Provided by: varnish_5.2.1-1ubuntu0.1_amd64 
NAME
vmod_blob - utilities for the VCL blob type
SYNOPSIS
import blob [from "path"] ;
# binary-to-text encodings
STRING blob.encode([ENUM encoding,] [ENUM case,] BLOB blob)
BLOB blob.decode([ENUM decoding,] [INT length,] STRING_LIST encoded)
STRING blob.transcode([ENUM decoding,] [ENUM encoding,] [ENUM case,]
[INT length,] STRING_LIST encoded)
# other utilities
BOOL blob.same(BLOB, BLOB)
BOOL blob.equal(BLOB, BLOB)
INT blob.length(BLOB)
BLOB blob.sub(BLOB, BYTES length [, BYTES offset])
# blob object
new OBJ = blob.blob([ENUM decoding,] STRING_LIST encoded)
BLOB <obj>.get()
STRING <obj>.encode([ENUM encoding,] [ENUM case])
CONTENTS
• BLOB decode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL}, INT, STRING)
• STRING encode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL}, ENUM {LOWER,UPPER,DEFAULT},
BLOB)
• STRING transcode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL}, ENUM
{IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL}, ENUM {LOWER,UPPER,DEFAULT}, INT, STRING)
• BOOL same(BLOB, BLOB)
• BOOL equal(BLOB, BLOB)
• INT length(BLOB)
• BLOB sub(BLOB, BYTES, BYTES)
• blob(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL}, STRING)
DESCRIPTION
This VMOD provides utility functions and an object for the VCL data type BLOB, which may contain
arbitrary data of any length.
Examples:
sub vcl_init {
# Create blob objects from encodings such as base64 or hex.
new myblob = blob.blob(BASE64, "Zm9vYmFy");
new yourblob = blob.blob(encoded="666F6F", decoding=HEX);
}
sub vcl_deliver {
# The .get() method retrieves the BLOB from an object.
set resp.http.MyBlob-As-Hex
= blob.encode(blob=myblob.get(), encoding=HEX);
# The .encode() method efficiently retrieves an encoding.
set resp.http.YourBlob-As-Base64 = yourblob.encode(BASE64);
# decode() and encode() functions convert blobs to text and
# vice versa at runtime.
set resp.http.Base64-Encoded
= blob.encode(BASE64,
blob=blob.decode(HEX,
encoded=req.http.Hex-Encoded));
}
sub vcl_recv {
# transcode() converts from one encoding to another.
# case=UPPER specifies upper-case hex digits A-F.
set req.http.Hex-Encoded
= blob.transcode(decoding=BASE64, encoding=HEX,
case=UPPER, encoded="YmF6");
# transcode() from URL to IDENTITY effects a URL decode.
set req.url = blob.transcode(encoded=req.url, decoding=URL);
# transcode() from IDENTITY to URL effects a URL encode.
set req.http.url_urlcoded
= blob.transcode(encoded=req.url, encoding=URL);
}
ENCODING SCHEMES
Binary-to-text encoding schemes are specified by ENUMs in the VMOD's constructor, methods and functions.
Decodings convert a (possibly concatenated) string into a blob, while encodings convert a blob into a
string.
ENUM values for an encoding scheme can be one of:
• IDENTITY
• BASE64
• BASE64URL
• BASE64URLNOPAD
• HEX
• URL
Empty strings are decoded into a "null blob" (of length 0), and conversely a null blob is encoded as the
empty string.
For encodings with HEX or URL, you may also specify a case ENUM with one of the values LOWER, UPPER or
DEFAULT to produce a string with lower- or uppercase hex digits (in [a-f] or [A-F]). The default value
for case is DEFAULT, which for HEX and URL means the same as LOWER.
The case ENUM is not relevant for decodings; HEX or URL strings to be decoded as BLOBs may have hex
digits in either case, or in mixed case.
The case ENUM MUST be set to DEFAULT for the other encodings (BASE64* and IDENTITY). You cannot, for
example, produce an uppercase string by using the IDENTITY scheme with case=UPPER. To change the case of
a string, use the toupper or tolower functions from vmod_std(3).
IDENTITY
The simplest encoding converts between the BLOB and STRING data types, leaving the contents
byte-identical.
Note that a BLOB may contain a null byte at any position before its end; if such a BLOB is decoded with
IDENTITY, the resulting STRING will have a null byte at that position. Since VCL strings, like C strings,
are represented with a terminating null byte, the string will be truncated, appearing to contain less
data than the original blob. For example:
# Decode from the hex encoding for "foo\0bar".
# The header will be seen as "foo".
set resp.http.Trunced-Foo1
= blob.encode(IDENTITY, blob=blob.decode(HEX,
encoded="666f6f00626172"));
IDENTITY is the default encoding and decoding. So the above can also be written as:
# Decode from the hex encoding for "foo\0bar".
# The header will be seen as "foo".
set resp.http.Trunced-Foo2
= blob.encode(blob=blob.decode(HEX, encoded="666f6f00626172"));
The case ENUM MUST be set to DEFAULT for IDENTITY encodings.
BASE64*
The base64 encoding schemes use 4 characters to encode 3 bytes. There are no newlines or maximal line
lengths -- whitespace is not permitted.
The BASE64 encoding uses the alphanumeric characters, + and /; and encoded strings are padded with the =
character so that their length is always a multiple of four.
The BASE64URL encoding also uses the alphanumeric characters, but - and _ instead of + and /, so that an
encoded string can be used safely in a URL. This scheme also uses the padding character =.
The BASE64URLNOPAD encoding uses the same alphabet as BASE6URL, but leaves out the padding. Thus the
length of an encoding with this scheme is not necessarily a mutltiple of four.
The case ENUM MUST be set to DEFAULT for for all of the BASE64* encodings.
HEX
The HEX encoding scheme converts hex strings into blobs and vice versa. For encodings, you may use the
case ENUM to specify upper- or lowercase hex digits A through f (default DEFAULT, which means the same as
LOWER). A prefix such as 0x is not used for an encoding and is illegal for a decoding.
If a hex string to be decoded has an odd number of digits, it is decoded as if a 0 is prepended to it;
that is, the first digit is interpreted as representing the least significant nibble of the first byte.
For example:
# The concatenated string is "abcdef0", and is decoded as "0abcdef0".
set resp.http.First = "abc";
set resp.http.Second = "def0";
set resp.http.Hex-Decoded
= blob.encode(HEX, blob=blob.decode(HEX,
encoded=resp.http.First + resp.http.Second));
URL
The URL decoding replaces any %<2-hex-digits> substrings with the binary value of the hexadecimal number
after the % sign.
The URL encoding implements "percent encoding" as per RFC3986. The case ENUM determines the case of the
hex digits, but does not affect alphabetic characters that are not percent-encoded.
decode
BLOB decode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL} decoding="IDENTITY", INT length=0, STRING encoded)
Returns the BLOB derived from the string encoded according to the scheme specified by decoding.
If length > 0, only decode the first length characters of the encoded string. If length <= 0 or greater
than the length of the string, then decode the entire string. The default value of length is 0.
decoding defaults to IDENTITY.
Example:
blob.decode(BASE64, encoded="Zm9vYmFyYmF6");
# same with named parameters
blob.decode(encoded="Zm9vYmFyYmF6", decoding=BASE64);
# convert string to blob
blob.decode(encoded="foo");
encode
STRING encode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL} encoding="IDENTITY", ENUM {LOWER,UPPER,DEFAULT} case="DEFAULT", BLOB blob)
Returns a string representation of the BLOB blob as specifed by encoding. case determines the case of hex
digits for the HEX and URL encodings, and is ignored for the other encodings.
encoding defaults to IDENTITY, and case defaults to DEFAULT. DEFAULT is interpreted as LOWER for the HEX
and URL encodings, and is the required value for the other encodings.
Example:
set resp.http.encode1
= blob.encode(HEX,
blob=blob.decode(BASE64, encoded="Zm9vYmFyYmF6"));
# same with named parameters
set resp.http.encode2
= blob.encode(blob=blob.decode(encoded="Zm9vYmFyYmF6",
decoding=BASE64),
encoding=HEX);
# convert blob to string
set resp.http.encode3
= blob.encode(blob=blob.decode(encoded="foo"));
transcode
STRING transcode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL} decoding="IDENTITY", ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL} encoding="IDENTITY", ENUM {LOWER,UPPER,DEFAULT} case="DEFAULT", INT length=0, STRING encoded)
Translates from one encoding to another, by first decoding the string encoded according to the scheme
decoding, and then returning the encoding of the resulting blob according to the scheme encoding. case
determines the case of hex digits for the HEX and URL encodings, and is ignored for other encodings.
As with decode(): If length > 0, only decode the first length characters of the encoded string, otherwise
decode the entire string. The default value of length is 0.
decoding and encoding default to IDENTITY, and case defaults to DEFAULT. DEFAULT is interpreted as LOWER
for the HEX and URL encodings, and is the required value for the other encodings.
Example:
set resp.http.Hex2Base64-1
= blob.transcode(HEX, BASE64, encoded="666f6f");
# same with named parameters
set resp.http.Hex2Base64-2
= blob.transcode(encoded="666f6f",
encoding=BASE64, decoding=HEX);
# URL decode -- recall that IDENTITY is the default encoding.
set resp.http.urldecoded
= blob.transcode(encoded="foo%20bar", decoding=URL);
# URL encode
set resp.http.urlencoded
= blob.transcode(encoded="foo bar", encoding=URL);
same
BOOL same(BLOB, BLOB)
Returns true if and only if the two BLOB arguments are the same object, i.e. they specify exactly the
same region of memory, or both are empty.
If the BLOBs are both empty (length is 0 and/or the internal pointer is NULL), then same() returns true.
If any non-empty BLOB is compared to an empty BLOB, then same() returns false.
equal
BOOL equal(BLOB, BLOB)
Returns true if and only if the two BLOB arguments have equal contents (possibly in different memory
regions).
As with same(): If the BLOBs are both empty, then equal() returns true. If any non-empty BLOB is compared
to an empty BLOB, then equal() returns false.
length
INT length(BLOB)
Returns the length of the BLOB.
sub
BLOB sub(BLOB, BYTES length, BYTES offset=0)
Returns a new BLOB formed from length bytes of the BLOB argument starting at offset bytes from the start
of its memory region. The default value of offset is 0B.
sub() fails and returns NULL if the BLOB argument is empty, or if offset + length requires more bytes
than are available in the BLOB.
blob
new OBJ = blob(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL} decoding="IDENTITY", STRING encoded)
Creates an object that contains the BLOB derived from the string encoded according to the scheme
decoding.
Example:
new theblob1 = blob.blob(BASE64, encoded="YmxvYg==");
# same with named arguments
new theblob2 = blob.blob(encoded="YmxvYg==", decoding=BASE64);
# string as a blob
new stringblob = blob.blob(encoded="bazz");
blob.get
BLOB blob.get()
Returns the BLOB created by the constructor.
Example:
set resp.http.The-Blob1 =
blob.encode(blob=theblob1.get());
set resp.http.The-Blob2 =
blob.encode(blob=theblob2.get());
set resp.http.The-Stringblob =
blob.encode(blob=stringblob.get());
blob.encode
STRING blob.encode(ENUM {IDENTITY,BASE64,BASE64URL,BASE64URLNOPAD,HEX,URL} encoding="IDENTITY", ENUM {LOWER,UPPER,DEFAULT} case="DEFAULT")
Returns an encoding of BLOB created by the constructor, according to the scheme encoding. case determines
the case of hex digits for the HEX and URL encodings, and MUST be set to DEFAULT for the other encodings.
Example:
# blob as text
set resp.http.The-Blob = theblob1.encode();
# blob as base64
set resp.http.The-Blob-b64 = theblob1.encode(BASE64);
For any blob object, encoding ENC and case CASE, encodings via the .encode() method and the encode()
function are equal:
# Always true:
blob.encode(ENC, CASE, blob.get()) == blob.encode(ENC, CASE)
But the object method is more efficient -- the encoding is computed once and cached (with allocation in
heap memory), and the cached encoding is retrieved on every subsequent call. The encode() function
computes the encoding on every call, allocating space for the string in Varnish workspaces.
So if the data in a BLOB are fixed at VCL initialization time, so that its encodings will always be the
same, it is better to create a blob object. The VMOD's functions should be used for data that are not
known until runtime.
ERRORS
The encoders, decoders and sub() may fail if there is insufficient space to create the new blob or
string. Decoders may also fail if the encoded string is an illegal format for the decoding scheme.
Encoders will fail for the IDENTITY and BASE64* encoding schemes if the case ENUM is not set to DEFAULT.
If any of the VMOD's methods, functions or constructor fail, then VCL failure is invoked, just as if
return(fail) had been called in the VCL source. This means that:
• If the blob object constructor fails, or if any methods or functions fail during vcl_init, then the VCL
program will fail to load, and the VCC compiler will emit an error message.
• If a method or function fails in any other VCL subroutine besides vcl_synth, then control is directed
to vcl_synth. The response status is set to 503 with the reason string "VCL failed", and an error
message will be written to the Varnish log using the tag VCL_Error.
• If the failure occurs during vcl_synth, then vcl_synth is aborted. The response line "503 VCL failed"
is returned, and the VCL_Error message is written to the log.
LIMITATIONS
The VMOD allocates memory in various ways for new blobs and strings. The blob object and its methods
allocate memory from the heap, and hence they are only limited by available virtual memory.
The encode(), decode() and transcode() functions allocate Varnish workspace, as does sub() for the newly
created BLOB. If these functions are failing, as indicated by "out of space" messages in the Varnish log
(with the VCL_Error tag), then you will need to increase the varnishd parameters workspace_client and/or
workspace_backend.
The transcode() function also allocates space on the stack for a temporary BLOB. If this function causes
stack overflow, you may need to increase the varnishd parameter thread_pool_stack.
SEE ALSO
• varnishd(1) • vcl(7) • vmod_std(3)
COPYRIGHT
This document is licensed under the same conditions as Varnish itself.
See LICENSE for details.
Authors: Nils Goroll <nils.goroll@uplex.de>
Geoffrey Simmons <geoffrey.simmons@uplex.de>
VMOD_BLOB(3)