_MIME_LEN_CONTENT_TYPE
const char* TS_MIME_FIELDCONTROL
"Control"
int TS_MIME_LEN_CONTROL
const char* TS_MIME_FIELDCOOKIE
"Cookie"
const char* TS_MIME_FIELDDATE
"Date"
int TS_MIME_LEN_DATE
const char* TS_MIME_FIELDDISTRIBUTION
"Distribution"
int TS_MIME_LEN_DISTRIBUTION
const char* TS_MIME_FIELDETAG
"Etag"
int TS_MIME_LEN_ETAG
const char* TS_MIME_FIELDEXPECT
"Expect"
int TS_MIME_LEN_EXPECT
const char* TS_MIME_FIELDEXPIRES
"Expires"
int TS_MIME_LEN_EXPIRES
const char* TS_MIME_FIELDFOLLOWUP_TO
"Followup-To"
int TS_MIME_LEN_FOLLOWUP_TO
const char* TS_MIME_FIELDFROM
"From"
int TS_MIME_LEN_FROM
const char* TS_MIME_FIELDHOST
"Host"
int TS_MIME_LEN_HOST
const char* TS_MIME_FIELDIF_MATCH
"If-Match"
int TS_MIME_LEN_IF_MATCH
const char* TS_MIME_FIELDIF_MODIFIED_SINCE
"If-Modified-Since"
int TS_MIME_LEN_IF_MODIFIED_SINCE
const char* TS_MIME_FIELDIF_NONE_MATCH
"If-None-Match"
int TS_MIME_LEN_IF_NONE_MATCH
const char* TS_MIME_FIELDIF_RANGE
"If-Range"
int TS_MIME_LEN_IF_RANGE
const char* TS_MIME_FIELDIF_UNMODIFIED_SINCE
"If-Unmodified-Since"
int TS_MIME_LEN_IF_UNMODIFIED_SINCE
const char* TS_MIME_FIELDKEEP_ALIVE
"Keep-Alive"
int TS_MIME_LEN_KEEP_ALIVE
const char* TS_MIME_FIELDKEYWORDS
"Keywords"
int TS_MIME_LEN_KEYWORDS
const char* TS_MIME_FIELDLAST_MODIFIED
"Last-Modified"
int TS_MIME_LEN_LAST_MODIFIED
const char* TS_MIME_FIELDLINES
"Lines"
int TS_MIME_LEN_LINES
const char* TS_MIME_FIELDLOCATION
"Location"
int TS_MIME_LEN_LOCATION
const char* TS_MIME_FIELDMAX_FORWARDS
"Max-Forwards"
int TS_MIME_LEN_MAX_FORWARDS
const char* TS_MIME_FIELDMESSAGE_ID
"Message-ID"
int TS_MIME_LEN_MESSAGE_ID
const char* TS_MIME_FIELDNEWSGROUPS
"Newsgroups"
int TS_MIME_LEN_NEWSGROUPS
const char* TS_MIME_FIELDORGANIZATION
"Organization"
int TS_MIME_LEN_ORGANIZATION
const char* TS_MIME_FIELDPATH
"Path"
int TS_MIME_LEN_PATH
const char* TS_MIME_FIELDPRAGMA
"Pragma"
int TS_MIME_LEN_PRAGMA
const char* TS_MIME_FIELDPROXY_AUTHENTICATE
"Proxy-Authenticate"
int TS_MIME_LEN_PROXY_AUTHENTICATE
const char* TS_MIME_FIELDPROXY_AUTHORIZATION
"Proxy-Authorization"
int TS_MIME_LEN_PROXY_AUTHORIZATION
const char* TS_MIME_FIELDPROXY_CONNECTION
"Proxy-Connection"
int TS_MIME_LEN_PROXY_CONNECTION
const char* TS_MIME_FIELDPUBLIC
"Public"
int TS_MIME_LEN_PUBLIC
const char* TS_MIME_FIELDRANGE
"Range"
int TS_MIME_LEN_RANGE
const char* TS_MIME_FIELDREFERENCES
"References"
int TS_MIME_LEN_REFERENCES
const char* TS_MIME_FIELDREFERER
"Referer"
int TS_MIME_LEN_REFERER
const char* TS_MIME_FIELDREPLY_TO
"Reply-To"
int TS_MIME_LEN_REPLY_TO
const char* TS_MIME_FIELDRETRY_AFTER
"Retry-After"
int TS_MIME_LEN_RETRY_AFTER
const char* TS_MIME_FIELDSENDER
"Sender"
int TS_MIME_LEN_SENDER
const char* TS_MIME_FIELDSERVER
"Server"
int TS_MIME_LEN_SERVER
"Set-Cookie"
const char* TS_MIME_FIELDSUBJECT
"Subject"
int TS_MIME_LEN_SUBJECTTS_MIME_LEN_SUBJECT
const char* TS_MIME_FIELDSUMMARY
"Summary"
int TS_MIME_LEN_SUMMARY
const char* TS_MIME_FIELDTE
"TE"
int TS_MIME_LEN_TE
const char* TS_MIME_FIELDTRANSFER_ENCODING
"Transfer-Encoding"
int TS_MIME_LEN_TRANSFER_ENCODING
const char* TS_MIME_FIELDUPGRADE
"Upgrade"
int TS_MIME_LEN_UPGRADE
const char* TS_MIME_FIELDUSER_AGENT
"User-Agent"
int TS_MIME_LEN_USER_AGENT
const char* TS_MIME_FIELDVARY
"Vary"
int TS_MIME_LEN_VARY
const char* TS_MIME_FIELDVIA
"Via"
int TS_MIME_LEN_VIA
const char* TS_MIME_FIELDWARNING
"Warning"
int TS_MIME_LEN_WARNING
const char* TS_MIME_FIELDWWW_AUTHENTICATE
"Www-Authenticate"
int TS_MIME_LEN_WWW_AUTHENTICATE
const char* TS_MIME_FIELDXREF
"Xref"
int TS_MIME_LEN_XREF

The header field names above are defined in ts.h as const char* strings. When Traffic Server sets the name portion of a header field (or any portion for that matter), it quickly checks to see if the new value is one of the known values. If it is, then Traffic Server stores a pointer into a global table instead of storing the known value in the marshal buffer. The header field names listed above are also pointers into this table, which enables simple pointer comparison of the value returned from TSMimeHdrFieldNameGet with one of the values listed above. It is recommended that you use the above values when referring to one of the known header field names to avoid the possibility of a spelling error.

Traffic Server adds one important feature to MIME fields that you may not know about: Traffic Server does not print a MIME field if the field name begins with the ‘@’ symbol. For example: a plugin can add the field “@My-Field” to a header. Even though Traffic Server never sends that field out in a request to an origin server or in a response to a client, it can be printed to Traffic Server logs by defining a custom log configuration file that explicitly logs such fields. This provides a useful mechanism for plugins to store information about an object in one of the MIME headers associated with the object.

The MIME header functions are listed below: